Biomakers in oil shale: Occurrence and applications

Biological markers, compounds derived essentially unchanged from living organisms, are found in oil-bearing rocks, petroleum and most ancient sediments. We are investigating the variation in ratios of certain biomarkers in shale oils and their use as tracers for relating oil to source rock during in-situ retorting. We have produced oil samples at 12°C/min from 1- and 2-foot shale composites from three Green River formation cores and have measured the occurrence of several isoprenoid and sterane compounds using capillary gas chromatography of these oils. Because alkene/alkane ratios of most of these compounds depend strongly on pyrolysis temperature and/or heating rate, we use ratios of alkenes plus alkanes that are largely independent of heating rate and are thereby indicative of in-situ shale oil and perhaps petroleum. Variations in biomarker content with depth, grade, odd/even ratios, ene/ane ratios and nitrogen to organic carbon ratio have been studied and cross correlations have been determined between these various properties.