United States
Environmental Protection
Agency
Office of
Research and
Development
Industrial Environmental Research
Laboratory
Cincinnati, Ohio 45268
EPA-600/7-77-039
Apri! 1977
ENVIRONMENTAL ASSESSMENT
OF GEOPRESSURED WATERS
AND THEIR PROJECTED USES
Interagency
Energy-Environment
Research and Development
Program Report
-------
RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6, Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the INTERAGENCY ENERGY-ENVIRONMENT
RESEARCH AND DEVELOPMENT series. Reports in this series result from the
effort funded under the 17-agency Federal Energy/Environment Research and
Development Program. These studies relate to-EPA's mission to protect the public
health and welfare from adverse effects of pollutants associated with energy sys-
tems. The goal of the Program is to assure the rapid development of domestic
energy supplies in an environmentally-compatible manner by providing the nec-
essary environmental data and control technology. Investigations include analy-
ses of the transport of energy-related pollutants and their health and ecological
effects; assessments of, and development of, control technologies for energy
systems; and integrated assessments of a wide range of energy-related environ-
mental issues.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
-------
EPA-6QO/7-77-039
April 1977
ENVIRONMENTAL ASSESSMENT OF GEOPRESSURED WATERS
AND THEIR PROJECTED USES
by
J. S. Wilson, J. R. Hamilton, J. A. Manning and P. E. Muehlberg
Dow Chemical U.S.A., Texas Division
Freeport, Texas 77541
Contract No. 68-02-1329
Project Officer
Robert P. Hartley
Energy Systems Environmental Control Division
Industrial Environmental Research Laboratory
Cincinnati, Ohio 45268
INDUSTRIAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
-------
DISCLAIMER
This report has been reviewed by the Industrial Environmental Research
Laboratory, U.S. Environmental Protection Agency, and approved for publication.
Approval does not signify that the contents necessarily reflect the views
and policies of the U.S. Environmental Protection Agency, nor does mention
of trade names or commercial products constitute endorsement or recommenda-
tion for use.
-------
FOREWORD
When energy and material resources are extracted, processed, converted,
and used, the related pollutional impacts on our environment and even on
our health often require that new and increasingly more efficient pollution
control methods be used. The Industrial Environmental Research Laboratory -
Cincinnati (lERL-Ci) assists in developing and demonstrating new and improved
methodologies that will meet these needs both efficiently and economically.
This report deals with the environmental aspects of the proposed
development of the deep geopressured hot fluids of the Gulf Coast sedimentary
basin for the production of electric power and as a source of heat. Although
this development is currently only in the study phase, it is desirable to
estimate the environmental considerations at this time and to propose a
study program to run concurrent with the development effort.
Geopressured geothermal is a unique resource with its own problems and
promises. It is the intent of this report to provide the environmental
research community with a source of understanding of the resource, the nature
of its waters, and the special problems associated with its utilization.
The hard data base is fragmentary, requiring much of the material presented
to be of the "consensus" type of information. Updating will be required as
real data become available.
The researcher desiring more information on the subject is referred to
the Industrial Environmental Research Laboratory, U. S. Environmental
Protection Agency, Cincinnati, Ohio, 45268.
David G. Stephan, Director
Industrial Environmental Research Laboratory-Cincinnati
111
-------
ABSTRACT
A possible source of alternate energy for the nation is believed to
exist in the deep geopressured reservoirs found in the Texas and Louisiana
Gulf Coast sedimentary basins. This unproven resource is believed to offer a
large potential supply of both natural gas and heat energy. Development is
some 5 to 15 years in the future, depending on priorities assigned to the
area by ERDA. Private development, because of the risk involved, must await
government proving of the resource.
This report considers the potential uses of the geopressured geothermal
resource and the environmental aspects of those uses. Economics of power
production are estimated as an aid to assignment of priority research and
development in the area. Literature values of near 45 mils per kilowatt-
hour are considered higher than other geothermal sources.
Principal environmental impacts of any of the proposed uses will result
from the waste fluid streams and from possible subsidence of the wellfield.
In some cases, the waste stream may be of low salinity and usable as agri-
cultural water. However, in most instances, disposal of this large volume of
saline fluid will require reinjection, canaling to a saline water body, or
some more imaginative method. Reinjection into the same strata will be un-
economic and require too much energy, due to the geopressure involved.
The area is one of natural subsidence. This may be accelerated by deep
fluid withdrawal. However, many experts feel the great depth will be a
mitigating factor on surface subsidence.
Environmental research and information will be necessary if the resource
is to be developed. However, in view of the uncertainty of extensive re-
source development and the relatively long time frame involved, only moderate
priority is assigned to environmental research effort at this time. Progress
of the Energy Research and Development Administration development effort
should be monitored, and environmental baselines should be established for
the area chosen for initial development. Particular attention should be
given to ground levels and other data necessary to establish subsidence
values. Close cooperation and joint effort between the Environmental
Protection Agency and the Energy Research and Development Administration is
recommended.
IV
-------
CONTENTS
Foreword iii
Abstract iv
Figures vii
Tables viii
Abbreviations and Symbols ix
Acknowledgments xi
1. Introduction 1
2. Conclusions 2
3. Recommendations 6
4. Description of the Resource 10
Origin of geopressure 11
Origin of high temperature 12
Nature of geopressured geothermal fluids 13
Geopressured reservoirs 15
Difficulties and limitations 17
5. Possible Uses of Geopressured Geothermal Waters 21
Production of electric power from geothermal energy . 21
Other potential uses 22
Industrial uses 22
Agricultural uses 23
Municipal and residential uses 23
Engineering aspects of electrical power production
from geothermal brines 23
Economics of geopressured geothermal power
production 24
Incentives for geopressured geothermal power
production 26
Nonelectrical power generation uses of geopressured
brines - . . . 30
Time frame for development 32
6. Projected Multimedia Emissions and Effects from
Potential Uses 37
Analysis of the waters 37
Expected emissions .-.,.. 42
Direct emissions . 42
Spent geothermal brine (stream 15) 46
Cooling tower blowdown (stream 32) . . 52
Cooling tower exhaust (stream'33) 52
Dehydrator effluent (stream 26) 53
Air-cooler exhaust (stream 21) - 53
Air-cooler exhaust (stream 29) 53
Air-cooler discharge (stream 30) . .• 53
v
-------
Contents (continued)
Separator condensate (stream 17) ... 53
Main condenser condensate (stream 14) 53
Main condenser purge (stream 11) 54
Septic tank effluent 54
Indirect emissions 55
Emissions expected during development phase
of wellfield 55
Emissions expected during plant construction
phase . . . 55
Environmental impact ..... 56
Air and water quality criteria 56
Impact of direct emissions 56
Spent geopressured brine (stream 15) 56
Cooling tower blowdown (stream 32) 62
Cooling tower exhaust (stream 33) 62
Dehydrator effluent (stream 26) 64
Air-cooler exhausts (streams 21, 29, s 30) ... 64
Separator condensate (stream 17) 64
Main condenser condensate (stream 14) 64
Main condenser purge (stream 34) 64
Septic tank effluent 64
Aesthetics * 64
Impact of indirect emissions 65
Impact of accidental emissions 66
Geological considerations 67
Subsidence 67
Earthquakes 69
7. Multimedia Waste Control Requirements in the Areas
of Potential Use 73
Emission control 73
Reinjection 74
Geology 75
Alternatives to reinjection ... 75
Blowout prevention 76
Subsidence prevention 78
References 79
Appendix - Estimation of Maximum Deposition Rates of
Cooling Tower 84
VI
-------
FIGURES
Number Page
1 Change in formation water salinity with depth, in relation
to the occurrence of the geopressure zone, Manchester
Field, Calcasieu Parish, Louisiana . . . . 14
2 Location map showing the extent of the assessed
geopressured zones .. 16
3 Geothermal fairways of the lower and middle Texas Gulf
Coast 18
4 Depositional style of the tertiary along the Texas Gulf
Coast 19
5 Required temperature of geothermal fluids for various
nonelectrical applications 31
6 Proposed plan for geothermal energy development on the
Gulf Coast 33
7 Business-as-usual geothermal plant development timeline . . 34
8 Overall time schedule, major activities 35
9 Flow diagram of fuel plant for double-stage power plant -
25 megawatts ." 44
10 Flow diagram of power plant - 25 megawatts - double-stage . 45
11 Total and partial stresses on jacketed specimen with
internal fluid pressure 70
VII
-------
TABLES
Number Page
1 Unit cost summary - 25-megawatt flash plants 25
2 Important parameters, alternative power plants 27
3 1980 apportioned busbar charges (power plant) 28
4 Most probable power capacities U.S.A. .... 28
5 Brine compositions from overpressured reservoirs 38
6 Parameters of streams involved in fuel plant for 25 MW(e)
double-stage flash plant 47
7 Parameters of streams involved in 25 MW(e) double-stage
flash plant , 48
8 Emissions from 25 MW(e) geopressured electric demonstration
power plant and associated brinefield - double-stage
flash process 49
9 Proposed water quality and ambient air standards . 57
10 Metal quantity levels for discharges to Texas tidal waters -
1975 standards of Texas Water Quality Board 58
Vlll
-------
LIST OF ABBREVIATIONS AND SYMBOLS
^ — approximate
bbl — barrel
BOD — biological oxygen demand
Btu — British thermal unit
CO2 — carbon dioxide
cm — centimeter
CU — copper
Darcy — a unit of permeability
db — decibel
°C — degree centigrade
°F — degree Fahrenheit
ft — foot
gm — gram
pg — microgram
gpm — gallon per minute
hr — hour
HsS — hydrogen sulfide
J — Joule, a unit of energy
kcal — kilocalorie
kg — kilogram
kkg — thousand kilograms, megagram
km — kilometer
kWh — kilowatt-hour
1 — liter
m — meter
Pm — micrometer
M — million
met — millidarcy
rug — milligram
min — minute
mo — month
Mscf — thousand standard cubic feet
MWc — megawatt century
MW(e) — megawatt (electrical)
N2 — nitrogen
NH3 — ammonia
Nm3 — cubic meters at normal conditions of temperature and pressure
NOX — oxides of nitrogen
O2 — oxygen
ppm — parts per million
psi — pounds per square inch
scfm — standard cubic feet per minute
sec — second
IX
-------
List of Abbreviations and Symbols (continued)
SOX — oxides of sulfur
IDS — total dissolved solids
yd — yard
-------
ACKNOWLEDGMENTS
In the course of the accumulation of information and data for the prepara-
tion of this report, various representatives of industry and government have
been contacted. These individuals have contributed significantly to the
preparation of the report. Particular appreciation is extended to Dr.
Sidney Kaufman of Cornell University for his critique of the manuscript and
his valuable comments and recommendations.
Water analyses, not in the open literature, were supplied by Dr. Paul H.
Jones of Louisiana State University, Mr. E, R. Blakeman of Superior Oil
Company, and Raymond H. Wallace, Jr., of U. S. Geological Survey. Suggestions
on water data sources were also received from Mr. John J. Mitchell of Texaco
and Mr. D. E. Powley of Amoco.
Information concerning present reinjection and waterflood operations were
obtained from Mr. George Singletary, Texas Railroad Commission, Mr. Robert
Kent, Texas Water Quality Board, and Mr. Robert Bates, Louisiana Department
of Conservation.
XI
-------
SECTION 1
INTRODUCTION
Declining national supplies of petroleum and natural gas along with in-
creased consumption has resulted in the United States becoming dependent upon
foreign sources for much of the hydrocarbons needed to supply the energy
demands of our society. This is an uneconomic and potentially dangerous
situation in terms of the national security. As a result, the nation has
embarked upon a program to develop alternate energy sources.
One of the proposed alternates is geothermal energy or energy in the form
of heat from beneath the surface of the earth. This heat is most readily
obtainable in the form of underground steam or hot water which can be brought
to the surface to perform useful work. Only a few steam fields are believed
to exist, but many hot water deposits are known. These later may be divided
into connective systems and closed systems. The connective waters are re-
generated by ground water percolating downward while the closed systems are
distinctive pockets or reservoirs and are depletable. Primary among the
closed reservoirs are the geopressured hot waters found generally at depths
in excess of 3,000 meters in the sedimentary basin of the Texas and Louisiana
Gulf Coasts. These waters are under very high pressure, being the load-
bearing portion of the unconsolidated formation in which they occur. The
available data on this resource has been a by-product of the extensive oil and
gas exploration which has taken place in the area. Thousands of wells have
penetrated the formations and the existence of the waters is well documented.
The extent and productivity of the depletable reservoirs is only a matter of
conjecture. Studies, using oil field data, have indicated the resource may be
considerable.
Proposed development under the sponsorship of the Energy Research and
Development Administration (ERDA) has reached the stage of preparing to test
the reservoirs through wells that have been drilled for petroleum and found
to be unproductive. One such well in southwest Louisiana is being tested by
McNeese State University, Lake Charles, Louisiana under contract to ERDA.
Contracts to test other such wells are anticipated.
Paper studies on the economics of power production have been made with
resulting marginal economics. However, the potential of the resource, which
includes a possible major source of natural gas dissolved in the fluids, is
sufficient to warrant-continued efforts.
This report describes the resource, the possible uses, the projected re-
sulting emissions, other impacts upon the land, the present stage of develop-
ment and projections of future developmental plans. Assessments are made of
the potential environmental impact and research needs to evaluate and minimize
these impacts are proposed.
-------
SECTION 2
CONCLUSIONS
A viable geothermal resource appears to exist in the geopressured hot
water reservoirs in coastal areas of Louisiana, Texas, and possibly Missis-
sippi. This resource is as yet unproven, and estimated economics are not
sufficiently attractive to encourage private development. However, because
of the possible large size of the resource (estimates vary from virtually zero
to 20,000 megawatt centuries) and the favorable location in an industrial
area, it will apparently be tested and developed through combined government-
industry effort.
For technical and environmental considerations, the reservoirs should
presently be classified as medium to low salinity and temperature geothermal
resources. The salinity, based on oil and gas well water samples, will range
from approximately 1000 TDS to as high as 10% salinity. The waters will most
assuredly be saturated with SiO2 (silica) and the components of the clays with
which they have been associated. However, there is evidence to suggest that
hydrogen sulfide, heavy metals and other components associated with highly
mineralized waters will be absent or at very low levels. Temperatures may
range as high as 260°C (500°F) but most reservoirs will be in the 120°C (250°F)
to 204°C (400°F) range.
This water is also estimated to be at or near saturation with natural gas
(primarily methane). Values up to 8.9 Nm3/m3 (50 scf/bbl) have been estimated
in the hotter, higher pressure reservoirs. This gas may someday be of suf-
ficient value to justify production of the waters for their,gas content alone.
In such case the waters would most likely be reinjected into non-geopressured,
but still deep, sands. Many of the environmental considerations discussed in
this report would be equally applicable to the operation of such a gas field.
The geopressured geothermal resource is currently being considered pri-
marily as a source of electrical power. However, the waters may also be used
for process and space heating, air conditioning, and other normal heat uses
either in combination with electrical generation or, in the case of the low
temperature reservoirs, as a low level heat source only.
The economics of the use of the resource in the production of electric
power by conventional means are not competitive with other energy sources such
as nuclear, coal, solar, or oil. However, if the water is saturated with
natural gas which can be recovered and sold, the total process may be an eco-
nomic power source within the next decade. This could be particularly true if
(1) the natural gas is recovered, (2) the high level heat above 120°C is used
for the generation of electricity, and (3) the low level heat below 120°C is
used as an industrial or commercial heat source.
-------
Environmental impacts of the development of the resource appear to be
small. Geothermal development is reported to be a relatively clean energy
source from an environmental standpoint and geopressured geothermal is one of
the cleaner forms due to the relatively low salinities and the indicated
absence of noxious gases such as hydrogen sulfide.
The environmental aspects are divided into two categories—emissions and
geological impacts. These are summarized as follows:
EMISSIONS CONSIDERATIONS
Information from three private sources was used to supplement the number
of formation-water analyses obtained from two published papers and two open-
file reports of government agencies. The relatively few published analyses of
the waters obtained from deep wells are usually not accompanied by sufficient
additional information to confidently distinguish between a normal and an
overpressured water. Conclusive evidence of geopressured origin is lacking
for about 70% of the formation waters whose analyses are listed here. These
are the brines from wells for which only the formation depth and completion
date are available. In these cases a formation depth greater than 2,743 meters
and a well-completion more recent than 1962 were arbitrarily chosen as in-
dication that the source formation was of the overpressured type. There is
little doubt that the remaining 30% of the analyses do represent geopressured
waters, as additionally evidenced by pressure-to-depth ratios, temperatures,
or salinity anomalies.
Many of the higher salinity waters likely were obtained from wells which
terminated at the first "pressure kick" or at the very top of the geopressured
zone where maximum salinity occurs. The data available makes it impossible to
further identify these samples.
The TDS content of the waters listed ranges from ^200 to 340,000 ppm.
However, the higher salinity waters should not be considered as typical of
those expected to be found and produced for the sand aquifers in question.
The waters in these formations are indicated to be within the salinity range
of 1,000 to 30,000 total dissolved solids (TDS). Minor elements, where re-
ported, are present at the following approximate levels, in ppm:
Li - <10
Sr - <10
Br - 15-200
I - 5-50
B - 20-60
The concentrations reported for barium in a considerable number of
analyses—between 200 and 1,000 ppm—are strongly doubted here. In these
cases, as in any situation where barite might be used in well-drilling fluids,
the validity of the sample must be suspect.
By far, the potential and actual emissions of greatest environmental
concern expected from any application of geopressured fluid are those of the
water itself and of the spent brine. The former is a potential emission only,
and might contact the surface environment as a result of accident, notably
-------
during a possible well blowout, but also from possible structural failure of
other equipment. Spent brine, a normal, designed effluent stream or emission,
can likely be reinjected into a receptor stratum, but could conceivably become
a fugitive emission as a result of possible structural failure of equipment.
The latter events have less probability of occurring than ruptures in the main
stream header, or steam-drum blowouts in conventional power plants.
A waste brine stream will be generated regardless of use of the geo-
pressured waters unless the waters are of such salinity that they become use-
ful for agricultural purposes. Disposal of this stream may be approached
either by reinjection into shallower non-geopressured formations or released
into existing water bodies of similar salinity. The latter method should be
the most economical for fields near the Gulf, even if some water clean-up or
cooling is necessary. Each situation will require evaluation on its own
merits. For more inland areas, reinjection will likely be the method of
choice. The alternate would be piping or canaling to the nearest saline water
body.
It should be noted that reinjection into the source formation will
be uneconomical. The high pressure in these sands would require large, high
energy-consuming pumps which would have serious effects not only on the cost
factor but also in the net energetics of the project. Therefore, reinjection
must be into shallower hydropressured strata. These, of course, will already
contain their own water so compatibility must be established and the possibil-
ity of intrusion of salt water into higher levels containing potable water
must be examined and monitored.
Accidental, large-volume discharges of either geopressured brine or spent
brine, although not expected to be frequent, are capable of causing consider-
able damage to the environment and harm to personnel if they do occur. Both
the relatively high temperatures—82°C to 188°C—and possible high salinities,
up to/say, 10% TDS, could completely destroy the vegetation contacted by the
brine. The area and time of greatest hazard to the environment is quite
obviously in the brine field during the well-drilling period.
Contamination of fresh water aquifers by salt is a possible result of the
reinjection of the spent brine. The occurrence of this, although remote,
could result from well leakage by corrosion, or from channeling of the brine
along a geologic fault induced by the increased pressure of reinjection.
The overall environmental impact of the cooling tower exhaust will be
greatly dependent on the exact location of the geopressured facility. In
predominantly agricultural areas, there would probably be some measurable, or
at least claimed, impairment in the health of row crops or orchards in the
vicinity, resulting from drift deposition. In or near a metropolitan area the
major impact might be the occasional periods of lowered visibility, the mild
increase in corrosion rates of nearby metal objects—notably, cars in any
adjacent parking lots—and, perhaps, noticeable effects on nearby ornamental
plantings. Actually, the exhaust expected from the cooling tower operating
under the parameters considered here will be far less harsh on the environment
than that from most industrial or public utility towers currently operating.
-------
GEOLOGICAL IMPACTS
The primary geological result of resource development is likely to be
surface subsidence. The waters to be produced are, at least partially, the
load-bearing portion of the reservoir. As withdrawal occurs, compaction of
the sands and clays of the reservoir will take place. Subsidence is the
normal result of such compaction. However, these are very deep reservoirs and
are very large in areal extent. These factors may prevent noticeable surface
effects.
The sedimentary basins in which the reservoirs occur are highly faulted.
These faults are subsidence faults rather than tectonic faults and are due to
naturally occurring subsidence as the sand and clay sections tend to slip
gulfward. Increasing the rate of subsidence by water withdrawal will likely
increase the activity of such faults and result in micro-earthquakes. How-
ever, no damage from the movement would be anticipated.
-------
SECTION 3
RECOMMENDATIONS
The two events which together would furnish the greatest impetus in
advancing the planned use of geopressured brine from its present conceptual
stage toward commercialization are the successful completion and operation of
a test well and the continuous disposal of the brine into the required number
(probably two) of reinjection wells. The concurrent operation of a methane
separator and the means of disposal for the methane are necessary appendages
whose successful functioning has already been demonstrated. Unfortunately,
the size of the necessary investment is relatively large, estimated to be
about $3.9 million.
Research work of a certain type is strongly recommended to commence im-
mediately following the choice of the tentative locality for a prospective
test well or demonstration plant. This work would be a "pre-plant" environ-
mental survey and would extend through the construction and well-drilling
phases. The program should be sustained for perhaps several years past the
initial well production or plant start-up. Some of the work should continue
throughout and perhaps even after the active life of the geopressure project.
The purpose of the first part of the survey would be to establish "base-line"
values or to indicate the state of the natural (or artificial) environment
before the physical start-up of the geopressure project, and the later phases
would measure the environmental effects of the operation relative to the base-
line values. The survey should include:
• Land surface evaluations
- Establishment of a system of local (say, 3-mile radius) benchmarks of
accurately determined evaluation relative to Mean Sea Level or other
relatively constant datum
- Monitoring of benchmark evaluations periodically after withdrawal of
geopressured water has commenced
• Groundwater information
- Measure water tables and water composition of reinjection formation
and of aquifer chosen as source of water supply
- Periodic analysis of other fresh water aquifers for TDS; temperature
readings
• Local natural surface water
- Periodic determination of TDS
• Monitoring of surrounding vegetation
- Color photographs of indigenous vegetation, ornamental plants and
economic crops
-------
- Periodic evaluation of vegetation by qualified agriculturalists
or botanists
• Atmospheric quality measurements
- Total particulates
- Sodium chloride
- Unburned hydrocarbons
- Hydrogen sulfide, if present
- Ammonia
• Seismic measurements
- Obtain recommendations from geologists or seismologists
• Photographs and other documentation of the condition of the exterior of
existing nearby buildings, particularly in the prevailing downwind
direction
In addition to the above environmental base-line effort for a given well
location, certain items of general concern should be given deeper study than
possible in this report. These suggested items are:
• Reinjection and other disposal methods
- Subsidence related to deep fluid withdrawal
• Micro-earthquakes related to reinjection or withdrawal of fluids
It is suggested that competent experts survey current experience in the
three above areas and prepare exhaustive reports on the current knowledge, ex-
periences of the past, and risk factors involved in each major area. Geo-
pressured geothermal resource development appears to be one of the favorable
alternate energy sources from the environmental viewpoint. However, the above
three items could present serious consequences should their impacts prove to
be negative to the environment. The risks involved should be clarified to
the extent possible before major development of the resource begins.
Large volumes of fluids of somewhat uncertain salinity must be disposed
of. Also the possibility of accidental discharge is always present.
Release of these fluids into local surface waters will be detrimental to the
fish and wildlife of the area. Monitoring of the surrounding water bodies
should be carried out for the life of the project.
The need for such research is manifest but the timing is still uncertain.
The present state-of-the-art in geopressured geothermal development is in its
infancy. The Energy' Research and Development Administration is in the process
of assigning contracts for the sampling of waters from existing depleted or
dry oil wells. Following this phase, test wells may be drilled in fiscal year
1977. A normal time span for preliminary research and testing would indicate
at least a 5-year period will pass before the first demonstration plant will
-------
be constructed. Negative results on test wells would negate the entire de-
velopment. In view of this possibility and the long time frame before re-
source development could begin, it is recommended that a moderate priority
rating would be proper for major environmental considerations and research
efforts.
Environmental studies aimed primarily or partially at geopressured geo-
thermal energy utilization are underway. The Energy Research and Development
Administration has taken the lead in this area. Their program as of September
1976 includes:
• A general environmental assessment underway at Oak Ridge National
Laboratory
• A program plan for controlling subsidence to be prepared by Lawrence
Berkeley Laboratory
• Guidelines for the preparation of environmental reports by Argonne
National Laboratory
• Background studies of Gulf Coast subsidence being carried out by the
U. S. Geological Survey
In addition to the above, work is expected to start soon on the establishment
of base line data on Gulf Coast elevations for later use in subsidence
evaluation.
Work is also underway on removal or control of hydrogen sulfide emissions
in geothermal power plant operation. This effort is aimed primarily at con-
nective geothermal systems where the sulfide is much more prevalent than is
expected in the geopressured zone.
It would be desirable for the Environmental Protection Agency to work
closely with and participate in the ERDA effort. This would serve to avoid
duplication and should result in increased information dissemination.
One area which must be explored as soon as possible is the disposal of
waste fluids. Very large volumes of wastewater, mostly saline, will be
generated. This brine must be reinjected, released into saline Gulf waters,
or otherwise disposed of in such manner as will be economically compatible
with the environment. Research on the problems of reinjection, the economics
of. transportation to the Gulf, and any alternate methods needs to get underway.
The second most important item of need is in the subsidence area. Every
effort should be made to determine the possibility of subsidence and the early
detection of subsidence. Studies of oil field subsidence in geopressured oil
and gas reservoirs should be made. Basic research on subsidence and prediction
of subsidence would be desirable. The Gulf Coast involved is an area of
natural subsidence laced with resulting faults. This increases the potential
hazard of extensive water withdrawal.
Another important area of environmental research is the problem of deal-
ing with accidental geothermal fluid releases. This may occur as a result of
-------
a well blowout, pipeline rupture, or other accidents. Methods of coping with
these possible occurrences should be determined and preventive measures taken
prior to drilling of test wells. Such fluid flows may be difficult to control
and release large volumes of saline water which could contaminate hundreds of
acres of farm land.
-------
SECTION 4
DESCRIPTION OF THE RESOURCE
Four broad categories of geothermal systems have been recognized:
• Magmatic
• Hot, dry rocks
* Convective
* Geopressured
Technology has not yet been developed to exploit the first two types;
therefore,they will not be discussed.
The third type, convective geothermal, is the only type now being com-
mercially exploited. In convective systems, circulating fluids within a
bounded reservoir transfer heat from a deep source to near the surface. Iso-
tope ratios and trace element studies indicate the source of the convective
water to be principally meteoric. Rainwater percolates downward, probably
along fault planes, becomes heated, and where impermeable rock overlies the
permeable reservoir, escape of the water is prevented and a convective. system
is created.
The ultimate source of heat to drive the convective engine is from magmas
within the earth's crust. These may be basaltic, such as in Iceland? acidic
intrusions, such as the Circumpacific geothermal areas frequently associated
with andesitic volcanics; or merely a thin crust composed of highly conductive
rock, such as in the Hungarian basin or the Battle Mountain, Nevada area.
Two major subtypes of the convective system exist: vapor-dominated and
liquid-dominated systems. Vapor-dominated systems are relatively rare, but
account for most of the commercial geothermal energy being produced today,
notably at the Geysers, California, and Larderello, Italy. The fluid produced
is dry, superheated steam characterized by an absence of nonvolatile constit-
uents. Liquid-dominated systems, such as Wairaki, New Zealand, produce a
mixture of wet steam and hot water. These fluids frequently possess high
saturations of soluble, nonvolatile substances, such as SiO2, and the ions Na,
K, Ca, Cl, SOu, HCOs, etc. The characteristics of liquid-dominated systems
vary widely, and numerous subtypes exist.
Geopressured zones occur throughout the world in basins where rapid sed-
imentation and contemporaneous faulting are taking place, and are character-
ized by abnormally high pressures and temperatures. The most studied and best
understood geopressured region in the world is the Gulf Coast of the United
States.
10
-------
ORIGIN OF GEOPRESSURE
Rubey and Hubbert1, and other numerous authors have attributed the origin
of geopressure to be due to undercompaction of the sediments. Much confusion
arises from the use of the word "undercompacted" as a genetic rather than as a
descriptive term. In theory, sediments, predominantly clays accumulate in a
rapidly subsiding basin. It has been demonstrated off the Mississippi delta
that pore water in the upper layer of this sediment can constitute 70% or more
by volume. As the process of burial occurs, the stress of an accumulating
overburden causes energy potentials to be created in the system according to
the formula:
S = P + O
S = Vertical component of geostatic stress
P = Interstitial fluid pressure
O = Normal component of grain-to-grain pressure
Burst2, in a definitive paper, discusses the diagenesis of Gulf Coast
clayey sediments. He describes fluid expulsion in three separate stages.
However, for purposes of explanation, the first stage has been subdivided
into two parts.
Approximately 80% of the clay deposited in the Gulf is composed of mont-
morillonite, or swelling clay. The clay lattice contains two interlayers of
tightly bound water and may contain many interlayers of loosely bound water.
Stage 1 in the burial process is the expulsion of excess pore water,
which represents about 60% of the original volume. This occurs at very
shallow depths and is essentially complete at depths of a few hundred feet.
The clay platelets are not in contact, but are greatly swollen with loosely
bound interlayer water.
The second part of Stage 1 involves the loss of this excess interlayer
water, which occurs above depths of 1,000 m., still well within the hydro-
pressure zone, and is a purely mechanical process. The clay lattice is now
in stable form, containing two interlayers of water. The sediment is "com-
pacted" , with grain-to-grain contacts supporting the lithostatic component of
the overburden load, and the capillary pore pressure supporting the hydro-
static component.
Burial continues until the sediments have reached a depth corresponding
to the critical temperature necessary for the second stage of clay dehydration
to occur. Burst demonstrates that this is a temperature-dependent phase
change occurring between 95°C and 100°C, which releases the next-to-last water
interlayer. The pressures and temperatures of the geopressured zone are in-
sufficient to liberate the last 'water interlayer.
Where fluid escape is possible within the system, water will move from
the higher energy potential to the lower in accordance with Darcy's law. If
the rate of accumulation of geostatic stress is very great and exceeds the
ability of the sediment to dewater under Darcy's law, then the interstitial
fluids must assume an increasing proportion of the total overburden load and
geopressure will occur. Fluid pressures in the geopressure zone commonly
11
-------
represent 0.6 to 0.8 of the total overburden. This process is generally im-
plied by the statement that geopressure is caused by the undercompaction of
sediments.
If the escape of fluids is not restricted vertically by the sedimentary
column, and laterally by contemporaneous faulting, then the change of relative
volumes of the solid and liquid phases forces the liquid to support a pro-
portionally greater part of the overburden load; i.e., the formation becomes
geopressured. Pressure gradients in the geopressure zone may approach litho-
static, or approximately 0.2 atm./m. (1 psi/ft.). Thus, bottom hole pressures
in the range of 680-1,360 atm. (10,000-20,000 psi) would commonly be encoun-
tered. Mechanical energy available at the well head is approximated by the
bottom hole pressure minus the hydrostatic head and frictional losses in the
bore hole.
If the aforementioned theory is entirely correct, one would expect to see
uniformly increasing geopressure with depth. Such, "however, is not the case.
Sediments in the Gulf Coast geosyncline are found in two distinct bounded,
pressure regimes: the upper hydropressured regime, extending to an approximate
depth of 1,500-3,000 m., and the lower geopressured regime. The boundary
between the hydropressured and geopressured zones is very distinct and is
characterized by abruptly increased pressures, thermal gradients, flowline
temperatures, and penetration rates, and decreased seismic velocity, shale
density, and shale resistivity.
ORIGIN OF HIGH TEMPERATURE
In a thermal system in equilibrium, heat can be neither created nor de-
stroyed, and the heat flow from the deep crust and mantle of the earth must
equal the heat flow at the surface. If this were not so, the crust of the
earth would soon heat up to temperatures sufficient to vaporize all rock.
The relationship of heat flow, thermal gradient, and thermal conductivity
is governed by Pourrier's law, expressed as:
Q = rk;
Where Q = heat flow;
r = thermal gradient; and
K = thermal conductivity
The "subcompacted" geopressured sediments possess a much lower thermal
conductivity than the overlying "compacted" hydropressured sediments. Because
heat flow remains constant, any decrease in conductivity must be counter-
balanced by a proportionally increased thermal gradient. This blanket effect
traps the upward flowing heat causing.the anomalously high temperatures en-
countered in the geopressured. zone. Temperatures may range from 110°C at
depths shallower than 3,000 m., to more than 260°C at 6,000 m. and deeper.
Some expert opinions have been expressed at various geopressured symposia
that salt diapirs, found in many of the geopressured areas are the true source
of the heat. These long columns of salt could act as heating rods to convey
high deep heat to upper areas. However, hot geopressured zones do exist in
the absence of salt diapirs. Consia< ing both theories it must be concluded
12
-------
that the explanation of the origin of the heat leaves room for further
research.
NATURE OF GEOPKESSURED GEOTHERMAL FLUIDS
Geothermal fluids possess several other characteristics in addition to
high temperatures and pressures. Water salinities are considerably lower than
those found in the hydropressured zone. This statement is made with little
supporting analytical data. Jones3 states that, "Waters of the geopressured
zone decrease in salinity with depth, and dissolved solids in the range of
5,000 to 20,000 mg/1. may be common." This statement is based upon salinity
estimates which can be obtained from spontaneous potential measurements on
electric logs. These potentials are analyzed in terms of the dissolved solids
in formation water, expressed as mg/1. of sodium chloride. This is a general-
ly accepted procedure in the petroleum industry, and thousands of geopressured
well logs have been examined in this way.
A plot of salinity versus depth from such a well shows very high salinity
as the well enters the geopressured zone followed by a sharp decline. Such a
curve taken from Jones is shown in Figure 1. Difficulties in obtaining
samples of these waters have precluded extensive analytical confirmation of
these low salinities. Most samples have been obtained from the top of the
zone and thus show misleading high salinity. We believe the water will be of
low salinity. However, in the environmental aspects of this report, we have
taken somewhat higher salinities to provide for what we feel may be the worst
cases. Typically, geopressured waters have salinities in the range of 5,000
to 20,000 ppm, as compared with 100,000 ppm or greater in the overlying
sediments. The cause of this is two-fold. First, the water expelled from the
clay lattice during the second stage of dehydration is essentially fresh. It
dilutes the residual saline pore water, thus reducing overall salinities.
Second, the shale itself may act as a semi-permeable membrane, concentrating
brines at certain interfaces and thus freshening adjacent waters. This
phenomenon is imperfectly understood at the present time. The abrupt change
in salinity and reverse of the salinity gradient is very apparent on electric
logs and has long been considered diagnostic of the geopressured zone.
Buckley4, Burst2, Phillippi5 and others have demonstrated that hydro-
carbon maturation begins at a temperature of about 75°C. Most, if not all,
of our hydrocarbon reserves have been generated in the geopressure zone from
indigenous carbonaceous matter present in the original sediments. Thus it is
no surprise that the geothermal fluid is expected to contain dissolved hydro-
carbons, principally methane, in large quantities. Culberson and McKetta
have shown that under the temperature, pressure, and salinity environment
postulated for the geopressured aquifers, the fluids could contain 1,132 std.
liters (40 scf) or more of methane per barrel. This dissolved methane could
be the largest component of geopressured geothermal energy in both financial
terms and in terms of extractable energy. Some EzS (hydrogen sulfide) may be
associated with the methane. However, the consensus of most researchers
seems to be that no HES will be present.
Because another by-product of the diagenesis of montmorillonite is silica,
the fluids are expected to be near the saturation level for SiO2. This could
13
-------
Sodium Chloride X 1000 (ppm)
0 20 40 60 80 100 120 140 160 180
0)
fci
10
4J
15
20
TOP OF
GEOPRESSURE
ZONE
From Jones
Figure 1. Change in formation water salinity with depth, in relation to the
occurrence of the geopressure zone, Manchester Field, Calcasieu
Parish, Louisiana.
14
-------
present scaling problems in the borehole and wellhead equipment, and may lead
to a permeability barrier developing around the wellbore if pressure drawdown
is allowed to occur too rapidly. This would plug the well. Therefore, care-
ful pressure maintenance programs must be followed. The silica problem common
in other geothermal fluids is also present in the geopressured waters.
GEOPRESSURED RESERVOIRS
The geopressured zones of the upper Gulf Coast occur in a broad band 300
to 500 km. wide that stretches from below the Rio Grande, along the coast and
into southern Mississippi and Alabama, a distance of more than .2,000 km. The
geopressured zones may extend offshore a distance of several hundred km. and
contain an accumulation of clastic sediments that exceeds 15,000 m. in thick-
ness in some areas.
The sediments range in age from the Eocene Wilcox formulation, approxi-
mate ly 50 million years old, to Pleistocene, only about 1 million years old.
Two types of sediments predominate: sands and lagoonal shales formed in the
great deltas which shaped the coast in the geologic past, and marine shales,
formed offshore and now generally occupying the deeper portion of the Gulf
Coast geosyncline. The sands may be of the transgressive type, where wave
action of an encroaching sea has produced a blanket of clean, well sorted
sandstone overlaid by a marine shale, or they may be regressive, or prograda-
tional, sand bodies composed of lenticular units that represent ancient bar-
rier bars, and the other discontinuous types of sand units that are formed as
a delta progrades into the sea. The transgressive sands are by far the most
favorable for fluid production, possessing greater porosity, permeability,
continuity, and areal extent. Unfortunately, regressive type sand bodies pre-
dominate on the Gulf Coast. When a sand body is contained in an interval of
geopressured shale, it becomes charged with the geothermal fluids and thus
becomes a potential reservoir.
The pattern and distribution of the sand bodies is determined largely by
the numerous contemporaneous, or growth, faults that lace the coast in a sub-
parallel trend to the present shoreline. These faults may have throws of 300 m.
or more and act as effective barriers to the escape of geopressured waters;
i.e., they form reservoir boundaries. Sand distribution are further effected
by complex diapirism and flowage of shale and salt underlying tertiary sediments.
The general distribution of sediments is in the form of a series of over
and offlapping clastic wedges or pads, each representing a cycle of deltaic
deposition, the oldest far inland and the youngest still being formed offshore
in the Gulf of Mexico. The top of the geopressure zone is deepest in the
oldest formations and becomes progressively shallower as growth faults are
crossed in a coastward direction, thus indicating that the fault planes have
acted as "valves" and eventually have allowed excessive pressure to bleed off.
Papadopulos, et al7, studied the onshore area of the upper Gulf Coast,
approximately 150,000 km2. They divided the area into 21 subareas, as shown
in Figure 2, based on age, lithology, and fault-trends, and calculated an
"idealized conceptual reservoir" for each subarea by assuming that all the
sand occurs in one thick, continuous bed bounded on both top'and bottom by
15
-------
50
lOOMiles
1 I I I
0 50 100 150 Kilometers
From Papadopulos
Figure 2. Location map showing the extent of the assessed geopressured zones.
-------
geopressured shale. Using this approach, a total volume of water of 78.39 x
1012 m3 is calculated for the Gulf Coast. Thermal energy contained is 457.5 x
1020 J, equivalent to 14.5 x 10s megawatt centuries (MWc), and contained
methane energy is 252.6 J, or 8 x 10s MWc. These numbers represent the total
resource base and do not in any way indicate the ultimate recoverable energy.
Factors such as recovery technology, reservoir size and location, costs, and
potential legal conflicts were not considered.
Dorfman , Bebout^, and others have used the "geothermal fairway" approach.
First, maps are prepared showing net sand in a given paleostratigraphic in-
terval. These maps are then correlated with isogeothermal maps and top of
geopressure maps. The result defines regions where favorable sand conditions,
high temperatures, and shallow geopressure combine to form "geothermal fair-
ways" or areas favorable for exploitation. The results of this approach
indicate that approximately 20,000 MWc of thermal energy may be available for
power generation. Bebout's fairway selection is shown in Figure 3.
The failure of the "geothermal fairway" approach is that it does net
identify or describe individual geothermal reservoirs. Since faults constitute
a barrier to water movement, each fault block must be considered individually
for geothermal potential. Tremendous quantities of water will have to be pro-
duced over long periods of time to sustain a commercial geothermal electric
power facility; therefore, any fault block that is physically too small to
satisfy these requirements is not potentially productive. This eliminates
approximately 50% of the entire Gulf Coast area for the production of elec-
tricity but not necessarily for other uses. Other problems such as sand dis-
tribution permeability, transmissivity, legal, and environmental restrictions
may eliminate 50% of the remaining fault blocks. Conversion efficiencies for
thermal energy are also low, on the order of 10%. These factors when applied
to Dorfman and Kehle's8 estimate of available electrical energy of 20,000 MWc
implies a practical recoverable energy on the order of 500 to 1,000 MWc, not
including dissolved methane.
DIFFICULTIES AND LIMITATIONS
There are two broad categories of problems that may be encountered in the
development of the geopressured resource: problems related to producibility,
and legal and environmental problems.
It has already been noted that a reservoir must be of a sufficient size
to be commercially viable. Moreover, the sand bodies that constitute the
reservoirs are more often than not of the regressive, discontinuous type. In
order for these discontinuous sand bodies to be productive over long periods
of time, it will be necessary for the surrounding shales to dewater into the
sands and replenish the withdrawn fluids. Jones^'10'11 has postulated that
this will occur; however, nq hard data now exists to either confirm or refute
this hypothesis. Knapp and Isokrari12 have suggested that a test well located
close to the sand/shale reservoir boundary could determine the influence of
shale dewatering in a short period of time.
Aquifer permeabilities must be adequate to provide the enormous flow rates
required by a commercial facility. Papadopulos, et al , report average
17
-------
<( uc ".''.': TfxT^T^sx . x \ // \^. .,';. "
-
I/ f^ "~^\ G 0 L
From Bebout
Figure 3. Geothermal fairways of the lower and middle Texas Gulf Coast,
18
-------
A
COASTAL PLAIN
A
CONTINENTAL SHELF
SLOPE
-LOW DENSITY:
TEXAS COASTAL AREA V; Xrf^-I >I HIGH-PRESSURE _S_HA_LE_:
From Bebout
PRE-TERTIARY SECTION
Figure 4. Depositional style of the tertiary along the Texas Gulf Coast.
-------
permeabilities in the range of 15 to 50 md. with porosities of about 20%,
which would probably be sufficient. Other data9, however, indicate that
permeabilities of less than 1 md. and porosities of 10% are not uncommon. It
is generally accepted that permeabilities are highest in Louisiana and lowest
in the south Texas area.
Transmissivity ratios reflect the rate at which an aquifer will draw down
during production; i.e., determine what the maximum allowable flow rate would
be to ensure production over a given period of time. The actual, in-situ
parameters of permeability, transmissivity, and shale water influx are essen-
tially unknown, but can be established with a thorough program of static and
dynamic well tests.
The technology for drilling wells in the geopressure zone is well known,
but costs are high. It may be necessary to find some way to reduce drilling
costs in order to make geopressured geothermal an economically competitive
form of energy.
Legal problems may develop with regard to ownership, particularly if a
well is produced for the dissolved gas content only. Conflicts may arise if a
geothermal well depletes the pressure drive of updip gas production.
Subsidence and fault movement are naturally occurring geologic phenomena.
It will be difficult to determine in a local area if these effects are being
caused or intensified by the withdrawal of geothermal fluids or are part of
the natural geologic cycle. Prior monitoring of subsidence, fault movement,
and microseismic activity in areas of contemplated geopressured production
will probably be necessary.
20
-------
SECTION 5
POSSIBLE USES OF GEOPRESSURED GEOTHERMAL WATERS
As pointed out by Wilson, et al13, geothermal, geopressured water along
the Texas Gulf Coast contains three forms of energy capable of utilization
through technology:
• Thermal
• Kinetic
• Dissolved methane
This energy may be harnessed to produce heat or electric power, as well as
feedstock for the chemical industry. However, as in the conversion of most
types of potential energy to readily usable forms, special problems exist re-
quiring some development work and unique solutions. Geopressured geothermal
water is not without these problem areas. These plus the unproven nature of
the resource casts doubt upon the near-term (5-10 yr.) usage of this potential
energy source. Should the resource prove out and development take place,
practical application will likely take form as follows.
PRODUCTION OF ELECTRIC POWER FROM GEOTHERMAL ENERGY
Geothermal water, as with all hot waters, can be used directly as a heat
source in the warming of buildings and for some other direct heating uses.
However, the distance to which such heat can be transmitted economically is
limited to an estimated 50 kilometers. The generation of electric power
produces a form of energy capable of widespread, economical distribution and
utilization for many purposes. Because of its many favorable characteristics,
geothermal energy will be used for the generation of electric power. This can
presently be done by two methods.
• Flashing steam from the geothermal water by reducing the pressure to
a predetermined point and passing the steam through a low-pressure
expansion turbine connected to an electric generator.
• Transferring heat from the geothermal water to a suitable secondary
fluid which is, as a result, vaporized and passed through an expan-
sion turbine connected to an electric generator.
Electric power may also be generated from the kinetic energy of the geo-
pressured waters. It is believed13 that well head pressures as high as
140 kg/cm2 (2000 psi) will be realized. This pressure may be converted to
electric power by a hydraulic turbine in much the same manner as hydroelectric
power is produced.
21
-------
If all of the potential geopressured geothermal resources of the Texas
Gulf Coast — offshore as well as on-shore — could be economically exploited
without adverse ecological impact, in the form of small, 10-100 MW(e) power
plants, the highest estimates are 10,000-40,000 MW(e) centuries of available
electrical power8'11' 13 'l •*.
OTHER POTENTIAL USES
A number of possible uses of geopressured geothermal energy other than
electrical power generation have been suggested*1*' ^' ^ dependent on the heat
and kinetic energy content of this resource. It is doubtful that many of
these alternates are economically viable without base load use of the geo-
pressured geothermal brine for power generation and without methane extraction
for additional saleable energy value. Ecological considerations such as
possible subsidence and brine disposal indicate that location of early sites
will be remote from highly urbanized or industrialized areas, further limiting
a number of these non-electrical power generation uses.
However, it should be noted that the efficiency of use of geothermal
resources for nonelectrical purposes is greater than for electrical power
generation. The conversion efficiency for electrical power production approx-
imates 10-12%, while conversions of up to 85% energy efficiency may be reached
in some non-electrical applications such as direct contact heating.
Highly corrosive or scaling brine may require the use of a secondary
fluid and heat exchange system for circulation in heating systems and equip-
ment. Fossil fuel fired peaking units may also be required with many of
these applications. Nonelectrical applications of geothermal resources are
already of primary importance in some parts of the world for space heating
and industrial power and to a lesser extent for greenhouses and miscellaneous
uses. Among these locations are Iceland, New Zealand, Hungary, France,
Italy, U.S.S.R., Japan, and several cities in the U.S.A. However, none of
the geothermal sources for these applications are of the geopressured geo-
thermal type covered by this report.
Industrial Uses
• Heat source for sugar cane and pulp and paper operations.
• Sulfur frasching if fluids can be obtained in reasonable proximity to
salt domes containing sulfur resources.
• Steam turbine driven natural gas and petroleum pipeline pumping and
compressing.
» Low level process and space heat for chemical, petroleum, petrochemical,
and other industries.
« Lumber, brick, and concrete block curing kilns.
• Water desalination by either flash steam condensation or by process heat
supply to distillation-type desalting units to provide industrial boiler
and pure process water.
• Injection of brine effluent for secondary recovery of petroleum
22
-------
• Drying and evaporation operations (cement, clays, fish, or other
marine products).
• Mineral recovery from hydrothermal fluids (salt concentration, chemical
extraction, etc.),
• Adsorption refrigeration and freeze-drying of foodstuff.
Agricultural Uses
• Greenhouse heating for limited specialty crops and ornamental plants.
* Rice and grain drying.
* Hydroponics temperature and humidity control.
• Refrigeration and frozen food preparation.
* Aquatic farming.
• Processing of agricultural products (waste disposal or conversion, drying,
fermentation, canning, etc.).
* Animal husbandry including space and water heating, cleaning, sanitizing,
and drying of animal shelters. Creating optimal thermal-environmental
conditions for maximum growth and production may become increasingly
important.
Municipal and Residential Uses
• Homes, multi-unit dwellings, and buildings, closed hot water or steam
space heating systems or district heating by thermal distribution systems.
• Water (potable, hot/cold utility, etc.) heating.
• Der-icing bridges, overpasses, and driveways.
• Heating of swimming pools, fish hatcheries, etc.
• Waste treatment (disposal, bio-conversion, etc.).
• Absorption refrigeration and space cooling.
ENGINEERING ASPECTS OF ELECTRICAL POWER PRODUCTION FROM GEOTHERMAL BRINES
The two primary methods of electrical power generation, the flash steam
process (one- or two-stage) and the secondary working fluid cycle, including
sample economics for the coastal area, have been presented by Wilson, et al
and updated and expanded by Dorfman, et al
The details of two proposed electric power production systems can be
found in the Proceedings Second Geopressured Geothermal Energy Conference
referred to in reference no. 17. These are the flash and the secondary
working fluid cycles. Outlines of this fuel plant for supplying these systems
plus those of the electric power generating plants are described further in
Section 6 where the possible emissions and other environmental considerations
are treated. These models are used because it is felt that they will be the
most likely methods of power production for this resource.
23
-------
Advanced power production methods are under study. Lawrence Livermore
Laboratory is developing a "Total Flow" expander using the nozzle principle
and Jet Propulsion Laboratory is investigating a helical rotary screw expander
approach. These efforts are in the research stage and likely some years away
from commercial application. Should they prove practical, geopressured geo-
thermal fluids would be very suited for the feed. These conversion methods
would utilize both the hydraulic pressure and the heat energy in one step.
The environmental aspects of such conversion would, however, not differ
greatly from those of the flash or secondary fluid systems.
A combined flash-secondary fluid system is presently being tested by San
Diego Gas and Electric Company. This facility uses very high salinity geo-
thermal fluids, and the flash system was installed to avoid the excessive scal-
ing of a normal heat exchange step. Geopressured fluids are expected to pre-
sent only minor scaling problems. Much development work is underway to cope
with this type of scaling, and it is anticipated that geopressured development
will not necessitate the use of the combined cycle system.
ECONOMICS OF GEOPRESSURED GEOTHERMAL POWER PRODUCTION
Studies on the economics of power production from geopressured geothermal
fluids are subject to many uncertainties due to the lack of firm data on the
resource. The most exhaustive study to date has been that of Gault, et al17.
The results of that study will be used in this report.
Two commercial-size, 25-megawatt flash plants were considered. These
were a single-flash plant and a double-flash plant, both recovering natural
gas and both converting the overpressure to electrical energy. These plants
required 12 and 10 production wells, respectively.
The single-flash plant requires $53,067,000 for the fuel plant and
$14,487,000 for the power section for a total of $67,554,000. This is the
less economical plant.
The double-flash plant required only $43,551,000 for the fuel plant and
$15,845,000 for the power portion for a total of $50,496,000. The cost per
kilowatt-hour for the power plant only was $678 per kWh. This compares
favorably with present-day fossil fuel plants. Comparative costs of the fuel
and power plant for single- and double-stage flash are shown in Table 1.
The fuel section for this plant will produce, in addition to the hot
water, 4,467,600 Mscf of natural gas per year. The value of this gas at a
cost of $2.00 per Mscf is $8,935,200 per year. Taking credit for this gas
results in a cost per usable Btu of water heat energy to the power plant of
63 cents per M Btu. This value compares tp_ the intrastate cost of natural
gas on today's market of nearly $2.00 per M Btu. However, the conversion
efficiency of the plant is only 10.3%, including the hydraulic source. Unit
cost of the electrical power produced was calculated on this basis to be 46
mills per kWh, which is very high.
24
-------
TABLE 1. UNIT COST SUMMARY - 25 MEGAWATT - FLASH PLANTS
Fuel plant
Single-stage
flash
Double-stage
flash
Capital, M $
Capital, $/kWh
Unit fuel cost, $/M Btu
Unit fuel cost, $/M Btu
53,067
2,122
2.44
43,551
1,742
2.00
0.63
Power plant
Capital, M $
Capital, $/kWh
Conversion efficiency*
Net power cost, mills/kWh
14,487
580
16,945
678
10.3%
46
* Includes hydraulic power.
25
-------
The conclusion reached is that either the water must be hotter or a more
efficient means of conversion must be used if economical power is to be
produced from the geopressured zone.
The Center for Energy Studies, University of Texas at Austin combined
the Dow 1976 study with a Brown & Root study with some minor changes in
economic assumptions17 and arrived at a capital cost of $738/kW(e) for a 25
MW(e) power plant only as shown in Table 2 for a two-stage steam plant and
$786-$821/kWh for a secondary working fluid plant with an estimated 1980 bus
bar price of 47.5 mills/kWh apportioned as shown in Table 3.
INCENTIVES FOR GEOPRESSURED GEOTHERMAL POWER PRODUCTION
The 1980 census of the ^36_ counties of Texas which might reasonably
have access to the geopressure geothermal fairways of the Gulf Coast shows a
population of 3,518,859, ranging in population density from 1-390 persons
per square kilometer18.
Assuming the population growth trend, per capita electrical usage and
estimated required generating capacity follows the national trends predicted
by Hittman Associates, Inc. in Table 4.
We would estimate the increased required power capacity in the
coastal area at:
Probable Power Capacities, 36 Counties,
Texas Gulf Coast Geopressure Geothermal Zone
(Does not include Louisiana area)
Estimated
Required
Capacity
(103MW)
4.96
9.34
16.83
25.65
Year
1970
1980
1990
2000
Population
(106)
3.53
3.99
4.56
5.29
Per
Capita
Use
(kW)
0.9
1.5
2.4
3.2
Total
Use
(106kW)
3.18
5.98
10.94
16.93
Plant
Load
Factor
0.64
0.64
0.65
0.66
Required New Capacity
(1970 to 2000}
= 20.69
However, due to the heavy industrialization of this area in chemical,
petrochemical, petroleum refining, ferrous and non-ferrous metal production,
etc., both the population growth and estimated required generating capacity
are probably appreciably higher than the figures in the table based on national
averages indicate.
A minimum of 20,690 MW(e) of new generating capacity must be added in
this area to meet the anticipated demand by the year 2000. Traditionally,
all power generation in the area has been based on natural gas fuel with some
conversion to dual gas/oil capability being added over the last few years.
As supplies decrease and costs increase for both these fuels (gas-oil), there
is increased interest in other power sources. The importance of the use of
26
-------
TABLE 2. IMPORTANT PARAMETERS, ALTERNATIVE POWER PLANTS
Parameter
1.
Brine
a.
b.
c.
to power
Flow rate
plant
(kg/sec.)
Temperature (°C)
Pressure
(kg/cm2)
Plant A:
Flash
Steam
6.29 x 10
160
140
Plant B:
Secondary
Working Fluid
7.82
x 10
160
140
5.
6.
7.
8.
Geohydraulic turbine/generator
output [MW(e)]
Steam or SWF turbine/generator
output [MW(e)]
Auxiliary power requirements [MW(e)]
a. Feed pumps
b. Circulating water pumps
c. Cooling tower fans
d. Other services
Heat rejection (kW)
Net power output [MW{e)]
Capital costs {total $}*
Installed cost [$/kW(e)]
5.61
20.83
6.65
27.84
6.
17,
0.00
1.44
0.73
0.12
38 x 10
24.15
800,000
738
5.07
3.26
0.98
0.18
1.01 x 10
25.00
19,652,000t
786(821)*
Notes:
* Contingency taken as 15% in flash steam plant, in secondary
working fluid plant.
"I*Total capital cost of SWF plant at 15% contingency is $20,546,000,
^First entry JLO% contingency, second entry 15% contingency.
[Does not include fuel plant costs.]
27
-------
TABLE 3. 1980 APPORTIONED BUSBAR CHARGES [POWER PLANT?] (100% DEBT FINANCED)
Factor
Busbar charge
(mills)
Operations, maintenance
Fuel
Capital
Taxes (federal, state, local)
TOTAL
6.08
13.06
18.48
9.88
47.50
TABLE 4. MOST PROBABLE POWER CAPACITIES, U.S.A.
Year
1970
1980
1990
2000
Population
(10s)
205
232
265
307
Per
Capita
Use
(kW)
0.9
1.5
2.4
3.2
Total
Use
(10skW)
185
348
636
982
Plant
Load
Factor
0.64
0.64
0.65
0.66
Estimated
Required
Capacity
(103 MW)
320
544
978
1488
28
-------
gas and oil as refinery and chemical feed stocks rather than fuels is widely
recognized by industrial users in this region.
Earlier projections19 of much of the national energy shortage through
the year 2050 being made up by new nuclear power plants are not being realized,
High plant capital costs, uncertain future fuel prices, complex regulatory
approvals required, adverse public opinion on the safety and ecological
aspects of such plants are all factors in the probability that much of the
future Gulf Coast pow.er needs through the year 2000 will not be met by nuclear
power.
Extensive relatively low-grade coal (lignite) deposits are available
several hundred miles from the coastal area. These deposits are in an arc
sweeping through Texas from the Rio Grande River in the Texas-New Mexico
border region, through central and east Texas into Louisiana. Some com-
mercial utilization of these deposits has been made in the past, but interest
has been spurred by the recent "energy crisis". Many industries and public
utilities are now engaged in plans for exploitation of these coal resources
as the fuel for power generation in the Texas area for the future. The
nature of these deposits is such that "strip" mining is the logical recovery
method.
Future costs for coal, either Texas lignite or conventional coal, are
difficult to project should Gulf Coast industry become largely dependent on
this fuel as an energy source. Coal mining has traditionally been a labor
sensitive industry. This combined with the possible high costs of transport
to point of useage, cost of conversion of existing boilers from gas to coal
firing, additional increased capital for emission controls, and land restora-
tion costs may not make coal as attractive an alternate as it originally
appeared.
Compromise bills now before the Senate (May, 1976) seek to end federal
price controls on some natural gas and allow prices to consumers to rise
gradually (10-15% per year). The current regulated price of $0.52/1000 scf
would be raised to $1.60/1000 scf for newly drilled on-shore gas sold in
interstate markets. Provision would be made for further increases based on
inflation. Gas sold within the same state in which it is produced would
continue to be unregulated. Some new current gas prices in unregulated
contracts in the Gulf Coast area are running as high as $1.95/106 Btu.
Using natural gas for "boiler fuel" or other low priority industrial uses
would be prohibited after 10 years.
Faced with the possible ultimate loss of this conventional fuel source,
natural gas, for electric power production and the long-range economically
unattractive alternates: Q.) use of increasing amounts of imported oil or (2)
costly conversion to coal; the Gulf Coast industrial power producer should
be more interested in exploiting the geothermal energy potential in this
region than ever before. However, he is unlikely to undertake such a high
risk venture without federal leadership and funding in:
• Drilling test production and reinjection wells
29
-------
• Proving the technical and economical feasibility of the concept and
equipment through construction and operation of demonstration
plants
• Solving the complex legal, jurisdictional, institutional, and
possible environmental problems associated with exploitation of this
energy resource.
NON-ELECTRICAL POWER GENERATION USES OF GEOPRESSURED BRINES
Worldwide, the greatest non-electrical use of geothermal energy is in
the area of residential and commercial space and water heating, representing
over 400 MW(e) average energy consumption. This usage is heaviest in colder
climates with relatively high population densities that can support district
heating systems. The cost of insulated supply and return brine lines is
relatively high. However, well over one-third of the U.S. fossil fuel con-
sumption is used for residential purposes, part of which could be supplied
from geopressure geothermal brines as could absorption refrigeration and air
conditioning.
9 n
As Lindal has pointed out, there are many possible examples for future
industrial geothermal utilization. Some of the temperature ranges for various
processes are shown in Figure 5. By using fluid in the higher temperature range
as feed for a slightly lower temperature for a number of processes down to
ambient temperature, maximum thermal energy can be extracted in a "cascading"
effect.
The concept of integrated agricultural applications to use geothermal
energy to improve the world's food supply has been suggested by a number of
authors.
More recently Swink and Schultz21 have presented a conceptual multi-use
integrated process plant for using low temperature (<150°C) geothermal water
for both electric power production and direct heat utilization in industry.
This work is directed to the Raft River area of southern Idaho and uses the
"cascading" temperature concept where one process takes as feed brine at a
lower temperature from a preceding process. This utilization of the maximum
quantity of usable heat, if taken as an economic credit, tends to reduce the
required selling price of geothermal electricity to competitive levels when
integrated into an "energy park" concept.
Selection of specific processes, sizing of possible industrial-agricul-
tural plants, energy balances, and optimization of the use of the residue
brine from the power plant in an energy park were beyond the scope of this
report.
It should be noted that the heat exchangers for evaporation, drying,
etc. in conventional plants are usually based on steam as the heating agent.
Plants using liquid-to-liquid exchangers would have to be specifically de-
signed to utilize cascading temperature geothermal brine as a heat source for
many unit operations.
30
-------
0)
-p
in
•o
V
-p
200-.
190-
180-
170-
160-
150-
140-
130-
120-
110-
100-
90-
80-
70-
60
50-
40-
30-
20J
Evaporation of high cone, solutions.
Refrigeration by ammonia absorption.
Digestion in paper pulp, Kraft.
Heavy water via hydrogen sulfide process.
Drying of diatomaceous earth.
Drying of fish meal.
Drying of timber.
Alumina via Bayers process.
Temp, range of
_ conventional
power production
Drying farm products at high rates.
Canning of food.
Evaporation in sugar refining.
Extraction of salts by evaporation and crystalization.
Fresh water by distillation.
Most multiple effect evaporations, concentration of saline solutions.
Refrigeration by medium temperatures.
Drying and curing of light aggregate cement slabs.
Drying of organic materials, seaweeds, grass, vegetables, etc.
Washing and drying of wool.
Drying of stock fish.
Intensive de-icing operations.
Space heating.
Greenhouse space heating.
Refrigeration by low temperature
Animal husbandry.
Greenhouses by combined space and hotbed heating.
Mushroom growing.
Balneological baths.
Soil warming.
Swimming pools, biodegradation, fermentations.
Warm water for year around mining in cold climates. De-icing.
Hatching of fish. Fish farming
From Lindal
Figure 5. Required temperature of geothermal fluids for various
nonelectrical applications.
31
-------
As the chemical composition of the residual brines cannot be completely
defined, corrosion and/or scaling could limit their usefulness in industrial-
agricultural process equipment.
TIME FRAME FOR DEVELOPMENT
It is difficult to estimate a time frame for development of the geopres-
sured geothermal resources along the Gulf coast despite the many studies
which have been made on this potential energy source. The technical and
equipment development and problems can be solved within estimable limits,
however, less specific barriers are listed by JPL22'23:
• Federal and state leasing practices and laws
• Inadequate incentives
• Cost/risk/time relationships
• Complex leasing interactions
• Multiple and complex regulation and approval requirements
• Time-sequential requirements
• Withholding of proprietary information
• Environmental restrictions and complicated procedures by federal,
state, and local agencies
• Availability of experienced personnel to carry out assessment
and exploration
• Availability of drilling equipment and crews for exploratory
geothermal drilling (available rigs and crews can keep quite busy
prospecting for oil and gas)
• Availability of deep-hole logging equipment suitable for the higher
temperatures of interest for geothermal wells (well-logging equipment
companies have not felt it worthwhile to invest in such equipment
except to a very limited extent)
These may well determine the time frame for development. Resolution of
the non-technological issues impeding geothermal energy development is im-
perative before real physical progress can be made in utilization of geo-
pressuredgeothermal energy.
Wilson21* suggested the time frame to demonstrate the feasibility of the
production of electric power, natural gas, and fresh water from the geopres-
sured waters of the Gulf Coast shown in Figure 6 while JPL23 estimated the
time required to complete the development cycle for single geothermal energy
plant (California site - Federal land) as shown in Figure 7.
Figure 8 shows the approximate timing and scheduling developed at the
University of Texas, Center for Energy Studies by Dorfman, et al15.
All of the time frames presented are partially directed toward achieving
the goals of energy independence by 1985. In view of the actual progress to
date they seem extremely optimistic.
32
-------
u>
U)
PHASE I - Geological and economic feasibility studies; environmental impact study;
and conceptual design of test facility
PHASE II - Site procurement; engineering design of test facility;
drilling of first well
PHASE III - Construction of test facility; testing of well;
conceptual design of demonstration plant
PHASE IV - Drilling and testing of additional wells;
engineering design of demonstration plant
PHASE V - Construction of demonstration
power and desalting plant
PHASE VI -
Operation of
total facility
I
J_
I
I
L
1975197619771978197919801981 1982 1983 1984 Date
01 234 5678 9 Yrs
Figure 6. Proposed plan for geothermal energy development on the Gulf Coast.
-------
U)
£>.
Item
Major
Decision
Points S
Regulatory
Activities....^;
Exploration
S Reservoir
Assessment.,,,,
Drilling
Plant
Design &
Construction
Years
1
Decision fc
/ Geothermc
f Explore tic
Obtaining
Notice of
/Intent
Preliminar;
Geophysica
Exploratio
2
3
ir Final Decision
1 for Exploratory
n Drilling
57 1
Process
Leases & Ea
Geop
Explo
' Reserve
c
nysical
ration 6
ir Assessnu
4
5
Final
Decision for Power
Plant Design S
Cons truction
57
Master
Development
Plan S EDS*
^
PI
nt Se
Exploratory
Drilling s Reservoi
Evaluation „
Peasibi
Study
lity Pre
De
/
Final
Negotiatio
'
ant Site
Lection
7
.iminary p
sign D
is
6
Obtain
Permits S
Process E:
inal
esign
7
S^7
8
Developmen
Drilling
S Piping
Construct!
9
>n
•EDS * Environmental Data Statement From JPL
Figure 7. Business-as-usual geothermal plant development timeline
(initial development, federal land, noncompetitive bidding).
-------
Year
Activity: Month
A. Fairway Review, Target
Selection
B. Environmental Baseline, Rpt.
C. Site Specific Geology,
Geophysics
D. Drill Test Wells
E. Effluent Disposal for Test
Wells
F. Legal, Institutional, Social
1. Legal
2. Social
G. Rock Mechanics Research
H. Geopressured Fluid Sampling
in Existing wells
I. Reservoir Simulation Researcl
J. Supporting Research & Tech-
nology Utilization
K. Preliminary Test Facility
1. Design Facility s, Test
Program
2. Fabricate, Install Test
Facility
3. Fabricate, Install Fuel
Facility
4. Operate Test Facility
L. Well Production Tests
1. Operations
2. Royalty Payments
M. Major Test Facility
1. Design, Construction
Management
2. Fabrication, Installation
Construct
Plant Modules
4. Operations - Overhead
N. Pilot Power Plant
1. Design & Procurement
a. Conceptual Design
(Power/Fuel Plant)
b. Purchase Turbine/
Generator Sets
c. Well Design (Field)
d. Purchase Methane
Separator, Compressors,
Glycol Dehydrators
e. Detailed Design,
Construction Management
2. Construction, Testing
a. Step-out Drilling of
Field
b. Land Purchase/Site
Development
c. Purchase Electrical
Equipment
d. Purchase Cooling Tower,
Condenser, C.T. Pumps
e. Fuel Plant Equipment
Procurement
f. Fuel Plant
Construction
g. Power Plant
Construction
h. Operational Testing
0. Management/coordination
1976 (Year 1) 1977 (Year 2) 1978 F k-vHiv^pfrv vMvkvta^v 'Ftv^fviv^p^r jfMvtvt^tf
0 *
KFIjk $fcpo n- nA
1
^tuy&o — a.
KtXv'^y n ^r 1 tf~ 2
ii ii o *Q
0 A
3ln Progress (Partial Funding) *
In Progress (Partial Funding)
J -^
°^£-o-*
9 •&
6 -A
Prelim. n,t,ii
RFP AWD Design 5™** Construction
.fabrication , Test ^
O ^
r\rAor t Del. Install
oraeri ^ ^ _^. ^
j Del. Install
f -,
PFP AWD i
" " 1 SjY» ^
Option '^ improve
\ Del.
n^.r i Pel- ,0 «
*b - -0 *&
Q »fa
From Dorfman
Figure 8. Overall time schedule, major activities
35
-------
In today's industrial power plant construction, five-year lead time from
the decision to proceed to actual plant completion are not unusual. In the
case of geothermal plants, much of the critical equipment cannot be considered
off-the-shelf items; large hydraulic turbines and low pressure steam turbines
must be designed and built to the final plant sizes which are chosen. Many
delays ranging from late equipment delivery to unexpected initial drilling
and operational problems should be anticipated for relatively new developments
on the outer fringes of technology such as the proposed geopressured geothermal
plant. If the plant development were to follow sequential steps;
• 1.5 MW(e) test well; prototype equipment test
• 10 MW(e) pilot plant
• 25 MW(e) demonstration plant
appreciably more time may be involved than shown on the time frames given in
this section. Factors of 1.5 or 2.0 times number of years shown in Figures
6, 7, and 8 may be more appropriate.
36
-------
SECTION 6
PROJECTED MULTIMEDIA EMISSIONS AND EFFECTS FROM POTENTIAL USES
ANALYSIS OF THE WATERS
As a preliminary to considering the various environmental aspects of the
resource, it is desirable that the composition of the waters be estimated as
accurately as possible. Representative analyses of waters from the geopres-
sured strata are limited and, as discussed in Section 4, are subject to con-
siderable question.
All available sources were used to collect a listing of water composition
values. However, the reader must recognize that the validity of the water
samples themselves is uncertain; few geopressured "sand" water samples are
available, with most samples likely being of the "shale" waters and with most
samples being from the top of the geopressured zone where salinity is maximum.
With these considerations in mind, a listing was prepared.
Water analyses were obtained from the following sources: Dickey
Taylor25, Jones27, Blakeman28, Schmidt2^, and the Texas Water Development
Board30. Each of the approximately one hundred analyses shown on Table 5
represents the water composition of what is believed here to be an overpres-
sured geothermal stratum. The overriding conditions required for including a
particular water analysis in the geopressured category were that:
• The source well was completed since 1962, and
• The source formation was encountered at a depth greater than 9,000 feet.
In the absence of further qualifying information, these two conditions were
accepted as sufficient evidence that the formation was geopressured. Approxi-
mately 60% of the analyses shown in Table 5 were classified as representing
geopressured waters on this basis. For the remaining analyses, additional
evidence of geopressured origin was available. This was almost always the
presence of one or both of the following two characteristics:
• The numerical ratio of formation pressure in psig to depth in feet
exceeded approximately 0.45.
• The salinity of the water was distinctly and appreciably less than
that of the adjacent overlying stratum, representing a reversal of
the trend of the salinity-versus-depth relationship.
Attention is called to the high barium concentration reported in more than
a dozen of the water analyses. In one of these cases the recorded value
37
-------
OJ
00
TABLE 5
BRINE COMPOSITIONS FROM OVERPRESSURED RESERVOIRS
Formation
General
Location
SW
Louisiana
n
it
»
H
it
»
*•
"
ft
n
"
It
tt
n
'. n
«
"
n
n
tt
"
H
tt
n
n
n
n
*t
Depth*
Ft.
15,300
11,955
11 ,-895
11,860
13,325
10,000
10,913
10,810
9,995
9,683
10,060
9,260
10,015
10,890
10,580
12,390
12,018
9,608
9,720
9,745
13,250
11,580
11,810
14,405
13,962
11,765
14,080
12,355
12,742
13,860
Press.
psi
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
Tanp.
°F
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
TDS
54,810
96,508
91,361
81,993
114,539
55,235
102,823
87,814
97,577
52,029
82,702
95,051
88,091
198,993
97,812
235,634
131,946
81,281
85,705
78,475
218,298
146,392
143,635
345,470
327,069
205,953
208,661
110,761
190,436
180,250
Na
21,445
36,650
31,500
28,275
36,190
19,450
41,500
31,800
41,732
31,100
32,500
32,900
32,500
57,850
43 , 500
82,100
47,840
29,400
33,900
31,573
75,590
56,750
80,305
101 , 400
103 , 000
78,700
68,330
44,450
69,230
54,500
K
518
247
200
204
267
85
208
230
162
134
262
181
192
427
315
813
427
172
155
157
830
324
376
782
640
798
771
137
1,154
631
Ca
1,074
2,214
1,379
1,379
3,850
1,385
2,727
2,021
3,048
2,310
2,951
2,662
1,572
21,558
1,893
15,232
2,951
2,662
2,175
na
15,655
7,387
3,304
28,808
33,160
14,340
18,446
3,613
18,253
14,436
Mtj
39
369
213
194
583
41
544
194
719
50
447
389
0
2,178
408
1,266
447
1,011
503
na
159
565
na
2,138
5,772
428
1,205
17
1,089
700
Cl
30,866
55,592
56,540
49,980
72,778
33,250
51,735
58,048
50,858
45,310
45,596
57,872
52,610
116,095
50,928
135,385
79,250
46,618
47,868
45,758
125,470
84,530
80,305
201,325
183,788
111,060
119,315
61,555
100,069
109,300
Composition in mg/i
SOu
0
407
234
38
tr
50
0
tr
33
0
tr
tr
0
0
67
na
0
60
72
na
0
tr
0
0
na
tr
0
0
0
0
HCO^
385
541
826
630
448
503
180
363
507
545
574
586
579
322
330
92
334
741
788
694
135
0
363
0
0
112
76
550
66
73
Li
10
7
6
6
6
3
5
4
6
4
4
4
5
9
9
9
10
6
5
4
15
7
9
17
17
12
18
5
17
13
Sr
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
Ba
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
8
50
5
5
8
19
na
na
na
na
na
na
na
na
na
Br
35
61
52
57
81
37
21
91
70
35
35
56
45
128
43
154
169
40
52
na
64
20
62
213
204
94
117
14
201
71
I
18
22
21
21
19
16
15
18
23
18
22
25
20
26
18
24
74
23
21
22
23
22
20
18
19
27
28
5
21
21
B
49
62
62
37
43
32
18
26
35
28
29
26
34
38
23
52
48
46
48
44
47
40
45
75
67
42
52
67
42
39
Ref .
25
ft
n
tt
H
H
*
tt
ft
tt
tt
tf
n
tt
rt
**
n
n
H
ft
tt
**
tt
tt
R
tt
*
tt
H
H
-------
VO
Table 5 (continued)
Formation
General
Location
SW
Louisiana
"
»
H
H
H
II
South
Louisiana
«
M
»
It
"
n
»
"
«
n
H
11
H
w
"
n
H
South
Texas
"
n
n
Depth*
Ft.
12,298
11,478
10,564
12,757
11,815
12,255
9,249
12,287
13,675
13,747
13,747
12,560
13,025
15,930
15,007
16,398
14,700
14,945
14,850
16,270
19,465
15,900
14,187
12,539
13,778
13,091
10,542
9,043
13,753
9,315
9,425
11,457
Press.
psi
na
na
na
na
na
na
na
na
7,918
8,308
8,308
8,976
8,716
na
na
na
na
na
na
na
na
10,740
9,276
6,516
7,586
5,901
4,631
na
na
na
na
na
Temp.
0F
na
na
na
na
na
na
na
na
248
249
249
234
237
na
na
na
na
na
na
na
na
302
243
234
227
240
202
na
na
na
na
na
_TDS
136,694
78,467
124,904
133,766
201,709
104,457
127,543
83,146
109,736
80,066
113,312
na
110,232
29,505
175,968
204,112
128,792
189
64,441
185
39,333
na
59,376
103,141
101,383
102,362
201
38,459
16,085
185,400
198,800
22,641
Na
52,520
31,200
47,470
na
73,760
43,300
47,800
30,250
39,327
1,886
40,981
45
40,041
7,728
50,729
12,621
41,729
32
19,934
10
11,316
138
20,843
37,071
36,282
37,586
47
10,129
5,904
51,966
55,365
7,718
K
392
160
294
na
375
176
264
71
na
na
na
na
na
na
na
na
na
na
na
na
na
na
t
f
t
t
t
t
t
t
t
t
Ca
2,759
1,508
3,272
4,555
5,614
3,208
2,951
1,784
2,448
3,129
2,724
10
2,259
3,180
14,400
28,000
7,080
30
4,090
44
3,068
19
1,643
1,642
2,444
1,442
8
2,788
266
16,200
17,300
984
Mg
35
447
564
0
564
136
855
141
413
389
73
0
312
2S5
1,640
23,781
na
2
493
9
428
0
219
49
243
462
0
925
29
2,050
2,540
16
Cl
79,970
44,424
72,250
128,720
120,545
54,495
74,420
49,714
66,150
73,500
68,200
10
66,488
18,254
108,459
138,500
78,860
104
39,462
106
23,762
228
35,700
58,950
61,000
62,000
33
23,369
9,457
11,400
123,000
13,555
Composition in
SOO
77
130
0
0
0
102
0
88
40
12
10
10
2
11
0
45
0
11
0
0
225
0
45
2
45
2
0
85
0
580
360
30
HCO3
270
244
234
80
240
539
249
482
614
593
584
135
708
56
91
na
199
0
0
13
394
37
306
2,501
523
102
100
456
371
634
256
270
Li
10
5
3
na
5
5
2
2
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
mcj/1
Sr
na
na
265
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
Ba
110
na
41
na
na
7
na
4
630
550
675
15
364
na
647
ipoo
206
na
400
na
60
na
500
375
750
450
8
na
_Br
110
70
58
174
134
40
79
60
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
_jt
34
35
18
24
38
26
18
35
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
B
34
36
33
41
43
52
26
43
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
Ref.
25
II
H
n
"
n
tt
n
28
w
M
n
n
tt
n
ft
*t
tt
n
tf
tt
M
tf
H
n
M
n
26
M
H
H
n
-------
Table 5 (continued)
Formation
General
Location
South
Texas
"
M
M
*•
n
E. Texas
South
Texas
"
E. Texas
South
Texas
n
it
H
"
n
sw
Louisiana
i*
M
H
H
n
H
H
£. Texas
M
n
H
Depth*
Ft.
10,679
10,832
12,180
11,823
11,774
13,430
13,200
9,880
10,250
9,244
11,315
9,863
11,077
10,258
11,337
12,420
12,495
12,970
9,260
11,170
12,042
12,350
12,400
12,753
12,673
12,673
12,866
12,866
15,578
9,726
10,100
13,500
Press.
psi
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
Temp.
°F
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
280
na
na
na
TDS
21,965
3,380
4,850
3,165
11,373
14,753
19,568
114,900
71,978
39,947
9,805
134,500
158,900
212,400
174,500
15,423
40,785
23 , 204
77,285
25,800
22,700
15,700
49,000
16,000
18,900
18,300
18,300
17,700
65,000
38,542
19,213
39,500
Na
7,233
900
1,370
1,035
3,600
5,347
7,030
41,049
20,464
7,575
3,375
38,951
na
54,800
40,793
5,505
14,641
8,515
6,770
9,280
8,380
5,660
17,300
5,640
6,700
6,580
6,400
6,330
na
10,779
7,180
14,760
K
t
t
t
t
t
t
na
t
t
t
t
830
na
2,592
1,300
t
t
t
t
65
58
55
208
81
84
86
89
89
na
na
na
na
Ca
1,174
350
450
150
760
156
230
2,960
6,864
7,300
400
10,500
15,050
17,510
21,700
394
835
291
.20,000
216
109
57
728
68
125
138
158
117
na
98
24
300
Kg
0
30
30
30
18
22
57
585
143
122
30
1,020
1,465
1,780
1,660
16
143
52
1,100
47
22
13
112
15
20
18
23
21
230
21
17
12
Cl
13,095
2,100
3,000
1,950
6,890
7,660
11,299
70,200
44,126
2,495
6,000
82,300
98,100
135,690
107,000
8,883
24,153
12,970
48,850
14,500
12,400
8,200
29,600
8,450
9,850
9,950
9,700
9,800
na
15,769
9,928
22,700
Composition in mg/1
SO*
17
na
na
na
na
88
17
33
9
na
na
590
148
16
13
4
0
165
240
na
na
175
183
232
215
175
170
128
na
60
256
na
HC03 Li Sr Ba Br I
277
na
na
na
na
1,810
859
56
182
na
na
312
243
27
1,990
610
731
1,211
225
1,710 1.9 8.3 2.9 na n«
1,810 1.6 5.8 1.3 na na
1,520 2.0 3.1 0 26 22
854 5.8 42 0 43 28
1,430 2.9 4.4 0 29 22
1,930 3.5 8.8 1.1 43 24
1,330 3.1 5.3 0 33 27
1,710 3.6 11 1.7 27 20
1,270 3.2 8.1 0 32 25
na na na na 60 na
1,815 na na na na na
1,808 na na na na na
1,468 na na na na na
B Ref.
26
n
it
u
"
u
H
II
U
H
H
H
H
H
»
M
W
U
It
na 29
na
na
na
na
na "
na
na
na
na Dow
na 30
na
na
-------
Table 5 (continued)
Formation
Composition in mg/1
General Depth* Press. Temp.
Location
South
Texas
E. Texas
11
11
"
if
South
Texas
n
"
H
Ft.
8,939
9,402
9,380
11,325
14,343
14,843
15,260
9,065
9,183
9,524
9,792
10,026
•Included with Na(
t Average
depth of
psi °f TDS
na na 12,539
na na 17,959
na na 33,675
na na 72,266
na na 71,540
na na 90,378
na na 75,008
na na 17,160
na na 9,677
na na 13,500
na na 13,806
na na 9,434
Na K
4,616 na
6,424 na
12,740 na
25,400 na
23,350 na
26,810 t
24,300 na
6,489 57
.3,289 27
4,673 51
4,795 30
3,128 70
Ca Hg Cl SO., HCOs Li Sr pa ^ I B Refr
64 28 6,560 112 1,159 na na na na na na 30
52 51 9,042 66 1,824 na na na na na na "
176 44 19,220 41 1,452 na na na na na na 6
2,000 329 43,620 0 476 na na 415 na na na "
3,740 366 43,440 4 537 na na 103 na na na "
6,909 592 55,290 0 376 na na 401 na na na »
4,180 317 45,750 5 250 na na 188 na na na »
42 5 8,675 80 1,748 na 6 1 na na na "
16 15 3,550 130 2,650 na na na na na na "
19 7 5,320 170 3,260 na na na na na na "
21 10 5,460 120 3,370 na na na na na na »
2 2 3,010 100 3,050 na na na na na na "
not separately determined.
sample interval.
-------
is 1,000 ppm barium for a water whose sulfate concentration is reported to be
45 ppm. These reported high barium concentrations are attributed here to the
possible entry into the formation of barium ion from the barite used as weight-
ing material in the drilling mud, and not to the natural barium content of the
interstitial fluid. The handbook value for the solubility of barium sulfate
in water at 100°C (212°F) is 3.9 ppm31. This translates to approximately 1.0
ppm for the barium concentration in a water having a sulfate concentration of
45 ppm. Even allowing for a discrepancy of two orders of magnitude resulting
from the effects of increased solubility at higher temperatures and for total
ionic strength of the interstitial water, the barium concentration would be
limited to only about 10 ppm.
This barium analysis illustrates perhaps the greatest problem affecting
the analyses of these waters —the reliability of the sample. Obtaining a
representative water sample, even with the best sampling techniques available
today, is precarious at best. No information concerning sampling technique is
available for most of these analyses. However, the most probable error source
would be partial flashing of the water. This would lead to higher-than-
analyzed TDS, or saltier waters. The fact that these waters, as analyzed,
contain less-than-expected TDS for their depth is a favorable indication of
their nature.
Collectively, the water analyses of Table 5 show that the average sal-
inity of the water contained in apparent geopressured strata encountered in
Louisiana is moderately greater than that for the corresponding waters from
south Texas. The range of salinity values, 180 to 340,000 ppm TDS, is also
greater for the Louisiana waters.
EXPECTED EMISSIONS
The emissions expected from the demonstration plant are classified here
into three categories:
• Normal direct emissions - are those unavoidably generated as designed
waste streams by the installation during conditions of normal operation—
and can be fairly accurately predicted.
• Indirect emissions - are "induced" by the installation, and include, for
example, emissions generated by earth-moving equipment during the con-
struction period, and also the increased amount of household garbage or
sanitary waste of the families of new, permanent employees taking resi-
dence in the area.
• Accidental emissions - will result infrequently from operational upsets
or unforeseen problems. They are expected, in a sense, since no op-
eration is perfect, but their frequency, time of occurrence and magnitude
are unpredictable.
Direct Emissions
The potential applications discussed in Section 4 all depend upon the
use of the thermal energy of the geopressured fluid. Common to all the
42
-------
applications visualized, regardless of their nature, are the emissions which
would result directly from the production of the geopressured brine and as-
sociated natural gas, and from the disposal of the spent brine. These are the
only emissions expected as a result of the use of geopressured fluid by a
particular process or industry in addition to those already inherent in the
process. For example, a proposed paper mill designed to use the heat of geo-
pressured fluid to cook its wood chips would still have the disposal of its
own process wastes to contend with. It would be spared the responsibility for
controlling the SOX, NOX and possible ash emissions of its existing conven-
tional counterpart which uses fuel oil or coal to fire its steam boilers.
The number of different types of emissions expected from a geopressured-
electric power plant includes all the types visualized from any of the other,
non-power, applications. In addition, electrical energy generation will prob-
ably be among the first uses for geopressured fluid to be commercialized.
The types and quantities of emissions expected from a projected geopressure-
electric energy installation would therefore represent at least the maximum
number of different kinds of emissions potentially resulting from any of the
proposed uses for the geopressured fluids.
One of the two proposed geothermal-electric demonstration plants whose
conceptual designs have already been mentioned in Section 5 is taken here as
the basis for estimating the types and quantities of emissions to be expected
from a typical power application of geopressured fluid. This is the nominal
25 MW(e) plant employing the double-stage flash process. Block flow diagrams
for this process and for the associated wellfield and methane recovery are
shown in Figures 9 and 10. The character and amount of emissions expected
from the alternative secondary-fluid process used in an installation of the
same nominal electrical output will be nearly identical to those of the double-
stage flash process17, except for the possible fugitive emissions of isobutane
from the former during abnormal operating conditions. Briefly, the fuel plant
may be considered as a wellfield and appropriate collection piping, a centrally
located methane extraction and purification plant, and a reinjection well-
field, if reinjection is the waste water disposal method selected. Following
the block diagram in Figure 9, the collected water and gas mixture from the
wells at 140 kg/cm2 (2,000 psia) is passed through a separator to remove the
undissolved gas. The methane gas after passing through a pressure reducer is
cooled, dried and sold. The hot water from the methane separator is passed
on to the electric power plant shown in Figure 10. Some methane will remain
in this water. Most of this gas is separated and returned to- the fuel plant
where it is cooled, dewatered, compressed, and added to the main stream for
final drying as shown in Figure 9.
The power plant receives the hot, high-pressure water stream from the
fuel plant. The feed is first passed through a hydraulic turbine, as shown
in Figure 10. The pressure drops in this turbine to 21 kg/cm2 (300 psia)
with the production o.f electric power. This pressure drop releases dissolved
methane which is returned to the fuel plant. A further pressure drop to
10.5 kg/cm2(9,L50 psia) produces more gas which is also returned.
The hot water is then flashed in two stages as shown. The low-pressure
steam is used to drive a two-stage turbine to furnish the shaft power for the
43
-------
10,883kg/nr (13.65 M SCFD at 15.5°C
Methane; 3.2 ker H2O I
per M SCF; 40.5°C; .52 Jcg/cm3
Pressure
Reducing
Station
Air
Cooler
Water
Separator Dehydrator
Compressor Separator Cooler
140 kg/cm2
Methane
Separator
Geothermal
Wells
Reinjection
Well
Methane front
Power Plant
_Methane from
]Power Plant
Geotherraal
Water to
Power Plant
Plash Chamber
i Effluent from
IPower Plant
Figure 9. Flow diagram of fuel plant for double-stage power plant - 25 megawatts.
-------
25 Megawatts
Electricity
Step-Up
Transfoiiaer
Methane to
Fuel.Plant
Methane to j ^Turbine
Fuel Plant
Geothermal
Water from
Fuel Plant
Flash
Chamber
Effluent
to Fuel
Plant
I Cooling
Pump f~|Tower
^ \ L
rr ^
-------
generator. The used steam is condensed in the condenser cooled by water
cycled through the cooling tower.
The physical conditions and magnitudes of the various material flows in-
dicated on the block flow diagrams are listed in Tables 6 and 7. From
the latter, the character and amount of all the normally resulting emissions
have been estimated and are listed in Table 8. These are the projected
"normal" direct emissions.
Each of the normal direct emissions listed in Table 8 is further
described below.
Spent Geothermal Brine (Stream 15)— This stream originates at the second
of the two flash vessels. If it contains no solids, it is pumped by a
centrifugal booster pump via a welded steel pipeline from the power plant
to one of several closed, top-vented surge tanks located in the brine
field area. From the surge tank it enters the suction line of a multi-
stage centrifugal reinjection pump to be injected into a reinjection
well. Barring emergencies (leaks, surge-tank overflows resulting from
instrument malfunctions, etc.), this waste stream does not actually
contact the environment until it reaches the receptor stratum, at a sub-
surface depth of 1,850 to 2,000 meters (6,000 to 6,500 ft). The flow is
substantially constant except for minor fluctuations and decreases only
during turn-downs in power generation. Its temperature of approximately
82°C (180°F) likewise normally undergoes only slight (±1°C;2°F) fluctua-
tions.
If solids form in the spent fluid they must be removed if reinjection
is used. Solids would plug the receiving strata. Solid removal by a
system of settling ponds would be the most economical. If this should
prove unfeasible, alternate disposal methods would be required.
Emissions from the proposed settling ponds would be negligible.
Some vapor condensation would occur on cold days with the formation of
"fog" clouds over the ponds. Periodically, the ponds would require
cleaning to remove the settled matter. This could best be accomplished
by the hydraulic dredge method. The resulting sludge, primarily silica,
could be disposed of by the landfill method.
The exact composition of the spent fluid will depend on that of the
incoming geopressured fluid. Whatever its precise composition, its
content of dissolved solids will be approximately 18% greater than that
of the incoming geopressured fluids, and the formation of solids will be
likely.
If the 25 MW(e) demonstration plant uses isobutane in the secondary
fluid process described in Section 4-B, the temperature of the spent
brine will be approximately 98°C (208°F), and its flow rate will be 0.79
m3/sec. (12,500 gpm). All other emissions will be increased by factors
of between. 1.2 and 1.4.
46
-------
TABLE 6. PARAMETERS OF STREAMS INVOLVED IN FUEL PLANT FOR 25 MW(e) DOUBLE-STAGE FLASH PLANT
Stream
No.*
1
2
3
4
6
9
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
35
36
Temp. Pressure
°C kg/cm2
162.7
161.7
162.7
161.7
160.0
82.2
•82.2
49
49
49
101
42
41
49
119
135
41
93
41
41
41
41
41
49
140.43
140,43
140.43
21.06
10.53
1.76
21.06
10.18
10.18
10.18
21.41
20.71
1.03
20.71
53.01
52.66
52.31
1.03
51.96
51.96
1.03
1.03
52,31
20.71
Mass flow (kkg/hr)
CHU H20 Total
10.84
6.36
4.59
4.08
0.40
0.0
0.0
0.40
0.0
0.40
0.40
4.49
0.0
4.49
4.49
10.84
10.84
0.0
10.84
10.84
—
—
0.0
0.0
2248.30
0.36
2248.30
1.95
0.67
1927.79
1927.79
0.67
2.97
0.67
0.67
1.96
0.02
0.03
0.03
0.39
0.39
0.02
0.02
0,0
—
0.37
2.30
2259.14
6.72
2252.89
6.03
1.07
1927.79
1927.79
1.07
2,97
1.07
1.07
6,45
0,02
4.52
4.52
11.23
11.23
0.02
10.86
10.84
—
—
0.37
2,30
Volume flow
mVmin."'' Remarks
41.95
1.78
41.83
10.38
3.62
33.22
33.22
1,12 Excl. 0.01 m3/min. water
0.05 Includes Stream 36
1.12
0.63 Excl. Stream 4
5.97 Excl. 0.03 m3/min. water
7.1 x 10"
5.97
2.82
7,42 Includes Stream 2
5.29 Excl. 0. 006m3 /min. water
2.6 x 10"""
5,29
5.29
1,7 x 10s
7.1 x 10"
6 x 10~3
3,8 x 10~2 Includes Stream 35
* Refer to Figure 9.
tActual m3/min. flowing at stated temperature and pressure.
-------
TABLE 7. PARAMETERS OF STREAMS INVOLVED IN 25 MW(e) DOUBLE-STAGE FLASH PLANT
*»
CD
Stream
No.*
3
4
5
6
7
7a
8
8a
9
10
11
12
13
14
32
33
Temp.
°C
162.7
161.7
160.0
160.0
160.0
121.1
121.1
82.2
82.2
43.4
65.6
30.6
38.9
43.3
38.9
37.8
Pressure
kg/ cm
140.43
21.06
21.06
10.53
10.53
2.09
2.09
0.53
1.76
0.09
1.05
—
—
3.52
—
1.03
CHu
4.59
4.08
0.57
0.40
0.18
0.08
0.10
0.08
0.00
0.18
0.18
—
—
0.00
—
Mass flow - kkg/hr
HaO
2,248.30
1.95
2,248.90
0.67
2,248.50
2,077.90
170.40
147.80
1,930.30
318.20
0.04
—
—
318.20
—
Total
2,252.89
6.03
2,249.50
1.07
2,248.70
2,079.00
170.50
147.90
1,930.30
318.40
0.20
—
—
318.20
84.00
Volume flow
m /min.t
41.83
10.38
41.75
3.62
41.74
36.81
2,453.80
7,724.30
7.31
8. 8x10*
6.23
365.11
365.11
5.31
0.63
1. 50x10 5
Remarks
Turbine exhaust
Non-condensibles
Condensate
Slowdown
Tower exhaust
*Refer to Figure 10.
tActual m /min. flowing at stated temperature and pressure.
-------
TABLE 8. EMISSIONS FROM 25 MW(e) GEOPRESSURED-ELECTRIC DEMONSTRATION POWER PLANT
AND ASSOCIATED BRINEFIELD - DOUBLE-STAGE FLASH PROCESS
Stream No.
Identity of emission (Figs 9 & 10)
Direct emissions:
Spent geothermal
fluid (liq.) 15
Temp.
°C
82
Probabl e
Composition
3.5% TDS:
12,479 ppm Na+
Discharge Rate
kg/hr
1.92 x 10s
(0.553 rnVsec)
Remarks
0.775 m3/sec if
isobutane used in
<£>
Cooling tower
blowdown (liq.
32
39
Cooling tower
exhaust (gas)
33
41
438 ppm Ca+2
78 ppm Mg+2
19,415 ppm Cl"
248 ppm (SO*)"2
1,465 ppm (HCOs)"
175 ppm (C03)-3
12 ppm Br~
>1 ppm H2S
9.2 ^ pH
7,500 ppm TDS
No heavy metals
3.8 x 106
(0.01 m /sec)
Sat'd air con- 10.2xl06 dry
taining 0,3 kg/sec basis (2.5 x
drift.
KT m Vsec)
secondary-fluid
process.
Assumes 1,500 ppm
TDS in makeup water.
Volume may be only
•vO.26 m3/min if
condensate is used
for makeup.
5 x 10" kcal/sec
discharged to
atmosphere (latent
plus sensible)
-------
Table 8 (continued)
Identity of emission
Stream No.
(Figs 9 & 10)
Temp.
oc
Probable
Composition
Discharge Rate
kg/hr
Remarks
Septic tank effluent
(liq.) Not shown
Ambient
HaO cont'g
soluble
organics
<0,25 I/sec
Discharged to
septic field of
conventional
design.
Indirect s Accidental
Emissions:
Geothermal fluid
(liq.; vapor)
1,3,5,7
ui
o
Drilling mud (slurry) Not shown
162 %3.0% TDS:
10,720 ppm Na+
380 ppm K+
376 ppm Ca+2
67 ppm Mg+
16,678 ppm Cl~
213 ppm (SO*)-2
1,550 ppm (HC03)-
10 ppm Br~
10 ppm H2S
125 ppm CO2
6.8 i> pH
Ambient Contains BaSOtt
Borehole cuttings
(solid)
Not shown
Ambient
Sand and shale
particles
-v7,600 m3
total
Possible emission
during mishaps;
steam or methane
release to atmos-
phere occurs.
Fluid at wellhead
contains 7.13 Nm
per m liquid.
Emissions by pos-
sible spills and
blowouts during
construction per'd
Used for earthwork
-------
Table 8 (continued)
Identity of emission
Dehydrator effluent
(liq.)
Air-cooler exhaust
(gas)
Air-cooler exhaust
(gas)
Air-cooler exhaust
(gas)
Separator condensate
(liq.)
Stream No. Temp,
(Pigs 9 & 10) °C
26 93
21 8° above
ambient
29 8° above
ambient
30 8° above
ambient
17 M9
Probable
Composition
Water contain-
ing ^40 ppm
glycols
Normal air
Normal air
Normal air
Water; 20 ppm
TDS
Discharge Rate
kg/hr
16.3
(0.27 I/sec)
3.2 x 105
(80.2 m3/sec)
7.7 x 105
(184 m3/sec)
1.6 x IQ5
(40.1 m3/sec)
2.968
(0.82 I/sec)
Remarks
May be combined
with cooling tower
makeup .
175 kcal/sec dis-
charged to atmos.
423 kcal/sec dis-
charged to atmos.
87.5 kcal/sec dis-
charged to atmos.
Kay be used to
augment cooling
Purge stream from
main condenser (gas)
11
260 25-50 vol% CHu
10-20 vol% C02
5-10 vol% Oa
20-40 vol% N2
15 vol% H20
vapor
trace
^220
tower makeup
Flared to HaO & CQz
at flare stack.
-------
Cooling Tower Slowdown (Stream 32)— The flow of blowdown from the
cooling tower shown in Table 8 assumes the following conditions:
• The maximum allowable concentration of dissolved solids in
the cooling tower sump is 7,500 ppm.
• A drift loss of 0.005% of recirculation rate.
• Cooling tower make-up is supplied entirely by brackish water
containing 1,500 ppm dissolved solids.
The first of these conditions is what might frequently be encountered
in industrial towers and should result in drift salinities no greater
than those from most industrial cooling towers. The choice of brackish
water for make-up requirement assumes that the condensate from the main
condenser will be sold for municipal use and will be unavailable for make-
up. A dissolved solids content of 1,500 ppm in available shallow well
water is a realistic expectation in much of the area of south Texas where
a demonstration plant might be located with the minimum risk of unforeseen
adverse environmental impact.
An alternative set of realistic conditions assumes that all the ex-
haust steam is used to supply the major portion of the cooling tower make-
up demand, and that the circulation water is carried through 20 evapora-
tion cycles. The requirement of brackish water is then reduced to about
0.44 m /min. (117 gpm) , and the blowdown rate to 0.27 mVmin. (71 gpm) .
Additionally, the concentration of dissolved solids in the drift from the
stack is reduced from 7,500 to approximately 2,500 ppm.
Cooling Tower Exhaust (Stream 33) — This stream issues from the stacks
of the cooling tower at an elevation estimated here to be between 15 and
18 meters (50 and 60 feet) above grade. About 4 to 8 tower cells would
probably be required. The total flow of exhaust air shown in Table 8
would be equally apportioned among the individual stacks.
The exhaust stream is air, very nearly saturated with water vapor
at the temperature shown. It discharges into the atmosphere about 1.8
x 108 kcal (7.2 x 108 Btu) per hour and carries a fine mist of water
droplets despite the use of demisters and foam eliminators of latest
design. The expected total quantity of the entrained water will be about
0.005% of the flow of water circulated over the packing (the upper limit
of the usual performance guarantee32'33) and the value used here in
estimating the required flow of blowdown. On this basis, the total
amount of liquid in the drift—18 1/min. (^4.83 gpm)—will contain a
maximum of 7,600 ppm TDS when the make-up used is brackish water contain-
ing 1,500 ppm TDS. The drift will also contain whatever additives have
been used as corrosion inhibitors and fungicides at substantially the
same concentration as prevails in the cooling water. Forecasting the
identity and concentration level of the additives is limited to conjecture
at this time. The use of chromates and phosphates, proven to be the most
effective as corrosion inhibitors, and zinc compounds as fungicides, has
been prohibited under existing federal regulations34'35. However,
silicates may be added to the cooling water sumps as corrosion inhibitors.
52
-------
Dehydrator Effluent (Strerin 26) — This will be a rather small flow of 1.9
1/min. (^0.5 gpm) of liquid water continuously discharged from the
methane dehydrator. The stream is discharged directly from the top of
the glycol concentrating tower as a vapor. Current practice is to con-
dense the latter in a small air-cooled pipe coil. The stream will con-
tain up to 40 ppm of glycols. The stream will be discharged into the
cooling tower sump.
Air-Cooler Exhaust (Stream 21) — This emission will be a stream of
moderately heated air of normal composition discharged vertically upward
by the axial-flow fan of the finned-tube air cooler. The latter will be
situated between 6 and 9 meters (20 and 30 feet) above grade. The
discharge temperature will vary, depending on the ambient. The design
parameters assume 32°C (90°F) ambient air temperature and an 8.3°C (15°F)
rise across the tube bank. Under these conditions approximately
6 x 105 kcal (2.5 x 106 Btu) per hr. will be dissipated to the atmosphere.
Air Cooler Exhaust (Stream 29) — Similar to Stream 21, except that the
quantity of heat discharged to the atmosphere will be about 1.5 x 106
kcal (5 x 106 Btu) per hour.
Air-Cooler Discharge (Stream 30) — Similar to Stream 21, except that
approximately 3 x 10 kcal (1.3 x 10s Btu) per hour will be discharged
to the atmosphere.
Separator Condensate (Stream 17) — This stream will be discharged from
the third of three water separators arranged co-current to the flow of
methane. It represents the combined quantities of water separated from
the methane in each of the three separating vessels. It is expected to
contain a low level of dissolved solids, but may possibly be contaminated
with small amounts, say, in the parts-per-million range, of higher-boiling
hydrocarbons. This is only a possibility which depends on the composi-
tion of the source fluid. The flow will be combined with the cooling
tower blowdown.
Main Condenser Condensate (Stream 14) — If the condensate is sold,
surface condensers will be used to condense the exhaust steam from the
main turbine. In this event the condensate will be a very pure water
containing less than 10 ppm of dissolved solids. However, one contaminant
of concern will be copper, acquired by the condensate in passing over the
copper-alloy condenser tubes. The copper content of condensate from the
main condensers of most utility and industrial steam plants is generally
less than 0.05 ppm. This is the value assumed here. The condensate in
this case will constitute an indirect emission.
In the alternative case, where the turbine exhaust steam is used for
cooling tower make-up, the steam contacts the cooling water in direct-
contact, barometric-leg condensers. No discrete condensate stream results.
Also, since the direct-contact condensers are of low-alloy steel con-
struction, no copper pick-up by the cooling water is expected.
53
-------
Main Condenser Purge (Stream 11) — This stream contains all the non-
condensibles from the main condenser plus water vapor. The principle
noncondensibles are methane (MO volume percent), along with some CO2.
In addition, the presence of minor percentages of H2S or NH3 is possible,
despite the complete lack of any indication by the available water
analyses that they are present in the original geopressured fluid. It
should be noted that the absolute amount of H2S (or NH3) vented from the
main condenser is only a small fraction of the amount of these gases
possibly present in the original geopressured fluid, the major part
having been removed along with the methane in the three separator vessels
located upstream from the flash chambers.
The CO2 present in the purge stream results from the decomposition
of the bicarbonate ion of the fluid as the latter passes through the
flash chambers. The concentration of CO2 shown is an estimate only.
With geothermal waters of higher bicarbonate content, the CO2 concentra-
tion of the purge stream may be too great to permit combustion unless
additional methane is added.
The presence of 02 and N2 results from the inleakage of air at the
second flash chamber, at the turbine, and at the main condenser.
After passing through a vacuum pump and chilled-water condenser, the
purge stream is routed to the top of a flare stack where it is burned in
the atmosphere.
Septic Tank Effluent (not shown on Figure 10) — This is the clear liquid
discharge from a septic system of conventional design.
In addition to the material waste streams, direct emissions from the
demonstration plant should include the expected noise generation. All of the
rotating equipment and most of the fluid-flow devices are noisy to a certain
degree. The items expected here to be the noise sources of greatest intensity
are listed in Table 8. The sound levels shown here are estimates only.
The actual values may vary considerably depending on the exact type and make
of equipment installed from the estimates and on the details of installation.
Since the estimates are based on actual measured sound levels of equipment of
similar type but of different size, the estimates themselves are subject to
wide margin of error. For example, the measured sound level near a 100 MW(e)
steam turbine/generator may be as high as 110 decibels. It is difficult to
accurately predict from this value the corresponding sound level for a 25 MW(e)
turbine/generator rotating at a lower speed.
All the direct emissions considered so far have been those expected
during normal operation of the plant. Of equal importance, but perhaps not
obviously so, are those which could occur under abnormal, unforeseen condi-
tions. The intent here is not to describe all the possible mishaps and
spills connected with a project of this type, but to consider only those
accidental emissions which could result in major widespread adverse effects
on the environment or on human health. The following types of emission have
the greatest potential for causing damage of the proportions just described.
54
-------
• Leaks of any proportion of either geopressured fluid or spent
geopressured fluid from source wells to fresh water aquifers.
• Uncontrolled, large-volume releases at any point in the system of
either geopressured fluid, spent fluid, 30-pound steam, or methane.
Indirect Emissions
During the construction phase of the demonstration plant, estimated to
require about two years, approximately 300 construction workers will be
employed at the site at any one time. Depending upon the locality of the
actual site selected, a temporary camp of mobile homes for families of the
construction crews may be necessary. This would probably be the case with
many sparsely settled areas in south Texas. If the site were within 3 to 6 km
(5 or 10 miles) of a city of moderate size, probably no construction camp
would evolve, and temporary buildings would be limited to a few field offices
plus mobile living quarters for several watchmen.
For development of the wellfield, approximately 5 months is the estimated
time required to drill each source well, and about ten weeks for each reinjec-
tion well. Three to five years is a reasonable estimate of the time required
to complete the wellfield from the start of the initial test well. Most of
the time interval would be concurrent with the construction period of the
power plant. The estimated time requirements mentioned above are an indica-
tion of the duration of the period during which the indirect emissions may be
expected.
Listed below are the various indirect emissions to be expected during
the construction phase:
Emissions Expected During Development Phase of Wellfield —
• Possible uncontrolled, large-volume releases of geopressured
fluid and steam
• Possible spills of salt water
• Possible spills of drilling mud containing BaSOu
• Septic tank effluent
• Domestic wastes from possible trailer camp
• Noise from drilling rigs
Emissions Expected During Plant Construction Phase —
• Scraps from form-lumber, dunnage and crating
• Sand from sand-blasting
• Earth removed from foundation excavations
• Mud discharged to streams during rainy periods
• Atmospheric emissions of unburned hydrocarbons from construction
equipment
55
-------
• Domestic wastes from possible trailer camp
• Septic tank wastes from construction shanties
• Noise from construction tools and equipment
By far the most serious potential emission will be the uncontrolled flow
of geopressured brine which could result from a blowout during drilling
operations despite precautions employing the latest technology. This will be
a hazard to be faced rather than a certain occurrence. Its probability of
being realized is conjectured here to be less than 5%.
