Abstract Several families of thiophenic organosulfur compounds (primarily benzo- and dibenzothiophenes) show promise for distinguishing oils derived from carbonate sources versus siliciclastic sources. This observation is based on analyses, using high-resolution gas chromatography coupled with a flame photometric detector, of several representative oils derived from carbonate sources (Smackover and Sunniland Formations, southeastern United States; Burgan and Minagish, Kuwait; and the Khatiyah Formation, Dubai) and, for comparison, of oils from siliciclastic sources (Ekofisk, North Sea; McKee, Texas; Muddy/Dakota, Wyoming; Beaverhill Lake, Alberta; and Klasaman, Indonesia). Some of the distinguishing features of carbonate-derived oils are an abundance of benzothiophenes, a fairly equal distribution among the dibenzothiophenes, and a distinctive distribution of methyldibenzothiophene isomers. Conversely, oils derived from siliciclastic sources commonly show low concentrations of benzothiophenes, decreasing amounts of dibenzothiophenes, and a different pattern in methyldibenzothiophene isomers. The distinguishing features of carbonate-derived oils are applicable through the main phase of oil generation. Additional thermal maturity results in a significant reduction in the amounts of benzothiophenes and a redistribution of methyldibenzothiophene isomers, making the differences between carbonate- and siliciclastic-derived oils less distinctive. However, in these cases the distribution of mono-, di-, and trimethyl substituted dibenzothiophenes is generally relatively uniform in carbonate oils, while siliciclastic oils show decreasing amounts of dimethyl- and trimethyldibenzothiophenes relative to methyldibenzothiophenes. Used in conjunction with such other geochemical parameters as total sulfur content, n-alkane compositions, and sterane/triterpane compositions, thiophenic organosulfur analysis provides a useful tool for oil-oil and oil-source-rock correlations as exemplified by a study of 20 oils from the Salawati basin, Indonesia.

Abstract A suite of common-source crude oils and tar sands from Murray and Garvin counties, Oklahoma, were analyzed in detail to define the physical and chemical effects of progressive biodegradation on a crude oil. Biodegradation decreases the gravity from 32° to 4°API and increases the sulfur from 0.6 to 1.6 wt % and metals content from 47 to 293 ppm. The changes in chemical class compositions are a decrease in saturates from 55 to 20 wt %, an increase in polars from 21 to 41 wt %, and an increase in asphaltenes from 2 to 21 wt% The chemical fossil composition is affected. The n-alkanes, isoprenoids, light aromatics, and light thiophenes are completely removed, with a resultant concentration of naphthenes and heavy or highly branched aromatics and thiophenes. In the most severely degraded samples, steranes are partially removed. Diasteranes and triaromatic steranes, however, appear to be resistant to bacterial attack.