--> --> Petroleum Geology of Cameia Field, Deepwater Pre-Salt Kwanza Basin, Angola, West Africa

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Petroleum Geology of Cameia Field, Deepwater Pre-Salt Kwanza Basin, Angola, West Africa

Abstract

Cobalt International Energy, and partners Sonangol Pesquisa & Produção, Nazaki Oil & Gas and Alper Oil, discovered the Cameia field in 2012. The field is located in nearly 1700 m of water, and lies 100 km offshore in Angolan block 21. Cameia is a very large 4-way dip closure in an Aptian reservoir, located immediately below the base of salt. The discovery well, Cameia-1, found approximately 300 m of extremely high-quality reservoir in a mound-shaped biogenic build-up. The Cameia-2 well confirmed the presence of the mound reservoir, and also discovered potential reservoirs in the deeper synrift section. Extensive log and core data indicate the mound reservoir is a mixture of chert, dolomite and limestone. Microbial chert boundstone is a major reservoir type, and dolomite grainstones and packstones also comprise significant portions of the reservoir. Calcite-rich lithologies are present, but are commonly of poorer reservoir quality. Stacking patterns, structural position, and well and seismic correlations suggest the microbialites grew as amalgamated reefal complexes on a subaqueous lacustrine structural high. Textural evidence from core, and petrographic and isotope data, suggest the reef-building organisms secreted silica directly from lakes, which had water chemistries that were similar to modern East African rift lakes. Grainstones and packstones, along with carbonate mudstone, accumulated around and within the reef complexes. Much of the original boundstone porosity remains as vugs. The original mineralogy of the grainstones and packstones is uncertain, as most intervals have been heavily dolomitized. Nonetheless, many intervals retain good intercrystalline and interparticle porosity. Permeabilities, based on log, core and test data, are variable but can be very high, as demonstrated by the Cameia-1 drill stem test that reached a rate of 5010 stbopd and 14.3 mmscfgd, with minimal pressure drawdown. Development planning for the Cameia field is progressing rapidly, and contemplates a Floating Production Storage and Offloading facility with subsea wells.