INCREASING HEAVY OIL RESERVES IN THE WILMINGTON OIL FIELD THROUGH ADVANCED RESERVOIR CHARACTERIZATION AND THERMAL PRODUCTION TECHNOLOGIES

Through June 2000, project work has been completed on the following activities: data preparation; basic reservoir engineering; developing a deterministic three dimensional (3-D) geologic model, a 3-D deterministic reservoir simulation model and a rock-log model; well drilling and completions; and surface facilities on the Fault Block II-A Tar (Tar II-A) Zone. Work is continuing on improving core analysis techniques, final reservoir tracer work, operational work and research studies to prevent thermal-related formation compaction in the Tar II-A steamflood area, and operational work on the Tar V steamflood pilot and Tar II-A post steamflood project. Work was discontinued on the stochastic geologic model and developing a 3-D stochastic thermal reservoir simulation model of the Tar II-A Zone so the project team could use the 3-D deterministic reservoir simulation model to provide alternatives for the Tar II-A post steamflood operations and shale compaction studies. The project team spent the third quarter 2000 revising the draft 1997-2000 Annual Report submitted last quarter, writing final reports on the research projects mentioned above, and operating the Tar II-A post-steamflood project and the Tar V horizontal well steamflood pilot. Thermal-related formation compaction is a concern of the project team due to observed surface subsidence in the local area above the Tar II-A steamflood project. On January 12, 1999, the steamflood project lost its inexpensive steam source from the Harbor Cogeneration Plant as a result of the recent deregulation of electrical power rates in California. An operational plan was developed and implemented to mitigate the effects of the two situations by injecting cold water into the flanks of the steamflood. The purpose of flank injection has been to increase and subsequently maintain reservoir pressures at a level that would fill-up the steam chests in the ''T'' and ''D'' sands before they can collapse and cause formation compaction and to prevent the steam chests from reoccurring. A new 3-D deterministic thermal reservoir simulation model was used to provide operations with the necessary water injection rates and allowable production rates by well to minimize future surface subsidence and to accurately project reservoir steam chest fill-up by October 1999. A geomechanics study and a separate reservoir simulation study have been performed to determine the possible indicators of formation compaction, the temperatures at which specific indicators are affected and the projected temperature profiles in the over and underburden shales over a ten year period following steam injection. Further geomechanics work should be conducted. It was believed that once steam chest fill-up occurred, the reservoir would act more like a waterflood and production and cold water injection could be operated at lower Injection to production ratios (I/P) and net injection rates. In mid-September 1999, net water injection was reduced substantially in the ''D'' sands following steam chest fill-up. This caused reservoir pressures to plummet about 100 psi within six weeks. Starting in late-October 1999, net ''D'' sand injection was increased and reservoir pressures increased back to steam chest fill-up pressures of 90% hydrostatic pressure by March 2000 and have been maintained through September 2000. When the ''T'' sands reached fill-up in October 1999, net ''T'' sand injection remained at a high rate through April 2000 and reservoir pressures stabilized at 98% hydrostatic pressure. The objective is to lower ''T'' sand pressure slowly to 90% hydrostatic. Net injection was reduced and ''T'' sand reservoir pressure was at 97% hydrostatic in September 2000. A more detailed discussion of the operational changes is in the Reservoir Management section of this report. A reservoir pressure monitoring program was developed as part of the poststeamflood reservoir management plan. This bi-monthly sonic fluid level program measures the static fluid levels in all idle wells an average of once a month