Hodgson, David¹, David Hodgetts¹, Stephen Flint¹, Nicholas Drinkwater², Erik Johannessen³ 
(1) University of Liverpool, Liverpool, United Kingdom 
(2) Schlumberger Cambridge Research, Cambridge, United Kingdom 
(3) Statoil, Stavanger, Norway

ABSTRACT: Reservoir Modeling of Deepwater Basin Floor Fans, Karoo Outcrops, South Africa 2: Insights into Fan Evolution and Reservoir Prediction

3-D reservoir models of the Karoo basin floor fans have provided insight into facies distributions and stacking patterns, not simply in 2-D dip sections but within the whole fan volume. Fourth order lowstand basin floor fans 1-4 are 35-60 m thick and stack in an overall progradational manner, with complications due to lateral switching. They are separated by 20-50 m of muddy turbidites and hemipelagic shales, interpreted as transgressive and highstand systems tracts. Each fan is built of 3-17 higher frequency (presumed 5th order) sequences, each comprised of a 2-20 m thick sandy lowstand and 0.5-5 m thick shaly transgressive/ highstand systems tracts. 4th and 5th order sequences typically stack in a progradational-aggradational-retrogradational pattern and exert an important control on shale geometries at reservoir scale. Highly amalgamated sheet turbidite zones (HASTZs) characterize the ‘mid-fan’ areas. The HASTZs are important because their axial zones are commonly characterized by sufficient erosion to locally connect with underlying sheet sandstones, although the topography of the basal surface is of low amplitude. In a reservoir this could result in pressure equilibration and the interpretation of good dynamic connectivity. Field mapping and 3-D visualization of the axial zones shows them to be dip-elongate scours, rather than continuous channels.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.