EFFECT OF HYDROSTATIC-PRESSURE AND SALINITY ON THE STABILITY OF GAS HYDRATES

The distribution of gas in the hydrate and the liquid phases for the two-phase systems methane hydrate-water and methane hydrate-seawater has been calculated as a function of hydrostatic pressure. It is found that at hydrostatic pressures higher than the three-phase hydrate-liquid-gas equilibrium pressure, a two-phase hydrate-liquid equilibrium exists in which the hydrate phase is increasingly enriched in and the liquid phase depleted of the gas as the hydrostatic pressure increases. At higher pressures, the methane content of water necessary to form and to stabilize the hydrate is much less than required for saturation with respect to the gas phase. Similar results are obtained for the methane hydrate-ice system where, at hydrostatic pressures above the three-phase hydrate-ice-gas equilibrium pressure, hydrates of increasingly higher cage occupancy are obtained at the expense of converting a small amount of hydrate to ice.