United States
Environmental Protection
Agency
Municipal Environmental Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-81-197 Oct. 1981
Project Summary
Assessment of Oil Production
Volatile Organic Compound
Sources
W. S. Eaton, G. R. Schneider, W. Unterberg, and F. G. Bush, III
Emissions of volatile organic com-
pounds (VOC) from oil production in
new fields were estimated based on
three types of information: (1) extent
of new oil and gas fields (those that
started production after 1974) in the
contiguous 48 states, (2) drilling
techniques used for oil and gas
exploration and production wells (and
their VOC potential), with specific
emphasis on the drilling fluids, and (3)
equipment and techniques for oil and
gas production in new fields and their
potential VOC sources.
The complete record obtained from
the U.S. Geological Survey Petroleum
Data System (PDS) has been provided
for post-1974 oil and gas production
within the 48 contiguous states.
Verification and updating of PDS has
been accomplished for all but nine
states.
A description of oil and gas explora-
tion and production drilling technology
is presented. Emphasis has been
placed on the makeup, use, and
disposal of drilling fluids. A simple
model for assessment of VOC emis-
sions accompanying drilling is pre-
sented along with an estimation of the
potential VOC emissions associated
with drilling activities.
Quantification of the VOC emissions
associated with oil and gas drilling and
production technology was hampered
by lack of data in several areas.
Recommendations for further efforts
are presented so that the assessment
of potential VOC emissions can be
made by state, county, or field.
This Project Summary was devel-
oped by EPA's Municipal Environ-
mental Research Laboratory, Cincin-
nati. 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
Petroleum production represents a
large potential source of volatile organic
compound (VOC) emissions. This effort
was intended as a step toward obtaining
sound estimates of the amount of VOC
emissions associated with new field
(after December 1974) oil and gas
exploration and production in the 48
contiguous states. The program con-
sisted of a survey with the following
tasks:
1. Determination of the new oil and
gas fields in the 48 states that
have started primary production
after December 1974.
2. Determination of the VOC emission
potential and techniques for drilling
gas exploration and production
wells and the handling of drilling
muds.
3. Documentation of equipment and
techniques in use for the assess-
ment and quantification (to the
extent possible) of potential VOC
sources (including mud operations,
waste oils, and fugitive emissions
from operating equipment). Five
new oil and gas fields were visited.
Current practices in well-drilling
techniques, drilling and workover fluids,
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and well servicing and workover are
discussed, and a survey of new fields is
described. The survey data are used in
conjunction with drilling information to
define prospective VOC sources, and
the VOC forecast is made.
Current Drilling Techniques
for Oil and Gas Wells
A brief review of well-drilling tech-
niques and equipment now in general
use is presented. Rotary drilling and
cable tool drilling are described, but
basic drilling equipment and rig compo-
nents, drilling operations, and auxiliary
rig equipment are detailed only for the
rotary drilling process.
The components associated with a
modern drilling rig are discussed in
terms of the four basic tasks the rig is
expected to accomplish: (1) producing
and transmitting power, (2) hoisting
equipment for the drilling string, casing,
and tubing, (3) rotating the drill string
and bit, and (4) circulating drilling mud
to remove cuttings and maintain a safe
hydrostatic pressure in the well bore.
Prime power sources for modern
drilling rigs are almost always diesel-
electric. Most rigs require from 0.75 to
2.2 MW supplied by two or more
engines, depending on the depth to be
drilled and the rig design. The electricity
generated is sent to electric switch and
control gear and then used to power
electric motors for the draw works,
rotary table, and mud pumps.
During the drilling process, the drill
string is often hoisted from the well bore
and disassembled to replace worn drill
bits, run casing into the well, test
formations, take core samples, etc. The
string is then reassembled and run back
into the hole. This cycle is accomplished
by the hoisting equipment (or the draw-
works), consisting of derricks and masts
for support and a block and tackle
system.
Rotary equipment comprising the
swivel assembly, the kelly, rotary table,
the drill string, and the drill bit are
described.
The drilling mud circulation and
treating system is discussed. Drilling
mud is pumped down into the well hole
through the drill string, jets out from the
drill bit, and flows upward out of the
hole in the annulus formed by the drill
pipe exterior and the wall of the hole.
Cuttings are removed from the drilling
mud by shale shakers. One of the pri-
mary purposes for the use of drilling
mud is to provide a safe hydrostatic
pressure in the drill hole to avoid blow-
outs. A number of safety valves, or
blowout preventers, are located in the
mud circulating system and are con-
trolled so as to shut off the drilling mud
flow and seal the system to prevent a
blowout if high-pressure formation fluid
is encountered.
The basic drilling operations are
briefly described: The setting of the
conductor pipe, blowout preventers and
recirculation of drilling mud to initiate
the rotary drilling process, the installa-
tion of surface casing, drilling and
adding new drill pipe to the drill string as
the hole deepens, and running and
cementing casing down to the promising
formation, where, if evidence warrants,
the production string is run into the
hole. Well completion details are also
presented.
Drilling Muds
A review of drilling muds is included
and covers water-based and oil-based
mud composition, factors affecting the
type of drilling fluid used, factors
affecting the quantity of mud and
cuttings generated, and disposal of
solid, liquid, and gaseous wastes
produced in the drilling process.
Among the mud components dis-
cussed are weighting material, clays,
dispersants (to lower viscosity, gel
strength, and filtration rates), organic
polymers (to aid in hole-cleaning, barite
suspension, and filtration control),
inorganic chemicals (to control alkalinity,
calcium ion concentration, scavenging
oxygen and sulfide, and corrosion),
surfactants, lost circulation materials
(to plug highly permeable formations
and avoid excessive mud loss), biocides,
salts, and oils.
Often the composition of the formation
to be drilled determines the type of mud
that should be used. Some formations,
such as shales, may require a special
mud to avoid excessive hole enlarge-
ment, whereas others such as sands
may result in the buildup of a filter cake
as the water base runs into the porous
formation.
Other formation properties that can
determine the type of mud additives
used are the formation pore pressures
anticipated, formation fluids (such as
salt water), hydrogen sulfide, and
formation temperature.
The mud volume and cuttings gener-
ated by the drilling process can be a
problem in soft shales containing
swelling-type clays or in water-soluble
formations. Brine-based or oil-based
muds can be used if the problem is quite
serious. |
Several commonly used methods of *
disposing of waste drilling mud and
cuttings are presented and very briefly
discussed.
Completion and workover fluids are
often the same fluids (muds) that were
used in drilling the well. Special
completion fluids are used, however,
when drilling mud solids would create
problems of productivity damage, settling
or solidification in annulus, or corrosion.
Salts, organic polymers, corrosion
inhibitors, a buffering agent, and
defoamers are briefly detailed as
components of typical solids-free fluids.
Solids-laden systems are also mentioned.
Oil Well Servicing
and Workover
As oil or gas wells age, production
problems develop. Tubes plug with
sand, a subsurface pump may fail,
reservoir pressure may decline, and
well casing may corrode. At this stage,
oil well servicing and workover is
required to correct and repair the well
and the equipment.
The servicing and workover rigs are
mobile. Truck-mounted rigs are used for
light- and medium-duty tasks, but for
heavier work required by deeper wells, A
the equipment will be designed into"
self-propelled carrier units developing
more than 0.45 MW (600 HP) and
capable of hoisting more than 114,000
kg (250,000 Ib).
Descriptions are given of the types of
remedial well work (swabbing, pump
repair production tubing replacement,
repair of packers), well cleanout (sand
cleanout, casing repair, sidetrack
drilling, drilling deeper) and well
stimulation (explosives, acid stimulation
and hydraulic fracturing).
Survey of New Oil and
Gas Fields, 1975-1979
Information was gathered for the
contiguous 48 states (onshore fields
only), with data limited to fields that
went into production after December
1974. The data were obtained from the
Petroleum Data System (PDS), a storage
and retrieval system sponsored by the
U.S. Geological Survey, and from state
files. Oil and gas agencies or divisions of
geology of all contiguous 48 states were
contacted, as these agencies regulate
oil and gas drilling and production. The
annual reports of these agencies were
requested for the years 1975-1979. The
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drilling and production data to be
acquired for each new field is as follows:
1. Field name and operator(s) in field
2. Formation/reservoir
3. County
4. Primary production start date
(January 1975 or later)
5. Type of field (oil, oil/gas, gas) and
API gravity (where applicable)
6. Well depth, feet
7. Producing zone, feet (or least and
greatest depth)
8. Number of wells as of recent date
(state date)
a. Producing
b. Exploratory
c. Abandoned
9. Annual production for 1975,
1976, 1977, 1978, and 1979 of:
a. Crude oil (bbl)
b. Condensate (bbl)
c. Nonassociated gas (ft3 x 106)
d. Associated gas (ft3 x 106)
e. Water (bbl)
The states varied greatly in their
publications. The printed reports dis-
seminated were often incomplete or not
in a form suitable for this study (e.g.,
production by county, not by field).
