Seismic-Based Stratigraphic Architecture of a Structurally Deformed Carbonate Shelf

The offshore Prospect K is an undrilled, faulted structure that is 10s square kms in area and part of a much larger, up to 1 km thick, basinward-thinning low angle carbonate system that is perched inboard a large escarpment margin. Careful 3D seismic mapping of faults and flattening on key horizons was critical to reconstruct depositional architectures and stratigraphic relationships prior to deformation. Non-layer-cake, complex stratal architectures within the carbonate accumulation were observed in seismic, including significant thickness changes of internal units, downlapping and toplapping clinoformal geometries, mounded topography, shelf margins, and stratigraphic pinchouts. Based on the reconstructed 3D arrangement of these architectures, a three-stage stratigraphic evolution was developed for the carbonate system: 1) a lower downstepping, forced regressive progradational shelf system capped with a karsted sequence boundary defined by toplap; 2) a middle retrogradational, landward-thickening shelf system with internal mounded buildup and infill phases overlain by an interpreted maximum flooding surface; and 3) an upper, weakly prograding low-angle ramp system that thins basinward and develops large-scale embayment paleogeography. Utilizing this framework and internal geometries, shallow platform/ramp, grainstone margin, reefal buildup, grainy slope, and muddy distal facies, as well as karst-prone intervals, were predicted across the dataset, and equated to high-, mid-, and low-quality reservoir facies. This seismic-based geologic framework was the basis for evaluation of recoverable resource within the prospect and exploration well planning optimization. From a carbonate systems standpoint, this study emphasizes the potential and often overlooked stratal complexity and facies heterogeneity within low angle carbonate accumulations.