Exploration and Development of the Lombo East and Estrela Oil Fields: Typical Pinda Carbonate Fields in the Lower Congo Basin, Offshore Angola

Tako Koning¹ and Mark Smithard^2
1 Tullow Oil Angola, N/A, Angola
² ChevronTexaco Angola, N/A, Angola

In the shallow water area of the Lower Congo Basin south of the Zaire River, presently almost all oil production is from Albian-aged Pinda carbonate oil fields.

Lombo East Field: In this field the hydrocarbons are trapped in a high energy carbonate shoal facies. Regional subsidence and localized structuring formed the Lombo East raft. The reservoir consists of fine to coarse crystalline vugular dolomites with 15 to 20% porosity. The oil gravity is 40 degrees API. The field occurs within a 1600 acre closure with vertical relief of 250 meters and an oil column of 130 meters. The field has produced over 130 million barrels of oil to date. Maximum production from the field occurred in 1996 when 33,000 BOPD was achieved. Current production is about 5,000 BOPO.

Estrela Field: This field was discovered in 1990 and produces from Pinda carbonate shelf edge shoals. Oil gravity is 37 degrees API. The field consists of two separate closures which share a common structural spillpoint. Net pay thickness averages 65 meters and reaches a maximum of 135 meters. A total of 8 wells were producing at a combined rate of 17,000 BOPO in 2001. Ultimate cumulative oil is estimated at 50 million barrels oil.

The life and profitability of fields like Lombo East and Estrela can be significantly extended by utilization of state-of-the-art 3D seismic surveys, integrated geology, geophysics and reservoir engineering teamwork, and by the drilling of high angle infill and horizontal wells. Indeed, the drilling of precisely emplaced horizontal drain holes in the remaining thin oil columns in largely depleted fields like Lombo East has proven to be highly effective.