United States
Environmental Protection
Agency
Municipal Environmental Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-81-241 Jan. 1982
Project Summary
Monitoring to Detect
Groundwater Problems
Resulting from Enhanced
Oil Recovery
Ron Beck, Bernard Aboba, Douglas Miller, and Ivor Kaklins
A study that developed a four-stage
monitoring program to detect
groundwater contamination events
that could result from enhanced oil
recovery (EOR) projects was
conducted by Energy Resources Co.
Inc. The monitoring system design is
based on a statistical analysis evolving
from a series of equations that model
subsurface transport of EOR spills.
Results of the design include both
spatial and frequency monitoring
intervals that depend on properties of
the local geology and dispersion
characteristics of the potential
contaminants. Sample results are
provided for typical reservoir
characteristics. Selection of
measures to be sampled is based on a
review of the identity of likely
contaminants, on the available
sample and analysis procedures, and
on the cost and time constraints on
analysis. Nonspecific indicator
measures are identified that can be
used to flag those intervals requiring
more intentisve and specific monitor-
ing.
The number of independent
variables in the analysis dictate that
EOR monitoring systems be designed
on a site-specific basis. Sampling
designs can be easily formulated to
conform to the peculiarities of chosen
EOR sites based on data already
available from federal and state
geological surveys and from oil
company statistics.
This Project Summary was
developed by EPA's Municipal
Environmental Research Laboratory.
Cincinnati, OH, to announce key
findings of the research project that is
fully documented in a separate report
of the same title (see Project Report
ordering information at back).
Introduction
Since the end of World War II, various
new fluid-injection methods have been
researched that provide the potential to
recover large volumes of oil left in
reservoirs after conventional recovery.
Little effort, however, has been applied
to identification of environmental
problems.
All enhanced recovery technologies
(both oil and gas) involve potential
groundwater concerns. Those
technologies that require injection of
chemicals into the reservoir or
fracturing of formations hold the most
potential for contamination. In situ
combustion is also of particular concern
because of the range of chemicals that
are formed during the subsurface
combustion process. Table 1
summarizes the types of pollutant
problems that may occur.
Relatively few data have been
collected from the aquifers that may be
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Table 1. Summary of levels of risk anticipated from various activities
carried out during enhanced recovery programs
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— Negligible risk
+ Potential for occasional pollutant events
* Significant potential for regular occurrence of pollutant events if no measures
are taken
contaminated from currently active
enhanced recovery programs. Many of
the enhanced recovery projects are
experimental in nature, and all
available resources were devoted to
assembly of engineering performance
data. Many of the early EOR projects
took place in sparsely populated areas
where no convenient water wells
useful for the sampling of aquifer
quality existed.
A monitoring system- is needed for
use by research and policy groups such
as the USEPA, USDOE, and API. They
will require nationwide data sets that
can be used to detect long-term trends,
to identify regional problems, and to
determine how much attention should
be paid to potential hazards to
groundwaters from EOR activities.
This study aims at meeting the data
needs for identifying the nature and
extent of groundwater contamination
due to EOR activities.
The primary objectives of this study
were to develop and design an efficient
groundwater monitoring program for
EOR projects and to provide the
groundwork for development of
standard principles to be used in
monitoring EOR projects.
Monitoring Program Design
Design of an effective yet realistic
groundwater monitoring program is a
difficult analytical problem and is
impeded by lack of information about
the baseline quality of aquifers and the
pollutant pathways that are required to
make informed decisions.
The major problems to be addressed
in the enhanced recovery environ-
mental monitoring report summarized
here are as follows'
1. How should monitoring stations
be located so that discharges from
the recovery processes are likely
to be detected?
2. What combination of measure-
ments, number of stations, and
frequency of sampling provides
the best information value per
dollar expenditure?
3. How can all of the various
monitoring variables be
standardized sufficiently so that
different recovery projects can be
compared and so that time-series
analysis can be carried out?
