Effects of Biodegradation upon Porphyrin Biomarkers in Upper Mississippian Tar Sands and Related Oils, Southern Oklahoma
Gerald E. Michael, R. P. Philp
Organic molecules present in oils which show a structural relationship to their biological precursors are referred to as biomarkers. These compounds are becoming widely used in oil exploration for making oil-oil, oil-source rock correlations and undertaking maturation and migration studies in basin analysis. Treibs first discovered the presence of porphyrins in oils, shales, and coals over 50 years ago. Porphyrins are predominantly derived from chlorophyll precursors present in plants and bacteria. Studies of changes in porphyrin distributions with increasing maturation due to the effects of increased time of burial and temperature have been performed. However, little is known as to how their distributions change with migration, biodegradation, or water washing of oils.|
In the present study, 16 tar sand samples were extracted from drill core at depths ranging from 16 to 256 ft obtained from a tar sand quarry in the Ardmore basin, Carter County, Oklahoma. Surrounding oil samples and possible source rocks have also been analyzed to determine the source of the oil in the tar sands. The effects of biodegradation on the porphyrin distributions can be discerned from the effects of migration and maturation by comparing other biomarker distributions within the sands, related oils, and suspected source rocks. Biodegradation of the tar sand samples can be observed within the alkane and other biomarker distributions. The relative effects of biodegradation on biomarkers such as alkanes, steranes, and terpanes have been well documented. By using this information, it is possible to determine the extent of biodegradation or water washing necessary to alter the porphyrin distributions. Once this information has been determined, porphyrin distributions may be used to determine the degree of biodegradation in oils where other biomarkers have been already removed or where other effects, such as maturation or migration, have altered the distribution of the biomarkers beyond the extent to which they are useful for correlation purposes.
AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.