Summary The Teak field, a mature oil field offshore southeast Trinidad, has produced266 million bbl oil since 1972. Production is from Pliocene sandstonereservoirs in a Pliocene sandstone reservoirs in a complexly faulted anticline. This paper summarizes the history and geology of Teak field, describes itsoil-producing reservoirs, and discusses the mature-field development strategyused since 1988, including case histories of two 1989 developmentprospects. Introduction The Teak field, the fourth largest oil field in Trinidad, is located 25miles off the south-east coast of the island in 190 ft of water (Fig. 1). Discovered by Amoco Production Co. in 1969, Teak has produced 266 million bblof oil and 1.1 trillion scf of gas from 1972 through 1990. Teak is a mature oilfield with significant depletion after its first 19 years of production. Despite a steep natural decline rate of 25%/yr, the field has respondedfavorably to renewed development drilling since 1989. A steady downward trendin production rate reversed, and the field achieved its highest rate in almost5 years in July 1990. A primary factor in the reversal of the decline rate wasa deliberate multidisciplinary team approach to reservoir development. Geology Structural Setting. The Teak field is located in a regionalcompressional-wrench terrain about 40 miles south of the current Caribbean and South American plate boundary along the El Pilar fault (Fig. 1). The fieldproduces hydrocarbons from Pliocene sandstones from 4,000 to 14,000 ft belowsea level. Hydrocarbons are trapped in a steep anticlinal structure along aneast/west-trending compressional ridge bisected by a large fault (Fig. 2). Thisfault dips east-northeast at 35 to 45 degrees, with vertical offset of 2,000 to3,000 ft, splitting the field into two separate hydrocarbon accumulations: oiltrapped to the west on the upthrown side of the fault and gas trapped to theeast on the downthrown side of the fault. In addition to normal offset, Fault Fexhibits left-lateral wrenching, indicated by displacement of the downthrownstructural crest about 1 mile north of the upthrown crest. This paper focusesprimarily on the upthrown oil reservoirs, which are arranged as stackedthree-way closures behind the major sealing Fault F and are between 4,000 and12,000 ft subsea (ss) (Fig. 3), informally called the Teak A-C-E field. The Teak structure is characterized by fairly steep bed dips that average 10degrees and steepen locally to more than 30 degrees. Bed dips are locallyvariable in both direction and magnitude. The structural geometry iscomplicated by myriad cross-cutting normal faults that segment the field intonumerous compartments. The oil accumulation up-thrown to Fault F is separatedinto two major fault blocks by Fault F (800 to 1,500 ft vertical offset) andseveral minor fault blocks. About 90% of the Teak field oil produced to datehas been trapped upthrown to both Faults F and F2, although deeper reservoirshave been (discovered and produced between these faults. Stratigraphy and Petrology. Teak oil reservoirs span an 8,700-ft-thickstratigraphic section in the Pliocene that contains approximately 60 % sand and 40% shale. Teak sands are typically very fine-grained (from 0.06 to 0.12 mm ingrain size) and extremely well-sorted, and average more than 90% quartz withlittle or no visible cement. Porosities average 27 to 33%. Teak shales Porosities average 27 to 33%. Teak shales exhibit a variable resistivity andgamma ray log response, unlike clean shales typical of the U.S. Gulf of Mexico. Shale lithologies vary from argillaceous shales to arenaceous mudstones, andtextures vary from soft to well-indurated and phyllitic. Oil-producing sandsexhibit no appreciable stratigraphic thickness variation across theoil-productive area. The Pliocene producing section is 10 to 20% thicker on thedownthrown side of Fault F, but individual sands maintain an excellentcorrelation across the field. The environment of deposition for the Pliocenesands is probably a broad, shallow Pliocene sands is probably a broad, shallowmarine shelf proximal to the Orinoco delta, where strong, steady coastalcurrents provided a uniform energy regime. Oil Reservoirs Reservoir and Fluid Parameters. High-quality crude oil, 27 to 33 degrees API, has been produced from 17 different sandstone reservoirs (Fig. 3 and Table1). Individual sands vary from 10 to 440 ft in thickness. Sand porosities rangefrom 18 to 33%, decreasing slightly with depth. Initial water saturationsaverage 25%, with residual oil saturation of 20%. Hydrocarbon columns rangefrom 170 to 900 ft of oil with thin gas caps. April 1991 P. 392

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThis paper outlines the successful integration of subsurface, water handling, well surveillance and production operations teams across the North Kuwait asset to significantly improve the operating procedure for waterflooding the Sabiriyah Mauddud field. This effort required a new way of managing this reservoir in NK: a multifaceted approach of balancing voidage with injection, conducting extensive surveillance/analysis within the reservoir to assess the efficacy of various courses of action and, most significantly, adjusting various teams' "key performance indicators" (KPIs) to align injection and production allowables with sound reservoir management principles.An innovative, unified information management system was used to monitor voidage replacement ratio (VRR) to provide a basis for pattern balancing. Extensive surveillance operations provides the data necessary to monitor individual pattern balance, watercut performance, optimize areal sweep efficiency by adjusting injection and production allowables, assist in planning water shutoff operations, and design new completions.Waterflooding the Cretaceous Mauddud reservoir is in an early stage of operations. Water injection commenced in 12 of 17 predrilled waterflood patterns in 2000. These wells were drilled on an inverted nine-spot pattern with spacing of 250 acres per well to quickly provide coverage over the major portion of the reservoir. Surveillance data indicates the reservoir is relatively well connected. Pattern VRR, pressures, and watercuts were somewhat out of balance prior to engaging in this effort. Now, individual waterflood pattern balance is significantly improved and the field-wide VRR is ~1.Sound reservoir surveillance and waterflood management procedures implemented within a diverse group of teams that have performance goals aligned with "best practice" has resulted in effectively re-balancing this major waterflood.This effective integration of teams retains the flexibility to adjust for an ongoing development of this super giant field.

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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.