--> Abstract: The Sespe Oil Fields: A Possible Kinetic Trap with a Subthrust Source, by M. S. Clark, P. G. Lillis, and G. Gregory; #90992 (1993).

Datapages, Inc.Print this page

CLARK, MICHAEL S., ARCO Oil and Gas Company, Bakersfield, CA, PAUL G. LILLIS, U.S. Geological Survey, Littleton, CO, and GLENN GREGORY, Santa Fe Energy, Bakersfield, CA

ABSTRACT: The Sespe Oil Fields: A Possible Kinetic Trap with a Subthrust Source

The Little Sespe, Tar Creek, Topatopa, Foot of the Hills, and Sections 23 and 26 fields comprise the Sespe oil fields. Since 1887, these fields have produced 42 million bbl of oil and 50 bcf of gas from the upper plate of the San Cayetano thrust. Although several Tertiary formations produce oil, fractured nonmarine redbeds of the Upper Eocene to Oligocene Sespe Formation account for 90% of the cumulative and current production.

Historically, the Sespe oils were assumed to be derived from Eocene shales (1-2% total organic carbon [TOC]) in the San Cayetano overthrust. However, biomarker and isotope data indicate that the oils are derived from Miocene shales (3-5% TOC) of the subthrust Monterey Formation. If so, secondary oil migration across the San Cayetano thrust from subthrust source rocks into overthrust reservoirs is required.

Tertiary oil migration is also evident: tar seeps west of the fields result from oil leaking updip out of upper plate reservoirs. Also, tar seeps along the San Cayetano thrust result from oil leaking out of subthrust reservoirs and/or source rocks. Furthermore, the field may be a "kinetic trap" with subthrust sources supplying oil to overthrust reservoirs. In other words, oil produced from the field is continually replenished by new supplies migrating in from below, and oil not produced slowly migrates to surface tar seeps and is lost. Since fractures associated with through-going, upper plate faults may be migration conduits, fractured upper plate reservoirs along these faults, and oil-filled subthrust reservoirs below the faults are potential exploration targets.

AAPG Search and Discovery Article #90992©1993 AAPG Pacific Section Meeting, Long Beach, California, May 5-7, 1993.