Forty Years of Improved Oil Recovery: Lessons from Low-Permeability Turbidites of the East Wilmington Field, California

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe U-P Ford zone in the Long Beach Unit of the East Wilmington Field consists of low-permeability (2-50 millidarcies) turbidites that have been waterflooded since field start-up. Forty years of successes and failures have provided valuable insights into how to best waterflood these reservoirs given their thin-bedded nature, lateral and vertical changes in reservoir quality, formation damage susceptibility, and sand control problems. Multiple techniques and technologies have been applied to describe their reservoir architecture, quantify reservoir performance, and extract the oil. This work has become more challenging as the waterflood has matured and will require the close integration of all disciplines to identify and exploit remaining opportunities.The gross thickness of U-P Ford zone is about 2100 feet, and depths to the top of the zone range from about 4200 to 4800 feet. The U-P interval is about 900 feet thick and consists of the AE, AF, AI, AK1, AL1, and AM subzones. The U-P has an average net-to-gross ratio of 0.25 and contains many thin sands separated by shales, as well as some thicker sands. The Ford interval is about 1200 feet thick and underlies the U-P interval. The Ford consists of the AO, AR, AU, AU2, AV, AW, AX, AX1, AY, AT, and AZ subzones. It has an average net-to-gross ratio of 0.45 and contains thicker sand units than the U-P, although many of the sand-rich intervals are frequently found in the aquifer. The major sandstone units show an overall thickening and higher net-to-gross values from west to east.Depositional Setting and Rock Properties. The interbedded sands and shales of the U-P Ford zone formed in a progradational, submarine-fan system trending from northwest to southeast 2 . The sands were deposited by sediment gravity flows that were funneled basinward by submarine canyons. These flows spread laterally across the surface of the fan to form lobes that exhibit compensating geometries. This pattern is characterized by the thick portion of an underlying lobe coinciding with the thin portion of an overlying lobe. Between