1、 Predictors of Water-soluble Organics (WS0s) in Produced WaterA Literature ReviewRegulatory and Scientific AffairsPUBLICATION NUMBER 4717MARCH 2002Predictors of Water-soluble Organics (WS0s) in Produced WaterA Literature ReviewRegulatory and Scientific AffairsPUBLICATION NUMBER 4717MARCH 2002PREPARE
2、D UNDER CONTRACT BY:Jerry M. Neff and Scott Stout, Battelle, Duxbury, MAFOREWORDAPI publications necessarily address problems of a general nature with respect to particularcircumstances, local, state, and federal laws and regulations should be reviewed.API is not undertaking to meet the duties of em
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8、, API Publishing Services, 1220 L Street, N.W., Washington, D.C. 20005.Copyright 2002 American Petroleum InstituteABSTRACTDischarge of treated produced water to offshore waters of the United States is regulated by NPDES permits.Current general permits for the discharge of produced water to Federal o
9、ffshore waters of the Gulf of Mexicohave total oil and grease limits of 42 mg/L (ppm) daily maximum and 29 mg/L monthly average. EPArequires oil and grease concentrations in produced water to be monitored by EPA Method 413.1 or 1664. Bothmethods are gravimetric. The methods tend to overestimate the
10、concentration of petroleum hydrocarbons inproduced water, due to interference from dissolved non-hydrocarbon chemicals. The objective of this report isto evaluate the chemical composition of produced water from oil and gas wells, and identify the water-solubleorganic chemicals (WSOs) in produced wat
11、er that interfere with gravimetric determination of oil and grease.An initial assessment is made of the physical and chemical properties of the produced water and theassociated fossil fuel reservoir, in an effort to predict which produced waters will contain high concentrationsof WSOs. Produced wate
12、r may contain up to 1,000 mg/L total organic carbon (TOC), most of it in solution. Most ofthe dissolved organic carbon in produced water is accounted for by C2through C5organic acid anions, suchas acetate, propionate, and butyrate. Acetic acid usually is the most abundant organic acid in produced wa
13、ter.These organic acids are identical to volatile organic acids produced by marine organisms and are not toxic orpersistent in the marine environment. A small fraction (usually less than 20%) of the dissolved organic matter in produced water is comprised oflow molecular weight alkanes and aromatic h
14、ydrocarbons. The most abundant dissolved hydrocarbons inmost produced waters are the aromatic hydrocarbons benzene, toluene, ethylbenzene, and xylenes (BTEX).BTEX concentrations usually are in the range of 0.07 to 500 mg/L. Benzene usually is the most abundant.Low concentrations of low molecular wei
15、ght alkanes (C5to C20) and traces of a few polycyclic aromatichydrocarbons (PAHs) also may be present in produced water. The concentration of total PAHs usually is lessthan about 2 mg/L. Naphthalene and alkyl naphthalenes usually are the most abundant.Phenols usually are present in produced water at
16、 concentrations lower than 20 mg/L. Phenol, C1-, and C2-phenols usually are the most abundant. Other dissolved hydrocarbon-like chemicals containing oxygen,sulfur, or nitrogen usually are present at trace concentrations. Produced water contains in solution most of the non-metal inorganic and metal i
17、ons found in seawater.Many produced waters, including most of those from the U.S. Gulf of Mexico, have a salinity (totaldissolved solids concentration) greater than that of sea water (35 g/kg). However, ionic ratios in producedwater may be different from those in sea water. A few metals may be prese
18、nt in produced water fromdifferent sources at concentrations substantially higher (1,000-fold or more) than their concentrations inclean natural sea water. The metals most frequently present in produced water at elevated concentrationsinclude barium, cadmium, chromium, copper, iron, lead, nickel, an
19、d zinc. Usually, only a few of thesemetals are present at elevated concentrations in a particular produced water sample. Produced water,particularly that from the Gulf of Mexico, contains radium isotopes (226Ra plus 228Ra) at concentrations upto about 2,800 pCi/L. Organic acids are the quantitativel
20、y most important WSOs in produced water that interfere with thegravimetric methods for determination of total oil and grease. Although they are not extracted efficientlywith the organic solvent used in the gravimetric methods (Freonor hexane), their concentrations in mostproduced waters are high eno
21、ugh that they contribute substantially to the mass of organic matter extractedfrom produced water. Treatment of the extract with silica gel (an option in Method 1664) decreases theamount of interfering non-hydrocarbon WSOs in the extract. Organic acids in petroleum or produced water are thought to f
22、orm by thermal degradation of oxygenatedorganic matter in source rocks or by hydrous pyrolysis of hydrocarbons. Organic acid anions are moresoluble in water than in oil and, so, partition into produced water from the oil in the reservoir. The optimumtemperature for these processes appears to be in t
23、he range of 80C to 120C. At lower reservoirtemperatures, microbial degradation of organic acids decreases their concentrations in the produced water.At higher reservoir temperatures, organic acids are unstable and undergo thermal decarboxylation, formingCO2and low molecular weight hydrocarbons (natu
24、ral gas). iiiBecause of these thermal processes, concentrations of total volatile organic acids in produced water tend toincrease with increasing temperature below about 80C, reach highest levels in reservoirs with temperaturesbetween about 80C and 120C, and decline in reservoirs with higher tempera
25、tures. However, manysecondary factors influence the concentration of organic acids in any given produced water. Thus, therelationship between temperature and organic acid concentration in produced water is only approximate. Itis not possible to use reservoir temperature alone to predict the concentr
26、ation of organic acids in producedwater. The main secondary factors affecting organic acid concentrations in produced water include thenature and amount of organic matter in source rocks, the age of the reservoir, the geology and migrationdistance between source rocks and the reservoir, and the sour
27、ces of connate water in the reservoir. The following recommendations are based on the results of this review: The optional silica gel cleanup step in Method 1664 should be used to remove most of the polarorganic chemicals that interfere with oil and grease measurement; and, Consistent correlations b
28、etween organic acid concentrations in produced water and physical/chemicalproperties of the hydrocarbon-bearing formation, the crude oil or gas, and/or the produced water itselfare needed, although the necessary composition and property data are rarely available. If such infor-mation can be obtained
29、 from operators, it may be possible to model the occurrence of organic acidsand total WSOs in produced water.ivACKNOWLEDGMENTSThe following participants are recognized for their contributions to this work:API STAFF CONTACTRoger Claff, Regulatory Analysis and Scientific Affairs DepartmentMEMBERS OF T
30、HE API OIL AND GREASE WORKGROUPSyed Ali, ChevronTexaco CorporationKris Bansal, Conoco, IncorporatedLarry Henry, ChevronTexaco CorporationSung-I Johnson, Phillips Petroleum CompanyTim Nedwed, ExxonMobil Upstream Research CompanyBhagwandas Patel, Equilon Enterprises, LLCJames Ray, Shell Oil CompanyLar
31、ry Reitsema, Marathon Oil CompanyJoseph Smith, ExxonMobil Upstream Research CompanyDonna Stevison, Marathon Oil CompanyZara Khatib, Shell Oil CompanyvTABLE OF CONTENTSPageSection1 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
32、 12 CHEMICAL COMPOSITION OF PRODUCED WATER. . . . . . . . . . . . . . . . . . . . . . 22.1 Origins of Produced Water. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22.2 Organic Chemicals in Produced Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
33、 . . . . 32.3 Inorganic Chemicals in Produced Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82.4 Production Chemicals in Produced Water. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 NATURE OF THE WATER-SOLUBLE ORGANIC MATTER IN PRODUCEDWATER . . . . . . . . .
