William G. Dickson¹, Al Danforth², Mark E. Odegard³
(1) Dickson International Geosciences (DIGs), Houston, TX
(2) Consulting Exploration Geologist, Houston, TX
(3) GETECH Inc. (Geophysical Exploration Technology), Sugarland, TX

Abstract: Gravity signatures of sediment systems – Predicting reservoir distribution in Angolan and Brazilian Basins

Petroleum exploration in the Tertiary sequences of West Africa and Brazil is resource-hungry, typically requiring large budget and staff to identify the prolific reservoir targets. Our recent regional study, SAMBA, of the South Atlantic Margin Basins, illustrates ways to improve this process.

There is a strong correlation between reservoir fairways and gravity signature on vertical derivative maps. Combining the underlying geology with enhanced gravity data from regional to sub-basin scale has allowed recognition of inter-raft sediment pathways and depocentres in Congo and Kwanza Basins, Angola, and basement control of entry points for Oligocene fans and bypass zones in the Campos Basin, Brazil.

Using gravity signatures of known sedimentary features, such as reservoir fairways, depocentres and source kitchens, the location and extent can be projected into areas covered only by gravity data. This is illustrated by projecting the locations of unconstrained seafloor fans offshore Angola.

At its current level of development, the technique has allowed exploration teams to focus their seismically oriented efforts on areas of greatest potential. This provides answers to exploration questions more quickly and clearly. The method can be extended using higher resolution gravity and bathymetry combined with additional gravity enhancements. These enhancements can be tuned to specific targets for each sub-basinal area.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana