API Publ 4717:2002 pdf download

API Publ 4717:2002 pdf download.Predictors of Water-soluble Organics(wSos) in Produced Water—
Literature Review.
2.2.4 Petroleum Hydrocarbons
Petroleum hydrocarbons arc thc organic components of greatest ensironmenial concern in produced 5441cr. Petrolcum hydrocarbons mcasurcd as oil and grease by infrared spectromelxy) account for 25 to 65% of the TOC in produced waler samples from Cou& lnkt (Lysyj. 19821 and 8.5 Lu 16% of the TOC in produced water samples from the Gulf of Mexico analyzed by Neff ci at (198.9). Ii should be poimed out that standard methods for analysis of oil and grease (e.g.. EPA gravimetnc Methods 413.1 and 1664 and infrared Method 41 ft. U arc not specilie for petroleum hydrocarbons and measure several other compounds in produced watel- (e.g., organic acids), in addition to petroleum hydrocarbons Hiuwn Cl a. 1992: Otto and Amok!. 1996).
The soluhility of petroleum hydrocarbons in water decreases as their size (molecular weight) increases (McAuIift. 1966:
Eastcou ci aL, 1988. Because the oiL/water separator equipment is efl’,cieni in removing oil droplets hut not dissolved oil from the produced water, most of the petroleum hydrocarbons remaining in the produced water after treatment are low molecular weight aromatic and saturated hydrocarbons that are dissolved in the produced water.
Volatile Aromatic Hydrocarbons. The most abundant hydrocarbons in produced watcr are the onc-nng arornatI hydrocarbons, ben,ene. toluenc. ethylbeniene. and zyknes (the BTEX compounds) and low’ molecular weight saturated hydrocarbons. BTEX may be present in produced water from different sources at concentrations ranging from 0.068 to occasionally as high 601) mgL (Table 2). In the North Sea, and piuhobly elsewhere, produced waler horn gas wells usually contains higher concentrations of HTEX than produced water from oil wells Stephenson Ct al., 19941. Produced waters from wells in the northwestern Gulf of Mexico contain 0.068 to 38 mgt total BTEX I Ne0 1997). Benzene often is the most abundant BTEX compound in produced water, followed by toluene TabIe 9). Exhylbenzene and the three xylene isomers usually are present at only a small fraction of the concentrations of henzene and toluene. Trimethyl- and tetramcthyl-benzcnes usually arc present at much lower concentrations than BTEX.
Saturated Hydrocarbons. Saturated (aliphatic) hydrocarbons or alkanes with molecular weights in the range of those of HTEX usually arc present at much lower concentrations (usually less than half) than the monoaromatic hydrocarbons in produced waters Middkditch. 1981; Saner. 1981; Neff et al., 1989). For example. two samples of produced water from coastal Louisiana analyzed by Neff ci a). (1989) contained 1.09102.14 mg.L Cl through C8 alkanes arid 2.43 to 95l mg/L BTEX. This is due in large part to the much greater aqueous solubility of HTEX than of saturated hydrocarbons of similar molecular weight tMcAulitfc. 1966).
Nomtal pairatlins from n-C10 to n-Ci, are generally much less abundant than BTEX in produced water (Table 10). Often. the most abundant normal alkane is in the Ci to C16 range and abuiidance decreases with increasing molecular weight. This is due to the volatility of the low molecular weight alkanes and the extremely low aqueous solubility of alkanes with mote than about 16 carbons (Coates ci a).. 198.5). In a typical crude oil, the concentration of n-paraftins decreases with increasing molecular weight and this trend is reflected in the relative concentrations of alkanes in produced water.
Alkanes have much lower aqueous soluhilities than aromatic hydrocarbons of similar molecubr weight. l’herefore. some of the alkancs in produced water, particularly the higher molecular weight ones. may he associated with dispersed oil droplets in the produced water. For cxaiiiple. the solubility of n-alkanes decreases with increasing molecular weight from I 14/I. br tridecane (n-C1) to less than 0.(XXXX)()6 igt for tetracosane (n-C24). These solubilities are lower than concentrations of thcsc alkanes in many produced waters (Table 10). iiidwaiing that the higher molecular weight alkaiies are not in solution in the produced water. The oiL’water separator system is designed to efficiently reniose oil droplets from the produced water:
thereftn. there is a strong inverse con’elatinn between the efficiency of oil/water separation and the concentration of nalkanes in produced water.
Polycyclic Aromatic Hydrocarbons (PAHs). Polycyclic aromatic hydrncarbons PAl-l also called polynuclear arumaOc hydiucwbuus,. delincd as hydrs.arbons containing two or inure fused aromatic rings, air the petroleum hydrocarbons of greatest ens ironmental concern in produced water. because of their toxicity and persistence in the marine ens ironnient (Nell’. 1987). Concentrations of total PAHs in produced water typically range from about 0.08 to 3,0 mgi. Table 2). Naphthalcnc and occa’ionally phcnanthrvnc and their alkyl homologucs we the only PAHs that arc sometimes present at higher than trace concentrations (Table II). Thcsc lowcr molecular weight PAHs often are present at higher concentrations in produced waler from gas wells than in produced waler from oil wells Stephenson ci al.. 1994 s.
Individual higher molecular weight PAHs. such as henzo(a)pyrene. rarely are present in produced water at concentrations greaser than about 0.0001 mg/I. The aqueous soluhility of beniota)pyrene is so low 5=0,0038 mgi) and its affinity for the oil phase so high slog K 6.04j that it would not be expected to be present in sol Wino in produced water. Crude oils rarely contain more than about I ppm benio(a5pyrene (Nell. 1979). Thus, high molecular weight PAHs. such as hento4a)pyrene. are not expected in produced water, unless the produced water contains a high concentration of dispersed oil droplets.