William R. Morris¹, Mark H Scheihing², De Ville Wickens³

(1) Phillips Alaska, Inc, Anchorage, AK
(2) Phillips Alaska Inc, 700 G Street, Anchorage, AK
(3) Department of Geology, University of Stellenbosch, Stellenbosch, South Africa

ABSTRACT: Reservoir Architecture of Turbidite Elements, Permian Tanqua Karoo, South Africa

The Skoorsteenberg Formation, is a well-exposed turbidite system where outcrops are of sufficient scale to document the geometries and stratigraphic relationships of turbidite elements. Sand-prone turbidite elements represented include channel thalwegs, aggradational and erosional channels, crevasse channels and splays, levees and layered and amalgamated lobes. Each turbidite element is characterized by different reservoir geometries and properties. Proximal channel-fill deposits associated with levee-overbank systems occur as laterally-stacked channel thalweg complexes (<656 feet wide, 16 feet thick) within larger (>26,000' wide) levee systems. More basinward channel types include, aggradational channels (over 3280 feet wide, 82 feet thick), or erosional channels (1640 feet wide, 59 feet thick) cut into levee deposits and back-filled by channel aggradation. Packages of sandy levee-overbank deposits extend well over 4920 feet away from channel axes. Such packages may exceed 90% net sand but have low kv/kh ratios. Associated crevasse channels (up to 1410 feet wide, 85 feet thick) have a complex fill architecture. Individual fan lobes, are commonly off-stacked and show an upward increase in degree of amalgamation. Distal lobe deposits are less well amalgamated. The kv/ kh ratio is highest in the aggradational and erosional channel fills, followed by channel thalweg, amalgamated lobes, layered lobes, crevasse channels, and levee deposits. Subsurface field analogs, however, indicate that permeability and porosity are highest in channel thalwag followed by aggradational channels, amalgamated lobes, layered lobes, crevasse channels, crevasse splays and lastly by levee deposits

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