4. Which procedures need to be
followed to ensure that the
measurements taken constitute
meaningful information?
The design of an efficient monitoring
program requires that the benefits of
monitoring be identified. Benefits of
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EOR groundwater monitoring will
include detection and prevention of
environmental risks and evaluation of
environmental control investments.
Table 2 summarizes the categories of
costs and benefits that enter into the
design of an EOR/EGR (enhanced gas
recovery) monitoring program
This analysis considers (1) selection
of pollutant indicators, (2) placement of
stations and frequency of monitoring,
and (3) development of a simple
generalized monitoring program.
"Detection" and "event-monitoring"
programs are considered as two
separate cases with detection systems
considered in more detail in the
analysis.
Pollutant Indicators
Enhanced recovery activities use a
wide variety of chemicals. Comprehen-
sive monitoring for each potential
pollutant will require extensive
budgetary commitments. The
measurement of indicator parameters
rather than specific chemicals provides
less detailed and precise information,
but is a more certain way of obtaining
useful returns for a given level of
investment.
Various indicators used to detect
relevant pollutants are:
1. Individual Contaminants. GC/MS,
gas chromatography, and high
pressure liquid chromatograhy
(HPLC) measures for organics, and
atomic absorption or inductively
coupled argon plasma (ICAP) for
metals are detection tests used for
the various contaminants
associated with enhanced
recovery.
2. Total Organic Carbon. This test
measures the presence of all
chemicals soluble in a given
solvent, such as methylene
chloride. Monitoring TOC in the
vicinity of EOR projects can be
expected to detect the presence of
organic polymers, organic
biocides, hydrocarbons, and
miscellaneous other organic
additives used in oil operations.
3. Methylene Blue Active Sub-
stances. The MBA test quantifies
the presence of a large class of
surfactants.
4. Conductivity. The conductivity
test is a surrogate measure to
determine the general presence
of salts and brines in water
bodies
5. Reservoir Pressure.Jhe pressure
maintained within the oil-bearing
Table 2. EOR/EGR Environmental Monitoring Costs and Benefits
Costs Benefits
Dollar costs of monitoring tests
Manpower costs of monitoring
Identification of public-health risks
Detection of violations of regulations
Identification of ecosystem risks
Identification of other environmental risks
(aesthetics, resource preemption,
synergistic effects, intermedia effects)
Identification of previously unrecognized
pollutants
Detection of degradation trends at levels
below currently recognized risk
thresholds
Detection of chemical or hydrocarbon
losses (economic benefit)
Evaluation of the effectiveness
of control investments
formation provides a monitor on
escape of fluids away from the
intended pathways. These
monitoring activities are usually
carried out as part of good
reservoir engineering practices.
Placement of Monitoring
Stations and Frequency of
Sampling
The key issues involved in developing
a monitoring program are selection of
sampling sites and frequencies. The
considerations affecting spatial
placement of monitoring stations are
different before and after a pollutant
event has occurred. Before a pollutant
event occurs, the emphasis is on early
detection leading to monitoring for
contamination close to possible
sources, whereas after an event the
emphasis is on determining the extent
of contamination, which may require
monitoring far from the source. For
these reasons, the design of a detection
and an event-monitoring system has
only a weak linkage. Because a
detection system requires greater
accuracy, higher sampling frequencies,
and fewer stations than an event-
monitoring system, data collection by
well samples is appropriate For an
event system, however, less expensive
methods will suffice.
Chemical-fate models fall into two
categories: miscible and immiscible
pollutant models. While brines and
biocides are soluble in water, oil and
surfactants are not, necessitating
equations in mathematical models of
fluid flow. Briefly, in the immiscible
case, equations must be written for the
movement of both the water and non-
water phases, while in the miscible case
an equation for transport only in the
water phase is developed.
The design of a detection system has
two phases: the first is a "baseline"
analysis characterizing total dissolved
solids (TDS), BOD, organic carbon, etc.,
and other levels before an event, and
the second phase is the design of the
system itself.
The purpose of the first phase is to
take out all "trends" or explicable
variations in groundwater quality so
that residual variation is uncorrelated (a
white noise). Seasonal trends in
groundwater quality have been noted
frequently in the literature; other
possible trends include a straight-line
time dependence, correlation among
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levels of chemical constituents, corre-
lations among nearby wells, and
relations of concentrations to the level
of the groundwater table and volume of
water pumped.
To determine which chemical tests
should be performed to detect EOR
chemicals for accidents at site, it is
important to collect the following
information:
1. A table of "likely" concentration
levels of EOR chemicals in every
EOR process in injected and
produced waters, in addition to
levels in the reservoir formation.
2. A table of contamination
scenarios, listing for each
scenario the groups of pollutants
that are likely to be released
together, concentration esti-
mates, and relative mobilities.
3. A summary of the relevant EOR
chemical degradation processes
and by-products.
4. A table of "likely" background
values for IDS, BOD, TOC,
Methylene Blue Active Sub-
stances, etc., in the local aquifers.
The above information will allow one
to discern which chemical tests have
high detection power for a particular
pollutant event.
The progress of a contamination
plume will resemble Figure 1. As can be
seen, the "center of gravity" of the
plume progresses at a speed of V in the
x direction, while the width of the plume
in the y direction is proportional to the
dispersion coefficient 0. Figures 2 and 3
illustrate the variations in locations and
frequencies as a function of spill
volume and diffusion rate for a set of
hypothetical conditions.
A Sample Program to Monitor
EOR Projects
Particular monitoring activities and
intensities of sampling will be
associated with different EOR
technologies and with each stage of an
EOR project. Table 3 depicts a general
scheme for monitoring. The scheme
involves assembly of background and
baseline information during the early
stages of a project, with routine
monitoring during the course of the
project and, in some cases, follow-up
monitoring for 5 years after the project
V = .01 cm/sec.
Figure 1. Progression of burst leak; dispersion rate = 6 times groundwater velocity.
1400
*7200
t
1/000
800
.
5
® 600
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5
8
$400
200
40
80 120
Volume of spill
160
200
Figure 2. Volume of spill (m3) for different dispersion coefficients.
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_ 5 x JO4
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2 5x10*
u>_
£ 4 x 104
I 3 x 104
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40
80 120
Volume of spill (m3)
160
200
Figure 3. Sampling frequency as a function of spill volume and for different
dispersion coefficients
is completed. For relatively low-risk
technologies such as thermal oil
recovery, less monitoring is required.
Table 4 and Figure 4 summarize the
overall concept of EOR/EGR monitoring.
Figure 4 gives a step-by-step outline of
the tasks to be carried out in an environ-
mental monitoring program. The
approach is a hierarchical one, in which
the simplest, broadest monitoring
activities are performed first and then
only those analytical tests relevant to
specific environmental problems are
incorporated in the detailed and com-
prehensive phases of a monitoring
program. Table 4 characterizes each of
four hierarchical stages in a monitoring
program.
To show how the general scheme in
Table 3 should be applied to a particular
project, two typical monitoring
programs are outlined—for a polymer
flood (Table 5) and for a steam flood
(Table 6).
Recommendations
The report summarized here presents
only a preliminary outline for
groundwater monitoring programs, The
following are recommendations for
further work needed regarding the
assembly of groundwater quality
information for enhanced recovery
projects:
1. Identify Projects That Require
Monitoring. Review ongoing and
planned EOR, EGR, and tar sands
projects. Select those projects
that are most likely to impose
groundwater quality degradation.
2. Identify Susceptible OH Regions.
Review the regional distribution
Table 3. General Scheme for Monitoring of EOR Impacts on Groundwater
^N\^ Stage of
^•x. Project
Type ^X^
of X.
Project ^\
Steam soak.
In situ combustion
Steam drive with
additives
CQz other
miscible gas
Advanced waterflood.
polymer flood
Alkaline flood
micellar/ polymer flood
Conception
^
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_
5 "-
1 i
* I
5 a
m 9)
3 5
* i
1
£
Field
management
(Rework or
seal old wells,
drill new wells)
9)
S •$
5 i=
« 8
IB £
» !
s !
4) O
!s *
! i
1
Preflush
N.A*
N.A.
N.A.
Carry out
tracer studies
Injection of
chemical
slugs
N.A.
N.A.
Monitor for pres-
ence of chemicals
in produced oil
and water
Carry out
tracer studies
Production by
water or steam
injection
Perform diagnostic
monitoring only if
unusual reservoir
conditions are
noted
Conduct routine
monitoring of
nearby
groundwater
Post
production
None
required
Conduct routine
monitoring of
nearby
groundwaters
N.A. = Not Applicable
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Table 4. EOR/EGR Environmental Monitoring Overview Matrix*
Stages of Monitoring
Parameters to be
measured
Purpose of
monitoring
General
strategy
I
Develop
baseline
Indicators
Determine existing
conditions
a. Measure baseline
levels
b. Identify spatial and
temporal patterns
II
Monitor
trends
Indicators
Identify changes
in levels
a. Select key stations
b. Take periodic
measures
c. Look for changes in
identification
patterns
III
Specifically
evaluate flagged
problems
Specify chemicals
Identify problem
contaminants; identify
violations of standards
a. Perform specific tests a.
to determine contam-
inants that have
caused trends
b. Determine if criteria
have been violated
c. Determine spatial
extent of contamination
IV
Assess
effectiveness
of controls
Specify chemicals
Compare levels with
regulatory criteria;
check for reduction in
levels to below criteria
values
Evaluate contaminant
trends in response to
controls
Major dimension(s)
of analysis
Spatial and temporal
Temporal for
representative sites
Profile of classes
of contaminants
Temporal for specific
problem zones
* 777/s display summarizes the major characteristics of the four types of monitoring needed
to evaluate environmental quality.
1A
Characterize Technology
a. Type of Method
b. Quantity of Chemicak
c. Other Environmental
Stresses
1B
Select Parameters
to Be
Monitored
2A
Characterize Environ-
ment of the Site
a. Geology
b. Oil Reservoir
c. Hydrology
d. Other Activities That
May Act
Synergistically
1
2B
Evaluate Frequency of
Samp/ing, Spatial
Location of
Sample Sites
3A
Monitor the Recovery
Project and Track
Material Balances
4A
Identify Apparent Losses
of Chemicals from Oil
Reservoir
3B
Carry Out Monitoring
Program Using Indicator
Variables (TOC, MBA.
Conductivity)
4B
Identify Generalized
Pollutant Trends
Develop Specific Trend
Monitoring Program
3C
Carry Out Specific
Diagnostic Monitoring
Activities in Response
to Observed Pollutant
Events
4C
Characterize Pollutant
Eventfs)
Figure 4. Monitoring program: water-quality degradation from EOR/EGR.
6
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Table 5. Monitoring Program for a Polymer Flood to be Conducted
Over a 20-year Period
Stage of project
Monitoring events
Design of project
1. Identify all freshwater aquifers.
2. Collect monitoring data on aquifer water quality;
utilize "kriging" statistics to develop average
values. Look for seasonal trends.
Rework oilfield wells
1. Develop maps of all old and all sealed wells, and
inventory the condition of all old wells.
2. Monitor reworking procedure to detect any
communication with aquifers.
Preflush
1. Conduct tracer studies to determine dynamics
of injected fluids.
2. Monitor quality of preflush fluids.
Injection of chemical slugs 1.
2.
Conduct tracer studies to determine dynamics
of chemical slug.
Inventory known degradation tendencies,
toxicity, carcinogenicity of chemicals used;
identify persistent potentially harmful
components.
