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The Challenges of Hydrocarbon Exploration in a Deepwater Complex Salt Cored Fold and Thrust Belt, Block 31 Angola

Geoffrey S. Hill
BP Exploration Operating Co. Ltd, Middlesex, United Kingdom

Block 31, offshore Angola is an area of approximately 5000sq.km with water depths between 1500m and 2500m of water. Much of the block has a near surface allochthonous salt canopy. As a result of gravitational sliding and substantial synchronous salt flow, this canopy overlies and is part of a fold and thrust belt at the base of the slope region of the Lower Congo Basin.

As a result significant variations in fold style and salt canopy development are observed across the block. In the east, there are elongated folds and thrusts with many individual salt canopies. Here a number of discoveries have been made in the open basins around these salt bodies. Further west in Block 31 however, the geometries are structurally more complex with the development of large, opposing fore and back-thrusts and amalgamated salt canopy extrusions. Accurate trap definition has been and remains a key determinant of exploration success in both extra and sub-salt areas.

The block 31 Contractor Group has embarked on an exhaustive imaging program to realize the block potential, bringing together expertise from deepwater salt basins around the world, in particular capitalizing on significant experience in the US Gulf of Mexico. The seismic data has been processed conventionally, and enhanced by prestack time Previous HitmigrationNext Hit to optimize extra salt attributes. In parallel with this effort the group has undertaken a significant pre-stack depth Previous HitmigrationNext Hit program using a combination of existing and newly developed Previous HitKirchhoffTop and Wave Equation seismic processing techniques. These techniques have quantified the prospectivity over around two thirds of the block. In order to fully explore the potential the group has therefore undertaken a new seismic survey, specifically designed to image in the most difficult parts of this challenging block.