--> Benchmarking, Calibrating and Validating Exploration Prospects in Offshore Ghana Using Global Field/Reservoir Analogs

2018 AAPG International Conference and Exhibition

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Benchmarking, Calibrating and Validating Exploration Prospects in Offshore Ghana Using Global Field/Reservoir Analogs

Abstract

To fully explore the hydrocarbon potential and calibrate the defined prospects and leads in offshore Central Ghana, an analysis of global fields/reservoirs analogs has been performed to: 1) to validate the exploration targets and plays identified against those observed in global analog reservoirs ; 2) benchmark the defined Aptian/Albian exploration prospects against global field/reservoir analogs; 3) calibrate the uncertainty ranges in each of the volumetric calculation parameters for each exploration target with knowledge from global reservoir analogs; 4) describe an efficient analog workflow for the remaining exploration targets; and 5) provide a framework for assessing risk. Global analogs of 215 fields and 270 reservoirs have been used to analyze the exploration targets in the Aptian/Albian section offshore Central Ghana. The characteristics of these analog reservoirs are as follows: 1) Source rocks are of Kerogen Type II (57%), Type I (22%), Type III (20%) in shales (90%) deposited in marine shelf (45%), offshore lacustrine (26%) and deep marine (9%) environments; 2) Seals are mostly shale (73%) deposited in coastal shelf (44%), Deep Marine (17%) and Lacustrine (17%) environments; 3) Traps are of both structural (e.g. tilted fault block (32%), inversion anticline (11%), horst block (7%)) and stratigraphic (e.g. paleostructural subcrop (14%), and lateral depositional pinch-out (13%)). Most global reservoirs do not have seismic DHIs (86%); 4) Reservoirs are dominantly sandstones (81%) from shoreface-shelf (13%), braided river (12%), lacustrine river-delta (8%), lacustrine fan-delta (6%) and mixed influence delta (5%); 5) Hydrocarbons are dominantly oil (67%) with mean gravity of 33o API.; and 6) The P50 EUR is 226 MMBO and mean EUR is 706 MMBO. A Paleo-structural subcrop prospect is first benchmarked and secondly calibrated using global analogs in terms of trap, seal, reservoir, fluid and recovery factor parameters. The Monte Carlo modeling of recoverable oil volumes of the prospect is carried out using the closure distribution based on local geological mapping and using the statistical distributions of hydrocarbon fill ratio, net pay thickness, porosity, oil saturation, formation volume factors, and recovery factors from the global analogs. The analogs analysis contributed to the final assessment of the exploration targets and recoverable volumes of the prospects in offshore Ghana.