EPA 600-2-82-034
July 1981
CHEMICAL COMPOSITION OF PRODUCED WATER
AT SOME OFFSHORE OIL PLATFORMS
by
Ihor Lysyj
Rockwell International
Newbury Park, California 91320
Contract No. 68-03-2648
Project Officer
John S. Farlow
Oil and Hazardous Materials Spills Branch
Municipal Environmental Research Laboratory
' Edison, New Jersey 08837
MUNICIPAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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FOREWORD
The U.S. Environmental Protection Agency was created because of increasing
public and government concern about the dangers of pollution to the health and
welfare of the American people. Noxious air, foul water, and spoiled land are
tragic testimonies to the deterioration of our natural environment. The com-
plexity of that environment and the interplay of its components require a con-
centrated and integrated attack on the problem.
Research and development is that necessary first step in problem solution;
it involves defining the problem, measuring its impact, and searching for solu-
tions. The Municipal Environmental Research Laboratory develops new and im-
proved technology and systems to prevent, treat, and manage wastewater and
solid and hazardous waste pollutant discharges from municipal and community
sources, to preserve and treat public drinking water supplies, and to minimize
the adverse economic, social, health, and aesthetic effects of pollution. This
publication is one of the products of that research and provides a most vital
communications link between the researcher and the user community.
This report presents the results of sampling and analysis of produced
waters, as well as final treated effluent, in a number of selected offshore oil
and gas extraction operations. Limited information on priority pollutant con-
tent in treated effluent is also reported. The results will be of interest to
all those interested in the treatment of oil-contaminated water.
Francis T. Mayo, Director
Municipal Environmental Research
Laboratory
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ABSTRACT
The effectiveness of produced water treatment was studied in a number of
selected offshore oil and gas extraction operations in Cook Inlet, Alaska, and
the Gulf of Mexico. Three offshore oil extraction facilities were examined in
the Cook Inlet production field, and seven platforms were studied in the Gulf
of Mexico. Overall treatment effectiveness, as well as effectiveness of indi-
vidual process units, was determined in the Cook Inlet study. Quality of the
final effluent was characterized in the Gulf of Mexico study.
The chemical composition of process streams and final effluents were char-
acterized in terms of total organic material balance. Determinations were made
for suspended organic matter (free oil), dissolved nonvolatile organic matter,
and volatile hydrocarbons.
The state-of-the-art treatment technology was generally found to be effec-
tive in reducing the free oil content (suspended organics) of produced water,
but it was less effective in reducing the aromatic hydrocarbon content. Aver-
age reduction in concentration of aromatic hydrocarbons was on the order of 30%
to 50%. Benzene, toluene, and xylenes/ethylbenzene (BTX) were found at all
stages of the processes and in all final effluents. The average BTX concen-
tration in treated effluents from Cook Inlet operations was 9 mg/L. In Gulf of
Mexico treated effluents, the BTX content averaged 2 mg/L.
High levels of dissolved nonvolatile organic matter (ranging from 60 to
600 mg C/L) were found in all treated effluents. Generally, the concentration
of this fraction increased rather than decreased as a result of treatment.
This increase may be due to addition of chemicals during the treatment and
oxidation of petroleum matter leading to formation of water-soluble oxygenated
organic compounds. Four organic priority pollutants (benzene, toluene, ethyl-
benzene, and phenol) and two inorganic priority pollutants (chromium and lead)
were found in all treated effluents analyzed. Intermittently present were
naphthalene, cadmium, zinc, nickel, silver, copper, and beryllium.
This 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. This report covers the period January 1980 to November
1980, and work was completed as of January 1981.
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CONTENTS
Foreword iii
Abstract - iy
Acknowledgments viii
1. Introduction 1
2. Conclusions 4
3. Recommendations 6
4. Methods 7
Sampling Procedures 7
Quality Control 7
Oily Wastewater Analytical Protocol 8
Priority Pollutant Analysis 10
5. Field Studies 11
Cook Inlet, Alaska 11
Gulf of Mexico 32
Dissolved and Suspended Oil 44
References 47
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FIGURES
Number
1 Oily wastewater analytical protocol 9
2 Trading Bay facility 13
3 Reduction of organic composition in produced water by a
multistage treatment plant, Trading Bay,
Alaska, production facility 23
TABLES
1 Station 1, Organic Composition of Heater-Treater Effluent,
Trading Bay Facility, January 23, 1980 15
2 Station 2, Organic Composition of Gravity Separator
Effluent, Trading Bay Facility, January 23, 1980 16
3 Station 3, Organic Composition of Gas Flotation Effluent,
Trading Bay Facility, January 23, 1980 18
4 Station 4, Organic Composition of Final Effluent,
Trading Bay Facility, January 23, 1980 19
5 Summary of Organic Composition of the Process Stream,
Trading Bay Facility 21
6 Stepwise Reduction of Organic Content in Process Water by the
Treatment Process, Trading Bay, Alaska,
Production Facility, January 23, 1980 22
7 Organic Composition of Effluent from Oil Separator,
August 7, 1980, Kenai Production Facility 25
8 Organic Composition of Final Effluent, August 7, 1980,
Kenai, Alaska, Production Facility 26
9 Effectiveness of Treatment Process, August 7, 1980,
Kenai, Alaska, Production Facility 27
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TABLES (continued)
Number Page
10 Organic Composition of Water Knockout Effluent,
August 6, 1980, Cook Inlet Offshore Platform . 29
11 Organic Composition of Final Effluent,
August 6, 1980, Cook Inlet Offshore Platform 30
12 Organic Composition of Process Stream,
August 6, 1980, Cook Inlet Offshore Platform 31
13 Organic Material Balance in Effluents from
Offshore Platforms in Gulf of Mexico 36
14 Volatile Aromatic Hydrocarbons in Treated Effluents from
Offshore Platforms in Gulf of Mexico and Cook Inlet 38
15 Estimates of Chemicals Added to the Process Stream
and Dissolved Organic Content of Treated Effluent 39
16 Purgeable Priority Pollutants in Offshore Produced
Water, Gulf of Mexico 40
17 Base-Neutral Priority Pollutants in
Offshore Produced Water, Gulf of Mexico 41
18 Acid-Neutral Priority Pollutants in
Offshore Produced Water, Gulf of Mexico 42
19 Metal Priority Pollutants in Offshore
Produced Water, Gulf of Mexico 43
20 Analysis for Dissolved and Free Oil, Trading Bay Production
Facility, Cook Inlet, Alaska, January 23, 1980 46
VII
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ACKNOWLEDGMENTS
We wish to thank Mr. Bill Lamoreaux, U.S. Environmental Protection Agency
(EPA), Alaska Operations Office, Anchorage, Alaska, for his assistance in car-
rying out field sampling operations in Cook Inlet; Commissioner Ernest W.
Mueller, State of Alaska, Department of Environmental Conservation, Juneau,
Alaska; and Mr. Doug Lockwood, Alaska Department of Environmental Conservation,
Valdez, Alaska, for use of their facilities and essential assistance.
Samples of produced water in the Gulf of Mexico were collected by Texas
Instruments Company personnel. Priority pollutant analysis was performed under
contract to the EPA by Analytical Research Laboratories, Monrovia, California;
Battelle, Columbus, Ohio; Monsanto Research Corp., Dayton, Ohio; and ERCO,
Cambridge, Massachusetts.
The Rockwell International team, composed of Ihor Lysyj, George Perkins,
David Janka, and Kathy Doering, conducted the field study in Cook Inlet.
VI 1 1
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SECTION 1
INTRODUCTION
A detailed study of ballast water treatment effectiveness was conducted in
Port Valdez, Alaska, in 1978-1980 (1). Port Valdez is a terminal of the
TransAlaska Pipeline, where oil from Prudhoe Bay is transferred into oil tank-
ers. Before accepting the oil, tankers must discharge large amounts of ballast
water into the rather sheltered waters of the small (5 km wide by 18 km long)
subarctic estuary. The volume of ballast water discharged is rather large; an
average of 50,000 m^ is discharged daily. This is as much as one-half of the
total discharge from all oil-producing platforms in the offshore coastal shelf
of the Gulf of Mexico (97,000 m3 per day during 6 months of 1979). Because of
such large discharges of contaminated water into the sheltered coastal fjord,
this problem is of major concern to the State of Alaska.
In order to characterize treatment plant effectiveness and determine the
quality of the final effluent, special analytical techniques and procedures
were developed (1,5). A technique based on organic material balance provided
a comprehensive picture of the chemistry of the ballast water in the treatment
process and receiving environment.
One of the principal findings of this EPA-sponsored research on ballast
water treatment (1) was the fact that benzene, toluene, and xylenes (BTX) con-
stituted almost half of the petroleum-derived material in the treated effluent
discharged to the environment. Approximately 7 to 9 tons of BTX are discharged
into receiving waters of Port Valdez by the treatment plant each month. Whether
this resulted from the nature of the treatment (gravity separation, gas flota-
tion and impoundment) or from contact of the saline water and the petroleum
either in the reservoir or in tanker cargo tanks was not known.
The purpose of the more limited study reported here was threefold:
a. To determine how applicable organic material balance procedures are
to analysis of offshore oil and gas produced water
b. To obtain some data on the range of variability of treated offshore
oil and gas produced water in terms both of the components of the
total organic material balance and of the various EPA-designated
priority pollutants
c. To collect limited information on the effectiveness of the treatment
of produced water in offshore oilfields of Alaska
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This information is of interest in planning the emphasis for future
research.
By a fortunate coincidence, a detailed study of the oil variability in
treated brine was just beginning the second round of field sampling on seven
Louisiana offshore oil and gas production platforms. By obtaining additional
samples of the treated effluent (which could be subjected to the same protocol
carried out with the same personnel and equipment at Valdez, Alaska), it might
be possible to shed some light on one corner of the question raised by the bal-
last water treatment study. At the same time, the field method developed for
the ballast water plant itself could be checked against the results of the
platform treated brine study.
As a further bonus, an opportunity to collect samples for priority pollu-
tant analysis would provide still another type of check (since both benzene and
toluene are priority pollutants).
It also turned out to be possible to obtain effluent samples from three
Cook Inlet, Alaska, production operations, providing yet another comparison of
treated brines from different oil fields.
It should be noted at the outset that, at most, only a few samples were
collected at each location during this brief study; this study is not nearly as
extensive or detailed as either the ballast water treatment plant study (1) or
the Louisiana platform brine study (2).
This study had two major field sampling efforts, each carried out in two
different locations:
Effort 1 - Collect samples for determining the organic material balance
at one or more points at each facility, and
Effort 2 - Collect samples for priority pollutant analysis at one or more
locations at each facility:
Location 1 - Louisiana offshore oil production area, and
Location 2 - Alaska's Cook Inlet oil production area.
The organic material balance samples from Cook Inlet were taken to Valdez,
Alaska, for analysis. Hydrochloric acid was added as a preservative (to pH 2),
and the total time elapsed from drawing the sample to arrival at the laboratory
was in the order of 36 hours.. The samples from the Gulf of Mexico were shipped
to Rockwell's base at Newbury Park, California. There, HC1 (to pH 2) was added
as a preservative, and the samples were shipped on to Valdez, Alaska, for
analysis. The total time from drawing the sample to arrival at the analytical
laboratory was approximately 7 days. Part of this time the samples from the
Gulf Coast were not preserved. The samples for material balance were maintained
at ambient temperature, while priority pollutant samples were maintained at
4°C.
The priority pollutant samples from Cook Inlet became delayed in transit
for almost a week and arrived at the EPA Effluent Guidelines Division contract
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laboratories too long a time after being drawn to be worth the effort of
analyzing.
The samples from the Gulf of Mexico (six effluent samples and three gas
flotation unit influent samples, one of which of the latter had obviously been
contaminated) were also shipped to EPA Effluent Guidelines Division contract
laboratories, and were analyzed.
Sampling operations were carried out by Rockwell or its subcontractors on
the following schedule:
Location
Gulf of Mexico
BM 2C
SS 107
ST 131
SS 198G
El 18CF
BDC CF5
SM 130B
Cook Inlet
Trading Bay (onshore)
Dillon (offshore)
Kenai (onshore)
Organic Material
_Ba1ance Sample Date
7 March
10 March
21 March
24 March
2 April
4 April
(no sample)
23 January0
6 August"
7 Augustc
Pr m'ty Pollutants
Sample Date
13 March
(no sample)
19 March
21 March
8 April
8 April
17 April
(no sample)
6 Augustd
7 Augustd
a. Three sample sets taken at discrete time intervals.
b. One set of triplicate samples taken between 0900 and 1200.
c. One set of duplicate samples taken between 0900 and 1200.
d. Samples reached laboratory after time limit expired; not analyzed.
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SECTION 2
CONCLUSIONS
As a result of brief studies dealing with the operation of three offshore
oil and gas extraction facilities in Cook Inlet, Alaska, and examination of the
effluent from seven offshore oil-producing platforms in the Gulf of Mexico, the
following conclusions can be drawn:
1. The treatment technology is (generally) based on gravity separation
and gas or air flotation. On the average, reductions in excess of
90% of the free oil in the produced water are realized.
2. The suspended organic matter (or free oil) in the treated effluent in
the Cook Inlet production field ranged between 5 and 36 mg C/L.*
The average free oil concentration in the treated effluent was 18 mg
C/L.
3. Suspended organic matter (or free oil) in the treated effluent in the
Gulf of Mexico ranged between* 9 and 46 mg C/L. The average free oil
concentration in the treated effluent was 26 mg C/L.
4. Volatile aromatic hydrocarbons composed largely of benzene, toluene,
and xylenes/ethylbenzene were found in all process streams and in all
treated effluents tested. Total aromatic hydrocarbon content in the
treated effluent was found to average 9 mg/L from Cook Inlet opera-
tions and approximately 2 mg/L in the Gulf of Mexico effluent.
5. Treatment processes were far less effective in the removal of vola-
tile aromatic hydrocarbons from the process stream. Removal rates
were on the order of 30% to 50%.
6. High concentrations of dissolved organic matter were found in all
treated effluents. Dissolved nonvolatile organic content in the
treated effluents from the Cook Inlet operation ranged between 141
and 423 mg C/L, averaging 276 mg C/L. Dissolved nonvolatile organic
content in treated effluents from the Gulf of Mexico operations
ranged between 57 and 624 mg C/L, averaging 376 mg C/L.
7. Up to 90% of all organic matter present in treated discharges of
produced water is made up of dissolved nonvolatile organics. Neither
the source nor the nature of the dissolved nonvolatile organic matter
present in produced water streams is known at this time.
* 1 mg C/L corresponds to approximately 1.16 mg/L of the oil.
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8. Four organic priority pollutants were found consistently in dis-
charges from offshore oil and gas extraction operations: benzene,
toluene, ethylbenzene, and phenol. One was found intermittently:
naphthalene.
9. Two metal priority pollutants were found in all treated produced
water effluents: chromium and lead. Intermittently present were
zinc, beryllium, cadmium, copper, silver, and nickel.
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SECTION 3
RECOMMENDATIONS
1. The source and nature of dissolved nonvolatile organics should be
established. Processes leading to the formation of such organic
compounds during treatment should be delineated.
2. Methods for reducing the concentration of principal organic priority
pollutants present in treated produced water (benzene, toluene, and
ethylbenzene and phenol) should be developed.
3. Methods for reducing the concentration of metal priority pollutants
should be considered.
4. Evaluation of the relative toxicity of dissolved nonvolatiles should
be determined.
5. An evaluation should be undertaken of alternative treatment technolo-
gies to remove some of these nonvolatile compounds contingent on
concentration and their toxicity.
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SECTION 4
METHODS
Two different types of analytical methodologies were used in this study.
One protocol was designed to establish the organic material balance in the
process stream. This protocol addressed quantitatively the principal fractions
of organic matter present in produced water: suspended organic matter, dis-
solved nonvolatile organic matter, and volatile hydrocarbons. The second
protocol was designed to determine priority pollutants quantitatively, includ-
ing: purgeables, acid-neutral, base-neutral, pesticides, and metals. EPA-
approved methods of analysis for priority pollutants were used.
A description of the methods used, as well as sampling procedures and
quality control, follows.
SAMPLING PROCEDURES
Two basic types of sampling procedures were used: one for material bal-
ance determination, and the second for priority pollutants. Samples for mate-
rial balance determinations were collected in 1-liter glass bottles, the caps
of which were lined with aluminum foil. Samples were preserved by acidifica-
tion with hydrochloric acid to pH 2.
Samples for priority pollutant analysis were collected according to the
EPA sampling procedure; purgeables were collected in 40-ml vials equipped with
Teflon-lined septums. Samples for acid-neutral, base-neutral, and pesticides
analysis were collected in glass containers, the caps of which were lined with
Teflon. Samples for metal analysis were collected in plastic containers.
QUALITY CONTROL
The objective of quality control in analytical chemical work is to assure
that generated data correctly reflect parameters of properly defined and ac-
curately measured phenomena. This is done by eliminating false-positive and
false-negative bias from the data and providing statistical validity in the
accuracy and reproducibility of the reported data. The principal elements of
a good quality control protocol are instrumental and procedural blank determin-
ation, recovery data, multiple analysis of samples, daily multipoint calibra-
tion of instrumentation, statistical documentation of the accuracy and repro-
ducibility of the methods used, and well-maintained documentation of all lab-
oratory and sampling operations. A discussion of the key elements of quality
control protocol utilized during the field and laboratory operations follows.
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Contamination Check
To assure the absence of contributions from the sample matrix and solvents,
determinations of blank values were carried out daily on the gas chromatograph
and TOC analyzer. The values for blanks were compensated for in the calcula-
tion of results.
Recovery
Recovery studies were conducted for all chemical compounds that required
separation from the water matrix as a part of the analytical procedure. Model
chemical compounds were introduced in known quantities in 850-ml water samples
and then analyzed in a manner identical to real samples. Recovery values were
established for benzene, toluene, and xylenes.
Replicates
All analyses were performed in triplicate, within a specified reproduci-
bility range.
Calibration
Multipoint calibrations for n-hexane (model for aliphatic hydrocarbons),
benzene, toluene, and xylenes were performed daily and new calibration graphs
were prepared each day and used only during that day of operation. Multipoint
calibration for TOC analysis was also performed daily using a potassium acid
phthalate standard solution. Comparisons of daily calibration curves were made
to detect any differences and/or drift in instrumental responses and/or changes
in the composition of standard solutions.
Accuracy and Reproducibility
Accuracy and reproducibility of all procedures used were established
either from the literature (for standard methods) or determined experimentally
for research procedures developed under this program.
OILY WASTEWATER ANALYTICAL PROTOCOL
In order to develop information on the effectiveness of oil removal and to
characterize the chemical redistribution taking place in the process, it was
necessary to measure the concentrations of each organic fraction and to charac-
terize chemically the principal compounds present.
To do so, an analytical protocol (Figure 1) (1, 5) was devised that
included:
1. Determination and chemical characterization of volatile organic
fraction
2. Determination of dissolved nonvolatile fraction
3. Determination of suspended organic matter
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PRODUCED
WATER
SPARGING
OF VOLATILE
HYDROCARBONS
TOC ANALYSIS
OF TOTAL
NONVOLATILES
COLLECTION OF
VOLATILE
HYDROCARBONS
GAS CHROMATOGRAPHIC
ANALYSIS
MICROFILTRATION
TOC ANALYSIS OF
DISSOVLED
NONVOLATILE
ORGAN ICS
Figure 1. Oily wastewater analytical protocol.
In order to define overall organic concentration in the process stream,
the Total Organic Load (TOL) was established. This corresponds to the sum of
the volatile organics, dissolved nonvolatile organic matter, and suspended
organic materials. The TOL value is expressed in mg C/L. The value of vola-
tile hydrocarbons (wh'ich were determined as mg hydrocarbons/liter) was con-
verted to mg C/L expression. Proportions of carbon to hydrogen in the princi-
pal hydrocarbons found (benzene, toluene, and xylenes) were used to calculate
mg C/L values. Values for dissolved nonvolatile organics and for suspended
organic matter were determined as mg C/L, and added to the converted values of
volatile hydrocarbons. All TOL values reported here were so calculated.
Analysis of ^/olatile Fraction
The volatile fraction of the process stream was composed largely of lower
aromatic hydrocarbons (benzene, toluene, xylenes, and ethy1 benzene). Some
lower aliphatic hydrocarbons were present in the effluent from the gravity sep-
arator. Gas chromatographic procedure was used for analysis of this fraction.
A water sample (850 to 1000 ml) was sparged by the nitrogen gas and vola-
tile hydrocarbons were adsorbed in an activated charcoal cartridge. Adsorbed
hydrocarbons were then dissolved into 1 ml of carbon disulfide, providing for
an 850- to 1000-fold concentration of volatile organic matter. A sample of
this concentrate was injected into a gas chromatograph, separated into dis-
crete fractions, and quantified using a hydrogen flame ionization detector.
Using this method and a Gow-Mac gas chromatograph, the detection limit for
individual hydrocarbons was estimated at 0.1 microgram/liter, or 0.1 ppb (parts
per billion). The identities of eluting peaks were established using
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computerized gas chromatograph - mass spectrometer (GC-MS). The quantification
was performed using either peak or area measurements on gas chromatograms.
Analysis for Dissolved Nonvolatile Organic Compounds
The suspended oil was separated from the dissolved organic matter by
Millipore filtration using a 0.45-micron HA filter. The acidified and sparged
filtrate was used for determination of total organic carbon (TOC) using Stan-
dard Method 510 (6).
D termination of Suspended Organic Matter
A water sample was acidified, sparged with nitrogen, and ultrasonated
u ing a Braun-Sonic Model 1510 probe at 300 watts power. The emulsified sample
was injected into the TOC analyzer and total organic carbon was determined
using Standard Method 510 (6). The suspended organic matter was determined as
a difference between the concentration of total nonvolatiles and dissolved
organics. This fraction contained primarily aliphatic hydrocarbons of petro-
leum origin, and was not further chemically characterized.
PRIORITY POLLUTANT ANALYSIS
Priority pollutant analysis was carried out according to EPA-specified
methods (40CFR136) (4) by other commercial laboratories under contract to the
EPA Effluent Guidelines Division.
10
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SECTION 5
FIELD STUDIES
Evaluation of the effectiveness of state-of-the-art technology in the
treatment of offshore produced water (brine) was carried out in Cook Inlet,
Alaska, and offshore in the Gulf of Mexico.
Three production facilities were examined in Cook Inlet. Two of these
treated offshore produced water onshore and one treated offshore produced water
on the platform itself. One onshore treatment facility treated produced water
by gravity separation (skim tanks), gas flotation (Wemco), and impounding. The
second onshore treatment facility treated produced water by gravity separation
and dissolved air flotation. The offshore treatment facility was a single-
stage separation by gravity.
Reduction of organic load in the process streams was studied by analysis
for suspended organic matter (free oil), dissolved nonvolatile organic compo-
sition, and volatile organic compounds at various points of the treatment
processes.
Seven offshore oil and gas production facilities were examined in the Gulf
of Mexico. All of those treated brine on-site. Primary treatment was by
gravity, and secondary treatment was by gas flotation. Treated effluents from
oil and gas producing platforms were examined in terms of organic material
balance, including suspended organic matter, dissolved nonvolatile organics,
and volatile hydrocarbon. Additionally, priority pollutants analysis was
performed for purgeables, acid-neutral, base-neutral, pesticides, and metals.
COOK INLET, ALASKA
Evaluation of the effectiveness of offshore produced water treatment in
Cook Inlet was conducted in 1980. Three different treatment operations were
selected to reflect various degrees of technical sophistication in the treat-
ment.
In one case, offshore produced water (brine) was treated in a modern,
well-operated onshore treatment plant. The second case also involved onshore
treatment of offshore produced water in a plant of older design. The principal
difference between the two plants was use of dissolved gas flotation in the
newer facility and dissolved air flotation in the older facility. The newer
facility (Trading Bay, Alaska) was also equipped with two holding ponds, while
the older (Kenai, Alaska) was not.
11
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In the third case, produced water was treated in a simple, one-step
gravity separation operation on the offshore platform.
It is believed that these selected treatment operations are representative
of principal practices in Cook Inlet.
Trading Bay Production Facility
Evaluation of treatment effectiveness at the Trading Bay production facil-
ity was conducted on January 23, 1980. This facility is located on the north-
western shore of Cook Inlet, approximately 60 air miles southwest c" Anchorage.
Four offshore platforms supply gross fluid for onshore processing. The fluid
is piped into a battery of heater-treaters where oil is separated f Dm the
water in heated chambers and then transferred into two batteries of storage
tanks. One battery consists of six 10,000-barrel (1590 m3) tanks, the other is
of two 45,000-barrel (7155 m3) tanks. Natural gas is also generated and
processed at this facility.
2
The production facility processes 131,000 barrels (20,829 m ) of gross
fluid per day and generates 67,000 barrels (10,653 m3) of oil and 62,000 bar-
rels (9858 m3) of produced water (brine). Natural gas is generated at a rate
of 28,000 MCFPD (792,880 standard m3/d). Storage capability of petroleum
products includes 150,000 barrels (23,850 m3) of oil and 10,000 barrels (1590
m3) of liquid petroleum gas (LPG).
Treatment Plant--
This modern plant for treatment of produced water (Figure 2) consists of
three gravity separators of 10,000-barrel (1590 m3) capacity, two gas flotation
units, and two water retention ponds of 50,000-barrel (7950 m3) capacity.
Treated ballast water is discharged offshore into Cook Inlet receiving waters.
The quality of the process water is monitored routinely by the oil company
personnel at various process points, and at the final discharge point.
The treatment plant at the Trading Bay production facility appeared to be
overdesigned for present loading in anticipation of future increases in volume
of produced water, and on the day of sampling it operated at approximately 50%
of its capacity.
Sampling and Analysis--
In order to characterize effectiveness of the three principal treatment
units (gravity separators, gas flotators, and retention ponds), four sampling
stations were selected (Figure 2). The effluent from the heater-treaters,
which separate oil from water, represents input into the produced water treat-
ment plant. A sample of this effluent was collected from an existing sampling
outlet, Station 1. Station 2 was an existing sample tap used by operating
personnel for routine sampling of process water from a line exiting the gravity
separator. The effluent from the gravity separators is directed into one of
two gas flotation treatment units. Unit No. 2 was in operation on the day of
sampling and water samples were taken from a tap used for routine sampling by
the plant operating personnel. This sampling point was designated Station 3.
Process water from the gas flotator enters one of two 50,000-barrel (7950 m3)
retention ponds, where it is kept under quiescent conditions prior to discharge
12
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into receiving waters of Cook Inlet. Water retention pond No. 2 was in opera-
tion on the day of sampling. Effluent from the retention pond was collected in
a sampling well from a sampling tap used for routine monitoring of treated
effluent. This sampling point was designated Station 4.
Three sets of samples were collected over a 5-hour period to provide a
daily average of typical chemical composition of produced water. Sampling dur-
ing each time sequence was initiated at Station 4 (final, treated effluent) and
proceeded upstream to Station 1 (effluent from heater-treaters).
Results
Station 1. Heater-Treater Effluent. Three sets of water samples were
collected at this station at 1310, 1359, and 1530 on January 23, 1980. The
results of oily wastewater protocol analysis, which represent material balance
for all organic matter present, are reported in Table 1. The average total
organic load of the heater-treater effluent was 454 mg C/L with a standard de-
viation of 137 mg C/L, or 30% fluctuation. Suspended organic matter, composed
primarily of free oil, was found to be 148 mg C/L with a standard deviation of
143 mg C/L. The wide fluctuation of free oil (97%) in the effluent from the
heater-treaters reflected nonhomogeniety of the stream at this point in the
processing.
Dissolved nonvolatile organic matter was present at a concentratidon level
of 293 mg C/L, with a standard deviation of 16 mg C/L, or a fluctuation of
approximately 6%. The concentration level of volatile hydrocarbons was found
to be 13 mg C/L with a standard deviation of 5 mg C/L, or a fluctuation of
38%. Volatile hydrocarbons were composed of 5.0 mg C/L aliphatic hydrocarbons
(38%) and 8.0 mg C/L of aromatic hydrocarbons (62%). Aromatic hydrocarbons
were composed largely of benzene, toluene, xylenes/ ethylbenzene in the follow-
ing ratio: 4.7:2.4:1.0.
Data reported in Table 1 reveals that the effluent from the heater-
treaters was composed of 32.6% free oil, 64.5% dissolved nonvolatile organic
matter, and 2.9% volatile hydrocarbons.
Station 2, Gravity Separator Effluent. Three sets of water samples were
collected at this station at 1141, 1354, and 1546 on January 23, 1980. The
results of protocol analysis, which represent material balance for all organic
matter present, are reported in Table 2. The average organic load of gravity
separator effluent was 458 mg C/L with a standard deviation of 30 mg C/L, or a
fluctuation of approximately 7%, a value considerably lower than that observed
in the effluent from the heater-treaters.
Aging under quiescent conditions and the averaging effect of a large-
volume water body in the settling tank reduced free oil content and contributed
to a greater degree of reproducibility from sample to sample. The average
concentration of suspended organic matter (free oil) was found to be 38 mg C/L
with a standard deviation of 16 mg C/L, or a fluctuation of approximately 42%.
The drop in free oil concentration was approximately 75% as a result of gravity
separator treatment, and reproducibility was considerably better at Station 2
than at Station 1.
14
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Dissolved nonvolatile organic matter was present in a concentration of 409
mg C/L, with a standard deviation of 16 mg C/L, or approximately 4% fluctua-
tion. Analysis of samples from this station indicated a 28% increase, rather
than a decrease, in concentration of dissolved organic fraction. Reasons for
this increase are unknown at this time (but might be due to sampling a differ-
ent oil parcel, addition of chemicals for treatment, and chemical changes in
the character of organic matter as a result of processing of gross fluid). The
concentration level of volatile hydrocarbons was found to be 11.3 mg C/L with a
standard deviation of 0.9 mg C/L, or a fluctuation of about 8%. Reduction in
concentration of this fraction was rather small (approximately 14%). Volatile
fraction was comprised of 3.6 mg C/L (31%) aliphatic hydrocarbons and 7.7 mg
C/L (69%) aromatic hydrocarbons. Aromtic hydrocarbons were composed largely of
benzene, toluene, and xylenes/ethylbenzene. The ratio of each was very similar
to ratios observed in samples from Station 1, i.e., 5.0:2.6:1.
Data reported in Table 2 reveals that the effluent from the gravity sep-
arator was composed of 8.3% free oil, 89.3% dissolved nonvolatile organic
matter, and 2.4% volatile hydrocarbons. When compared with effluent from the
heater-treaters, a proportional decrease in free oil and an increase in dis-
solved nonvolatile fraction is apparent.
Station 3, Gas Flotation Effluent. Three sets of water samples were col-
lected at this station at 1090, 1351, and 1543 on January 23, 1980. The re-
sults of oily wastewater protocol analysis, which represent material balance
for all organic matter present in the stream, are reported in Table 3. The
average total organic load of the gas flotation effluent was 436 mg C/L with a
standard deviation of 8 (a fluctuation of only 2%). Suspended organic matter,
comprised primarily of free oil, was found to be 33 mg C/L, with a standard
deviation of 21 mg C/L (a fluctuation of 64%). Dissolved nonvolatile organics
were present at a concentration level of 394 mg C/L, with a standard deviation
of 28 mg C/L (approximately 7% fluctuation). Concentration of volatile hydro-
carbons was found to be 8.6 mg C/L with a standard deviation of 0.8 (9% fluc-
tuation). The volatile fraction was composed of 2 mg C/L aliphatic hydrocar-
bons (23%) and 6.6 mg C/L aromatic hydrocarbons (77%). The aromatic hydrocar-
bons were composed essentially of benzene, toluene, and xylenes/ethylbenzene,
which were present in a 4.1:2.2:1 ratio. This ratio appears to be similar to
samples from two upstream stations.
Data reported in Table 3 reveals that dissolved nonvolatile organics con-
stitute the bulk of organic load (90.4%) at this point of wastewater proces-
sing. Free oil accounted for only 7.6% of the total organic load and volatile
hydrocarbons contributed only 2%.
Station 4 - Final Effluent. The results of oily wastewater protocol anal-
ysis, which represent material balance for all organic matter present in the
samples, are reported in Table 4. The average total organic load of the final
treated effluent was 435 mg C/L, with a standard deviation of 14 mg C/L (a
fluctuation of only 3%). Suspended organic level was low, with an average
equal to 5.3 mg C/L and a standard deviation of 9 mg C/L. Dissolved organic
matter constituted the bulk of organic matter in the final discharge, with a
concentration of 423 mg C/L (standard deviation of 10 mg C/L). It constituted
17
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97.2% of all organic matter found in the discharge. Volatile hydrocarbons were
present at a concentration level of 6.5 mg C/L with a standard deviation of
0.4 mg C/L (a fluctuation of approximately 6%). Volatile hydrocarbons were
composed of 1.1 mg C/L aliphatic hydrocarbons (20%) and 5.4 mg C/L aromatic
hydrocarbons (80%). Aromatic hydrocarbons were composed of benzene, toluene,
and xylenes/ethylbenzene in a ratio of 6.8:3.4:1.
Data reported in Table 4 reveals that the final effluent was composed
largely of dissolved nonvolatile organic matter (97.2%), with a very low level
of free oil (5.3 mg C/L). lexicologically important aromatic hydrocarbons were
present in significant amounts.
Discussion--
The compositional data for all four sampling stations is summarized in
Table 5 as mean values of measured parameters and the standard deviation.
Significant fluctuation in suspended organic matter content, as indicated by
the large standard deviation values, were observed. Fluctuations in the output
from the heater-treater unit and nonhomogeneity of oil-water mixtures are
reasons for the wide fluctuation in such compositions.
Dissolved nonvolatile organic content, however, fluctuated very little
from sample to sample and from sampling time to sampling time. Volatile
hydrocarbon content fluctuated significantly in the effluent from the heater
treatment, but was more stable downstream from the gravity separators.
The effectiveness of the treatment of produced water is reflected in
stepwise reduction of various organic fractions, as depicted in Table 6 and
Figure 3. Analysis of the reported data indicates that the treatment process
is effective in reducing suspended oil and volatile aliphatic hydrocarbon con-
centrations. A 97% reduction in suspended organic matter resulted in an efflu-
ent containing 5 mg C/L of suspended organics. The concentration of volatile
aliphatic hydrocarbons was reduced approximately 75%.
The process, however, was less effective in reducing volatile aromatic
hydrocarbons. A reduction of only 30% was realized, and treated effluent con-
tained, on average, 6 mg C/L of volatile aromatic hydrocarbons.
Very high concentrations of dissolved nonvolatile organic matter were ob-
served at all stages of the treatment process. As a matter of fact, dissolved
organic content of the final effluent was significantly higher than that of
untreated effluent from the heater-treater. The increase in concentration of
dissolved, nonvolatile organic matter, in all cases, took place in initial
stages of treatment of produced water (between heater-treaters and gravity
separators). Such an increase might be due, in part, to addition of organic
chemicals used as part of the treatment. Oxidation of petroleum composition
might be an additional factor in the formation of water-soluble organic mat-
ter. When essentially anaerobic produced waters are exposed to an oxygen
environment at relatively high temperatures (above 100°F), autocatalytic pro-
cesses might lead to oxidation of some components of organic matter present in
produced water, resulting in formation of water-soluble oxygenated organic
compounds.
20
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21
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TABLE 6. STEPWIDE REDUCTION OF ORGANIC CONTENT IN
PROCESS WATER BY THE TREATMENT PROCESS, TRADING BAY, ALASKA,
PRODUCTION FACILITY, JANUARY 23, 1980
Effluents (Concentration in
Organic Composition
Suspended Petroleum
Reduced by (%)
Dissolved Organics
Reduced by (%)
Volatile
Hydrocarbons
Reduced by (%)
. Aromatic
Reduced by (%}
. Aliphatic
Reduced by (%)
Heater- Gravity
Treater Separator
148 38
(74.3)
293 409
(-)
13.1 11.2
(14.5)
7.9 7.7
(2.5)
5.0 3.6
(28.0)
mq C/L)
Gas Impound Basin
Flotator (Final Effluent)
33
(77.8)
394
(-)
8.6
(34.4)
6.6
(16.5)
2.0
(60.0)
5
(96.6)
423
(-)
6.5
(47.3)
5.4
(29.1)
1.1
(74.0)
(c -c )
% Reduction = °r n . 100 where C is initial concentration in the effluent
Co °
from the heater-treater and C is the concentration in effluents from various
n
process units.
22
-------
u
O)
£
200 -
TOTAL ORGANIC LOAD (TOL) OF
PROCESS STREAM, mg C/L
DISSOLVED NONVOLATILE ORGANIC
CONTENT, mg C/L
<3> SUSPENDED ORGANIC MATTER, mg C/L
S VOLATILE ORGANIC MATTER, mg C/L
(A VOLATILE AROMATIC
^ HYDROCARBONS, mg/L
VOLATILE ALIPHATIC
HYDROCARBONS, mg/L
SAMPLING
POINTS
1 PRODUCED
HEATER-TREATER
2 GRAVITY SEPARATOR
EFFLUENT
3 GAS FLOATATION EFFLUENT
4 FINAL EFFLUENT
1234
SAMPLING POINTS
Figure 3. Reduction of organic composition in produced water by a multistage
treatment plant, Trading Bay, Alaska, production facility.
23
-------
Kenai Production Facility
Evaluation of the treatment effectiveness at the Kenai production facility
was conducted on 7 August 1980. This facility is located approximately 60 air
miles southwest of Anchorage on the southwestern shore of Cook Inlet. Three
offshore platforms servicing a number of wells provide gross fluid for onshore
processing. Processing includes free water knockout, followed by additional
separation of oil from water in heater-treaters. Produced water is treated in
skim tanks (gravity separators) followed by dissolved air flotation with addi-
tion of flocculating agents.
The retention time of produced water in the treatment plant is approxi-
mately 6 hours. The facility processes 21,000 barrels (3339 m3) of gross fluid
a day and typically generates 13,000 barrels (2067 m3) of oil and 8000 barrels
(1272 m3) of produced water. This facility produces gross fluid with a higher
oil content than the two other facilities evaluated in this study.
Sampling and Analysis--
The process stream was sampled at two points: Station 1, effluent from
the oil separator, and Station 2, final effluent from the dissolved air flota-
tion unit. Duplicate samples were collected at each station and analyzed for
suspended organic matter, dissolved nonvolatile organic matter, and volatile
hydrocarbons.
Results
Station 1, Effluent from Oil Separator. Two samples were collected at
this station on August 7, 1980. The results of oily wastewater protocol anal-
ysis, which represents material balance for all organic matter present in the
sample, are reported in Table 7. The average total organic load in the efflu-
ent from the water separator was 544 mg C/L (a range of 445 to 643 mg C/L).
Suspended organic matter, composed primarily of free oil, was found to average
190 mg C/L (79 to 301 mg C/L range). Dissolved nonvolatile organic matter was
present in an average concentration of 336 mg C/L (a range of 322 to 350 mg
C/L). Volatile hydrocarbon fraction averaged 18 mg C/L (a range of 16 to 20 mg
C/L). Volatile hydrocarbons were composed of 1.4 mg C/L aliphatic hydrocarbons
(8%), and 16.4 mg C/L aromatic hydrocarbons (92%). Aromatic hydrocarbons were
composed essentially of benzene, toluene, and xylenes/ethylbenzene in a ratio
of approximately 4.3:1.8:1. The effluent from the oil separator was composed
of 35% free oil, 62% dissolved nonvolatile matter, and 3% volatile hydrocar-
bons.
Station 2, Final Effluent. Two samples were collected at this station on
August 7, 1980. The results of oily wastewater protocol analysis, which
represent material balance for all organic matter present in the sample, are
reported in Table 8. The average total organic load in the final effluent was
288 mg C/L (a range of 285 to 291 mg C/L). Free oil was present in a concen-
tration of 14 mg C/L (a range of 13 to 14 mg C/L), while dissolved nonvolatile
organic matter was found at 264 mg C/L concentration (a range of 262 to 266 mg
C/L). Volatile hydrocarbons were present at approximately the 10 mg C/L
level, and consisted of 90% aromatic hydrocarbons. The principal compounds
found were benzene, toluene, and xylenes/ethylbenzene in an approximate ratio
of 5.7:2.6:1. The final effluent was composed largely of dissolved nonvolatile
24
-------
TABLE 7. ORGANIC COMPOSITION OF EFFLUENT FROM OIL SEPARATOR,
AUGUST 7, 1980, KENAI PRODUCTION FACILITY
Concentration (mq C/L)
Total Organic Load
Suspended Petroleum
Dissolved Nonvolatile
Organic Matter
Volatile Hydrocarbons
Volatile Aliphatic
Hydrocarbons
Volatile Aromatic
Hydrocarbons
Benzene
Toluene
Xylenes
Hiqh
643
301
350
19.6
2.1
17.5
10.2
4.3
3.0
Low
445
79
322
16
0.7
15.3
9.8
4.0
1.5
Average %
544
190 35
336 62
17.9 3
1.4 0.3
16.5 3.0
10.0
4.2
2.3
Note: Water temperature was 45°C.
matter (92%). Free oil was at 5%, while volatile hydrocarbons were at 3%.
Discussion--
The reported data (Table 9) reveals that the treatment process reduced
concentrations of suspended oil from an average of 190 mg C/L to 14 mg C/L, or
approximately 93%. The volatile hydrocarbons were reduced approximately 45%,
and the treated effluent contained significant amounts of volatile aromatic
hydrocarbons. The BTX (benzene, toluene, and xylenes/ethylbenzene) was pres-
ent in the effluent at an average concentration level of 9 mg C/L.
Dissolved nonvolatile organic matter was present in the effluent from the
oil/water separator at a concentration of 336 mg C/L and at 264 mg C/L in the
final treated effluent. It constituted approximately 92% of the total organic
load discharged into the receiving environment.
An effort was made to determine the source of the high concentrations of
dissolved nonvolatile organic matter in the treated effluent. Discussions with
25
-------
TABLE 8. ORGANIC COMPOSITION OF FINAL EFFLUENT,
AUGUST 7, 1980, KENAI, ALASKA, PRODUCTION FACILITY
Concentration (mg C/L)
High Low Average
Total Organic Load 291 284 288
Suspended Petroleum 14 13 14 5
Dissolved Nonvolatile
Organic Matter 266 262 264 92
Volatile Hydrocarbons 11.2 8.9 10.1 3
Volatile Aliphatic
Hydrocarbons 1.0 0.7 0.9 0.3
Volatile Aromatic
Hydrocarbons
Benzene
Toluene
Xylenes
10.2
5.9
2.9
1.4
8.2
5.4
2.3
0.5
9.3
5.7
2.6
1.0
3.0
Note: Water temperature was 43.9°C.
plant operating personnel disclosed that because chemical additives are used at
at many points of gross fluid processing, obtaining a sample of produced water
that was not treated in some way is very difficult. A possible source of
untreated produced water would be at well heads of newer oil wells, which do
not require reinjection. Such a sample of untreated gross fluid was obtained
from one of the offshore oil wells supplying the Kenai production facility.
The sample consisted of approximately 80% oil and 20% water. Analysis of
the aqueous phase revealed that average concentrations of dissolved nonvolatile
organics in this sample was equal to 50 mg C/L.
There was apparently a substantial rise in dissolved organic content be-
tween the oil well head (50 mg C/L) and the effluent from the oil/water sep-
arator (336 mg C/L). The rise could be attributed in part to the addition of
chemicals and in part to chemical compositional changes that resulted in the
formation of additional water-soluble organic composition.
26
-------
TABLE 9. EFFECTIVENESS OF TREATMENT PROCESS, AUGUST 7,
1980, KENAI, ALASKA, PRODUCTION FACILITY
Average Concentration (mg C/L)
Station 1
Water/Oil Station 2 %
Separator Final Effluent Reduction
Total Organic Load 544 288 47
Suspended Petroleum 190 14 '93
Dissolved Nonvolatile
Organic Matter
Volatile Hydrocarbons
Volatile Aliphatic Hydrocarbons
Volatile Aromatic Hydrocarbons
Benzene
Toluene
Xylenes
336
18
1.4
16.5
10.0
4.2
2.3
264
10
0.9
9.3
5.7
2.6
1.0
22
45
36
44
43
38
56
Note: Water temperature was 44.5°C.
Offshore (Dillon) Platform, Cook Inlet, Alaska
Evaluation of treatment effectiveness on the Cook Inlet offshore platform
was conducted on August 6, 1980. This platform is one of the older ones in
Cook Inlet. The gross fluid is processed on the platform, as is the produced
water, which is then discharged into Cook Inlet. The platform typically pro-
cesses 13,000 barrels (2067 m3) of gross fluid per day, generating 2000 barrels
(318 m3) of oil and 11,000 barrels (1749 m3) of produced water. Extracted
gross fluid contains approximately 85% water. The oil/water separation process
and treatment of produced water are very simple, one-step operations. The oil
separation process consists of a free water knockout unit (no heater-treaters),
and the produced water is treated in one step by a gravity separator.
Sampling and Analysis--
Two sampling points were selected on this platform: Station 1, the efflu-
ent from the water knockout unit, and Station 2, final effluent. Triplicate
samples were collected at each station and analyzed for suspended oil, dis-
solved nonvolatile organic matter, and volatile hydrocarbons.
Results--
Station 1, Water Knockout Effluent. Three samples were collected at this
27
-------
station on August 6, 1980. The results of protocol analysis, which represents
material balance for all organic matter present in the sample, are reported in
Table 10. The average total organic load of the water knockout effluent was
656 mg C/L, with a standard deviation of 298 rug C/L (an approximate fluctuation
of 53%). Suspended organic matter, composed primarily of free oil, was found
to be at a 405 mg C/L level, with a standard deviation of 309 mg C/L.
Dissolved nonvolatile organic matter was present in an average concentra-
tion of 129 mg C/L, with a standard deviation of 5 mg C/L (a fluctuation of
approximately 4%). A low order of fluctuation in dissolved organic content of
the process stream observed was consistent with observations at other test
sites, indicating a constancy of this fraction of organic load. The concentra-
tion level of volatile organic fraction was found to be 31 mg C/L, with a stan-
dard deviation of 10 mg C/L (an approximate fluctuation of 32%). Volatile
hydrocarbons were composed of 7.8 mg C/L aliphatic hydrocarbons (25%) and 22.7
mg C/L aromatic hydrocarbons (75%). Aromatic hydrocarbons were composed es-
sentially of benzene, toluene, and xylenes/ethylbenzene, in a ratio of approxi-
mately 2:1.2:1.
Data reported in Table 10 reveals that the effluent from the water knock-
out unit was composed of 72% free oil, 23% dissolved nonvolatile organic mat-
ter, and 6% volatile hydrocarbons. The lowest value (129 mg C/L) and lowest
proportion (23%) of dissolved organic matter in incoming process water was
observed at this processing facility. This facility was the simplest in de-
sign, involving only one unit process for separating oil from water, and only
one unit for treating produced water. There were no heater-treaters in the
process.
It appears that the contribution from the processing of gross fluid at
this platform was a minimum, and this fact was reflected in low values for
dissolved nonvolatile matter observed.
Station 2, Final Effluent. Three samples of gravity separator effluent
were collected on August 6, 1980. The results of oily wastewater protocol
analysis are reported in Table 11. The total organic load of the gravity sep-
arator effluent was 188 mg C/L, with a standard deviation of 8 mg C/L (a fluc-
tuation of approximately 4%), a value considerably lower than that observed in
the effluent from the water knockout unit. Suspended organic matter, or free
oil, was found to be 36 mg C/L, with a standard deviation of 11 mg C/L (a
fluctuation of approximately 30%). The concentration of free oil in effluent
from the gravity separators in the onshore facility in Trading Bay (38 mg C/L)
was close to the concentration of free oil observed on the offshore platform
(36 mg C/L).
Dissolved organic matter was present in a concentration of 141 mg C/L,
with a standard deviation of 6.1 mg C/L (a fluctuation of approximately 4%).
High reproducibility of dissolved organic content in this case was consistent
with all previous observations on the consistency of this fraction in process
streams and samples thereof. Volatile hydrocarbons were present at an 11 mg
C/L level (standard deviation of 0.4 mg C/L) and were composed of 0.7 mg C/L
aliphatic hydrocarbons and 10.2 mg C/L aromatic hydrocarbons. Benzene, tolu-
ene, and xylenes/ethylbenzene were the principal hydrocarbons present. Their
ratio was 4.9:2.6:1.
28
-------
TABLE 10. ORGANIC COMPOSITION OF WATER KNOCKOUT EFFLUENT,
AUGUST 6, 1980, COOK INLET OFFSHORE PLATFORM
Concentration (mg C/L)
Component
Total Organic Load
Suspended Petroleum
Determinations
677
524
790
638
228
54
Avg
565
405
Standard
Deviation
298
309
%
72
Dissolved Nonvolatile
Organic Matter
Volatile Hydorcarbons
Volatile Aliphatic
Hydrocarbons
Volatile Aromatic
124 131 133
29.3 21.7 40.7
10.7
4.7 8.1
129
30.5
7.8
4
10
3.0
23
5
1
Hydrocarbons
Benzene
Toluene
Xylenes
18.6
9.4
5.2
4.0
17.0
8.4
4.6
4.0
32.6
15.2
9.2
8.2
22.7
11.0
6.3
5.4
8.7
3.7
2.5
2.4
4
Note: Water temperature was 52.2°C.
Data reported in Table 11 reveals that dissolved nonvolatile organics
were the largest component of the treated effluent (75%). Free oil contrib-
uted 19% to the total organic load of the effluent, while volatile hydrocar-
bons added 6%.
Discussion--
A summary of compositional data is presented in Table 12. Reported are
average values of all parameters measured and their standard deviation. Sig-
nificant fluctuations in levels of free oil in triplicate samples was observed.
The reason for this is nonhomogeneity of oil-water mixtures. It appears that
multiple or composite (perhaps 24-hour composites) mode of sampling for free
oil is indicated in this type of installation. The dissolved organic content
of the process stream as reflected in multiple sampling appears to be far more
reproducible and single grab samples in this case should suffice. The volatile
hydrocarbon content of process stream influent fluctuates to a significant
degre, but is quite reproducible downstream from the gravity separator. Gener-
ally speaking, reproducibility of multiple sampling on the offshore platform
was very similar to reproducibility of samples obtained during a 5-hour period
of sampling at discrete time intervals at the onshore Trading Bay facility.
29
-------
TABLE 11. ORGANIC COMPOSITION OF FINAL EFFLUENT,
AUGUST 6, 1980, COOK INLET OFFSHORE PLATFORM
Concentration (mg C/L)
Component
Total Organic Load
Suspended Petroleum
Determinations
185
26
197
48
181
33
Avg
188
36
Standard
Deviation
8
11
%
19
Dissolved Nonvolatile
Organic Matter
Volatile Hydrocarbons
Volatile Aliphatic
Hydrocarbons
Volatile Aromatic
148 138 137
10.9 11.4 10.8
0.7
0.8 0.7
141
10.9
0.7
6
0.5
0.1
75
6
0.4
Hydrocarbons
Benzene
Toluene
Xylenes
10.2
5.8
3.1
1.3
10.6
6.1
3.2
1.3
10.1
5.9
3.1
1.1
10.2
5.9
3.1
1.2
0.3
0.2
0.1
0.1
5.4
Note: Water temperature was 47.2°C.
This similarity suggests that the principal reason for poor reproducibil-
ity of free oil measurement might be due to sampling operations and consequent-
ly, composite sampling for this parameter is indicated when the process stream
or final effluent are sampled. The reproduction of measurements for dissolved
organic content including volatile hydrocarbons appears to be good, especially
downstream from the gravity separator-, and single grab samples might be suffi-
cient for measurements of priority pollutants.
Reduction in concentration of various fractions of organic load of the
process stream is reported in Table 12. The suspended oil content was reduced
from 405 mg C/L to 36 mg C/L (approximately 91%). The volatile aromatic
hydrocarbons were present in the final effluent at an 11 mg/L concentration,
the highest level observed in this study. The dissolved nonvolatile organic
compounds were present in significantly high levels, both in the effluent from
the water knockout unit (129 mg C/L) and in the final effluent (141 mg C/L).
Such compounds constitute approximately 75% of the total organic load in the
effluent.
30
-------
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31
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GULF OF MEXICO
Characterization of the effluent quality from seven offshore platforms was
carried out in the Gulf of Mexico. Two different types of analyses were per-
formed. Using oily wastewater protocol analysis (1, 5), the total organic load
of the samples was characterized including free oil content, dissolved nonvola-
tile organics, and volatile hydrocarbons. Using EPA priority pollutants analy-
sis, determinations were made of purgeable, acid-neutral, base-neutral, pesti-
cides, and metal priority pollutants.
