Seismic-Based Geologic Framework and Reservoir Prediction of a Backstepping Isolated Carbonate Platform

The offshore Prospect W is an undrilled, isolated carbonate platform structure with over 1 km of depositional relief, steep slopes, and up to 5 km across in its youngest stages. High quality 3D seismic images a terraced peripheral morphology, the classic ‘wedding cake’ margin signature of a backstepping isolated carbonate platform, as well as complex, non-layer-cake stratal architecture internal to backstepping surfaces. Key stratal geometries observed between backsteps include: 1) mounded or buildup surfaces interpreted as depositional topography generated during high accommodation settings; 2) downlapping clinoforms interpreted as progradation during low accommodation settings; 3) toplap indicating minimal platform-top accumulation and potential exposure; and 4) shingled architectures interpreted as carbonate debris complexes suggesting margin collapse. Based on these criteria, five sequences were mapped across the structure consisting of mounded transgressive systems tracts and prograding highstands capped by sequence boundaries defined by toplap. Within this framework, shallow buildup, shallow platform, lithified margin, coarse slope, and fine toeset facies were interpreted, as well as collapse-prone margins and their associated debris aprons, internal baffles, possible karst horizons, and draping drowning facies. Utilizing this facies motif and seismic amplitude anomalies potentially indicating non-matrix porosity, fracture-karst-prone, matrix-dominated, and non-reservoir regions were predicted. Ahead of the drill bit, this purely seismic-based predictive framework enables more granular analyses for resource evaluation, improved high grading of exploration well locations, and considerably more detailed well prognoses in terms of pay prediction. Furthermore, this study underscores the often-oversimplified internal complexity of isolated carbonate platforms and their backstepping evolution.