1999 Abstract: McCaffrey and Kneller
Stratigraphic Trap Potential on the Margins of Confined Turbidite Systems: Optimized Well Placement and Process Controls on Trap vs. Leak
William
D. McCaffrey
School
of Earth Sciences
University of Leeds
Leeds LS2 9JT, UK
Benjamin
C. Kneller
School
of Earth Sciences
University of Leeds
Leeds LS2 9JT, UK
Abstract
Many turbidite-hosted fields rely on stratigraphic trapping on pinchout margins. In such fields, a key appraisal issue is characterization of the pinchout. In laterally or obliquely confined systems, for example, outcrop analog studies show that there are two end-member configurations. In end member (1), sand turbidites thin onto the confining surface, although the sandstone pinchout is commonly abrupt and individual events tend not to erode into earlier deposits. As a consequence of the poor connectivity between adjacent sandstones, targeted production wells must be drilled parallel or subparallel to the confining surface in order to sweep the reservoir effectively. In end member (2), turbidite sandstones commonly thicken toward the onlap slope, and individual events may incise into earlier deposits. Although slope angle, flow incidence angle, and flow steadiness all play a role in determining onlap character, we maintain that the principal control is flow magnitude, with smaller magnitude flows producing end member (1) and large-magnitude flows producing end member (2). As paleoflow magnitude may be assessed from core, it becomes possible to make reasonable estimates of onlap character, even using core from wells placed away from the field margins. Where the position of the slope is poorly constrained, it can be difficult to optimize well placement. However, systematic facies and paleoflow variations are seen in individual turbidite sandstones as they approach the onlap, and they can potentially be exploited to provide information on both slope presence and proximity.