Abstract: Lacustrine Carbonate Reservoirs of Cabinda, Angola

Lomando, A. J. - Chevron Overseas Petroleum

Major production from lacustrine carbonate reservoirs occurs offshore West Africa and Brazil, and the onshore and offshore basins of eastern China. All of these areas and others hold significant opportunities for new discoveries and continued development of existing fields.

In Cabinda, Angola, a partnership among Chevron, Sonangol, Elf, and Agip has been actively producing from lacustrine carbonates since the 1970s.

There are five lacustrine carbonate fields in the Cabinda concession. Three of them, Takula, Malongo West, and Kambala, represent the spectrum of field types found in Angola and Brazil. In the southern part of the concession at Kambala Field, the nature of the upper and lower TOCA reservoirs is distinctly different, but both are the result of the interplay between primary depositional processes, structure, and later secondary diagenetic changes.

Malongo West Field, in the central part of the concession, is a stratigraphic trap developed on the eastern flank of a major intralake basement high. The carbonate accumulation is dominated by pelecypod-ostracod grainstones to mudstones which have been significantly leached by multiple periods of exposure.

In Takula Field, in the northern part of the concession, the TOCA is one of three main pay zones in the field and deposited on an intralake horst block known as the Takula High. Exposure created secondary porosity and the development of thick debris aprons.

The common thread that binds the fabric of these Cabinda fields are their complexity, and therefore may be the most challenging exploration targets in rift systems.

AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil