Geophysicists have expressed an interest in understanding how pore water composition affects methane hydrate stability conditions in the marine environment. It has previously been demonstrated in the chemical engineering literature that methane hydrate stability conditions in electrolyte solutions are related to the activity of water. Here we present additional experimental data in support of this relationship, and then use the relationship to address issues relevant to geophysicists. Pressure and temperature conditions of methane hydrate dissociation were determined for 10 solutions containing variable concentrations of chloride, sulfate, bromide, sodium, potassium, magnesium, ammonium and copper(II) ions. The reciprocal temperature offset of methane hydrate dissociation between the methane- pure water system and each of these solutions (and for other electrolyte solutions in literature) is directly related to the logarithm of the activity of water. Stability conditions for methane hydrate in any pore water system, therefore, can be predicted simply and accurately by calculating the activity of water. The effect of salinity variation and chemical diagenesis on methane hydrate stability conditions in the marine environment can be evaluated by determining how these processes affect the logarithm of the activity of pore water.
AGU Index Terms: 3025 Marine seismics; 4825 Geochemistry; 4850 Organic marine chemistry; 4271 Physical and chemical properties of seawater
Keywords/Free Terms: Hydrate, methane, pore water, BSR.
JGR-Solid Earth 96JB02941
Vol. 102
, No. B1
, p. 773