A Novel Fit-for-Purpose Methodology for Predicting Pore Pressure Associated with Gas Hydrates in the Deep-Water Rakhine Basin, Bay of Bengal

Gas hydrates, solid crystalline substances composed of water and gas molecules with methane as the predominant component, are increasingly recognised as a significant industrial geohazard in oil and gas operations. Drilling deepwater targets is costly and risky, making reliable geohazard prediction and accurate well planning imperative. Understanding pore pressure is essential to avoid shallow hazards, as the riserless section is susceptible to fracturing given the narrow drilling margin and could even result in well loss. In the deep waters of the Rakhine Basin in the Bay of Bengal, the challenge was to distinguish the effects of cemented hydrates from overpressure, as they are acoustically fast and, at the base, create a velocity inversion. Velocity-based pore-pressure prediction requires a slowdown in interval velocity where overpressure occurs. It will not discriminate between normal and overpressure in faster gas hydrate-related sediments. In this context, an innovative approach was adopted. After interpreting the base of the gas hydrate stability zone (GHSZ) from seismic data, pore pressure was predicted by inverting Miles's pressure-temperature equations. Gas hydrates are thermodynamically stable in the low-temperature, high-pressure regimes of deep oceans. The inverse model-based pore pressure prediction was validated in the test well. It predicted more accurately than the velocity-based prediction, prompting its application in other wells. The technique works well in the gas hydrate-related shallow stratigraphy of deepwater wells in the Rakhine Basin in the Bay of Bengal (BOB). The inverse modelling technique, based on gas hydrate thermodynamics and the depth of the GHSZ base, is therefore a reliable tool for predicting gas hydrate pore pressure in the Bay of Bengal, which is surrounded by a host of sedimentary basins on both the eastern and western flanks, which become candidates for application of the methodology.