--> Abstract: Seismic Evidence for'Heel-Toe' Structural Rotation, 96-G Prospect, Cabinda, Offshore Angola, by Pete J. Chimney; #90914(2000)

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Pete J. Chimney1
(1) Chevron Overseas Petroleum, San Ramon, CA

Abstract: Seismic evidence for'heel-toe' structural rotation, 96-G prospect, Cabinda, offshore Angola

The 96-G prospect is located in Area A, Cabinda, offshore Angola. The prospect was defined in 1995 using the Malongo-Limba 3D seismic dataset and drilled in January-February, 1999 as the 84-49X well in the Limba SW field.

The stratigraphic section offshore Cabinda is divided in pre-salt lacustrine and post-salt marine salt, sandstone/shale sections. The primary exploration targets in the prospect were sandstones of the post-salt Vermelha Formation.

The post-salt structural style in Cabinda is characterized by large, down-to-the-southwest listric faults while sole out at the base of the Loeme Salt allowing thick rafts of Cretaceous age sediments to slide downslope. The salt is wadded up into ridges below structural highs and is thin or absent between structural culminations at the Vermelha level. Rotation above the salt causes strong east-northeast closing dips at Vermelha and Pinda levels.

The structure at the 96-G prospect was mapped at the top Vermelha as a tilted horst block with strong counter-regional west to southwest structural dip. The structural evolution of the Limba SW and Limba structural blocks was examined with five time-flattened seismic sections and then compared to the modern structural configuration to develop a conceptual model for fault block formation and rotation.

The 96-G block exihibits classic "heal-toe" type rotation, that is the paleo-high rotated due to salt removal through time down into a structurally low position. The former structurally low growth section rotated in a structural high. Sand distribution from well control and seismic amplitude analysis supports the "heel-toe" rotation model.

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