The quantity of many of the emissions shown in the above list will
obviously vary considerably from one location to another. Even for a given
location their magnitude would be influenced by such a large number of factors,
with the variation so wide, that to express a value here as being "typical"
would be meaningless.
ENVIRONMENTAL IMPACT
Air and Water Quality Criteria
Listed in Tables 9 and 10 are proposed and existing standards for air and
water quality pertaining to the polluting factors contained in the emissions
described in the previous subsection. The conclusion drawn here is that, in
general, the available methods for ultimate disposal of the expected emissions
will permit operation of the demonstration geothermal plant without violation
of proposed or existing air and water quality criteria. Exceptions may arise
if the geothermal fluid actually used contains certain pollutants (H2S, NH3,
Ba or heavy metals) at considerably higher concentrations than those assumed
here. For example, if the geothermal fluid should contain more than ^0.8 mg/1
of barium, discharge of the spent fluid into tidewater would not be in com-
pliance with Texas Water Quality Standards. The possible impacts of the
separate emissions are discussed below.
Impact of Direct Emissions
These are primarily the separate environmental effects of the respective
direct emissions, both normal and accidental, but also include local aesthetic
values.
Spent Geopressured Fluid (Stream 15) — The properties of the spent fluid
making its disposal an environmental problem are:
• Salinity CV35,000 ppm TDS)
- Temperature of 82°C (180°F)
• Total quantity of heat to be dissipated
• Essentially zero dissolved oxygen content
• Possible trace amounts of H2S, NH3, or toxic metal ions.
56
-------
TABLE 9. PROPOSED WATER QUALITY AND AMBIENT AIR STANDARDS36
Ambient Air
Potential Pollutant
Ammonia
Barium
Copper
Water*
mg/1
0.5
-
1.0
Waters
mg/1
0.4
0.05
0.0005
Primary
yg/rn
n.s.
n.s.
n.s.
Secondary
Ug/m
n.s.
n.s.
n.s.
Remarks
Value listed fo:
H2S
Methane
Particulates
Temperature
BOD
Total quantity heat
Salinity
0.002
0.001
0.12 ppmt n.s.
-
-
2°C
rise#
n.s.
n.s.
n.s.
-
-
2°C
rise#
**
n.s.
n.s.
160§
75
n.s.
n.s.
n.s.
n.s.
160§
60
n.s.
n.s.
n.s.
n.s.
marine water is
1/6 of Cu cone'n
in normal sea
water.
These factors
governed by re-
sults of environ-
mental impact
study in each
specific case.
NOTE: Except where indicated to the contrary, the values or lack of values
shown apply to proposed Federal criteria.
n.s. = no specific standards, existing or proposed.
*Public water supplies
tTexas Water Quality Board Standard, Regulation II, Rule 203.
§Environmental Protection Agency Regulations on National Primary and
Secondary Ambient Air Quality Standards. (40 CFR 50; 36 PR 22384,
November 25, 1971; as amended by 38 FR 25678, September 14, 1973;
40 FR 7042, February. 18, 1975)
ttActually 1°C rise during June thru August and 2°C rise during Sept.
thru May. Maximum resulting temperatures limited to 35°C. Water
Quality Criteria, FWPCA 168.
**Cone of dissolved 02 must be >6 ppm.
57
-------
TABLE 10. METAL QUANTITY LEVELS FOR DISCHARGES TO TEXAS TIDAL
WATERS - 1975 STANDARDS OF TEXAS WATER QUALITY BOARD37
Maximum Concentration Allowed, mg/1.
Metal
Arsenic
Barium
Cadmium
Chromium
Copper
Lead
Manganese
Mercury
Nickel
Selenium
Silver
Zinc
Average
0.1
1.0
0.1
0.5
0.5
0.5
1.0
0.005
1.0
0.1
0.05
1.0
Daily
Composite
0.2
2.0
0.2
1.0
1.0
1.0
2.0
0.005
2.0
0.2
0.1
2.0
Grab
Sample
0.3
4.0
0.3
5.0
2.0
1.5
3.0
0.01
3.0
0.3
0.2
6.0
58
-------
It is quite obvious that its discharge to a convenient natural
surface feature—say, to a freoh water stream, arroyo, or natural depres-
sion—would be catastrophic, resulting in at least the destruction of
indigenous wildlife and vegetation, potentially arable land, potable
water and aesthetic values. The two most likely methods of disposal of
the spent fluid appear to be:
• Reinjection into a subterranean receptor stratum, if such a stratum
exists and provided both its geology and permeability are suitable,
• Discharge into naturally saline bodies of surface water.
The choice of which of these two possibilities is actually employed,
assuming reinjection is geologically feasible, will be influenced by
economics and by the probable environmental consequences of each method.
Concentration levels of toxic metals in the spent fluid higher than those
shown in Table 10 will definitely rule out discharge into surface waters.
Disposal by reinjection should be feasible throughout much of the
extent of the geopressured fairway. In general, there are many highly
saline aquifers overlying the overpressured zones, at depths between 1,500
and 2,500 meters (^4,900-8,100 feet). Many of them are known to com-
municate at depth with the Gulf, and their permeability and porosity is
favorable to receiving the projected volumes of spent fluid. Jones11
presents data from representative deep wells in south Texas showing a
cumulative sand thickness upward of 300 meters (975 ft.) down to a depth
of 2460 meters ('vSOOO ft) . Salinities of the contained waters ranged up
to 12% TDS. Neither the temperature nor the salinity of the spent fluid
would adversely affect the subterranean environment if injection were
into sands such as those just described. A considerable amount of
reservoir engineering and testing would be necessary in selection of the
most favorable stratum and in the design of the reinjection wellfield.
Reinjection of the spent fluid poses two major environmental hazards:
• Possible seismic effects. These are discussed in a following
subsection.
• Possible contamination of fresh water aquifers. This could
result from either outright leakage of the injection well, or
from possible flow from the receptor stratum along a fault
plant into the fresh water aquifer.
Although the likelihood of occurrence of either one of these events is
believed to be fairly low, the consequences could be extremely serious if
either event does indeed happen.
With surface disposal methods, a consideration of the possible fate
of the TDS content of the spent fluid limits the possibilities to dis-
charge into the open Gulf itself, or into certain saline bodies of water
having relatively unimpeded communication with the Gulf. Examples of the
latter are Sabine Lake and Calcasieu Lake. The ability to accommodate
both the salinity and temperature from an environmental standpoint must
be determined beforehand, not only for the body of water under consideration,
59
-------
but also for the exact point of discharge. The salinity of the spent
fluid, if no higher than assumed in Table 8, will probably not create
environmental problems if discharge into the open Gulf is attempted.
Discharge into most natural back-bays, having restricted communication
and poor tidal interchange with the Gulf, will probably not be environ-
mentally acceptable. Harm to existing ecosystems may result. Favorable
results of an estuarine ecological impact study would be one of the
requisites for permission to discharge the spent fluid.
The results of such a study would indicate whether the temperature,
absence of dissolved oxygen, and the possible trace amounts of HaS, NH3,
or toxic metal ions (such as Ba+2) in the effluent would be non-injurious
to the aquatic life present in the receptor body of water under consider-
ation. This is the general criterion to be satisfied. Compliance with
the additional, specific criteria of temperature rise and maximum tem-
perature created in the natural body of water would also be necessary.
Compliance might necessitate the use of an evaporative cooling tower on
the stream of spent fluid. This would accomplish three objectives:
• Lowering its temperature
• Increasing its dissolved oxygen content
• Displacing possible trace amounts of HzS or
Potential discharge of H2S or NH3 into the atmosphere from the tower
would be governed by the Texas Ambient Air Quality Standard of 0.12 ppm
by volume, since apparently no quantitative federal standard exists.
In the case of surface disposal, the means of transporting the spent
fluid to the receiving body of water must be considered. The two viable
methods appear to be :
• Pumping via enclosed pipeline
• By nominal gravity flow in an open ditch system
A crude cost comparison shows that surface disposal employing pipe-
line transfer is at an economic stand-off with reinjection when the
plantsite lies approximately 65 km (40 miles) distant from the nearest
suitable body of surface water. This comparison assumes:
• A total cost of $180 per meter ($55 per foot) in moderately
rural areas for a buried, 20-inch pipeline, including road and
stream crossings, right-of-way, and booster stations.
• A total completed cost of $12 million for 19 reinjection
wells, including pumps.
The economic distance could decrease considerably in urbanized areas and
would be greater for a surface pipeline laid on grade. Aside from pos-
sible leaks and from impairment o:: s esthetic values along the right-of-
way, no environmental problems are foreseen resulting from the pipeline
itself.
60
-------
An open-ditch system might be the economically preferred means of
spent-fluid transport in certain cases where the following ideal con-
ditions are approached:
• Rural environment
• Gently sloping terrain with little topographic relief
• Little likelihood of run-off flood waters greater than about
0.66 meter (2 feet) deep
• Few obstructions in the form of natural streams, irrigation
ditches, floodways, or highways.
Many areas can be found in the tier of counties adjacent to the Gulf and
between the Rio Grande and Calcasieu Lake where these conditions are
approximated. In general, such areas extend perhaps not more than 25 to
35 km (15 to 20 miles) inland from tidewater. On the basis of the ideal
conditions outlined above, a leveed, open ditch, lined with chlorinated
polyethylene sheet and adequately sized to accommodate the spent fluid
from the demonstration plant, might be installed at a cost crudely
estimated here to lie between $30 and $45 per meter (between $10 and $15
per foot). This estimated cost range may be only a fraction of the
actual cost for a ditch system in areas where conditions deviate widely
from the ideal. The reasons are mainly because:
• The ditch must either follow surface contours, or else be provided
with tunnels, "aqueducts", siphons, or pressured sections to pre-
serve straight-line distances.
• Culverts or inverted siphons must be provided to preserve local
natural drainage and to crossroads, irrigation ditches, floodways
and other surface features.
• Right-of-way costs may be higher.
The principal ways the ditch system might adversely affect either
human welfare or the environment are by:
• Addition of salt to adjacent soil through possible leaks in ditch
liner, by failure of levees, or by flood waters topping the levees
• Impairment of aesthetic values
• Release to the atmosphere of possible trace amounts of HzS or NHa
• Creation of mists in cool weather and creation of a scaling "booby-
trap" (in the event the spent fluid is not further cooled prior to
discharge to the ditch).
In addition to.the material emission of the spent geothermal fluid
itself, there is the noise emitted by the reinjaction pumps and motors.
The latter will probably be multi-stage centrifugal pumps directly
coupled to the motors. Characteristically, these produce a whine of high
sound intensity. Since the locations of reinjection wells would be
limited, almost by definition, to areas no more densely populated than
suburban, the chief environmental impact of the noise would probably be
61
-------
its effect on livestock and the indigenous wildlife.
Cooling Tower Slowdown (Stream 32) — The characteristics expected of the
blowdown stream requiring selectivity of disposal methods are its salinity,
7500 ppm TDS, and possibly its temperature (39°C; 120°F). EPA has already
promulgated new plant standards prohibiting the discharge of corrosion
inhibitors. Therefore, the presence of these compounds is not expected
in the blowdown. The latter flow, if discharged to the local land surface
would be injurious to vegetation because of its salinity. If discharged
directly to most natural streams, both the temperature and the salinity,
and possibly the total quantity of heat, would degrade the water quality.
If maintained as a separate stream, the blowdown might allowably be
discharged into tidewater at coastal locations. Generally, what would
probably be the most acceptable means of disposal would be to add the
blowdown stream to the flow of spent geothermal fluid.
Cooling Tower Exhaust (Stream 33) — It is expected that this nominally
gaseous emission to the atmosphere will have the potential for creating
the same general types of environmental problems confronting any other
cooling tower of similar type and size. The adverse effects will be
caused by the following characteristics of the exhaust stream and of the
cooling tower accessories:
• The high moisture content (nearly saturated) and relatively high
temperature (40.6°C; 105°F). These properties in relation to usual
ambient conditions result in opaque plumes a considerable portion of
the time.
• The entrained brine content (drift). This will result in a fallout
at ground level consisting of the brine droplets themselves and of
the fine solid particulates of the evaporated brine residue.
• Total quantity of heat present above ambient temperature.
• Noise emitted by forced-draft or induced-draft fans and motors, and
by recirculating water pumps and motors.
The possible ultimate effects of each of these characteristics of
the exhaust stream are discussed in the following.
The behavior of the exhaust plumes in the atmosphere will be highly
variable in time, in elevation, and in horizontal areal extent, depending
upon the ambient atmospheric conditions. Under ambient conditions of low
humidity, high temperatures, moderate, steady wind speed, and under sunny
skies, the visible portion of the plumes may typically disappear within a
horizontal distance of considerably less than 30 meters (^100 feet). At
the other extreme, normally to be expected at night under "stable" con-
ditions of moderate humidity, lower temperatures, and steady wind direc-
tion and speed, the plumes would probably merge with one another within a
short distance of the stacks. The resulting combined visible plume could
then persist for at least several thousand meters (^2 miles), with its
longitudinal axis at a fairly constant elevation and with increasing
diameter of the visible portion. Intermediate types of plume behavior—
62
-------
i.e., looping, fumigation, lofting, etc.—will also be frequent, and will
correspond respectively to other types of atmospheric conditions.
The ultimate adverse environmental effects of a foggy plume are
situations involving poor visibility at varying distances from the
cooling tower. These include danger to aircraft operations at a possibly
nearby airport, highway traffic hazards, and the creation of generally
undesirable conditions for most outdoor activity. Regardless of whether
or not the plume is visible, the potential effects of its high moisture
content will be principally on the surface of man-made structures. Under
the so-called "trapping" conditions, it will contribute modestly to the
normal decay rate of wood and to the corrosion of metal surfaces. Since
the demonstration plant would probably be sited in a rural area, the
major effects of the moisture content of the exhaust, including any fog,
would be felt principally by the outdoor structures and occasionally by
the personnel of the plant itself, and at times by traffic on any nearby
road during weather conditions causing a "fumigating" visible plume.
The effect of the drift on vegetation, as discussed in Roffman^3,
will depend on the exact species of plant and on the proximity to the
tower. The magnesium and sulfate ions present in the drift may con-
tribute some nutrient value to certain types of cultivated crops grown in
solids deficient in these two elements. It is almost always the sodium
and chloride ions of windborne salts which account for most of any
deleterious effects.
The long-term increase in the salinity levels of the surrounding
soil will not, in general, assume the same horizontal distribution
pattern as the relative drift deposition rates, but will be influenced
greatly by natural topography and drainage patterns. The increase in
residual soil salinity could adversely affect the growth of some nearby
crops and possibly even some indigenous vegetation. The extent of this
effect in the present case is not expected here to be serious.
No environmental problems other than the effects of fogging, already
mentioned, are foreseen from the magnitude itself (5 x 104 kcal/sec.,
V723 x 10s Btu/hr.) of the sensible plus latent heat unavoidably
transferred from the cooling tower exhaust to the atmosphere.
Sound levels from cooling towers, representing the combined noise
output of fans, fan motors and falling water, but excluding that produced
by recirculation pumps and motors, are believed to lie generally in the
range between 80 and 90 db. The maximum noise intensity occurs near the
tower base in the forced-draft type, and near the top of an induced-draft
tower. If enclosed within the walls of a pump-house, the recirculation
pumps and motors may produce sound levels approaching 100 db.
In summary, the overall environmental impact expected from the
cooling-tower exhaust, as defined by the foregoing appraisal, probably
will be less harsh than the majority of towers of similar size and type
now in operation by private industry or public utilities.
63
-------
Dehydrator Effluent (Stream 26) — The most probable disposition of this
small-volume liquid stream will be to discharge it into either the cool-
ing tower blowdown or cooling tower make-up. No adverse environmental
effects are foreseen in its ultimate disposal by either method.
Air-Cooler Exhausts (Streams 21, 29 and 30) — The unavoidable discharge
into the atmosphere of the 2.8 x 10J kcal/sec. (^1 x 107 Btu/hr) of
sensible heat contained collectively in these three streams will have no
adverse environmental impact other than to create higher local ambient
air temperatures. The latter may result in moderately uncomfortable
working conditions on nearby equipment during hot weather.
Even the best designed, properly maintained air-coolers are noisy.
Sound intensities may reach 90 to 95 db near the fans and motors, and may
be only slightly less at ground elevation.
Separator Condensate (Stream 17) — No adverse environmental impact is
expected from this stream. The probable disposition will be its addition
to the make-up demand of the cooling tower.
Main Condenser Condensate (Stream 14) — If used to furnish the major
part of the make-up water demand of the cooling tower, this stream will
not constitute an emission. Its highest grade economic use, however, may
be as industrial process water or as a potable water supply to a muni-
cipality, where the revenue derived might contribute modestly to the
economic success of the geopressure project. In the event of its sale,
the condensate would ultimately meet the environment in at least one, and
possibly a large number of emission points. The possible effects, which
are here classified as indirect, are discussed in the following subsection.
Main Condenser Purge (Stream 34) — Venting this stream is a necessity,
since it provides the required purge of non-condensible gases from the
main condenser. It will be uneconomical to recover its methane content.
The stream actually contacts the environment as a continuously burning
flare, producing water vapor and carbon dioxide as the principal materials
ultimately released to the environment. Additionally, small amounts of
SO., or NOV may also be released, but only if the source geothermal fluid
X A
contains appreciable concentrations of H2S or NH3. Whether or not the
flaring of this stream will be in compliance with existing air quality
standards will depend jointly on the actual concentrations of HaS and NHs
in the stream and the actual background concentrations of SOX and NOX of
the ambient air.
Septic Tank Effluent (not indicated on Figure 10) — This will be the
clear overflow from a septic system of conventional design. The clear
liquid percolates into a porous layer of sand and gravel laid one or two
feet below grade. No adverse environmental effects are expected.
Aesthetics — Aesthetically, a geopressured-electric plant will be less
harsh on the existing landscape than an oil-fired steam plant. The
absence of boilers will enable the installation to present a low profile.
The tallest structures of the plant itself will be the cooling tower
stacks, which might be no taller than about 15 meters (50 feet). The use
of tall power transmission line towers will be unavoidable.
64
-------
Impact of Indirect Emissions
Ultimate disposal of the approximately 7600 m3 (^990 yd3) of solid wastes
(drill-stem cuttings) generated during the wellfield development period will be
an addition to the volume of earth fill required for the peripheral dikes
surrounding the containment areas at each of the 30 well-heads.
No factual information is available concerning the probable fate in the
environment of the barium sulfate contained in the relatively small amounts of
drilling mud and weighting fluids inevitably spilled during a drilling op-
eration. Although the barium ion is highly toxic to animal life, its extreme
insolubility suggests that it might not enter a food chain through assimila-
tion by plants. If ingested by higher animal forms, barium sulfate is ex-
creted with no apparent toxic effects. It is conjectured here that the small
amounts involved in possible spills would pose no threat to the environment,
nor to the health of humans, livestock or wildlife.
Injury or destruction to vegetation will result from any discharge of
geopressured fluid onto the land surface. During the completion and testing
of both source wells and reinjection wells, some spills and initial leakage
from pipe joints can be expected. If these situations do indeed occur, the
amount of harm to the environment and to health will be limited to a practical
extent by the use of blowout preventers during drilling and by the containment
areas around the well-heads. The means of disposal of spent fluid, whether
via reinjection wells or by surface methods, should be completed and operable
prior to the bringing-in of a source well. The full flow of each source well
can thus be accommodated during testing procedures. During plant shut-downs
the disposal system will handle the full flow of the source wells.
In the event the condensate from the main condenser is sold, either as
potable water to a municipality, or as process water to private industry, its
ultimate discharge to the environment will be beyond the direct control of the
geopressure project. Consideration should, nonetheless, be given to its
copper content, conjectured to be approximately 0.05 ppm. This value, although
well below the proposed federal standards36 for public water supplies (<1
ppm), for irrigation water (<0.2 ppm), or for livestock (<0.5 ppm), might be
high enough to pose a possible threat to aquatic life, particularly to fish in
marine waters, where the 96-hour LCso dose is apparently 0.05 ppm for most
species. These situations might be realized if the total flow of condensate
were to be discharged to a small, sheltered estuary or bay. If used as in-
dustrial process water, possible adverse synergistic effects in the ultimate
effluent should be considered. These might result from the joint presence of
the copper and a possible second contaminant acquired by the condensate in the
satellite process.
Regardless of whether or not the condensate from the main condenser is
used to supply the major part of the-make-up for the cooling tower, the geo-
pressure-electric plant will be a net consumer of either brackish or fresh
water, although to a far lesser extent than a fossil-fueled plant of equal
capacity. If the condensate is sold, the additional water requirement, equal
to the entire cooling tower make-up demand, will be about 0.11 m3/sec. (1800
gpm). This requirement will be reduced to about 7.2 x 10~3m3/min. (115 gpm)
if the condensate is used for make-up with the previously assumed concentration
65
-------
ratios. In the former case the 9.9 x 10" rn /sec. (^1,400 gpm) of condensate
would supplant an existing or planned use of an equal amount of well water or
surface water by a municipality or industry, resulting in a net ultimate water
withdrawal from the environment of 2.5 x 10~ m /sec. (^400 gpm). This net
water withdrawal will certainly create no problems in the case of a single 25-
MW(e) demonstration plant. However, in the possible long-term picture, the
potential location of several thousand megawatts of geopressured-electrical
capacity in the water-short areas of the south Texas portion of the geopres-
sured fairway, at sites directed by the location of a geopressured lens, will
require long-term planning to insure the best possible use of existing water
supplies. Changes in cooling tower design and operating parameters, from
those assumed here, may be necessary. Some of the obvious alternatives are:
• Use of dry cooling towers.
• Use of ground water too saline for other purposes. Saline ground water
aquifers are relatively plentiful in the south Texas area.
• Use of once-through seawater, or salt water cooling towers, at coastal
locations.
Impact of Accidental Emissions
It is a foregone conclusion that releases of either geothermal fluid or
spent fluid of greater volume than small leaks will cause damage to whatever
vegetation is contacted as a result of the fluid temperature and possibly the
salinity. To restrict the areal extent of the potential harm, diked con-
tainment areas, already mentioned, will be required at each wellhead. Ad-
ditionally, low dikes, about 1.5 meters (^5 feet) high will surround the
entire wellfield area. Large-volume releases of either of the fluids have the
potential for causing thermal burns on humans and other animal life.
The impacts of possible accidental releases of methane from the methane
separation and collection systems could range from being almost inconsequen-
tial to extremely serious, depending upon the exact nature of the emergency.
In the unlikely event of pipeline rupture, or similar type of failure of
pressure vessels, the major effect would be the hazard to personnel. Such
occurrences, although possible, are rare. There is no reason to believe their
incidence will be any greater in the geopressure-electric installation than
with the many existing natural gas gathering or transmission systems.
The flare on the purge stream from the main condenser may become ex-
tinguished during operational upsets or because of extreme weather conditions.
During these intervals a release to the atmosphere of about 0.09 Nm3/sec. (200
scfm) of methane will occur. Although these events will be environmentally
undesirable, they are expected to be infrequent and brief, with no serious
adverse impact.
In the event that the secondary fluid process, rather than the two-stage
steam flash process, is the one chosen for the demonstration plant, the effects
of possible emissions of isobutane should be considered. These potential
emissions would include the small quantities which would escape into the
atmosphere from possible undetected leaks and the large releases resulting from
possible major failure of equipment. The likelihood of either of these events
occurring, although very small in the absolute sense, is theoretically greater
66
-------
than for the corresponding releases of steam in the flash process because of
the higher pressures involved with isobutane. A possible effect would be the
creation of a fire or an explosion with resultant injury to personnel.
GEOLOGICAL CONSIDERATIONS
Subsidence
Land subsidence as a result of the subsurface withdrawal of gaseous hydro-
carbons was noted as early as 1918 in the Goose Creek field in Harris County,
Texas38. Active subsidence is occurring today in the Galveston Bay area o£
Texas as the result of the withdrawal of shallow ground water. Okumara39 and
Hirono40 attribute subsidence in the Niigata district of Japan to the produc-
tion of methane dissolved in water. Gabrysck*41 of the United States Geological
Survey studied the Houston-Galveston area of Texas and notes that more than
5 feet of subsidence has occurred in some areas since 1943. This effect is
principally due to the pumping of water from the Chicot and Evangeline aqui-
fers. He concludes that records from compaction recorders in the Houston-
Galveston region are insufficient to relate compaction to depth; however, most
of the compaction is probably occurring near the surface because near-surface
clays have been subjected to less overburden than deeper clay. These examples
of subsidence are all from withdrawals of less than 200 meters depth. They
may or may not be of significance for geopressured zone consideration.
There are several negative environmental effects that may be engendered
by land subsidence. Kreitler and Gustavson1*2 report that the area that will
be inundated by hurricane tides in the Galveston Bay area has increased by
20% since 1961, principally due to subsidence caused by the withdrawal of
shallow ground water. In low-lying coastal areas, a subsidence of just one-
third of a meter could subject large new areas to tidal flooding. Potential
flood damage, moreover, is not limited to coastal regions. Numerous inland
areas of the Gulf Coast are periodically subjected to fresh water flash flood-
ing and could be adversely affected if significant subsidence were to occur.
The amount of potential damage from flooding is related to land use. Heavily
urbanized areas, obviously, would suffer the most damage, while unimproved
pasture land would probably suffer the least.
Major growth faults often act as reservoir boundaries; hence production
from an isolated aquifer could result in a differential subsidence, or fault
activation. Kreitler112 reports that a 6-foot fault escarpment has developed
in Saxet field near Corpus Christi, Texas since the onset of hydrocarbon
production in 1942. Moreover, episodes of maximum fault movement seem to
correlate with maximum gas production within the field. Tiltmeter measure-
ments on the Eureka Heights and Long Point faults in the north Houston area
indicate movement associated with a declining water level in the shallow
Chicot aquifer. Fowler1*3 has noted, in the Chocolate Bayou field in Brazoria
County, Texas approximately 30 cm of differential subsidence in association
with gas production from relatively -shallow geopressured zones; however, no
fault activation has occurred. Fault movement could cause foundation damage
to homes, factories, highways, and many other types of structures. Moreover,
secondary environmental damage could occur from fault movement; for example,
if it were to rupture a pipeline, cause extensive damage to a railbed, or,
possibly, crack the foundation of a nuclear power plant. The
67
-------
potential for such hazards should be thoroughly evaluated at any proposed
geopressured geothermal site.
Stream drainage patterns are often controlled by local faulting, and
could be affected by differential fault movements, resulting in environmental
and legal problems.
What are the chances of significant subsidence and fault activation
taking place as a result of geopressured production? Yerkes and Castle44
conducted a search for documented subsidence over oil and gas fields in the
U.S. and found only a few examples, mostly in California, where geologic
conditions are very different from the Gulf Coast. Giertsma" concurs
that such occurrences are the exception rather than the rule.
Giertsma1*5 studied the problem extensively, and drawing from the science
of rock mechanics and the previous work of Biot , Gassmann , Hall , and
others have developed and refined the theory of poroelasticity. This theory
states that stresses and strains in porous and permeable solid materials
caused by pore pressure and pore pressure gradients can be predicted on the
basis of an extension of the linear theory of elasticity, i.e. poroelasticity,
provided the porous and permeable skeleton behaves like a linear, elastic body.
Giertsma45 concludes that some or all of the following criteria must be
met for significant subsidence to occur:
1. A significant reduction of reservoir pressure takes place during
production.
2. Production is from a large vertical interval (continuous or stacked).
3. Fluids are contained in loose or poorly cemented rock.
4. The reservoirs have a shallow depth of burial.
The contemplated geopressured reservoirs fulfill the first three conditions,
but not the last. Until field tests and measurements can be made, potential
for subsidence must be evaluated from mathematical models that predict: (1)
the amount of reservoir compaction that will occur, and (2) the amount of com-
paction that will be translated to the land surface as subsidence. There is
little agreement among authors as to the best model or what values to assume
for rock compressibility and the other parameters needed for the various
calculations.
Almost all of the subsidence that occurs in the first few years is ex-
pected to be derived from the compression of the sandstone reservoir. After
eight years, the components of sand compression and shale compaction are
approximately equal; and at the end of the production period, the subsidence
due to shale compaction is approximately twice that caused by sand compression.
It seems likely that some subsidence will occur; however the degree is
uncertain. Herrin and Goforth50 and Winslow and Wood51 cite the alarming rate
of subsidence caused by withdrawal of shallow ground water in the Houston area
as an argument against geopressured geothermal production. As previously
68
-------
noted, several authors, notably Giertsraa, point out that the compaction/sub-
sidence ratio is very much dependent on depth.
One major problem that must be faced is the differentiation of subsidence
and fault movement, which occurs as a natural geological process from that
which is engendered by the production of geothermal fluids. Kreitler and
Gustavson'*2 outline a 12-point program of baseline environmental studies that
should be completed prior to initiation of a test well or construction of
production/generating facilities. This includes continuing leveling surveys,
seismic monitoring, and strain gauge observations to determine subsidence and
fault movement. Such a comprehensive study would provide enough working data
to begin to assess the environmental impact of geopressured geothermal pro-
duction. Many years of such monitoring will probably be necessary to accu-
rately differentiate natural phenomena from artificially induced effects.
Earthquakes
No earthquakes have occurred on the Gulf Coast of the U.S. as a result
of man's various activities, despite the fact that tremendous volumes of
fluids have been withdrawn from the subsurface over a period of many years.
The one earthquake that appears in the historical record occurred near
the town of Hemphill, Texas, in April, 1964. Four distinct shocks were re-
corded, ranging from 3.4 to 4.4 in magnitude on the open-ended Richter scale.
A high level of microseismic activity continued following the shocks which
diminished after a period of six months and disappeared after a total period
of seven months. The quakes were shallow, in the upper few kilometers of the
earth's crust, and the foci appear to have been aligned with major growth
faults in the area. Herrin50 has concluded that the quakes were a natural
event, although no definitive explanation of why these faults "locked up"
at that particular time has been offered. A regional gravity anomaly in the
Hardeman County area suggests that typical basement tectonics may be a
contributing factor.
Earthquakes are caused by the buildup of tectonic stresses within the
earth's crust. Strain accumulates until it reaches a critical level, where-
upon movement in the form of elastic rebound occurs. This movement generally
takes place along pre-existing faults because they are zones of crustal weak-
ness. The strain may be dissipated in slow movements along fault planes,
known as creep. Or, if sufficient strain accumulates, movements of the earth
may be rapid and violent; i.e., earthquakes occur.
Hubbert and Rubey^2 describe in detail the role of pore pressure in
(thrust) faulting. Figure 11 shows the orientation of the principal stress on
a pressurized, confined, rock specimen, based on experiments by McHenry53 on
concrete. The principal axial stress in Si, the principal radial stress is
S3, and the principal shear stress is T. The effective shear stress, T, is
the governing force in controlling fa-ult movements, and is a function of the
effective axial and radial stresses, o^, o3, given by:
Oi = Si - p
o3 = S3 - p
where p = interstitial pore pressure.
69
-------
X X X X X X X X X X X X
Figure 11. Total and partial stresses on jacketed specimen
with internal fluid pressure.
70
-------
It is readily apparent from these equations that as the pore pressure,
p, becomes large, the effective confining stresses become small, thus facil-
itating the release of accumulated strain in the form of creep and/or earth-
quakes .
This effect was amply demonstrated at the Rocky Mountain Arsenal disposal
well near Denver, Colorado, where after decades of quiescence, numerous earth-
quakes occurred between 1962 and 1965. A number of investigators, notably
Evans5 , have attributed the quakes to the increase in pore pressure caused by
the deep well injection into fault zones, and have correlated the frequency and
magnitude of the quakes with the volume and pressure of the injected fluids
during that period of time. Lomnitz55 notes a number of earthquakes have been
caused by dam construction and subsequent reservoir impoundment increasing the
pore pressure and triggered by the trip-loading effect of the reservoir.
Conversely, one might expect that a significant depletion of pore pressure
might cause a slowly "creeping" fault, such as the typical growth faults of the
Gulf Coast, to "lock up" and accumulate sufficient tectonic strain eventually
to be released in a violent earthquake.
Most evidence argues against this happening on the Gulf Coast. First,
with the questionable exception of the Hemphill quakes, this effect has not
been observed, even in areas where considerable pressure depletion has occur-
red. Second, the formations of the Gulf Coast are lithologically "soft"
compared to Colorado and other areas. They have a low elastic limit and
tend to deform plastically under fairly low stresses. Hence, it seems un-
likely that the rocks could store sufficient strain to cause a major earth-
quake. Third, the sedimentary section of the Gulf Coast contains thick
sequences of plastic shale and is underlain by a thick and mobile layer of
salt, the Louann of Permo-Triassic age. The mobility of these formations
allows them to absorb tectonic stresses by flowage, as is evidenced by the
innumerable salt domes and related structures, and shale diapirs that occur
on the Gulf Coast. It is interesting to note the absence of salt in the
Hemphill area as a possible factor in the 1964 earthquakes-
It should be emphasized that strain accumulation and resultant earth-
quakes are naturally occurring geologic processes. Induced variations in pore
pressure will neither cause nor prevent earthquakes, but rather may advance
or delay the timing of tectonic movements which must inevitably take place.
Totally aseismic areas probably do not exist; however, the possibility of a
major shock occurring on the Gulf Coast is probably as remote as any place on
earth.
Geopressured geothermal production is not expected to cause faults to
"lock up" with subsequent release of strain through earthquakes for the reasons
previously cited; nevertheless, continuous monitoring of faults should be
undertaken using seismographs and strain meters. Strain meters, or gauges,
are devices which are anchored on both sides of a fault and can accurately
measure the accumulation of strain that occurs across that fault. Thus, if
it appeared that geopressured production was causing an undue buildup of
strain across a growth fault, production could be halted well before the
critical level of strain accumulation is reached.
71
-------
As in the case of subsidence, it will be necessary to establish
baseline values for fault movement and strain accumulation before geopressured
production begins, so that an accurate determination of the effects of the
production can be made.
72
-------
SECTION 7
MULTIMEDIA WASTE CONTROL REQUIREMENTS
IN THE AREAS OF POTENTIAL USE
The requirements for controlling emissions and other environmental effects
arising from the development of the geopressured geothermal potential along
the Gulf Coast are not believed to be severe. The geopressured waters appear
to present even fewer environmental problems than do conventional geothermal
resources, which are themselves believed to offer the most environmentally
"clean" alternate sources of energy.
The problems that do exist have been presented in Section 6 of this
report. These problems are treated in this section (number 7) in terms of the
present technology for coping with the problem, research needs, and proposed
actions. These items follow.
EMISSION CONTROL
Present technology, properly employed, is capable of controlling the
quantity and quality of the emissions, as well as the methods of their dis-
posal, to meet promulgated EPA standards. In addition to the combined stream
of spent fluid plus cooling tower blowdown, whose disposal by reinjection will
be discussed later, the cooling tower exhaust is the only major designed
emission. The present day guaranteed performance of cooling towers includes a
maximum allowable drift rate commonly held to 0.005% of circulation rate.
This represents a vast improvement over the 0.02% guarantee usually available
five to ten years ago. This improvement is the result of advances in the
design of demisters and drift eliminators. Any objectionable effects of
visible plume, which might be particularly evident in urban areas during damp
weather, can be either minimized beforehand, through judicious site selection
and optimum orientation of the tower on the site, or alleviated by the op-
eration of previously installed exhaust heaters. The latter adds measurably
to operating costs.
Adequate instrumentation, embodying "fail-safe" interlocks, can greatly
reduce the hazards of possible equipment failure by limiting the quantity of
fugitive emissions escaping in the interval between time of the failure oc-
currence and the time of corrective action. Collectively, the common-sense
type of design details -can greatly reduce the potential harm to the environ-
ment resulting from possible emergency emissions. Examples would.be the use
of diked containment areas around each of the wellheads, and the establishment
of local surface drainage in the optimum direction.
It is assumed that these geopressured waters will not contain hydrogen
sulfide. Should this assumption prove erroneous, hydrogen sulfide will be an
73
-------
emission of consequence, primarily due to its noxious odor. Present tech-
nology does not adequately provide for prevention of this gas from the waste
streams. Containment of the waters is theoretically possible but the odor
does escape in actual practice. Research on ways to oxidize or otherwise
destroy the hydrogen sulfide is being carried out in this laboratory as well
as elsewhere. An early solution to the problem is anticipated.
REINJECTION
A commercial geopressured geothermal power plant generating 25 MW(e)/yr
will produce on the order of 45,000 m3/day of liquid wastes that will have to
be disposed of. Environmental considerations indicate that deep well rein-
jection is the favorable method of disposal, however, the economic factors are
highly variable. House et al56 indicate that flow rates and net power output
would be significantly enhanced by utilizing surface disposal. Overall eco-
nomics are dependent on a number of factors, not the least of which are the
price of energy and existing environmental restrictions.
The average salt water disposal well in the Texas Gulf Coast reinjects
approximately 1500 m3/day. The average waste disposal well reinjects approx-
imately 320 m3/day. The maximum reinjection rate for a waste disposal well is
a little over 2000 m3/day. Some wells in Louisiana are reported to be rein-
jecting as much as 3200 m3/day. (Source of information: Louisiana State
Department of Conservation, Texas Railroad Commission, Texas Water Quality
Board.) Assuming high volume disposal wells would be utilized by a hypothet-
ical 25 MW facility producing 45,000 m3/day liquid wastes, approximately 30
disposal wells will be required. Cost per well is estimated to be $500,000,
for a total net cost of approximately $15,000,000. This estimate does not
include the cost of the high volume, high pressure pumps that will be re-
quired, nor does it include the cost of lined holding tanks or a solids removal
plant to filter out Si02 and CaC03 precipitates. Overall total capital costs
for waste disposal could easily exceed $50,000,000.
There are several requirements in planning a reinjection program. The
disposal aquifers must be 300 to 450 meters below the base of usable quality
water. Most water disposal is carried out at depths of 900 to 1,400 meters,
hence this requirement should pose no problems. The injection aquifer must be
bounded above and below by effective confining beds, aquacludes. These may be
evaporites, dense limestone, or more commonly on the Gulf Coast, shale. Any
faults which intersect the aquifer must not be sufficient to completely dis-
place the aquacludes.
Injection pressure is normally limited to 0.10 kg/cm2 per meter of
depth and pressure buildup is limited to 3 kg /cm2 increase per 1,000 meters
of depth. Injectability tests must be performed prior to the issuance of a
waste disposal permit to determine transmissivity and calculate pressure
buildup curves from which allowable injection rates can be determined.
Records of all wells which penetrate the injection horizon within a
radius of 4 kilometers of each injection well must be obtained, and each well
must be squeezed and replugged in that zone to prevent possible leakage.
Contamination of fresh water sands is virtually unknown where these precau-
tions have been observed.
74
-------
The two agencies in the state of Texas that are responsible for waste
and salt water disposal are the Texas Water Quality Board and the Texas Rail-
road Commission. In Louisiana, the State Department of Conservation is re-
sponsible for waste water disposal. Their counsel and approval must be sought
in designing any scheme for geopressured geothermal water disposal.
GEOLOGY
The obvious question with regard to reinjection is whether or not there
are sufficient suitable potential reinjection aquifers for geothermal waste
disposal for this method to be feasible. The answer is a qualified yes.
The oldest potential geopressured reservoirs on the Gulf Coast are in the
Wilcox formation and are Eocene in age. These are overlaid by the Oligocene
Jackson and Frio formations, into which the effluent waste of any Wilcox
production would be reinjected. Unfortunately, the Oligocene sands are not
well developed along this band, some one hundred miles or more inland. Some
shallow aquifers do exist in this area; however, many fault blocks containing
potential geopressured reservoirs will not contain adequate aquifers for waste
disposal. The most promising geothermal fairways are in the Frio formation,
coastward from the Wilcox. The Frio is overlaid by formations of Miocene age
which contain numerous potential sands for waste disposal. These sands com-
monly have porosities as high as 30% and permeabilities approaching one Darcy,
and are ideal disposal aquifers. The sands are often stacked; hence a number
of aquifers could be utilized simultaneously to accept the large volumes of
effluent. In Louisiana and certain locations on the Texas Coast and just
offshore, the Miocene sands may themselves be geopressured reservoirs. These
are almost invariably overlaid by shallower, hydropressured Miocene and young-
er sands that could be used for effluent disposal.
Obviously, it will be technically feasible to dispose of the effluent
from a single, moderately sized geopressured geothermal facility by reinjec-
tion into shallower zones, although it may be economically unattractive to do
so. Real problems develop, however, in projecting the large scale development
of the resource. Consider that the hypothetical 25 MW(e) power plant would
more than double the total amount of waste effluent now being reinjected in
the entire state of Texas! This undoubtedly could be accomplished; however,
it seems unlikely that the effluent from, say, a 1,000 MW(e) or more electrical
generation could be practically disposed of in this manner. The environmental
impact of reinjecting 2 million m3/day, and even the physical ability to do
so, remain unknown at the present time. Thus, effluent disposal may be the
greatest limiting factor in the exploitation of the geopressured geothermal
resource.
ALTERNATIVES TO REINJECTION
The most attractive alternative to reinjection is to find an economic
secondary use for the effluent water. Dry areas such as south Texas could
utilize the water directly for irrigation, if it is reasonably fresh. More-
over, because the water will contain some residual heat, it should be amenable
to a self-desalination process and could provide fresh water for drinking,
irrigation, and industrial processes. Other potential uses include shrimp
75
-------
farming and secondary oil recovery by waterflooding techniques. Waterfloods
frequently have been cited as a possible mode of geopressured effluent dis-
posal due to the very large volumes of water that are injected into the pro-
ducing formations. The largest waterflood operation in the state of Texas is
in the Kelly-Snyder field of Scurry County, Texas where more than 41,000
m /day of fresh and salt water is being injected through a total of 210
injection wells. While this is an impressive volume of fluid, a number of
factors make waterflooding impractical as a method strictly for waste disposal.
The Kelly-Snyder operation and most large volume waterflood operations
are of the pressure maintenance variety. Large volumes of fluid are produced
concurrent with injection, from about 80% to well over 100% of the injected
volume. In fact, it is often difficult for injection to keep pace with pro-
duction which sometimes results in an eventual pressure decline within the
reservoir. Some proportion of the injected fluid displaces the produced oil,
gas, and condensate, and this is the net make-up water which must be con-
tinuously supplied to the water flood. In practice this may be as much as two-
thirds of the total volume injected. At Kelly-Snyder, fresh water is pipe-
lined from the El Capitan area and added to the produced water to supply the
total waterflood needs. Two or three waterfloods the size of Kelly-Snyder
would be required to dispose of-all the effluent from a 25 MW(e) geopressured
geothermal power plant.
The picture is not as favorable in the geothermal fairways along the Gulf
Coast. Instead of highly porous and permeable formations such as the lime-
stone reef complex (Canyon Reef) which is the producer at Kelly-Snyder, most
waterfloods are performed in much tighter sandstone formations, and volumetric
requirements may be diminished by an order of magnitude, or more.
The most feasible alternative to reinjection along the Gulf Coast present-
ly appears to be pipelining or canaling to a salt water body. These tech-
niques are discussed in Section 6 in some detail. Both methods are fully
developed and can be accomplished with no additional technical research or
development.
BLOWOUT PREVENTION
Problems experienced in drilling geopressured formations include lost
circulation, stuck drill pipe and resultant fishing jobs, and uncontrolled
wells, or blowouts. Today, however, techniques for drilling wells in abnormally
pressured zones have been developed to the point that there is little chance
of a blowout occurring in a judiciously planned well.
Critical to blowout prevention is a good knowledge of where the top of
the geopressure occurs. Detection can begin prior to drilling. Pennebaker57
and Aud" describe seismic techniques based on the reduced acoustic velocity
associated with geopressure that can qualitatively and, in many cases, quanti-
tatively define abnormally pressured zones. Various borehole logs from nearby
wells can be used to further define the geopressure and predict the depth at
which it will occur.
76
-------
Data obtained while drilling is used to monitor a standardized rate
of penetration (drillability), mud flowline temperature, shale cuttings
density, volume, and size, and the presence of "trip" gas. Jordan and Shirley
in a classic paper59 describe how these data can be used to detect abnormal
pressure and demonstrate that quantitative estimates of pore pressure can be
made.
Good management of the drilling mud program is essential in drilling
abnormally pressured zones. Due to the increased pressure gradient in the
geopressured zone, much higher mud weights are required, on the order of 2
to 2.5 gin/cm , as compared to the approximately 1 gm/cm3 mud used in the
hydropressured zone. Heavy mud cannot be used in shallow zones because it
retards drilling, spalls the bit/ and can fracture the formations. Conversely,
geopressures are sufficient to blow out a lighter drilling mud. Wells are
therefore drilled to the top of the geopressure with a normal weight mud,
cased,and cemented. Then the mud weight is increased to the proper density by
the addition of heavy materials such as barite, and drilling is continued into
the geopressured zone. Drilling parameters are monitored and mud weights
adjusted accordingly to maintain balanced conditions within the borehole. In
some cases, intermediate casing must be set within the geopressured zone.
Blowout prevention is accomplished by utilizing drilling data systems to
closely monitor all aspects of the drilling operation and by installing
warning devices to detect the early signs of an impending blowout. High-
pressure blowout preventers, which are hydraulic or electrical devices used to
close in the well in the event it begins to flow, are always used in areas
known to contain geopressure. Several of these devices may be mounted in
series at the wellhead, and they are considered extremely effective and
reliable.
Several methods can be used to bring a flowing well under control in the
unlikely event that the blowout preventers fail. One is to attempt to pump
heavy mud or cement into the wellbore to shut off the flow. If this method is
impossible or unsuccessful, then a second well, known as a relief well, is
drilled into the well that is out of control; and heavy mud or cement is pumped
from one well into the other. Many wells that blow out actually stop flowing
of their own accord after a few days, as the formation heaves and eventually
plugs the well bore. A hole that has blown out usually sustains considerable
damage and is generally junked and a new well drilled.
Large volumes of water may be released to the land surface between
the time a blowout occurs and the time it can be brought under control. In
order to prevent widespread environmental damage, a diverter valve may be
placed downstream of the blowout preventer which will channel the flow in a
desired direction. Permits may be granted, in some cases, for emergency
surface disposal into streams or canals. Obviously, this method is undesir-
able and should be avoided if possible. Other alternatives are to divert
the flow into lined tanks or unlined pits. If unlined pits or natural basins
are used, provisions should be made to dispose of the water as soon as possible
by reinjection into disposal aquifers, or by other means, so that environmental
damage is minimized.
77
-------
SUBSIDENCE PREVENTION
Land subsidence is not expected to be a major problem created by the pro-
duction of geopressured geothermal fluids for the reasons outlined in the
preceding section. Nevertheless, it is necessary to consider methods to
minimize any potential damage.
The surest method to prevent subsidence would be to reinject the fluids
back into the producing aquifer. Formation pressures on the order of 985 to
2,110 kg/cm and the very tight sand permeabilities expected in the geopres-
sured formations would necessitate high pumps and a vast number of disposal
wells, perhaps hundreds, to accomplish this type of reinjection. Add to this
the fact that each reinjection well would have to be 4,500 to 7,000 meters
deep and probably would cost several million dollars each; and it becomes
apparent that, from an economic standpoint alone, this method is totally im-
practical. Evidence exists to show that it may be physically impossible, as
well, to pump these volumes into geopressure using present technology. Hence,
this method of subsidence prevention can be summarily dismissed as unfeasible.
Careful selection of the geothermal site will be the best method of
preventing subsidence. The most critical parameter is the selection of a
reservoir in a large fault block so that the compaction of the reservoir may
be translated over a very large surface area. Happily, the selection of a
large fault block is desirable, not only for subsidence prevention, but because
it coincides with the need for very large reservoirs capable of sustaining
production for a period of twenty years or more. Producing wells should be
located as far as is practical from faults so that a differential subsidence
or fault activation does not occur. The first plant sites should be chosen in
undeveloped, somewhat inland, areas so that if subsidence does occur, damage
will be minimal. Faults should be mapped using all available means, including
reflection seismic techniques, to determine if any structures could suffer
damage from a differential fault movement. These precautions will minimize,
but probably not totally eliminate, subsidence and the resulting environmental
damage. Hopefully, if these precautions are followed, any subsidence and re-
sulting environmental damage will be minimal.
78
-------
REFERENCES
1. Ruby, W. F. and M. K. Hubbert. Role of Fluid Pressure in Mechanics
of Overthrust Faulting, II: Overthrust Belt in Geosynclinal Area of
Western Wyoming in Light of Fluid Pressure Hypothesis, Bull. No. 71
Geol. Soc. Am., 1959. pp. 167-206.
2. Burst, J. F. Diagenesis of Gulf Coast Clayey Sediments and its
Possible Relation to Petroleum Migration. Bull. No. 53-1. Am. Soc.
Pet. Geol, 1969. pp. 73-93.
3. Jones, P. H. Geothermal and Hydrocarbon Rigemes, Northern Gulf of Mexico
Basin. In: Proceedings First Geopressured Geothermal Energy Conference,
Center for Energy Studies, Univ. of Texas, Austin, Texas, 1975. pp.15-89.
4. Buckley, S. E., C. R. Hocott and M. S. Taggart. Distribution of
Dissolved Hydrocarbons in Subsurface Waters, Habitat of Oils. In:
Proceedings of Louis Weeks Symposium. Am. Assoc. Pet. Geol., 1955.
pp. 850-882.
5. Phillippi, G. T. On the Depth Time and Mechanism of Petroleum
Generation. Geochiin. et Cosmochina. Acta. (29): 1021-1049. 1965.
6. Culberson, 0. L. and J, J. McKetta. Phase Equilibria in Hydrocarbon
Water Systems III - The Solubility of Methane in Water at Pressures
to 10,000 psia. Trans., AIME (192): 223. 1951.
7. Papadopulas, S. S., R. H. Wallace, Jr., J. B. Wesselman and R. E. Taylor.
Assessment of Onshore Geopressured-Geothermal Resources in the Northern
Gulf of Mexico Basin. In: Geol. Surv. Circ. 726. Assessment of
Geothermal Resources of the Unites States. U.S. Dept. of the Interior.
1975.
8. Dorfman, M. H. and R. O. Kehle. Potential Geothermal Resources of Texas.
Bur. Econ. Geol. Geol. Circ. 74-4. Univ. of Texas, Austin, Texas, 1974.
33 p.
9. Bebout, D. G., M. H. Dorfman and 0. K. Agagu. Geothermal Resources,
Frio Formation, South Texas. Bur. Econ. Geol. Geol. Circ. 75-1.
Univ. of Texas, Austin, Texas,' 1975 36 p.
10. Jones, P. H. Hydrodynamics of Geopressure in the Northern Gulf of
Mexico Basin. J. Pet. Geol., (21): 803-810. 1969.
79
-------
11. Jones, P. H. Geothermal Resources of the Northern Gulf of Mexico
Basin. In: Proceedings U.N. Symposium on the Development and
Utilization of Geothermal Resources, Pisa, Italy, 1970. (2)1: 14-26.
12. Knapp, R. M. and O. F. Isokrari. Aspects of Numerical Simulation of
Future Performance of Geopressured Geothermal Reservoirs. In:
Proceedings Second Geopressured Geothermal Energy Conf. (II), Center
for Energy Studies, Univ. of Texas, Austin, Texas, 1976. pp. 103-161.
13. Wilson, J. S., B. P. Shepherd and S. Kaufman. An Analysis of the
Potential Use of Geothermal Energy for Power Generation Along the
Texas Gulf Coast. NTIS PB-243 324, Texas Governors Energy Advisory
Council, Austin, Texas, 1974.
14. Hornburg, C. D. and 0. J. Morin. Geothermal Resources Utilization -
Paper and Cane Sugar Industries. In: Proceedings First Geopressured
Geothermal Energy Conf., Center for Energy Studies, Univ. of Texas,
Austin, Texas, 1975. pp. 233-260.
15. Dorfman, M. H. and R. W. Deller. Summary and Future Projections. In:
Proceedings Second Geopressured Geothermal Energy Conference (I), Center
for Energy Studies, Univ. of Texas, Austin, Texas, 1976. pp. 27-29.
16. Present Status and Future Prospects for Non-Electrical Uses of Geothermal
Resources, Howard, J. H. ed. UCRL-51926, Lawerence Livermore Laboratory,
Univ. of California, Livermore, Calif., 1975.
17. Gault, J., et al. Preliminary Analysis, Electric Generation Utilizing
Geopressured Geothermal Fluids. In: Proceedings Second Geopressured
Geothermal Energy Conf. (IV), Center for Energy Studies, Univ. of
Texas, Austin, Texas, 1976.
18. Vanston, J. N., et al. Legal, Institutional, and Environmental. In:
Proceedings Second Geopressured Geothermal Energy Conf., Univ. of
Texas, Austin, Texas, 1976.
19. Hittman Assoc., Inc. Electrical Power Supply and Demand Forecasts
for the United States through 2050. NTIS PB-209 266, National Technical
Information Service, 1972.
20. Lindal, B. Geothermal Engineering. Unesco Press, Paris, France, 1983.
21. Swink, D. G. and R. J. Schultz. Conceptual Study for Total Utilization
of an Intermediate Temperature Geothermal Resource. ANCR-1260, Idaho
National Engineering Laboratory, Idaho, 1976.
22. Status Report: Geothermal Program Definition Project. Part I:
Program Plan Development, Geothermal Energy Development Status,
Contract No. NAS 7-100, NASA-ERDA, 1200-205, Jet Propulsion Labora-
tory, Calif. Inst. of Tech., Berkeley, Calif., 1975.
80
-------
23. Status Report: Geothermal Program Definition Project. Part II:
Geothermal Energy Development Status, Contract No. NAS 7-100, NASA-
ERDA, 1200-205, Jet Propulsion Laboratory, Calif. Inst. of Tech.,
Berkeley, Calif., 1975.
24. Wilson, J. S. A Plan to Develop the Geothermal Resources of the
Gulf Coast Basin. Dow Proposal No. 7741143, submitted to Division
of Applied Technology, Atomic Energy Commission, 1974.
25. Dickey, P. A., A. G. Collins and I. Fajardo M. Geological Notes:
Chemical Composition of Deep Formation Waters in Southwestern
Louisiana. Bull. No. 56(8): 1530-1570. Am. Assoc. Pet. Geol., 1972.
26. Taylor, R. E. Chemical Analyses of Ground Water for Saline-Water
Resources Studies in Texas Coastal Plain. Report 75-79 (I, II),
Geol. Survey, St. Louis, Miss., 1975. 669 p.
27. Jones, Paul H. Private Communication, Louisiana State Univ., Baton
Rouge, La., 1976.
28. Blakeman, E. R. Private Communication, Superior Oil Company, Houston,
29. Schmidt, G. W. Interstitial Water Composition and Geochemistry of
Deep Gulf Coast Shells and Sandstones. Bull. No. 57(2): 321-337,
Am. Assoc. Petro. Geol., 1973.
30. Saline water Resources Survey of the State of Texas, Texas Water
Development Board, Austin, Texas, 1971. pp. 27-29; 226-227.
31. Linke, W. F. Seidell's Solubility of Inorganic and Metal-Organic
Compounds, 4th ed. (I). D. Van Nostrand, New York, 1958. p. 387.
32. Cooling Tower Fundamentals and Application Principles. The Marley
Company, Kansas City, Mo., 1969.
33. Roffman, A., et al. The State of the Art of Salt Water Cooling
Towers for Steam Electric Generating Plants. Report of ACE Contract
No. AT (11-1)-221, Westinghouse Electric Corp., Pittsburg, Pa., 1973.
34. EPA, Effluent Guidelines and Standards: Steam Electric Power
Generating Point Source Category, Federal Register, 39(196) Part III.
Washington, D.C., October 8, 1974. pp. 36185-36207.
35. Rosain, R. M. Understanding the EPA's Effluent Guidelines and
Standards. Power Engineering 74(4): 55. 1975.
36. Proposed Criteria for Water Quality (I), USEPA, Washington, D.C., 1973,
37. Texas Water Quality Board, Order No. 75-1125-5, Austin, Texas, 1975.
38. Pratt, W. E. and D. W. Johnson. Local Subsidence of the Goose Creek
Field. J. of Geol, 34: 577. 1926.
81
-------
39. Okumara, T. Analysis of Land Subsidence in Niigata. Land Subsidence,
No. 88, AIHS-UNESCO (I). p. 130.
40. Hirono, T. Niigata Ground Subsidence and Ground Water Change. Land
Subsidence, No. 88, AIHS-UNESCO (I). p. 44.
41. Gaybrisk, R. K. Land Surface Subsidence in the Houston-Galveston
Region, Texas. In: Proceedings Land Subsidence Symposium, Tokyo,
Japan, IASH/AIHS-UNESCO, 1969. (Pub. auth. by Dir. U.S.G.S.)
42. Kreitler, C. W. and T. C. Gustavson. Geothermal Resources of the
Texas Gulf Coast - Environmental Concerns Arising from the Production
and Disposal of Geothermal Waters. In: Proceedings Second Geopressured
Geothermal Energy Conf. (5), Center for Energy Studies, Univ. of Texas,
Austin, Texas, 1976. pp. 85-100.
43. Fowler, W. A., Jr. Pressures, Hydrocarbon Accumulation and Salinities -
Chocolate Bayou Field, Brazoria County, Texas. J. Pet. Tech, 22: 411-423.
1970.
44. Yerkes, R. F. and R. 0. Castle. Surface Deformation Associated with
Oil and Gas Field Operation in the United States. Land Subsidence,
No. 88, AIHS-UNESCO (I). p. 55.
45. Giertsma, J. Land Subsidence Above Compaction Oil and Gas Reservoirs.
J. Pet. Tech, 25:734-744. 1973.
46. Biot, M. A. General Theory of Three-Dimensional Consolidation.
J. Appl. Phys, 12: 155. 1941.
47. Ibid. Theory of Elasticity and Consolidation for a Porous Anisotrophic
Solid. J. Appl. Phys, 22: 182. 1955.
48. Gassmann, F. Elastic Waves through a Packing of Spheres. Geophysics,
16(4): 673. 1951.
49. Hall, H. N. Compressibility of Reservoir Rocks. Trans. AIME, 198: 309.
1953.
50. Herrin, E. and T. Goforth. Environmental Problems Associated with
Power Production from Geopressured Reservoirs. In: Proceedings
First Geopressured Geothermal Energy Conf., Center for Energy Studies,
Univ. of Texas, Austin, Texas, 1975. pp. 311-318.
51. Winslow, A. G. and L. A. Wood. Relations of Land Subsidence to
Ground Water Withdrawals in the Upper Gulf Coast Region of Texas.
Mining Eng., Am. Inst. Mining Metall. and Pet. Eng. Trans.,
214: 1030-1034. 1959.
52. Hubbert, M. K. and W. W. Rubey. Role of Fluid Pressure in Mechanics of
Overthrust Faulting. Bui. of Geol. Soc. Am, 70(21): 115-206. 1959.
82
-------
53. McHenry, D. The Effect of Uplift Pressure on the Shearing Strength of
Concrete. Congres des Grandes Barrayes, 1: 1-24, question no. 8, R. 48.
Stockhom, Sweden. 1948.
54. Evans, D. M. The Denver Area Earthquakes and the Rocky Mountian Arsenal
Disposal Well. Mountain Geologist, 3(1): 23-36. 1966.
55. Lomnitz, C. Earthquakes and Reservoir Impounding, State of the Art.
Eng. Geol, 8: 191-198. 1974.
56. House, P. A., P. M. Johnson and D. F. Towse. Potential Power Generation
and Gas Production from Gulf Coast Geopressured Reservoirs. In:
Proceedings First Geopressured Geothermal Energy Conf., Center for
Energy Studies, Univ. of Texas, Austin, Texas, 1975. pp. 283-294.
57. Pennebaker, E. S. An Engineering Interpretation of Seismic Data,
preprint SPE 2165 of AIME, Houston, Texas, September 29, 1968.
58. Aud, B. W. Reflective Seismic Techniques Locate Geopressured Geothermal
Anomalies. In: Proceedings First Geopressured Geothermal Energy Conf.,
Center for Energy Studies, Univ. of Texas, Austin, Texas, 1975.
pp. 133-147.
59. Jordan, J. R. and Shirley, 0. J. Application of Drilling Performance
Data to Overpressure Detection, JPT 1387, November 1966. (Shell Oil Co.
Report, Oct. 1963)
83
-------
APPENDIX
ESTIMATION OF MAXIMUM DEPOSITION RATES OF COOLING TOWER
From pp. 585-596 of "Cooling Tower Environment - 1974 "36:
Maximum deposition rate of example mechanical-draft cooling tower:
Under slightly unstable conditions: 4 x 10" kg/m at 230 m downwind.
Under neutral conditions: 2.43 x 10" kg/m /day at 330 m downwind.
Water recirculation rate: 12.5 m /sec.
TDS concentration: 10,000 ppm
Recirculation rate of example tower = 12.6 x 60 x 7.48 x 35.3
= 199,700 gpm
Maximum deposition rates of cooling tower considered here:
Under slightly unstable conditions:
4 x 10~5 x 7,500 x 96,400 . ..0 n^_sn 2
— = 1.448 x 10 kg/m /day
10,000 x 199,700
= 434 kg/km /mo at ^230 m downwind
= 0.1675 yg/m /sec.
From the Chemical Engineer's Handbook37, the terminal velocity of (assumed)
50 ym diameter brine droplets in air is ^0.07 m/sec. The concentration of
drift particles in the atmosphere at near-ground levels will be approximately
0.1675/0.07 = 239 yg/m3.
84
-------
TECHNICAL REPORT DATA
(Please read Inslructions on tlie reverse before completing}
REPORT NO.
EPA-600/7-77-039
3. RECIPIENT'S ACCESSION-NO.
j. TITLE AND SUBTITLE
Environmental Assessment of Geopressured Waters
and Their Projected Uses
5. REPORT DATE
April 1977 issuing date
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
J. S. Wilson, J. R. Hamilton, J. A. Manning,
and P. E. Muehlberg-
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORG "VNIZATION NAME AND ADDRESS
Dow Chemical U. S. A.
Texas Division
Freeport, Texas 77541
10. PROGRAM ELEMENT NO.
EHE 624B
11. CONTRACT/GRANT NO.
Contract No. 68-02-1329
Task 18
12. SPONSORING AGENCY NAME AND ADDRESS
Industrial Environmental Research Laboratory-Cin., OH
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati. Ohio 45268
13. TYPE OF REPORT AND PERIOD COVERED
Final Report
14. SPONSORING AGENCY CODE
EPA/600/12
15. SUPPLEMENTARY NOTES
16. ABSTRACT
The deep geopressured reseivoirs along the Texas and Louisiana Gulf Coast are
believed to offer a large potential supply of both natural gas and heat energy.
Major environmental effects of development are divided into emissions and geological
considerations. The potential emissions consist of brine from well mishaps, waste
brine of higher salinity, cooling tower emissions, and noncondensible gases. Little
or no hydrogen sulfide or other noxious gases are anticipated. Environmentally,
these waters appear to be cleaner than normal convective geothermal sources.
Geological considerations are more serious. They include possible subsidence
and earthquakes. The area is already low and naturally subsiding. Because the
reservoirs are depletable and the waters act, at least partially, as the load-
bearing element, more rapid subsidence is very possible. The great depth of the
formations is one hope for avoiding subsidence.
Earthquakes are not common to the Gulf Coast, but many subsidence faults exist.
Slippage might be accelerated by deep water withdrawal. Only micro-earthquakes
could be expected, however.
In view of the uncertainty of extensive resource development and the
relatively long time frame involved, only moderate emphasis should be placed on
environmental research at this time.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
Geothermal prospecting
Electric power plants
Pollution
Land use
Gulf Coast
geopressured systems
geothermal energy
environmental
assessment
COSATI l-'ioid/Group
08G
10A
10B
13B
13H
3. DISTRIBUTION STATEMENT
Release unlimited
19. SECURITY CLASS (This Report}
unclassified
21. NO. OF PAGES
97
2O. SECURITY CLASS (This page)
unclassified
22. PRICE
EPA Form 2220-1 (9-73)
85
>V U.S. GOVERNMENT PRINTING OFFICE: 1977-757-056/5607
-------
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
Technical Information Staff
Cincinnati, Ohio 45268
POSTAGE AND FEES PAID
US ENVIRONMENTAL PROTECTION AGENCY
EPA-335
OFFICIAL BUSINESS
PENALTY FOR PRIVATE USE. S3OO
AN EQUAL OPPORTUNITY EMPLOYER
Special Fourth-Class Rate
Book
If your address is incorrect, please change on the above label.
tea/ off. and return to the above address.
If you do not desire to continue receiving tht*,technical report
series. CHECK HERE d. tear off '•
above address.
------- |