Sets of samples were collected from each platform for oily wastewater
protocol analysis. These samples were acidified (after arrival at Newbury
Park, California) to pH 2 with hydrochloric acid and then analyzed. A set of
samples for priority pollutant analysis was collected by Rockwell anc analyzed
by EPA Effluent Guidelines Division contract laboratories according to sampling
and analytical instructions as described in the Federal Register (4).
Offshore Platforms
The seven offshore production platforms selected for this study repre-
sented a range of the variables found off the Louisiana coast (2). All exam-
ined sites treated produced water offshore, while specifics of hardware design
and the nature and quantity of chemicals used differed from platform to plat-
form, the treatment principles were the same: primary treatment by gravity
separation, followed by secondary treatment by gas flotation.
Platform 1 (BM 2C)
Samples on platform 1 were collected for protocol analysis on March 7,
1980, and for priority pollutants on March 13, 1980. The estimated daily
production of the 23 wells that were supplying gross fluid for processing was
16,483 barrels of gross fluid (2621 m^/d) and 13,085 MCFD (370,530 standard
nvvd) of natural gas. Oil production corresponded to 11,957 barrels per day
(1901 m3/d) and water was produced at a rate of 4526 barrels per day (720 nvV
day). Water constituted approximately 22% of the gross fluid.
The produced water treatment on this platform consisted of two units: a
corrugated plate interceptor (CPI) unit and a gas flotation (Wemco) unit. In
this system the primary produced water from a low-pressure separator flows to
the CPI (manufactured by Monarch Separators, Inc.) for gravity separation and
then into the Wemco gas flotator (mechanical eductor) for gas flotation. The
effluent from the gas flotator is discharged overboard.
Two chemicals are added to the process stream. Tretolite RP-34 (a demul-
sifier) is added at the low-pressure separator inlet manifold at a rate of 15
dm3/day. A flotation aid (Tretolite FR-87) is added at the flotation unit
inlet at a rate of 17 dm3/day. Based on an approximate 720 m3/day discharge,
it can be calculated that added chemicals correspond to approximately 44 ppm
concentration in the process stream.
32
-------
Platform 2 (SS 107)
Samples on platform 2 were collected for oily wastewater protocol analysis
on March 10, 1980. No samples were collected for priority pollutants on this
platform. The estimated daily production of five wells at this platform was
610 bpd (97 m3/d) of oil, 3979 bpd (633 m3/d) of water, and 470 MCFD (13,300
standard m3/d) of natural gas. Total gross fluid output was 4589 bpd (730
m3/d) with water contributing 87% to the flow.
The treatment of produced water at this platform consists of two units:
a gravity separator and a gas flotator. In this system the fluids from the
low-pressure separator flow to the oil treater, which is a dual-purpose unit
providing for the gravity separation of water from oil, producing processed
oil. It also provides for gravity separation of oil from water to prepare the
water for treatment by flotation. The flotation unit is a proprietary four-
cell assembly with mechanical gas eduction. The effluent from the gas flotator
is discharged.
Four chemicals are added to the process stream: methanol was added at the
lift gas point at a rate of 8 dm3/d; Tretolite RN3003 (a demulsifier) is added
at the well manifold at a rate of 8.6 dm3/d; Tretolite SP175 (a scale inhibi-
tor) is added at the low-pressure separator outlet at 7.3 dm3/d; and a flota-
tion aid, Tretolite FR98D, is added upstream of the flotation unit at an
average rate of 10 dm3/d. Based on an average measured 730 m3/d discharge, it
can be calculated that added chemicals constitute 47 ppm in the process stream.
Platform 3 (ST 131)
Samples on this platform were collected for oily wastewater protocol
analysis on March 21, 1980, and for priority pollutants on March 19, 1980. The
estimated production of this platform was 1853 bpd (295 m3/d) of oil and 870
bpd (138 m3/d) of water, for a total of 2723 bpd (433 m3/d) of gross fluid.
Calculated water content is 32%. Additionally, 7623 MCFD (215,700 standard
m3/d) of natural gas is produced.
The treatment process for produced water at this platform consists of two
steps: gravity separation in a gun-barrel unit, and gas flotator with mechan-
ical gas dispersion. The effluent from the gas flotator is discharged.
Two chemicals were added to the process stream: Tretolite RP-101 (a de-
mulsifier) was added at the low-pressure well manifold at a rate of 3.8 dm3/ d,
and Tretolite FR-81 (a flotation aid) was added at the flotation unit inlet at
14 dm3/d. From the discharge rate it can be calculated that 129 ppm of chemi-
cals are added to the process stream.
Platform 4 (SS 198G)
Samples on this platform were collected for oily wastewater protocol
analysis on March 24, 1980, and for priority pollutant analysis on March 25,
1980. The average daily production for this platform was 593 bpd (94 m3/d) of
oil and 195 bpd (31 m3/d) of water, for a total of 788 bpd (125 m3/d) of gross
33
-------
fluid. The water cut was approximately 25%. Additionally, 14,320 MCFD
(405,000 standard m3/d) of natural gas is produced.
The produced water is treated on the platform in three steps: gravity
separation by corrugated plate interception (CPI) and in two flotation units
operating in series. The CPI unit is a gravity separator of proprietary design
supplied by Monarch Separators, Inc. The first flotation unit is a Tridair (a
proprietary three-cell dispersed gas flotator with hydraulic gas eduction), the
second flotator was a one-cell proprietary device manufactured by Monosep. The
gas for the flotator was educted hydraulically.
Three chemicals were added to the process stream. Tretolite RP2327 (a
demulsifier) was added at a rate of 13.2 dm3/d, and Tretolite SP246 (a scale
inhibitor) was added at a rate of 1.7 dm3/d at the well manifold. A flotation
aid, Tretolite FR88, was added upstream of the flotation unit at an average
rate of 1.8 dm3/d. This addition of chemicals relative to treated effluent
discharge amounted to a concentration of 539 ppm.
Platform 5 (El 18CF)
Samples of treated effluent were collected for material balance on April
2, 1980, and for priority pollutants on April 8, 1980. The average daily pro-
duction on this platform is estimated at 18,893 bpd (3004 m3/d) of gross fluid
which contained approximately 90% water. Oil was produced at a rate of 1856
bpd (295 m3/d) and water at a rate of 17,037 bpd (2709 m3/d). Additionally,
38,089 MCFD (1,078,000 standard m3/d) of natural gas was produced.
The treatment process on this platform was a two-step operation. Produced
water from the oil treater is directed into a skim tank, where residual oil is
separated by gravity. The effluent from the skim tanks enters the dissolved
gas flotator where additional separation takes place. The effluent from the
flotation unit is discharged.
Methanol was added at the high-pressure well heads to prevent hydrate
formation at a rate of 115 dm3/d. No other chemicals were added to the pro-
cess. The addition of methanol corresponded to an approximate 42 ppm concen-
tration contribution relative to the discharge rate.
Platform 6 (BDC CF5)
Samples for oily wastewater protocol analysis were taken at this platform
on April 4, 1980. Samples for priority pollutant analysis were taken on April
8. 1980. The estimated daily production for this platform was 13,026 bpd (2070
m3/d) of gross fluid that contained approximately 91% water. Oil was produced
at a rate of 1131 bpd (180 m3/d) and water at a rate of 11,895 bpd (1890 m3/d).
Additionally, 5145 MCFD (145,000 standard m3/d) of natural gas was produced.
The oil was separated from water in two heater-treaters connected in
parallel. The effluent from the heater-treaters was introduced into two grav-
ity separators, which were also connected in parallel. The effluent from the
two gravity separators was recombined and introduced into a gas flotation unit
(Monosep) with hydraulic gas dispersion.
34
-------
Three chemicals were added to the process stream. A scale inhibitor,
Tretolite WF-123, was added to the manifold ahead of the low-pressure separ-
ators at a rate of 0.95 dm^/d. A demulsifier, Tretolite BR-4050, was added at
a rate of 5.3 dm^/d at the same manifold. A flotation aid, Tretolite JW8206,
was added at an average rate of 9.4 dm^/d at the inlet to the flotation unit.
This addition of chemicals contributed approximately 8 ppm relative to the
discharge flow.
Platform 7 (SM 130B)
Samples for priority pollutant analysis were collected at this platform on
April 17, 1980. No oily wastewater analyses were performed at this site. The
average daily production of gross fluid at this site was 21,136 bpd (3361
m3/d). Oil was produced at a rate of 17,170 bpd (2730 m3/d) and water at a
rate of 3966 bpd (631 m3/d). The calculated water cut was 19%. Additionally,
8377 MCFD (237,200 standard m3/d) of natural gas was produced.
The treatment process included gravity separation by two corrugated plate
interceptors (CPI) connected in parallel, followed by secondary treatment in a
flotation unit with mechanical gas eduction.
A foam inhibitor (Dow Corning 200) was added to produced fluids at the
manifold ahead of the low-pressure separator. The inhibitor was diluted with
diesel to a concentration of 15%. The diluted mixture was fed at a concentra-
tion of 3.5 ppm.
Organic Material Balance Results
Organic material balance in the effluents from offshore platforms in the
Gulf of Mexico is reported in Table 13. The total organic load of treated ef-
fluents ranged between 68 and 661 mg C/L, with an average value of 404 mg C/L.
Dissolved nonvolatile organic matter constituted the great bulk of organic
matter in the discharge. The concentration of this fraction ranged between 57
and 624 mg C/L, with an average of 376 mg C/L. On the average, this fraction
constituted 93% of all organic matter discharged from platforms. Similarly
high nonvolatile dissolved organic content was observed in treated produced
water in Cook Inlet fields. On the average, 88% of the organic matter dis-
charged there was composed of dissolved nonvolatile organics.
Concentrations of suspended organics (free oil) ranged between 9 and 46 mg
C/L, averaging 26 mg C/L. This range was not unlike the one observed in Cook
Inlet production fields, where the range of suspended organics was from 5 to 36
mg C/L.
With the exception of platform 5, the concentration of volatile hydro-
carbons was low, and fluctuated in a narrow range of 0.9 to 2.2 mg C/L. This
fraction constituted only 0.5% of the total organic load in the discharged
water and was considerably lower than that observed in Cook Inlet platform
effluent. The range for volatile hydrocarbons in samples from Cook Inlet was
7 to 11 mg C/L.
35
-------
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36
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It must be noted that hydrochloric acid was added to Gulf of Mexico pro-
duced water only after samples were received in Newbury Park, California, and
considerable time was spent in transit between the Gulf Coast and Valdez,
Alaska, where the samples were analyzed. The possibility of some aromatic
hydrocarbon decomposition in unpreserved samples during shipment cannot be
ruled out.
Benzene, toluene, xylenes/ethylbenzene constituted the principal organic
compounds present in the effluent. On the average, 1.1 mg/L of benzene, 0.8
mg/L of toluene, and 0.3 mg/L of xylenes/ethylbenzene were present in the ef-
fuent from offshore platforms in the Gulf of Mexico and, for comparison, in
Cook Inlet (Table 14).
Because dissolved nonvolatile organic matter constituted the bulk (93%) of
all organic matter discharged from offshore platforms in the Gulf of Mexico,
its possible source is of some interest. It is possible that part of it may
originate in brine, part is formed during the processing of gross fluids, and
part derives from chemicals used in processing and treatment of produced water.
Chemicals added to the process stream include demulsifiers, corrosion in-
hibitors, and flotation aids. Methanol is sometimes added to prevent hydrate
formation at high-pressure well heads. An estimate (in ppm) of additives added
to the processing stream at each platform studied was made and is reported in
Table 15, as is the contribution to the Total Organic Load (TOL). The values
ranged from 8 to 539 ppm. Low concentrations for chemical addition were nor-
mally observed at platforms discharging high volumes of brine, i.e., water
discharge from platform 6 was 1890 m^/d and an equivalent of 8 ppm of chemical
additives were in the process stream. On the other hand, platform 4 was dis-
charging only 31 m-Vd of produced water and chemical additions to the process
stream amounted to 539 ppm. The weighted (by volume of discharge) average
addition of chemicals to the process stream for the platforms studied was 37
ppm. This value can account for approximately 10% of the dissolved nonvolatile
organic fraction, found in discharges from offshore platforms.
From this it may be concluded that the bulk of dissolved nonvolatile
organics originate either in brine or are formed during the processing of gross
fluid. It is unknown at this time which source (original brine composition, or
effects of processing) contributes to what degree to the observed high level of
dissolved organic content. Completed studies indicate only that such organic
matter is universally present in all treated effluent from offshore oil extrac-
tion operations, and constitutes approximately 90% of all organic matter dis-
charged. Neither source nor exact chemical nature of this fraction is known at
this time.
Priority Pollutants Analysis
After receiving the results of the EPA Effluent Guidelines Division con-
tract laboratories' analyses, four groups of organic priority pollutants were
examined in effluents from six offshore platforms in the Gulf of Mexico:
purgeable, base-neutral, acid-neutral, and pesticides.
37
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TABLE 14. VOLATILE AROMATIC HYDROCARBONS IN TREATED EFFLUENTS FROM
OFFSHORE PLATFORMS IN THE GULF OF MEXICO AND COOK INLET
Concentration in mg/L
Date, 1980
Gulf of Mexico
3/7
3/10
3/21
3/24
4/2
4/4
Average and
Standard
Deviation
Cook Inlet
1/22
7/7
7/6
Average and
Standard
Deviation
Platform
1
2
3
4
5
6
1
Trading Bay
Kenai
Offshore
Cook Inlet
5
Benzene
0.9
0.5
0.8
0.4
2.4
1.4
.1 ±0.6
3.7
6.3
6.5
.5 ±1.6
Purgeables. Samples were analyzed
Only benzene,
were the only
toluene, and ethyl
three priority pol
benzene
lutants
Toluene
0.7
0.6
0,4
0.4
2.1
0.7
0.8 ±0.6
1.9
2.9
3.4
2.7 ±0.8
Xylenes/
Ethyl benzene
0.3
0.3
0.2
0.2
0.3
0.3
0.3 ±0.05 2.
0.5
0.9
1.3
0.9 ±0.4 9.
Total
1.9
1.4
1.4
1.0
5.8
2.4
2 ±1.8
6.1
10.1
11.2
1 ±2.7
for 31 purgeable priority pollutants.
were found in
consistently
treated effluents
present in samples
. They
of pro
duced water from offshore platforms in the Gulf of Mexico (Table 16). Benzene
concentration as determined by the priority pollutant analysis ranged between
170 yg/L (0.17 mg/L) and 1900 ug/L (1.9 mg/L), averaging 0.9 mg/L. The range
for benzene as determined by oily wastewater protocol analysis was 0.4 mg/L to
2.4 mg/L, with an average of 1.1 mg/L (Table 14).
38
-------
TABLE 15. ESTIMATES OF CHEMICALS ADDED TO THE PROCESS STREAM
AND DISSOLVED ORGANIC CONTENT OF TREATED EFFLUENT
Concentration (ppm)
Production
Date,
1980
3/7
3/10
3/21
3/24
4/2
4/4
Platform
1
2
3
4
5
6
Oil
m3/d
1901
97
295
94
295
180
Water
m3/d
720
633
138
31
2709
1895
Dissolved
Nonvolatile
Organics
495
561
382
624
136
57
Added
Chemicals
Estimated
44
47
129
539
42
8
% Added
Chemicals
in TOL
9
8
34
86
31
14
Average and
Standard Deviation
376 ±232 135 ±202
The toluene concentration in the treated effluent ranged between 770 yg/L
(0.77 mg/L) to 3300yg/L (3.3 mg/L), averaging 2.074 mg/L. This value was gen-
erally higher than that determined by oily wastewater protocol, where the aver-
age value for toluene was found to be 0.8 mg/L and the range 0.7 to 2.1.
Ethylbenzene was found in the range from 42 yg/L to 200 yg/L. This value
cannot be compared with material balance protocol analysis because ethylbenzene
and xylenes are not resolved in the latter.
One sample (Platform 6) was found to contain rather large quantities of
methylene chloride (35,000 yg/L) and carbon tetrachloride (140 yg/L). There
was no record of use of such chemicals on Platform 6, and analysis of the in-
fluent (untreated brine) disclosed an absence of both methylene chloride and
carbon tetrachloride in incoming produced water. Because those chemicals are
common laboratory solvents and were found to be absent from all other samples
analyzed, they might be due to laboratory contamination of this specific sam-
ple. Because of possible sample contamination, the data from Platform 6 is
not considered in this discussion.
Base-Neutrals. Naphthalene was found in effluents from three platforms
(out of six analyzed). (See Table 17.) Its concentration ranged between 12
yg/L to 44 yg/L. Anthracene/phenanthrene was found in effluent from one plat-
form in a concentration of 15 yg/L. None of the other base-neutral priority
pollutants was found in any of the samples analyzed.
39
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40
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TABLE 17. BASE-NEUTRAL PRIORITY POLLUTANTS IN
OFFSHORE PRODUCED WATER, GULF OF MEXICO
Platform:
Date of Sampling:
1
3/13/80
3
3/19/80
4
3/25/80
5
4/8/80
7
4/17/80
Concentration in Micrograms/Liter
Treated Effluent
Naphthalene 24 12 ND 44 ND
Anthracene/
phenanthrene ND ND ND ND 15
Note: ND means not detected at the 10-microgram/liter level.
Acid-Neutrals. Only phenol was found in treated effluent from all plat-
forms studied, as shown in Table 18. Its concentration ranged between 18 and
840 yg/L, with an average value of 486 yg/L. None of the other acid-neutral
priority pollutants were found.
Pesticides. No pesticides were found in any of the analyzed effluent.
Metals
Treated effluent from five offshore platforms in the Gulf of Mexico were
examined for 13 metal priority pollutants: antimony (Sb), arsenic (As), beryl-
lium (Be), cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb), mercury (Hg),
nickel (Ni), selenium (Se), silver (Ag), thallium (Tl), and zinc (Zn).
Chromium and lead were found in the effluent from each and every platform
examined (see Table 19). Lead was found in a range of 160 to 915 yg/L, aver-
aging 597 pg/L; chromium in a range of 59 to 390 yg/L, averaging 260 yg/L.
Nickel and zinc were found in effluents from four platforms (out of five
reported). Nickel ranged in concentration from 68 to 1674 yg/L, while zinc
was present in a concentration range of less than 25 to 640 yg/L.
Copper, silver, cadmium, and beryllium were found in effluents from
three platforms (platforms 4, 5, and 7). Copper was present in a concentra-
tion range of less than 25 to 137 yg/L; and silver in a concentration range
of less than 1 to 152 yg/L. Cadmium was present in a concentration range of
less than 25 to 56 yg/L, and the concentration range for beryllium was less
than 1 to 4 yg/L. Concentrations of antimony, arsenic, mercury, selenium, and
thallium were generally below the limit of detection for the methods used.
41
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The generated data indicates that significant amounts of metal priority
pollutants are discharged from offshore oil extraction platforms. Four metals
(lead, chromium, nickel, and zinc) are the most widely distributed inorganic
priority pollutants in treated effluent and, together with four organic prior-
ity pollutants (benzene, toluene, ethylbenzene, and phenol), constitute the
principal contribution of toxicants discharged from offshore oil-producing
platforms.
DISSOLVED AND SUSPENDED OIL
The organic composition of treated and untreated produced we :er (brine) is
complex. The produced water contains many types of dissolved orr nic compounds
in addition to suspended or free oil (composed largely of higher liphatic and
aromatic hydrocarbons and other water-soluble components of crude oil). Some
dissolved organics originate in the crude oil being extracted (e.g., benzene,
toluene, xylenes, ethylbenzene, phenol, plus additional higher molecular weight
water-soluble compounds such as esters, carboxylic acids, ketones, pyridines,
quinolines, carbozoles, and others). Additional sources of dissolved organic
matter in process water are the proprietary demulsifiers, defoamers, and floc-
culation aids used to facilitate treatment.
Compounds formed during the processing of gross fluid are an additional
and (at this time) largely unexplored source of dissolved organics. Oxidation
of some compounds of petroleum is believed to be an important source of dis-
solved organic contribution to the process stream. Studies carried out in
offshore fields in Cook Inlet, Alaska, and the Gulf of Mexico have disclosed
that dissolved organic compounds are present in large quantities at all pro-
duced water processing steps and constitute up to 90% of the total organic load
in the treated effluent.
The brine treatment technology is designed to remove suspended organic
matter, or "free oil," from the produced water. The oil/water separation is
physical in nature and takes advantage of the relative immiscibility and the
density differential of oil and water. Separation is achieved by gravity and
gas or air flotation. State-of-the-art methods for the physical treatment of
oily wastewaters are not designed for removal of petroleum-derived dissolved
organics, nor are they capable of such removal.
In order to determine concentration levels of free or treatable oil in
produced water, modifications of standard methods for analysis of oil and
grease are practiced by industry. The object of such modified determinations
is to establish the quantity of free oil considered to be treatable by the
state-of-the-art technology, and to rate performance characteristics of the
treatment process in terms of removal of treatable (free) oil (rather than in
terms of total oil and grease as determined by liquid/liquid extraction tech-
niques, followed by gravimetric or IR spectrometric quantification). It must
be mentioned that such methods are used in-house by the oil companies, and are
not currently used in setting standards for oil discharges.
The most commonly used methods for determination of free oil are (1)
silica gel adsorption analysis, (2) filtered brine method, (3) equilibration,
and (4) IR scan (2). All such methods are somewhat empirical in nature and are
44
-------
greatly influenced by the specific chemical composition of a given source of
produced water.
A limited comparison study of two modified methods (silica gel adsorption
and filtered brine) were carried out on brine samples collected at Trading Bay,
Alaska, production facilities. The differentiation between free and dissolved
oil in silica gel adsorption methods is accomplished in the following manner.
Oil and grease analysis is performed on Freon TF extract in a routine manner by
IR means. Then 3 grams of silica gel are added to the Freon TF extract (100
ml) and the resulting suspension is agitated for 10 minutes using a magnetic
stirrer. After the silica gel is settled, the Freon TF extract is reanalyzed
for oil and grease. In this procedure an assumption is made that water-soluble
petroleum compounds, being of greater polarity than pure hydrocarbons, are
selectively adsorbed by the silica gel and consequently removed from solution.
The modified method provides a value for free oil, while the differential
between standard oil and grease analysis and silica gel modification of the
method produces the value of the dissolved oil.
In the filtered brine method, water samples are filtered through a Whatman
No. 40 filter prior to extraction into Freon TF and analysis for oil and
grease. In this method, dissolved oil is determined directly by extraction of
organics from filtered brine into Freon TF, and then analyzing the Freon TF
solution for oil and grease by either gravimetric or IR spectrometric proce-
dure. The quantity of free or suspended oil is determined indirectly as a
differential between the values obtained by standard oil and grease analysis
and the filtered brine method.
Samples of produced water were collected at Station 1 (effluent from
heater-treaters), Station 2 (effluent from gravity separator), Station 3 (ef-
fluent from gas flotator), and Station 4 (final treated effluent) (Figure 2),
on January 23, 1980 at the Trading Bay production facility, Cook Inlet, Alaska.
All samples were approximately 1 liter in size. Brine filtration was performed
on-site immediately after sample collection. All samples were preserved by
acidification to pH 2 and extracted into Freon TF within 2 days of collection.
Results of the analyses are presented in Table 20. In analyzing this
data, dissolved oil content should not be confused with dissolved nonvolatile
organic matter determined by the TOC method on 0.45-micron filtrate. The TOC
value reflects all dissolved organic matter present in the sample, while the
dissolved oil value reflects only those organic compounds that are extractable
into Freon TF. Many of the dissolved organic compounds present in produced
water are not extractable into Freon TF, and consequently dissolved oil values
are usually considerably lower than dissolved TOC values.
All analyzed samples contained dissolved oil as defined by silica gel ad-
sorption and filtered brine tests. Generally, the filtered brine method pro-
duced higher values for dissolved oil and consequently lower values for free
oil than the silica gel adsorption method. Dissolved oil content as determined
by the brine filtration method was consistently higher (by 11% to 15%) than
similar values obtained by the silica gel adsorption method. Since both
methods of analysis are somewhat empirical, no great significance can be
ascribed to this fact. It is believed, however, that the silica gel adsorption
45
-------
TABLE 20. ANALYSIS FOR DISSOLVED AND FREE OIL, TRADING BAY PRODUCTION
FACILITY, COOK INLET, ALASKA*, JANUARY 23, 1980 (mg oil/liter)
Effluent Source:
Time of Sampling:
S" cia Gel Adsorp-
f n Method:
Total Oil
Free Oil
Dissolved Oil
Filtered Brine
Method:
Total Oil
Free Oil
Dissolved Oil
Station 1
1310
Effluent,
Heater-Treater
68.1
54.9
13.2
68.1
48.5
19.6
Station 2
1141
Effluent,
Gravity
Separator
54.6
42.7
11.9
54.6
38.1
16.5
Station 3
1090
Effluent,
Gas Flotator
18.9
11.8
6.6
18.4
9.8
8.8
Station 4
1015
Final
Effluent
14.2
7.9
6.3
14.2
6.7
7.5
* Single sets of samples collected at indicated times were used for analysis.
method provides a good indication of aliphatic hydrocarbon content of the oily
water sample when quantification is performed by IR spectroscopic means.
It was found that dissolved oil fraction as determined by the silica gel
adsorption method constituted approximately 20% of the total oil in the efflu-
ent from the heater-treater and gravity separator. The same fraction contrib-
uted 30% to the total oil in the effluent from the gas flotator and 40% in the
final treated effluent. This trend appeared to be consistent with the princi-.
pies of treatment involved, that is, more efficient removal of nonpolar (and
consequently nonwater-soluble) petroleum, with a resulting shift to predomi-
nance of dissolved oil in the final treated effluent. Looking at the data in
another way, it appears that the treatment process, while removing 86% of the
free oil, removes only 48% of the dissolved oil.
Both silica gel adsorption and filtered brine analytical data suggest
that treated effluent contains on an average 40% to 50% dissolved oil.
46
-------
REFERENCES
1. Ly yj, I. Treatment Effectiveness: Oil Tanker B.allast Water Facility.
Ro well International, Newbury Park, California. EPA report.
2. JacKSon, G.F., E. Humes, M.J. Wade, and M. Kirsch. Oil Variability in
Effluent Brine on 10 Louisiana Production Platforms. Rockwell Inter-
national, Newbury Park, California. EPA report.
3. Lysyj, I., and E.G. Russell. Dissolution of Petroleum-Derived Products
in Water. Water Res. 8., 863-868. 1974.
4. Federal Register. Guidelines Establishing Test Procedures for the Analy-
sis of Pollutants; Proposed Regulations. Monday, December 3, 1979.
5. Lysyj, I., R .Rushworth, R W. Melvold, and E.G. RusseTl . A Scheme for
Analysis of Oily Wastewaters. Advances in Chemistry Series No. 185:
Petroleum in Marine Environment, pp. 248-266. American Chemical Society,
Washington, DC. 1980.
6. American Society for Testing Materials. ASTM Book, Part 31. 1977.
47
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
5. REPORT DATE
Chemical Composition of Produced Water at Some Offshore
Oil Platforms
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
I nor Lysyj
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Rockwell International
2421 West Hillcrest Drive
Newbury Park, California 91320
10. PROGRAM ELEMENT NO.
1NE826
11. CONTRACT/GRANT NO.
68-03-2648
12. SPONSORING AGENCY NAME AND ADDRESS
Municipal Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Edison, New Jersey 08837
13. TYPE OF REPORT AND PERIOD COVERED
Final Report. 1/80 to 11/80
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
John S. Farlow, Project Officer (201-321-6631)
16'ABSTne%ffectiveness of produced water treatment was briefly studied in offshore
oil and gas extraction operations in Cook Inlet, Alaska, and the Gulf of Mexico.
Three offshore oil extraction facilities were examined in the Cook Inlet production
field, and seven platforms were studied in the Gulf of Mexico. Overall treatment
effectiveness, as well as effectiveness of individual process units, was determined
in the Cook Inlet study. Quality of the final effluent was characterized in the
Gulf of Mexico study.
The state-of-the-art treatment technology was generally effective in reducing
free oil content (suspended organics) of produced water. The treatment was less
effective in reducing aromatic hydrocarbon content in produced water (average
reduction in concentration was of the order of 30% to 50%). Benzene, toluene, and
xylenes/ethylbenzene (BTX) were found at all stages of the processes and in all
final effluents. The average BTX concentration in treated effluents from Cook Inlet
operations was 9 mg/L. In Gulf of Mexico treated effluents, the BTX content
averaged 2 mg/L. High levels of dissolved nonvolatile organic matter (ranging from
60 to 600 mg C/L) were found in all treated effluents. Four organic priority
pollutants (benzene, toluene, ethylbenzene, and phenol) and two inorganic priority
pollutants (chromium and lead) were found in all treated effluents analyzed.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b. IDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Oil Recovery
Water Treatment
Water Pollution
Oils
Aromatic Hydrocarbons
Oil and Gas Extraction
Water Treatment Effective'
ness
Dissolved Organics
Offshore Platforms
Cook Inlet (Alaska)
Gulf of Mexico
18. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (This Report)
UNCLASSIFIED
21. NO. OF PAGES
56
20. SECURITY CLASS {Thispage)
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (9-73)
48
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing}
REPORT NO.
3. RECIPIENT'S ACCESSIO/*NO.
ri_E AND SUBTITLE
Chemical Composition of Produced Water in Selected
Offshore Oil and Gas Extraction Operations
5. REPORT OATS
July 1981
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
8. PERFORMING ORGANIZATION REPORT NO,
Inor Lysyj
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Rockwell International
2421 West Hillcrest Drive
Newbury Park, California 91320
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
68-03-2648
12. SPONSORING AGENCY NAME AND ADDRESS
Municipal Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Edison. New Jersey 08837
13. TYPE OF REPORT AND PERIOD COVERED
Final Report, 1/80 to 11/80
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
John S. Farlow, Project Officer (201-321-6631)
16. ABSTRACT
The effectiveness of produced water treatment was studied in offshore oil and gas
extraction operations in Cook Inlet, Alaska, and the Gulf of Mexico. Three off-
shore oil extraction facilities were examined in the Cook Inlet production field
and seven platforms were studied in the Gulf of Mexico. Overall treatment effec-
tiveness, as well as effectiveness of individual process units, was determined in
the Cook Inlet study. Quality of the final effluent was characterized in the Gulf
of Mexico study. It was found that the state-of-the-art treatment technology was
generally effective in reducing free oil content (suspended organics) of produced
water. The treatment was less effective in reducing aromatic hydrocarbon content
in produced water. Average reduction in concentration was in the order of 30% to
50%.. Benzene, toluene, xylenes/ethylbenzene (BTX) were found at all stages of the
processes and in all final effluents. The average BTX concentration in treated
effluents from Cook Inlet operations was 9 mg/L. In Gulf of Mexico treated efflu-
ents, the BTX content average 2 mg/L. High levels of dissolved nonvolatile
organic matter (ranging from 60 to 600 mg C/L) were found in all treated effluents.
Four organic priority pollutants (benzene, toluene, ethylbenzene, and phenol) and
two inorganic priority pollutants (chromium and lead) were found in all treated
effluents analyzed.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Oil Pollution, Offshore Platforms,
Aromatic Hydrocarbons, Waste Treatment,
Priority Pollutants
Oil and Gas Extraction,
Dissolved Organics, Cook
Inlet, Alaska, Gulf of
Mexico, Treatment
Effectiveness
13. DISTRIBUTION STATEMENT
Release to public
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
56
20. SECURITY CLASS iThis page/
Unclassified
22. PRICE
SPA Form 2220-1 (9-73)
48
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