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Samuel K. Huisman1
(1) Louisiana State University, Baton Rouge, LA

Abstract: Reservoir Characterization of Fine-Grained Outer Sheet Sands, Tanqua Karoo, South Africa

Submarine turbidite systems continue to be important for hydrocarbon production. Much information is available from subsurface studies about the overall architecture of large fans. Little, however, is known about sub-seismic reservoir characterization of fine-grained submarine fans, connectivity of sands, or fans which are thinner than seismic resolution. Lack of good analog outcrop for fine-grained fans has prevented investigations of such properties.

The Tanqua Karoo of South Africa provides excellent outcrops of fine-grained, mud-rich bypassing system turbidites. The distal portion of Fan 3 permits detailed studies on reservoir characteristics, sand and shale bed connectivity/ continuity, and gamma ray profiles. Outcrops up to 2 km show that a few sandstone beds, some as thin as 50 cm, extend up to 2 km in strike direction. Compensationally stacked sand beds form potential reservoirs that reach 2 km in width by way of amalgamation with sandstones. Shale beds (interpreted as flow barriers), separating sandstone beds, can also spread 2 km in width. Average net-to-gross percentages in this "mud-rich" fan range from 80 to 85%. Such detailed information can only be obtained from outcrop studies. Although Fan 3 is thinner than seismic resolution, it proves thin sheet sands of submarine fans to be viable resource potentials. Data from this study yields a better understanding of the transport, depositional processes and reservoir characterisitics of such fans.

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