--> ABSTRACT: Source and Charge Risk in the Deepwater Kwanza Basin, Offshore Angola, West Africa, by Gary Cole, Bruce Farrer, Alan Yu, Jim Brooks, and Bernie Bernard; #90906(2001)

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Gary Cole1, Bruce Farrer1, Alan Yu1, Jim Brooks2, Bernie Bernard2

(1) BHP Petroleum, Houston, TX
(2) TDI-Brooks International Inc, Houston, TX

ABSTRACT: Source and Charge Risk in the Deepwater Kwanza Basin, Offshore Angola, West Africa

Large volumes of petroleum have been discovered in the deepwater offshore Lower Congo basin of Angola, but the deepwater Kwanza basin to the south remains unexplored. Since no wells have been drilled, the exploration risks remain relatively high for source presence, maturity, and charging (migration of hydrocarbons) of potential structures and traps. This paper will address how those risks were evaluated using seepage, surface heat flow probes, and 2D fluid flow modeling.

Evidence for an actively working petroleum system are several macroseeps above shallow salt piercement structures that have been typed to a marine marl source origin. From wells on the shelf and from DSDP364 the most likely source interval is the basal Albian marls, but there may be potential marine source rocks within the pre-salt sag sequence. DSDP364 data suggests a source interval of 100+ meters thickness with excellent oil-prone source quality. Data from the sag sequence suggests a thinner source thickness (40-75m), but with excellent oil-prone character.

The Albian marls are expulsion mature in the deep sediment troughs, though volumes expelled are a critical risk. Constraining the heat flows, hence maturity, is a critical factor in the deepwater Kwanza. Heat flow probes suggest similar to slightly higher heat flows than shelf wells. The sag sequence can contribute hydrocarbon volumes through the salt withdrawal windows, thereby lowering charge risks. 2D fluid flow models showed that the main structures could be charged using the heat flow probe data from the deepwater region.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado