Recognizing, Targeting and Developing Bypassed Pay in a Mature, Complexly Faulted, Multipay Oil Field, Teak Field, Trinidad and Tobago
Authors: Muller D.S. , Wharton S.R. , Hoffman K.S. 
Published: October 2008

Teak Field is a complexly faulted anticline discovered by Amoco Production Company in 1969 in one hundred ninety feet of water twenty-one miles offshore of Trinidad in the Columbus Basin1(Fig. 1). Production commenced in 1972. During the thirty years since discovery over 235 wellbores have been drilled into Teak reservoirs (Fig. 2), extracting 335 MMBO and 1.3 BCF of gas to date. Production has come from twenty-three reservoir intervals in a multitude of fault blocks.

Understanding the complex geometries of entrapment and patterns of fault-impacted fluid-flow is a critical component of drilling and repair well expense decision-making as Teak approaches its fourth decade of production. The task at Teak is complicated by poor seismic resolution over much of the field (Fig. 3). Three-dimensional geologic interpretive and visualization technology has played an increasingly important role in recognizing, evaluating, targeting, and successful drilling of stackable undrained compartments. The full threedimensional model has also been helpful in constructing well trajectories that permit successful avoidance of or adequate preparation for problematic pressure-depleted intervals.

Introduction

Since its discovery in 1969, Teak Field, offshore Trinidad, has proven to be both a worthy challenge and a gracious host to the development geologist. Multiple pay sands have been encountered within an overall domal geometry traversed by a complex of multigenerational, multi-orientation crosscutting faults. Production has been established from Pliocene sandstones at depths ranging from 4000 to 12,000 feet below sea level2. The "F Fault" is the main trapping fault for the oil accumulations at Teak (Fig. 4). The footwall reservoirs are primarily oil-bearing. Most of these upthrown oil traps are three-way high-side closures behind the F Fault, though some subsidiary low-side traps are present behind down to the west faults within the footwall of the F Fault. Hydrocarbon accumulations in the hanging wall of the F Fault contain primarily gas.

The F Fault is a high integrity seal, regardless of lithology in the hanging wall as demonstrated by water over sand relationship observed in the TA12B01 (Fig. 5)

Geology

Teak Field lies approximately 40 miles south of the El Pilar Fault, which defines the plate boundary between the Caribbean and South American plates3. The tectonic setting results in a complex interplay between transpressional features and apparent normal offset faults. Teak sits astride a transpressional ridge, and is bisected by the F Fault, with apparent vertical offset of 2000-3000' (Fig. 6) in the vicinity of the field. Offset dies out rapidly to the north and south. Offset of the crest of the field suggests that approximately 6000' of sinistral strike-slip has also occurred along the F Fault.

Teak Field produces from fine-grained, sedimentologically mature sandstone reservoirs deposited by the Orinoco River delta system4. The Eastern Venezuela Basin of which Trinidad is a part is filled with more than 40,000 feet of Orinoco-derived sediment of Cretaceous to Pleistocene age. Production at Teak occurs over approximately 9000 feet of stratigraphic section of Pliocene age5. Cement is largely absent except in the deepest reservoirs, and gravel-pack completions are required for the shallower sands. Although there is some thickening of the Pliocene section observed on the downthrown (eastern) side of the F Fault, there is excellent stratigraphic correlation within the field. Individual sands can be correlated with a high degree of confidence within the footwall of the F Fault. Thic