Abstract: The Controls on Biodegradation in the San Joaquin Valley

CLAY, ELIZABETH R.,

The San Joaquin Valley contains over 2 billion barrels of producible oil, making it the second largest oil province in the continental United States. The greatest challenges with regard to oil production in this region are the viscosities of the oil.. The oils can be heavy and viscous for several reasons: thermal maturity (relatively immature oils are heavier than more mature oils from the same genetic group); and secondary processes such as waterwashing, reservoir fractionation, and biodegradation, all of which yield a heavier residue. The dominant cause of low API gravity (heavy) oils in the San Joaquin Valley is hypothesized to be biodegradation. Correlation of API gravities and viscosities with biodegradation biomarker parameters will support this hypothesis. This will be useful for well completion strategies to select zones that have producible oil in place. The conventional model of in-reservoir biodegradation is aerobic. The oil must come in contact with meteoric water for significant biodegradation to occur. However, anaerobic degradation does occur in situ in oil reservoirs. A series of aerobic and anaerobic experiments will show that a combination of both of these processes makes a more plausible model of in situ biodegradation in oil reservoirs. A more thorough understanding of the process of biodegradation and its relation to viscous, low API gravity oils would aid in the more efficient management of oil production in the San Joaquin Valley.

Search and Discovery Article #90945©1997 AAPG Pacific Section Meeting, Bakersfield, California