GAS HYDRATE LAYERS TRAPPING FREE GAS IN THE GULF OF OMAN

It has been postulated that the sediments of the Gulf of Oman, in the northwest Indian Ocean contain a number of localised accumulations of free gas which are apparent on continuous seismic reflection profiles as horizons with anomalously high amplitude reflections. We suggest that the gas is trapped beneath a relatively impermeable gas hydrate layer which is stable within the uppermost 350-700 m of sediment. The depth beneath the sea floor of all the observed highly reflective horizons varies with water depth in a manner similar to that predicted from theoretical estimates of the depth at which the phase change occurs from gas hydrate to free gas. Further evidence that the gas is trapped by a hydrate layer is provided by the detailed shape of gas layers within the cores of gentle anticlines. The curvature of the gas reflector mirrors that of the sea floor above it, but transgresses the local bedding, suggesting that the gas is trapped by a hydrate phase change governed by the pressure and temperature conditions rather than by a stratigraphic trap. © 1979.