Images of the Base of Gas Hydrate Stability, Northwest Walker Ridge, Gulf of Mexico

摘要

The gas hydrate stability zone, the zone below the seafloorrnwhere gas and water should form gas hydrate is predicted tornbe present in the tophole sections in deepwater areasaroundrnthe world including the deepwater Gulf of Mexico. Few, ifrnany, bottom simulating reflectors (BSR) or otherrnmanifestations of the gas hydrate stability zone have beenrninterpreted in the Gulf of Mexico. This paper presentsrnconvincing images of the base of the gas hydrate stability zonernextracted from exploration 3-D data in Northwest WalkerrnRidge in the Gulf of Mexico from the upper 1,050 m ofrnsediment. This area is on the margin of an uplifted andrncompressed mini-basin and in the vicinity of numerous giantrngas mounds at the seafloor. Interpreted tophole stratigraphyrnincludes laterally extensive, steeply dipping basin floor siltsrnand sands. This paper shows images of hydrate-trapped gas atrnmultiple reflectors at depths that are coincident with thernpredicted base of the hydrate stability zone if modeled with arngeothermal gradient of 19.6 ± 0.5 oC/km. A BSR is seen inrnthe seismic data in vertical section, but the more convincingrnimages of the base of gas hydrate stability are seen inrnmap view. W e expect that the subsurface conditions here are notrnunique and the hydrate stability zone is similarly imaged, butrnperhaps has not been recognized, in similar settings in otherrnparts of the Gulf of Mexico and elsewhere in the world.rnRecognition of hydrate-trapped gas can aid in betterrndecision making for shallow-gas avoidance strategy forrnexploration drilling and optimal design and placement ofrnconductor strings for deepwater development wells.rnThe possible concentrations of gas hydrate reservoirsrnin the updip margins of hydrate traps should also be of interestrnto those that are evaluating the feasibility of commercialrnexploitation of gas hydrates.