New Models for Mixed Carbonate Siliciclastic Pinda System in Block 14, Offshore Angola

Younis Altobi¹, Art Saller², Greg Raskin¹, and Meghan Playton^2
1SASBU, Chevron, Houston, TX
²ETC, Chevron, Houston, TX

Pinda reservoirs in Angola Blocks 0 and 14 contain carbonate and siliciclastic material. Carbonate occurs as grain-rich carbonate beds (porous and nonporous), nonporous muddy carbonate beds, grains in sandstones, and cements in sandstones. Malange #1 discovered oil in the Pinda in eastern Block 14 in 2007. A regional study of the Pinda including Malange #1 provides a better understanding of depositional and diagenetic processes that control reservoir properties in the western part of Block 0 and eastern part of Block 14. Prograding siliciclastic shoreface sands grade upward into carbonate shoreface sands in the middle of the Upper Pinda in that area. The uppermost part of the Pinda is a transgressive unit containing carbonate shoals, thin sands and carbonate-rich muddy facies.

Carbonate grainstone shoals have produced significant amount of oil in Lomba Field (northwest Block 0), however, most carbonate beds in other Block 0 fields are non-reservoir units. Skeletal-intraclast grainstones in Lomba Field are up to 100 ft thick and 300-700 m wide, and have intergranular and vuggy porosity. Burrowed outer-shelf carbonate-rich beds are generally micritic and not porous. Micritic dolomites with limited reservoir quality were deposited in lagoons.
Porosity development is controlled by diagenesis including non-fabric selective dissolution and partial dolomitization. Carbonate cements in Pinda sandstones have retarded compaction in Pinda sandstones and helped preserve porosity during burial. Future exploration will target structural highs within Block 14 that contain porous sandstones and carbonate grainstones in the Upper Pinda.

AAPG International Conference and Exhibition, Cape Town, South Africa 2008 © AAPG Search and Discovery