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Abstract: Petroleum Geology of Block 2, Offshore Congo Basin, Angola
1Texaco Angola Inc., Luanda, Angola
2Sonangol, Luanda, Angola
The major basins of Angola include the oil producing Congo and Kwanza Basins and the non-producing Benguela and Namibe Basins. Block 2 is located within the offshore portion of the Congo Basin which extends southwards from the Cabinda area to the Precambrian Ambrizete Spur, a basement high that marks the boundary between the Congo Basin and the Kwanza Basin. Dolomitized Albian-age Pinda formation carbonates are the primary reservoirs within Block 2. Tertiary (Eocene and Oligocene) turbidite sands are also locally oil-bearing on Block 2.
Northwards trending listric and antithetic faulting has resulted in a variety of oil-trap ping structures including simple rollovers and horst blocks. Salt rafting and down-to-the-basin (westwards) gravity sliding of Pinda "rafts" has resulted in a number of oil fields consisting of separated blocks of Pinda carbonate with variable oil-water contacts. Texaco (operator) and its partners, Sonangol, Braspetro and Total have recorded 3D seismic over all of the fields in Block 2 in order to optimize management of the Pinda and Tertiary reservoirs. Extensive core coverage has been obtained to develop a full understanding of the depositional environment and reservoir characteristics of the Pinda reservoirs.
Lombo East is an example of a Block 2 field producing from the Pinda formation. This field has produced over 80 million barrels of 40 degree API crude since its discovery in 1984. The Lombo East "raft" has a closure of 1600 acres, vertical relief of 250 meters and an oil column of 130 meters. The reservoir is a high-energy shoal facies with vugular porosity ranging between 15 and 20%. The Essungo fled is the only field on Block 2 which produces from the Tertiary. Essungo was discovered in 1975 and has produced 30 million barrels of oil to date. Sand deposition is interpreted to have occurred in a deep water environment. The average porosities within the field range from 16 to 22% and oil gravities vary between 32 and 39 degrees API.
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