4. Effect of Biodegradation and Water Washing on Crude Oil Composition 51 (a NONDEGRADED OIL 一,2、a() SEVERELY BIODEGRADED OIL e’·之52 √“NM 28A8 MM 253-.-20-1220130 car to Czs distributions(m/z =21n)of (a) a nondegraded oil and (b a severely biodegraded oil. Normal sterar -11 and 15-22)are consumed by bacteria in(b), leaving an abundance of rearranged steranes(peaks 1-7 and 12-13) re 5 for names of individual steranes. tetracyclic compounds, the 8, 14-seco-hopanes, are formed Water Washin by opening the C ring(ring number 3 out of 5) ( Rullkotter and Wendish, 1982). In such cases, demethylated hopanes in Water washing is most readily recognized by cha the composition of the gasoline-range hydrocarbons can also be present and the steranes may be only slightly because these compounds are more water soluble than th processes can operate to produce severely biodegraded given carbon number, ring formation, unsaturation, and required to allow specific bacteria to grow on oils. would expect that when water washing occurs, aromatic The C1 to C2 three-ring naphthenes(tricyclic terpanes) hydrocarbons of a given carbon number would decrease survive extreme biodegradation, although demethylated first, followed by naphthenes, branched paraffins, and n tricyclic terpanes have been tentatively identified(e.g, paraffins. Generally, the loss of benzene and toluene is a Howell et al., 1984; Philp, 1985a). Because of their resis- good indicator that water washing has occurred.These tance to biodegradation, tricyclic terpanes have been used low molecular weight aromatics are also biodegradable, for oil-oil correlation in severely biodegraded oils. Their however, their high water solubilities make them useful distributions also supply information concerning deposi- indicators of water washing. Other indicators of water onal environments(e. g, Zumberge, 1987) washing are the loss of ethy naphthalenes relative to As previously mentioned, the stable carbon isoto dimethylnaphthalenes(Eganhouse and Calder, 1976)and composition of crude oils can also be altered by biodegra- possibly(as discussed in the previous section)the loss of dation, although not in a consistent manner. For example, C2o and C2 triaromatic steranes wardroper et al., 1984) in a 42-day simulated oil biodegradation study, Stahl Experimental water washing studies by Lafargue and (1980)observed that the saturated hydrocarbon fraction Barker(1988)do support the loss of gasoline-range (less was enriched inC(ie, more positive 8 C values), but than C1s)aromatic hydrocarbons relative to naphthenes he isot ition of the aromatic hydrocarbon and paraffins in line with the solubility studies previously fraction remained unchanged. Sofer(1984)and Momper noted. and williams(1984)showed that the saturated fraction of An example of the effect of water washing on the Cl naturally biodegraded oils is also enriched in c. hydrocarbon composition involved a field study of However, field examples showing no or little change in Philippine oils having abundant sulfur-containing isotopic composition or changes in both the saturated and aromatic hydrocarbons( dibenzothiophenes). Based on the aromatic fractions have also been reported(Sofer, 1984). idea that heteroatomic compounds are more water soluble Connan(1984)has reviewed other studies in which the than aromatic, cyclic, branched, and straight-chain hydro isotopic composition of crude oil fractions other than the carbons(e-g, Price, 1976), water washing was thought by saturated hydrocarbons also become enriched Palmer (1984)to cause the loss of dibenzothiophene 12H8S)and methyldibenzothiophene(C13H1oS)relative4. Effect of Biodegradation and Water Washing on Crude Oil Composition 51 < 217 . b l :0 6 6-4 (a) NONDEGRADED OIL c.6;S4 c-^:4=i ?Z:42 iao-. = io;5s9 (b) SEVERELY BIODEGRADED OIL 1:0s r.4:rt.j ^^iS4 .^H' : 72)42 7S|36 78|36 12 4 9| 1 6 " 19 a, • » w># ' i l l 3 ,!' w^ miwy is Du ieo.j ebb '2898 Figure 3. C27 to C» distributions (nVz = 217) of (a) a nondegraded oil and (b) a severely biodegraded oil. Normal steranes (peaks 8-11 and 15-22) are consumed by bacteria in (b), leaving an abundance of rearranged steranes (peaks 1-7 and 12-13). See Figure 5 for names of individual steranes. tetracyclic compounds, the 8,14-seco-hopanes, are formed by opening the C ring (ring number 3 out of 5) (Rullkotter and Wendish, 1982). In such cases, demefhylated hopanes can also be present and the steranes may be only slightly altered. These examples suggest that various degradative processes can operate to produce severely biodegraded oils. Perhaps certain environmental conditions are required to allow specific bacteria to grow on oils. The C19 to C26 three-ring naphthenes (tricyclic terpanes) survive extreme biodegradation, although demefhylated tricyclic terpanes have been tentatively identified (e.g., Howell et al., 1984; Philp, 1985a). Because of their resis￾tance to biodegradation, tricyclic terpanes have been used for oil-oil correlation in severely biodegraded oils. Their distributions also supply information concerning deposi￾tional environments (e.g., Zumberge, 1987). As previously mentioned, the stable carbon isotopic composition of crude oils can also be altered by biodegra￾dation, although not in a consistent manner. For example, in a 42-day simulated oil biodegradation study, Stahl (1980) observed that the saturated hydrocarbon fraction was enriched in 13C (i.e., more positive #3C values), but the isotopic composition of the aromatic hydrocarbon fraction remained unchanged. Sofer (1984) and Momper and Williams (1984) showed that the saturated fraction of naturally biodegraded oils is also enriched in 13C. However, field examples showing no or little change in isotopic composition or changes in both the saturated and aromatic fractions have also been reported (Sofer, 1984). Connan (1984) has reviewed other studies in which the isotopic composition of crude oil fractions other than the saturated hydrocarbons also become enriched in1 13C Water Washing Water washing is most readily recognized by changes in the composition of the gasoline-range hydrocarbons because these compounds are more water soluble than the C15+ hydrocarbons (McAuliffe, 1966; Price, 1976). For a given carbon number, ring formation, unsaturation, and branching cause an increase in water solubility. Thus, one would expect that when water washing occurs, aromatic hydrocarbons of a given carbon number would decrease first, followed by naphthenes, branched paraffins, and n￾paraffins. Generally, the loss of benzene and toluene is a good indicator that water washing has occurred. These low molecular weight aromatics are also biodegradable; however, their high water solubilities make them useful indicators of water washing. Other indicators of water washing are the loss of ethylnaphthalenes relative to dimethylnaphthalenes (Eganhouse and Calder, 1976) and possibly (as discussed in the previous section) the loss of C20 and C21 triaromatic steranes (Wardroper et al., 1984). Experimental water washing studies by Lafargue and Barker (1988) do support the loss of gasoline-range (kss￾than-Cis) aromatic hydrocarbons relative to naphthenes and paraffins in line with the solubility studies previously noted. An example of the effect of water washing on the Q54- hydrocarbon composition involved a field study of Philippine oils having abundant sulfur-containing aromatic hydrocarbons (dibenzothiophenes). Based on the idea that heteroatomic compounds are more water soluble than aromatic, cyclic, branched, and straight-chain hydro￾carbons (e.g., Price, 1976), water washing was thought by Palmer (1984) to cause the loss of dibenzothiophene (G2H8S) and methyldibenzothiophene (C13H10S) relative