Status of the 10-Pattern Steamflood, Kern River Field, California

Summary The 10-pattern steamflood was converted to water injection in Sept. 1975 after 7 years of operation. Recovery is now 59 % of the presteam oil in place (OIP), with 22 % of this oil produced during the waterflood. Poststeam water injection apparently works best in reservoirs with large hot and unaffected zones remaining at the end of steam injection. Introduction Finding a way to end a steamflood project has been a problem for many operators. Usually this is done by stopping steam injection at the economic limit on the steam/oil ratio (SOR) and producing the reservoir to its new economic limit without steam assistance. Simulation studies conducted by Chevron U.S.A. Inc. have shown that higher ultimate recovery was possible by injecting water after a steamflood. This subsequent recovery results from heat scavenging (areally and vertically) and pressure maintenance effects. Maintaining reservoir pressure aided well productivity, prevented lateral resaturation of the depleted zone by oil from outside steamdrive areas, and prevented possible subsidence. Project economics also are improved because fuel is not needed to generate steam for the recovery of this additional oil. A successful poststeam water-injection project was reported previously. This project followed an unsuccessful steam injection program. A similar poststeam project, using a mixture of air and water, also has been reported. To our knowledge, no other poststeam waterinjection projects currently exist. Our first application of poststeam water injection was in the 10-pattern steamflood, Section 3 of the Kern River field. Steam injection began in Sept. 1968. The project was converted to cold-water injection in Sept. 1975. A previous papers described this project and its performance through Sept. 1973. Our paper updates the project's performance and status as of Jan. 1, 1981. Project Description The changes in well completions, operating practices, surface facilities and reservoir data since the first report are discussed in the following Fig. 1 shows the location and status of all wells in the project. Well Completions No temperature observation wells have been added or reworked since the beginning of the steamflood. Two of the 14 observation wells, T5-1 and T5-6, are no longer used because of apparent cement breakdowns. The 10 injection wells were 5 1/2-in. jet-perforated completions without packers. All injectors were completed in the middle of the drive zone, although originally this was not recognized. None of the injection wells have required work since completion. Wellhead injection pressures during the final steamflood period ranged from 150 to 200 psi. All injection wells have been on vacuum since water injection began. Even a change in April 1979 to unfiltered produced water apparently has not hurt injectivity. Thirty-three producers now are included in the project. Well 12-4 was drilled in Jan. 1977 to replace Well 163, which was in poor mechanical condition. Well 12-4 was completed with a 6 5/8-in. liner with 40-mesh slots. Producer 7-7 was redrilled in May 1977 to sidetrack a collapsed liner. It was completed the same way as the previous wells but with 50-mesh slots. All producers in the project have slotted liners opened to other producing intervals. Slot plugging and lack of control of placement during steam stimulations are the major drawbacks to liner completions. JPT P. 2251^