x-xEPA
United States
Environmental Protection
Agency
Municipal Environmental Research •^*
Laboratory
Cincinnati OH 45268 ,
Research and Development
EPA-600/S2-82-034 August 1982
Project Summary
Chemical Composition of
Produced Water at Some
Offshore Oil Platforms
Ihor Lysyj
The effectiveness of produced
water treatment was briefly studied in
offshore oil and gas extraction opera-
tions 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.
Final effluent quality was determined
in the Gulf of Mexico study.
The chemical composition of process
streams and final effluents was char-
acterized in terms of total organic
material balance. Determinations
were made for suspended organic
matter (the oil); dissolved, nonvolatile,
organic matter; and volatile hydro-
carbons.
State-of-the-art treatment was
generally effective in reducing the free
oil content (suspended organics) of
produced water. Such treatment was
less effective in reducing the aromatic
hydrocarbon content of produced
water; the average reduction in con-
centration was 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 milligrams per liter (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 milligrams carbon per liter (mg
C/L), were found in treated effluents.
Generally, the concentration of this
fraction increased, rather than de-
creased, as a result of treatment. This
increase might be due to addition of
chemicals during the treatment and to
oxidation of petroleum matter leading
to the formation of water-soluble,
oxygenated, organic compounds.
Four organic priority pollutants
(benzene, toluene, ethylbenzene, and
phenol) and two inorganic priority
pollutants (chromium and lead) were
found in all the treated effluents
analyzed. Naphthalene, cadmium,
. nickel, zinc, silver, copper, and
beryllium were intermittently present.
This Project Summary was devel-
oped by EPA's Municipal Environ-
mental Research Laboratory, Cincin-
nati, OH, to announce key findings of
the research project that is fully
documented in a separate report of the
same title (see Project Report ordering
information at back).
Introduction
The gross fluid that is produced by all
oil extraction operations usually con-
tains a mixture of oil and water. The
water content of gross fluids ranges
from 0% for new oil wells to more than
90% for old oil wells. The subterranean
water, or brine, that remains after the oi I
is separated and processed is called
produced water. All produced waters
are contaminated by petroleum matter
and chemicals used in oil processing
operations and in subsequent treatment
of produced water. The produced water
is usually treated before it is discharged
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into the receiving environment or
reinjected. The treatment is performed
either on the production platforms or on
shore, and is usually conducted co-
incidentally with oil/water separation,
which produces processed oil. Produced
water treatment ranges from relatively
simple gravity separation and flotation
used on offshore platforms to complete
oily wastewater treatment at land
installations
The principal contaminants in pro-
duced water are water-soluble and
water-insoluble petroleum compounds
and the chemical compositions added
as part of gross fluid processing and
treatment of produced water. The
Water-soluble petroleum fraction is
composed mainly of aromatic hydro-
carbons (benzene, toluene, xylenes/
ethylbenzene) and diaromatics (naph-
thalene and derivatives). Also present in
this fraction are nonhydrocarbon com-
pounds of petroleum origin, including
phenolic and carboxylic acids, andother
oxygen-, nitrogen-, and sulfur-contain-
ing compounds The water-insoluble
fraction consists primarily of higher
aliphatic hydrocarbons and other high
molecular-weight, water-insoluble
components of crude oil. The organic
chemicals added to the process stream
as part of processing or treatment may
include a significant amount of pro-
prietary formulations.
The produced water treatment tech-
nology is designed primarily for removal
of water-insoluble petroleum and not
for removal of the water-soluble organic
fraction that might originate in crude oil
or in chemical additives used as part of
processing.
Experimental Design and
Methodology
The principal objective of this study
was to determine how effective state-
of-the-art technology is in producing
acceptable-quality effluents in produced
water from offshore oil extraction
operations. Additionally, an attempt
was made to generate comprehensive
information on the chemical composi-
tion of produced water and composi-
tional changes in the process stream.
The quality of the final effluent in terms
of total organic content was established.
This included determination of free oil;
dissolved, nonvolatile, organic com-
pounds; and volatile hydrocarbons.
Special attention was given to aromatic
hydrocarbons and their role and fate in
the treatment process.
To obtain the necessary information,
the organic composition of the process
stream was established at various
stages of treatment, and rates of
reduction in concentrations of sus-
pended oil, dissolved nonvolatile or-
ganics, and purgeable hydrocarbons
were determined.
The analytical procedures for the
determination of purgeable hydro-
carbons and dissolved and suspended
organic fractions were carried out as
follows. Purgeable hydrocarbons, com-
posed largely of benzene, toluene,
xylenes, and ethylbenzene, were
sparged by nitrogen and adsorbed in
activated charcoal tubes. This was
followed by desorption into carbon
disulfide using reaction vessels equipped
with Mmmert* caps. The desorbed
extract was analyzed by gas chroma-
tograph for purgeable hydrocarbons. An
800- to 1000-fold concentration of
hydrocarbons was realized using this
procedure.
After ultrasonation of the sample, the
total nonvolatile organic content was
determined by total organic carbon
(TOC) analysis. Following this procedure,
suspended oil was removed by
Millipore® filtration (a 0.45-micron
filter), and the filtrate was re-analyzed
by the TOC analyzer. The difference
between total nonvolatile and dissolved,
nonvolatile, organic content cor-
responded to suspended organic matter.
Quality assurance procedures included
contamination checks; blank deter-
minations; duplicate or triplicate anal-
yses; and documentation of recoveries,
accuracy, and precision of all methods
used
Results
Cook Inlet, Alaska,
Production Field
Trading Bay, Alaska,
Production Facility
Four offshore platforms at this
production facility supply gross fluid for
onshore processing. The processing
includes separation of oil from water in
a battery of heater-treaters, and a multi-
stage treatment process for produced
water. The produced water treatment
plant includes three gravity separators,
two gas flotation units, and two water
retention pits. The facility is capable of
processing 131,000 barrels of gross fluid
per day. Its typical production is 67,000
barrels of oil and 62,000 barrels of
produced water per day. Additionally,
"Mention of trade names or commercial products
does not constitute endorsement or recommenda-
tion for use
28,000 MCFPD (million cubic feet per
day) of natural gas are produced.
To characterize the chemical compo-
sition of the process stream, the
following four sampling stations were
selected: Station 1, effluent from the
heater-treater; Station 2, effluent from
the gravity separator; Station 3, effluent
from the gas flotation unit; and Station
4, effluent from the retention pit (final
effluent)
Three sets of samples were collected
at each sampling station at discrete time
intervals and analyzed for suspended
oil; dissolved, nonvolatile, organic
matter; and volatile hydrocarbons. The
results are reported in Table 1. The
stepwise reduction of various organic
fractions present in produced water is
also depicted in Table 1.
The analysis of the reported data
indicates that the treatment process is
effective in reducing suspended oil and
volatile aliphatic hydrocarbon concen-
trations. A 97% reduction in suspended
organic matter resulted in a effluent
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 purgeable aromatic
hydrocarbons. A reduction of only 30%
was realized, and treated effluent
contained, on average, 6 mg C/L of
purgeable 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, the dis-
solved organic content of the final
effluent was significantly higher than
that of untreated effluent from the
heater-treater. The increase in concen-
tration of dissolved, nonvolatile, organic
matter, in all cases, took place in the
initial stages of produced water treat-
ment (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 com-
pounds might be an additional factor in
the formation of water-soluble organic
matter. When essentially anaerobic
produced waters are exposed to an
oxygen environment at relatively high
temperatures (usually above 100°F),
autocatalytic processes might lead to
oxidation of some components of the
organic matter present in produced
water, resulting in the formation of
water-soluble, oxygenated, organic
compounds.
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Table 1. Stepwise Reduction of Organic Content in Process Water by the
Treatment Process, Trading Bay, Alaska. Production Facility, January 23,
1980
Effluents (concentration in mg C/L)
Organic Composition
Suspended petroleum
Reduced by (%)
Dissolved organics
Reduced by (%)
Volatile hydrocardons
Reduced by (%)
• Aromatic
Reduced by (%)
• Aliphatic
Reduced by (%)
Heater-
Treater
148
293
13.1
7.9
5.0
Gravity
Separator
38
(74.3)
409
H
11.2
(14.5)
7.7
(2.5)
3.6
(28.0)
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
(-)
6.9
(47.3)
5.6
(29. 1)
1.3
(74.0)
% Reduction =
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1.1 mg/L; toluene, 0.8 mg/L; and
xylenes/ethylbenzene, 0.3 mg/L.
Treated effluents from six offshore
oil-producing platforms in the Gulf of
Mexico were also examined for priority
pollutants. Sampling, preservation, and
transport of samples were carried out in
accordance with EPA procedures as
reported in the Federal Register (Decem-
ber 3 and 18, 1979). Collected samples
were analyzed for purgeables, acid-
neutral, base-neutral, and metallic
priority pollutants.
Consistently present m all treated
effluents were three priority pollutants
in the purgeable group (benzene,
toluene, and ethylbenzene), and one
priority pollutant in the acid-neutral
group (phenol). Lower concentrations of
naphthalene (base-neutral group) were
found intermittently. No pesticides were
found in the effluent.
Average concentrations of organic
priority pollutants found consistently in
effluents discharged from offshore
operations in the Gulf of Mexico were as
follows:
Concentration,
Pollutant fjg/L
Benzene
Toluene
Ethylbenzene
Phenol
836
2074
101
480
Treated effluents were examined for
13 priority pollutant metals: antimony
(Sb), arsenic (As), beryllium (Be),
cadmium (Cd), chromium (Cr), copper
(Cu), lead (Pb), mercury (Hg), nickel (Ni),
selenium (Se), silver (Ag), thallium (Tl),
and zinc (Zn). Chromium (Cr) and lead
(Pb) were found in the effluent from
every platform examined. Lead was
found in the greatest concentration,
averaging 597//g/L Chromium averaged
260 fjg/L. Nickel, zinc, copper, silver,
cadmium, and beryllium were found
intermittently. Nickel was present in
concentrations ranging from 68 to 1674
fjg/L, copper in the concentration range
of <25 to 137 fJig/L, and silver in a
concentration range of <1 to 152//g/L
Cadmium was present in a concentra-
tion range of <25 to 56 //g/L; the
concentration range for beryllium was
<1 to 4 //g/L, and zinc was found in a
concentration range of <25 to 640
//g/L. Concentrations of antimony,
arsenic, mercury, selenium and thallium
were generally below the limit detection
limits of the methods used.
The generated data indicate that
significant amounts of priority pollutant
metals 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 priority
pollutants (benzene, toluene, ethyl-
benzene, and phenol) constitute the
principal contribution of toxicants
discharged from offshore oil producing
platforms.
The full report was submitted in
partial fulfillment of Contract No. 68-
03-2648 by Rockwell International
under the sponsorship of the U.S.
Environmental Protection Agency.
Ihor Lysyj is with Rockwell International, Newbury Park, CA 91320.
John S. Farlow is the EPA Project Officer (see below).
The complete report, entitled "Chemical Composition of Produced Water at
Some Offshore Oil Platforms," (Order No. PB 82-22 7 489; Cost: $9.00, subject
to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield. VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Oil and Hazardous Materials Spills Branch
Municipal Environmental Research Laboratory-Cincinnati
U.S. Environmental Protection Agency
Edison, NJ 08837
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Postage and
Fees Paid
Environmental
Protection
Agency
EPA 335
Official Business
Penalty for Private Use $300
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