Reservoir Implications of Attached and Detached Lobe Complexes in a Base-of-Slope Clinothem from the SW Karoo Basin, South Africa

Attached deepwater channel-to-lobe systems are commonly observed and described in modern and ancient deepwater systems around the world. However, the description and recognition of systems where lobes are spatially detached from their feeder channels is rare. The extensive exposures (>4500 km2) of slope to base-of-slope to basin-floor systems in Units C-F of the Fort Brown Formation in the Permian Laingsburg depocentre provide an opportunity to describe and differentiate between attached and detached lobe systems.

Units C and D include entrenched channel systems that pass downslope through levee-confined channels to attached lobe complexes over distances of >30km. Units E and F are characterised by up-dip upper slope valleys filled mainly by mudstone and siltstone. Down-dip transitions are complex, and the sandy and thick lobe complexes are detached. The detachment areas show thin facies associations of distal levee fringes and areas of soft sediment deformation. Establishment of the detached systems suggest a more abrupt break-in-slope possibly related to the underlying topography on Units C and D.

This dataset provides an exploration scale insight and understanding of how different segments of a prograding slope evolved over time in terms of gradient, morphology and hence the degree to which sand was stored or bypassed to the basin floor for attached and detached systems. The study also suggests that up-dip seal geometries and the distribution of sedimentary facies and architectural elements at reservoir scale are complex but predictable.
 

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California