Chapter 4 Effect of Biodegradation and Water Washing on Crude oil Composition Susan e. palmer Amoco Production Company Tulsa, Oklahoma, U.s.A INTRODUCTION Eganhouse and Calder, 1976; May et al, 1978a, b; Lafargue and Barker, 1988). Extensive review articles covering The study of crude oil geochemistry becomes difficult work done prior to 1985 on biodegradation and water when crude oils are altered by microbial action(biodegra washing have been prepared by Milner et al.(1977)and dation)and/or water washing. These processes can alter Connan( 1984). These two reviews give an overview of parameters used to compare oils when determining the effects of biodegradation and water washing gleaned genetic relationships (oil-oil correlation), depositional from the many exemplary papers found in the literature environments, and time of oil generation (i.e. thermal Also, Lafargue and Barker(1988)have reviewed and maturity of the source rock at the time of oil generation discussed data obtained from laboratory water washing and expulsion ). Much of this knowledge comes from experiments and present their own observations and histories of such occurrences through the years(e.g chapter is to compile and present Winters and Williams, 1969; Bailey et al., 1973a, b, the results of these studies and review articles in an abbre- Rubinstein et al., 1977; Connan et al, 1975, 1980; Seifert viated form to aid the explorationist in understanding the and moldowan, 1979: Rullkotter and Wendish 1982 Volkman et al, 1983: Momper and williams, 1984; Palmer, regard, the reader is directed to the literature for details of In addition, microbiologists and petroleum individual studies. Results of more recent studies geochemists have studied the action of bacteria on (1985-1988) are also included here. Examples of para ters and hydrocarbon distributions demonstrating the petroleum in the laboratory (e. g McKenna, 1972, effects of biodegradation and water washing are given to Horowitz et al., 1975; Jobson et al, 1979: Connan, 1981; aid the reader in recognizing altered oils. Because many Goodwin et al., 1983). Some workers have isolated products of bacterial metabolism of crude oils or classes of geochemical laboratory groups have developed their own hydrocarbons(e.g, Gibson, 1976 Higgens and gilbert, ways to portray data, some of these techniques will be 1978; Cripps and Watkinson, 1978; Cain, 1980; Mackenzie referenced in this discussion. Organic geochemical et al., 1983). Connan(1984) illustrates the metabolic parameters and types of hydrocarbon classes referred to products recognized by some of these workers and others. here are defined in the Glossary at the back of this volt Products of aerobic degradation are most often organic cids and CO. Anaerobic bacteria can live on the metabo- GEOLOGICAL CONSTRAINTS AND lites of the aerobes but do not grow on hydrocarbons. PHYSICOCHEMICAl CONdItIoNS tion is only sligh FOR BIODEGRADATION AND Alteration of crude oil by water washing has been indi- ctly studied in the laboratory through determination of WATER WASHING yater solubilities of individual hydrocarbons and The processes of microbial degradation and water mixtures of several hydrocarbons and by studying washing of crude oils occur when certain conditions are compositional changes of whole crude oils( e.g., met. Milner et al. (1977) and Connan(1984 )have outlined McAuliffe, 1966, 1980; Bailey et al., 1973b, Price, 1976; the requirements for both processes in their reviewChapter 4 Effect of Biodegradation and Water Washing on Crude Oil Composition Susan E. Palmer Amoco Production Company Tulsa, Oklahoma, U.S.A. INTRODUCTION The study of crude oil geochemistry becomes difficult when crude oils are altered by microbial action (biodegra￾dation) and/or water washing. These processes can alter parameters used to compare oils when determining genetic relationships (oil-oil correlation), depositional environments, and time of oil generation (i.e., thermal maturity of the source rock at the time of oil generation and expulsion). Much of this knowledge comes from petroleum geochemists who have been documenting case histories of such occurrences through the years (e.g., Winters and Williams, 1969; Bailey et al., 1973a, b; Rubinstein et al., 1977; Connan et al., 1975, 1980; Seifert and Moldowan, 1979; Rullkotter and Wendish, 1982; Volkman et al., 1983; Momper and Williams, 1984; Palmer, 1984; Williams etal., 1986) In addition, microbiologists and petroleum geochemists have studied the action of bacteria on petroleum in the laboratory (e.g., McKenna, 1972; Horowitz et al., 1975; Jobson et al., 1979; Connan, 1981; Goodwin et al., 1983). Some workers have isolated products of bacterial metabolism of crude oils or classes of hydrocarbons (e.g., Gibson, 1976; Higgens and Gilbert, 1978; Cripps and Watkinson, 1978; Cain, 1980; Mackenzie et al., 1983). Connan (1984) illustrates the metabolic products recognized by some of these workers and others. Products of aerobic degradation are most often organic acids and CQ2. Anaerobic bacteria can live on the metabo￾lites of the aerobes but do not grow on hydrocarbons. Thus, the impact of anaerobic bacteria on oil biodegrada￾tion is only slight. Alteration of crude oil by water washing has been indi￾rectly studied in the laboratory through determination of water solubilities of individual hydrocarbons and mixtures of several hydrocarbons and by studying compositional changes of whole crude oils (e.g., McAuliffe, 1966, 1980; Bailey et al., 1973b, Price, 1976; Eganhouse and Calder, 1976; May et al., 1978a, b; Lafargue and Barker, 1988). Extensive review articles covering work done prior to 1985 on biodegradation and water washing have been prepared by Milner et al. (1977) and Connan (1984). These two reviews give an overview of the effects of biodegradation and water washing gleaned from the many exemplary papers found in the literature. Also, Lafargue and Barker (1988) have reviewed and discussed data obtained from laboratory water washing experiments and present their own observations and conclusions. The purpose of this chapter is to compile and present the results of these studies and review articles in an abbre￾viated form to aid the explorationist in understanding the effects of biodegradation and water washing. In this regard, the reader is directed to the literature for details of individual studies. Results of more recent studies (1985-1988) are also included here. Examples of parame￾ters and hydrocarbon distributions demonstrating the effects of biodegradation and water washing are given to aid the reader in recognizing altered oils. Because many geochemical laboratory groups have developed their own ways to portray data, some of these techniques will be referenced in this discussion. Organic geochemical parameters and types of hydrocarbon classes referred to here are defined in the Glossary at the back of this volume. GEOLOGICAL CONSTRAINTS AND PHYSICOCHEMICAL CONDITIONS FOR BIODEGRADATION AND WATER WASHING The processes of microbial degradation and water washing of crude oils occur when certain conditions are met. Milner et al. (1977) and Connan (1984) have outlined the requirements for both processes in their review 47