34、 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133.1 WSOs in Produced Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133.2 Interference of WSOs with Oil DOE,1997) and from three offshore production f
35、acilities in Indonesia (Neff and Foster,1997). Concentrations are mg/L. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7viiPageSection10 Concentrations of n-alkanes in produced water from two platforms in coastal Loui-siana and two platforms in Thailand. Concentrations
36、 are mg/L. From Neff et al.(1989) and Battelle (1994). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 811 Concentrations of individual PAHs in seven produced waters from the U.S. Gulf ofMexico (DOE, 1997; OOC, 1997), three produced waters from Indonesia (Neff
37、 andFoster, 1997), and one produced water from Thailand (Battelle, 1994). Concentrations are mg/L. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 912 Concentration ranges of selected cyclic alkanes and heterocyclic compounds in pro-duced water from three pr
38、oduction treatment facilities in Indonesia. Concentrations are mg/L. From Neff and Foster (1997) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1013 Concentrations of several elements and inorganic ions in produced waters from dif-ferent geologic ages. Concentrations are mg/kg (ppm)
39、. From Collins (1975) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1114 Concentration ranges of several metals in produced water from seven platforms inthe northwestern Gulf of Mexico. From DOE (1997) and OOC (1997).Concentrations are mg/L. . . . . .
40、. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1115 Activities of natural 226radium and 228radium in produced water from the U.S. Gulfof Mexico. Activities are pCi/L. 1 picocurie (pCi) = 0.037 bequerels (BQ).From Neff (1997). . . . . . . . . . . . . . . . . . . . . . .
41、 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1116 Amounts of production chemicals used on production platforms in the North Seaand amounts discharged with produced water to the ocean or injected into a well.Masses are metric tons/year. Table from Hudgins (1994) . . . . . . . . . . . . .
42、. . . . . . 1317 Aqueous solubilities and values for log Kowfor several low molecular weight petro-leum hydrocarbons. Concentrations are mg/L. From TPH Criteria WorkingGroup (1997). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1418 Factors
43、 potentially influencing the concentration of organic acids in produced water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16viii1PREDICTORS OF WATER-SOLUBLE ORGANICS (WSOs) IN PRODUCED WATERA LITERATURE REVIEW1 IntroductionThe U.S. Environm
44、ental Protection Agency (EPA) or a state agency designated by EPA issues region wide (general) or site-specific National Pollutant Discharge Elimination System (NPDES) permits to regulate discharges of treated producedwater to State and Federal offshore waters of the United States. Produced water in
45、tended for ocean discharge is first treatedin various oil/water separation devices to remove dispersed oil droplets. Current general permits for Federal offshore watersof the Gulf of Mexico have limits for total oil and grease in produced water of 42 mg/L (ppm) daily maximum and 29 mg/Lmonthly avera
46、ge. EPA requires oil and grease concentrations in produced water to be monitored by EPA Method 413.1 or 1664 (EPA, 1983,1995). Both methods are gravimetric. Nonpolar and slightly polar organic matter in produced water is extracted withFreon(Method 413.1) or n-hexane (Method 1664). In Method 1664, th
47、e analyst has the option to treat the hexane extractwith silica gel to remove polar interfering compounds. The extract is dried and weighed to derive a concentration of totalextractable organic matter (total oil and grease). Although the oil and grease methods are inexpensive and easy to perform, th
48、ere are two technical problems that may haveimplications for the regulation of discharges of produced water to offshore marine waters. First, low-molecular-weight,volatile alkane and aromatic hydrocarbon (BTEX) analytes are lost by evaporation during sample processing. Second,many non-hydrocarbon or
49、ganics, and possibly some metals, are extracted by the solvent and measured as part of the totaloil and grease in produced water, even after extract cleanup with silica gel.Loss of volatile hydrocarbons is not a concern, since these chemicals are not persistent in surface waters and so are unlikelyto contribute to the toxicity of produced water plumes to marine animals (Neff, 1997). In a regulatory context, the secondproblem is more of an issue. The analytical methods may grossly overestimate the concentration of petroleumhydrocarbons in produced water if the concentration of n
