Use of Thiophenic Organosulfur Compounds in Characterizing Crude Oils Derived from Carbonate Versus Siliciclastic Sources
William B. Hughes, 1984. "Use of Thiophenic Organosulfur Compounds in Characterizing Crude Oils Derived from Carbonate Versus Siliciclastic Sources", Petroleum Geochemistry and Source Rock Potential of Carbonate Rocks, James G. Palacas
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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.