--> Abstract: Main Body B-Western 31S Waterflood, Elk Hills Field, Kern County, California, by M. L. Wilson and G. S. McJannet; #90992 (1993).

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WILSON, M. L., Bechtel Petroleum, Tupman, CA, and G. S. McJANNET, U.S. Department of Energy, Tupman, CA

ABSTRACT: Main Body B-Western 31S Waterflood, Elk Hills Field, Kern County, California

The Main Body B-Western 31S waterflood project occupies the entire 31S structure at Elk Hills. It includes 109 peripheral and pattern water injectors and 387 production wells. The project currently produces 20,000 BOPD. Water injection of 95,000 bbl/day maintains a reservoir pressure of 2300 psi. Water production has been kept at less than 50% of gross production through remedial programs that exclude water from downdip producers. As of August 1992, a total of 156 million bbl of oil had been produced of an original recoverable reserve of 244 million bbl.

The Main Body B-Western 31S reservoirs are amalgamated turbidity current deposits within the Miocene Stevens zone and have an overall thickness ranging up to 450 ft of net pay.

Although both the Main Body B and Western 31S sands had similar outer fan origins, slight differences in geometry have resulted in significant variations in the behavior of waterflooding. The Western 31S is somewhat channel-like and the resultant lack of lateral continuity has made propagation of flood fronts difficult. Near the base of the Main-Body B, relatively thin fining-upward sequences topped with relatively thick shales have produced tight reservoirs where flood fronts propagate very slowly. In contrast, the upper portion of the Main Body B was deposited with only brief periods of quiescence. The resultant reservoirs have many sand-on-sand contacts with vertical and lateral continuity that provide excellent waterflood propagation and recovery.

As the waterflood project matured, management emphasis shifted from simple pressure maintenance to oil recovery per layer. Although monitoring the waterflood includes production logging and production testing by layers, important data have been derived from open hole logging and coring of infill wells. Selective drilling has led to the recent assessment of reserves bypassed by principle flood fronts. Geologic studies defining the geometry and reservoir quality coupled with feasibility studies of cement squeezing, polymer squeezing, and packer isolation of watered out layers are testing the viability of producing these behind-the-flood-front reserves.

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