Twenty-one of the 48 states have no
new fields. In 18 of the states with new
fields, state data were scanned, identi-
fied, edited, and added to the PDS
'computer compilation. The limited
scope of this project did not permit
completion of such tasks for the nine
remaining states with new fields; the
PDS compilation and partially processed
state data for the nine states are
preserved.
The information headings listed
earlier are presented on a statewide
basis (18 states) in several tables of the
full report. Selected information is given
in Table 1 for the 18 states.
VOC Emissions for Oil and
Gas Drilling Operations
The emissions addressed in this study
are from formation fluids, high-pressure
formation gases, and H2S from trouble-
some formations. Formation gases
entering the drilling mud will be
removed in the shale shakers, degassers,
mud pits, choke manifold (around the
blowout preventers, when necessary),
and in small quantities from valves,
flanges, and fittings. VOC emissions
will be sporadic and negligible until
certain troublesome formations are
penetrated; then emissions will depend
on the skill of the drilling crew and mud
handler in plugging such a formation.
Once such a formation is plugged or
permanently sealed off with well
casing, the VOC emission rate will again
decline.
Data are given on the number of oil
and gas wells drilled and the number of
drilling rigs in operation (drilling activity)
from 1974 through 1979.
Model for Drilling Operations
A model for VOC emissions occurring
during drilling operations is given that
includes (1) the oil and gas brought out
of the well in the pores of the rock
cuttings removed from the producing
zone, (2) the leakage of oil and gas into
the drilling mud multiplied by the length
of time the producing zone is directly
exposed to the mud (no means of
estimating the leakage rate is given),
and (3) the rate of loss of diesel fuel oil
from oil-based mud multiplied by the
length of time the oil-based mud is used.
Estimates were made of the order of
magnitude of the VOC emissions
occurring during the drilling of oil and
gas wells. With data given for 1979 on
the total number of wells and footage
drilled in the 48 contiguous states
(excluding offshore drilling) and the
average number of active drilling rigs for
1979, the average depth drilled per day
was calculated. This figure was used
with new field data for five states (Table
2). If it is assumed that the average well
diameter is 0.23, the formation porosity
is 0.2, the oil and gas density is 600
kg/m3, and the thickness of the produc-
ing zone is that given in Table 2, the total
amount of oil and gas (VOC) removed
from the well in the cuttings ranges
from 51.7 to 91.5 kg (Table 3). The
average VOC emission rate per day
ranged from 2.0 to 6.2 kg (Table 3).
Table 1. Statewide New Field Data: Fields, Wells, Depth, Gravity
No. Wells in New Fields
New Fields
State
Alabama
Arkansas
Colorado
Florida
Illinois
Indiana
Kentucky
Louisiana
Michigan
Mississippi
Montana
Nevada
Oregon
Pennsylvania
South Dakota
Texas
W. Virginia
Wyoming
Total
23
62
107
4
96
1
18
35
141
91
99
1
1
26
2
4.208
21
6
Oil
11
50
58
4
/VG+
7
>77
8
>79
>62
55
1
0
NG
2
>1,408
0
NG
Gas
21
18
57
1
NG
0
>3
29
>28
>15
45
0
1
NG
0
>1,922
21
NG
Produc-
ing
102
2,174
138
3
>151
0
>32
55
169
123
419
14
5
NG
2
6,392
21
NG
CAPDG*
0
0
0
O
(total wells)
2
(total wells)
4
22
12
0
0
0
NG
0
4,303
0
NG
Shut In
0
0
11
3
0 .
8
1
19 .
104
0
0
NG
0
0
0
NG
Average Depth,
m(ft)
3,014 (9,889)
1,853 (6,078)
1,734(5,689)
3,934(12,906)
1,352 (4,435)
344.4(1,130)
569.7(1,869)
3,324(10,906)
1,623 (5,325)
3,667(12,030)
2,720(8,924)
1.246 (4.087)
833(2,700)
1,165(3,823)
2,728(8,950)
2,276 (7,468)
1,095 (3,591)
2,880 (9,450)
Average Pay
Zone, m (ft)
5.2(17)
6.7(22)
9.1 (30)
4.9 (16)
NG
NG
NG
6.7(22)
NG
11.3(37)
7.9 (26)
NG
183 (600)
(sands)
NG
3.05 (10)
NG
4.6 (15)
18.6 (61)
Average API
Gravity
40
36
38
31
18
NG
NG
47
50
41
40
27
NA\
NG
33
42
NA
24
*Capable of producing.
+Not given.
applicable.
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Table 2. New Field Data Summary
State
Average well depth
drilled/day Producing zone. Producing zone interval (Am)
m (ft) A m (A ft) Average well depth ' m
Alabama
Arkansas
Colorado
Louisiana
Montana
3,014 (9,887)
1,853 (6,078)
1,734(5,689)
3,324 (10,906)
2,720(8,924)
5.2(17)
6.7(22)
9. 1 (30)
6.7(22)
7.9 (26)
0.00172
0.00362
0.00527
0.00202
0.00291
Table 3. Estimated VOC Emissions from New Field Well Drilling
State
Alabama
Arkansas
Colorado
Louisiana
Montana
VOC/well
(kg)
51.7
66.9
91.5
67.0
78.8
Average well
drilling time
(days)
25.7
15.8
14.8
28.3
23.2
Average VOC/
well per day
(kg)
2.0
4.2
6.2
2.4
3.4
The contribution of the leakage rate of
oil and gas from the producing zone into
the drilling mud is unknown.
Model for Production
Operations
The emissions during production
operations are primarily fugitive, and
the equipment components comprise
valves, connections, pumps, com-
pressors, meters, hatches, diaphragms,
and pits. The following model is appli-
cable:
Emission
Rate
kg/day
= 1
;compo-\ /emission \
nent |/ rate per \
inven- M compo- I
tory / \ nent /
No. of kg/day/
compo- component
nents
The emission rate per component for
production operations has been devel-
oped by Rockwell under the sponsorship
of the American Petroleum Institute
(W.S. Eaton et al., 1980. Fugitive
Hydrocarbon Emissions from Petroleum
Production Operations, 2 vols. American
Petroleum Institute.)
Conclusions
1. Drilling activity in 1980 will surpass
the activity of the last several years,
with an estimated 13,607 explora-
tory wells to be drilled.
2. Drilling has made many techno-
logical improvements in the past
several decades, but the basic rotary
4
method remains the one most often
used.
3. VOC emissions from oil and gas
exploration and production drilling
are small, although several potential
sources of VOC emissions (entrained
gas and oil in drilling fluids, emissions
from oil-based muds, and the number
of valves, flanges, etc. associated
with fuel systems) are not well
defined. The VOC emissions calcu-
lated using simple assumptions are
less than 10 kg per well per day.
4. Reporting of state oil and gas
production information is not uniform
from state to state and is not up to
date.
5. The number of new fields reported
yields a general estimate that can be
useful, but the different definitions
used by the individual states makes a
direct comparison difficult. The
collected information is adequate for
use as a parameter and estimate of
the VOC potential if a satisfactory
model is developed for the VOC
emissions associated with an oil and
gas well or field.
6. Additional data in several key areas
are required to estimate the VOC
emissions associated with oil and
gas well drilling and production.
These areas are (a) drilling (including
data on emissions from mud de-
gassing and oil-based muds and the
number of components within the
fuel gas system) and (b) oil and gas
production (including a model of
major subsystems (e.g., compressor)
that will allow estimates of compo-
nents and application of currently I
developed emission factors). *
Recommendations
1. Measurements should be made to
verify the magnitude of the estimated
VOC emission values presented in
this study.
2. Further efforts should be devoted to
defining VOC emissions more ac-
curately for representative new oil
and gas facilities or sites. These
efforts should include a survey of
additional sites to establish one or
more models for assessing potential
VOC emissions.
3. Component population estimates
obtainable from photographic docu-
mentation should be supplemented
with stream composition data so that
existing emission factors can be
applied.
4. Oil and gas production data from
new fields should be verified beyond
the information presented in this
report.
The full report was submitted in
partial fulfillment of Contract No. 68-
03-2648 by Rockwell International
under the sponsorship of the U.S.
Environmental Protection Agency.
i
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I/I/. S. Eaton, G. R. Schneider. W. Unterberg. andF. G. Bush. III. are with Rockwell
International. Newbury Park, CA 91320.
Leo T. McCarthy. Jr., is the EPA Project Officer (see below).
The complete report, entitled "Assessment of Oil Production Volatile Organic
Compound Sources." (Order No. PB 82-108 176; Cost: $8.00, 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
5
U. S. GOVERNMENT PRINTING OFFICE: I98I/559-092/3344
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