Oy. Zatsepina et Ba. Buffett, PHASE-EQUILIBRIUM OF GAS HYDRATE - IMPLICATIONS FOR THE FORMATION OF HYDRATE IN THE DEEP-SEA FLOOR, Geophysical research letters, 24(13), 1997, pp. 1567-1570
We calculate the solubility of methane gas over a range of pressure an
d temperature. The gas is dissolved in liquid water, which coexists wi
th free gas at high temperature or solid hydrate at low temperature an
d high pressure. We show that solubility is significantly altered by t
he presence or absence of the hydrate phase. When hydrate is absent at
high temperatures, our calculations reproduce experimentally observed
increases in solubility with decreasing temperature. When hydrate is
present, however, we find that the gas solubility decreases sharply wi
th decreasing temperature. Such an abrupt decrease in solubility permi
ts hydrate to crystallize directly from the aqueous solution, without
the need of any free gas. This result has important implications for t
he formation of gas hydrate in marine environments, where the gas supp
ly may not be sufficient to provide free gas. We apply our calculation
s at typical pressure and temperature conditions in marine sediments t
o establish the gas concentration needed to stabilize hydrate. Estimat
es of the vertical distribution of hydrate in marine sediments and the
rate of accumulation are obtained using simple models of hydrate form
ation.