Development of a Mature Giant Offshore Oil Field, Teak Field, Trinidad

Abstract

ABSTRACT The Teak Field is located 25 miles off the southeast coast of Trinidad in 190 feet of water, and has produced 250 million barrels of oil in its first 18 years since 1972. The original oil-in-place is estimated at 740 million barrels and daily production peaked at 58,000 BOPD (barrels of oil per day) in 1975. Production declined to a minimum of 29,000 BOPD in 1988, but rebounded to 34,000 B0PD in 1989, due to renewed 1989 development drilling which has yielded encouraging early results, and reversed an earlier fairly steep production decline. The Teak Field produces very high quality crude oil, API 30-35 degrees, from a series of clean, very fine-grained Pliocene quartz sandstones, occurring at sub sea depths between 4,000 and 12,000 feet. Porosities average 21-33 percent. Reservoirs are normally pressured, and drive mechanisms range from depletion-drive to strong water drive. Primary oil recovery factors are 17 to 65 percent. Individual reservoirs are 10 to 440 feet thick, extending across 100 to 800acres. The field is a large anticline within a regional wrench terrain, with fairly steep bed dips averaging 10 degrees. The geometry of the structure is considerably complicated by numerous cross-cutting normal faults which segment the field. Traps are arranged as stacked 3-way closures behind a major sealing fault. Recently continued field development has benefited from a team study approach, utilizing a geologist, geophysicist and reservoir engineer in a study group, to generate detailed structure maps and accurate reservoir models. The group worked in close cooperation with operations personnel. Case histories are included for two 1989 development wells, which were completed at a cumulative rate of almost 9,000 BOPD, about 25 percent of the total field rate. The A-6XX well was drilled to recover bypassed attic oil pay in a layered reservoir in the central part of the field, while the E-3X well was drilled to the south flank of the field as a high risk field extension into a previously untested and unmapped fault block. The success of these two wells illustrates the value of a team study approach in optimizing production from a mature oil field. These field studies are continuing at Amoco Production Company. INTRODUCTION This paper summarizes the history of Teak Field1, describes the various oil producing reservoirs, and discusses mature-field development strategy employed by Amoco since 1988, including brief case histories of two 1989 oil development prospects. The Teak Field is the fourth largest oil field in Trinidad, located 25 miles off the southeast coast in 190 feet of water (Fig. 1). Discovered by Amoco Production Company in 1969, Teak has produced 250 million barrels of oil and about 1 trillion cubic feet of gas from 1972 through 1989. Teak is a mature oil field with significant depletion after its first 18 years of production. Despite a steep natural decline rate of 25 percent per year, the field has responded favorably to renewed development drilling in 1989, and reversed a steady downward trend in production rate, achieving its highest rate in four years in January, 1990.