KNAUER, L. C., and J. D. DAVISON, Bechtel Petroleum Operations Inc., Tupman, CA, H. V. WEYLAND, U.S. Department of Energy, Tupman, CA, and J. N. FRICKE, Chevron U.S.A., Tupman, CA

ABSTRACT: Pliocene Shallow Oil Zone Reservoirs, Elk Hills Field, San Joaquin Valley, California

The Pliocene depositional environment at Elk Hills was a fluvial-deltaic system controlled by a series of barrier-island paleoshorelines that prograded from west to east.

Intervals in the Shallow Oil zone (SOZ) which are productive include Olig, Calitroleum, Gusher, Wilhelm, Bittium, Sub-Mulinia, Mulinia, Sub-Scalez 2, Sub-Scalez 1, and Above Scalez.

Accumulation of hydrocarbons in the SOZ is controlled primarily by the Elk Hills anticline and secondarily by faulting and stratigraphic changes. The areal extent of the SOZ pools is greater than any of the other reservoirs, encompassing all or part of 48 sections or approximately 20,000 ac. The oil-productive sands occur at a drilled depth of 2000-5000 ft. There are 1431 SOZ wells of which 515 are currently on production.

Estimated original oil in place for the Pliocene reservoirs is 1251 million bbl. Total production through October 1992 was 442 million bbl with remaining recoverable reserves of 156 million bbl. Average daily production for October 1992 was 13,163 BOPD, 15,436 BWPD, and 5209 MCFGD.

Reservoir pressure varies from a high of 1650 psig in the Calitroleum to a low of 4 psig in the Sub-Scalez 1. Gravity drainage is the primary production mechanism in the younger eastern SOZ pools with solution gas drive being the primary production mechanism in the older western SOZ pools. Peripheral water influx affects portions of some of the pools.

Production decline over the last 3 yr is 4-5% and matches a hyperbolic curve. Remedial activity and drilling new wells have kept up with the optimum decline rate. Injection of natural gas and produced water is underway to repressurize the Sub-Scalez 1 in a fault block in the southeast corner of the pool.

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