Production
Monitor for unusual levels of indicators (Total
Organic Carbon, Methylene Blue Active Sub-
stances, Conductivity, Reservoir/Welltest
Pressure, Resistivity, and the Geophysical Logs)
on a weekly to monthly basis, depending on the
proximitiy of the aquifer to the producing zone.
Sampling sites to be spaced at not more than 4
times well spacing if possible.
Post-production
1. Monitor for unusual levels of indicators
on a yearly basis.
2. Monitor pressure for a statistically selected
sample of oil wells.
Table 6. Monitoring Program for a Steam Flood to be Conducted Over a
20-Year Period
Stage of Project
Monitoring Events
Design of Project
1. Identify all freshwater aquifers.
2. Collect monitoring data on aquifer water quality;
utilize "kriging" statistics to develop average
values. Look for seasonal trends.
Rework Oilfield Wells
1. Develop maps of all old and all sealed wells,
and inventory the condition of all old wells.
2. Monitor reworking procedure to
detect any communication with aquifers.
Steam-soak Selected Wells
Monitor produced oil and water phases to detect
heat-induced synthesis of hazardous organics.
Fieldwide Steam Soak
Monitor produced oil and water phases to
detect heat-induced synthesis of hazardous
organics.
Post-production
None
of EOR, EGR, and tar sands
projects. Evaluate the regional
environmental issues, existing
environmental quality, and
groundwater use.
3. Select Trend Monitoring Sample.
Develop a statistically based
sample of projects based on
compartmentalization of the
sample by region and by inferred
pollution potential.
4. Select Initial Sample. Select a
small set of projects for sampling.
This initial set of from one to five
sites should be selected based on
the accessibility of the site, the
availability of existing wells to use
in the sampling effort, and the
anticipated costs of sampling at
that site.
5. Develop Samp/ing Plans for
Sample Set. Design a site-specific
sampling plan for the initial set of
sites based on the monitoring
guidelines presented in this report.
6. Development Cooperative
Sampling Procedure. Working
with the DOE and industry, the
EPA should develop a workable
plan for conducing monitoring at
the initial sample of stations and
on a nationwide basis.
7. Training.EPA. and DOE should
jointly develop training programs
for federal, state, and industry
personnel who will be responsible
for carrying out the EOR
monitoring programs.
In addition to the work recommended
for the implementation of a ground-
water monitoring program. The follow-
ing more general activities should be
undertaken to complement the topics
covered by this report:
1. Water Usage Monitoring. A
program needs to be developed to
account for water usage by EOR
and EGR projects It will need to
take the form of monthly
tabulations of water usage by
projects as compared with
unallocated water supplies at that
locality.
2. Produced Water Disposal
Formations. An information base
needs to be developed and kept
•&U. S. GOVERNMENT PRINTING OFFICE: 1982/559-092/3368
-------
updated regarding the usage of
subsurface formations for
produced water disposal and the
volumes disposed of at each
formation.
3- Monitoring Programs for Related
Technologies. (Tar Sands, Heavy
Oil Mining). The EPA Las Vegas
laboratory has developed detailed
protocols for the monitoring of
wastewater from oil shale
projects. These protocols, together
with this report, need to be
extended to the tar sands and
heavy oil mining technology
areas.
The full report was submitted in
partial fulfillment of Contract No. 68-
03-2648 with Rockwell International
under sponsorship of the U.S. Environ-
mental Protection Agency.
Ron Beck, Bernard Aboba, Douglas Miller, and Ivor Kaklins are with ERCO/
Energy Resources Co.. Inc.. Cambridge, MA 02138.
John S. Farlow is the EPA Project Officer (see below).
The complete report, entitled "Monitoring to Detect Groundwater Problems
Resulting from Enhanced Oil Recovery," (Order No. PB 82-119 074; Cost:
$13.50, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Oil and Hazardous Materials Spills Branch
Municipal Environmental Research Laboratory—Cincinnati
U.S. Environmental Protection Agency
Edison, NJ 08837
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Postage and
Fees Paid
Environmental
Protection
Agency
EPA 335
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Penalty for Private Use $300
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