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.