AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Borehole Images as a Vital Tool to Constrain the Architecture of a Channelized Slope System, Karoo Basin, South Africa
(1) Geotechnology, Delft University of Technology, Delft, Netherlands.
(2) Strat Group, University of Liverpool, Liverpool, United Kingdom.
The complex geometry and lithofacies assemblages of submarine channel-levee slope system are difficult to unravel from well data alone. In a well-controlled analogue study in the Permian Fort Brown Formation (Laingsburg-Karoo Basin, South Africa) with excellent outcrop exposures six research wells were drilled to simulate data that are typically acquired from wells in oil and gas fields in similar depositional settings. The main lithofacies observed and mapped in the outcrop exposures could all be observed on the cores and were found to have typical expressions on the electrical borehole images. Once this validation was completed, it was possible to obtain complete lithofacies sequences from the borehole images, helped by the standard wireline logs. In addition, borehole images provided a diversity of directional indicators that, although rare, were found to be crucial in constraining the geometry of the system. These indicators include cross-bedding, climbing ripples, erosional surfaces, slump direction, and large-scale load structures. Combining the analysis of these directional data with the lithofacies assemblages provided a set of possibilities for the larger-scale geometry of the channel-levee system. Specifically, estimations on the channel orientations, the channel widths, and to some degree the extents of the levee units could be obtained. By including the general knowledge of a particular setting, as was the case in this relatively well-controlled experiment, and seismic interpretations these architectural models can be further constrained and refined, leading to more accurate estimations of the geometry and volumes of the different reservoir units, therefore providing a useful input for field development planning.