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James P. Brandon1, Mark I. Smithard1, John R. Smith1, Tako Koning1, Eugénio Silva2
(1) Texaco Panama Inc - Angola, Luanda, Angola
(2) Sonangol, Luanda, Angola

Abstract: Discovery and development of the Estrela oil field (Pinda carbonate), lower Congo basin, offshore Angola

The Estrela field produces 37° API crude oil from Albian age Pinda carbonates along a shelf edge shoal trend within the northern Lower Congo Basin. Estrela is located in offshore Angola Block 2/85, and encompasses two independent closures that share a common structural spill point. Elongate, curvilinear-shaped reservoir blocks comprising both culminations, termed A and B, are the result of basinward listric faulting and lesser shoreward compensatory displacement. The Estrela-1 discovery well was drilled in 1990, encountering over 50 feet of porous, oil-bearing dolomite on the northwest plunging flank of the field. Net oil pay thickness inside the developed concession area averages 220 ft, but ranges as high as 450 ft. A total of eight producing wells currently flow at a combined rate of approximately 17,000 BOPD. Ultimate cumulative reserves are estimated above 50 MMBO. Geochemical correlation of crude samples indicate that the northern Estrela A and southern Estrela B hydrocarbon accumulations lie in distinctly separate reservoir compartments. Well control and 3D seismic mapping confirm the presence of a saddle between the respective closures, coincident with a change in regional structural grain.

High energy, oolite-oncolite precursor grainstones of the prospective Middle Pinda reservoir sequence have undergone partial early dolomitization, followed by later dissolution of remnant calcareous allochems. The resulting interconnected moldic pore system is pervasive across stacked shoaling cycles. A 3D reservoir model was built for the Estrela field, through an iterative process involving detailed geophysical interpretation of dipping dolomite layers truncated by an overlying erosional unconformity, multi-well log evaluation, and simulation to history match field performance.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana