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The AAPG/Datapages Combined Publications Database

Pacific Section of AAPG


Tomorrow's Oil from Today's Provinces: Selected Papers Presented at the 51st Annual Meeting, AAPG Pacific Section, in San Francisco, 1976
Pages 19-38

Reservoir and Source Bed History in the Great Valley, California

D. L. Zieglar, J. H. Spotts


The application of geochemical concepts along with reservoir relationships (porosity-permeability-depth) should help focus exploratory efforts on the favorable parts of geologic trends. Porosity data from 165 producing reservoirs ranging in age from Upper Cretaceous to Pleistocene show that the “best reservoirs” lose porosity at a rate of approximately 1.52% per 1,000 feet of burial. Reservoirs on the large amplitude folds on the westside of the San Joaquin Valley have a more rapid loss with depth. A crossplot of porosity-permeability indicates a “best reservoir” relationship of a 10-fold increase in permeability for each increase of 7 porosity units.

Within the Great Valley four major depocenters are definable with isopach data. Each has had a different source bed history. Upper Cretaceous continental margin sediments contain largely structured organic material which is believed to be the source of gas in the Sacramento Valley fields. Although a Tertiary depocenter exists in the Delta area, it did not subside enough to place Paleocene and Eocene source beds into the thermal zone for oil and gas generation. Gas trapped in Paleocene and Eocene reservoirs must have migrated from more deeply buried Cretaceous source beds.

Tertiary beds in the Buttonwillow and Tejon depocenters in the San Joaquin Valley contain large amounts of sapropelic organic material which is believed to be the source of oil and gas in the San Joaquin Valley fields. Source beds in the Buttonwillow depocenter have been in the thermal zone for generation for only the last five or so million years. In marked contrast source beds in the Tejon depocenter started subsiding into the thermal zone more than 15 million years ago.

Explorationists who recognize the “best reservoirs” and relate them to source, migration and trap parameters in undrilled areas will be successful in finding “Tomorrow’s Oil From Today’s Provinces.”

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