Gr. Dickens et Ms. Quinbyhunt, METHANE HYDRATE STABILITY IN PORE-WATER - A SIMPLE THEORETICAL APPROACH FOR GEOPHYSICAL APPLICATIONS, J GEO R-SOL, 102(B1), 1997, pp. 773-783
Geophysicists have recently expressed an interest in understanding how
pore water composition affects CH4 hydrate stability conditions in th
e marine environment. It has previously been shown in the chemical eng
ineering literature that CH4 hydrate stability conditions in electroly
te solutions are related to the activity of water (a(w)). Here we pres
ent additional experimental data in support of this relationship and t
hen use the relationship to address issues relevant to geophysicists.
Pressure and temperature conditions of CH4 hydrate dissociation were d
etermined for 10 solutions containing variable concentrations of Cl-,
SO42-, Br-, Na+, K+, Mg2+, NH4+, and Cu2+. The reciprocal temperature
offset of CH4 hydrate dissociation between the CH4-pure water system a
nd each of these solutions (and for other electrolyte solutions in lit
erature) is directly related to the logarithm of the activity of water
(lna(w)). Stability conditions for CH4 hydrate in any pore water syst
em therefore can be predicted simply and accurately by calculating lna
(w). The effect of salinity variation and chemical diagenesis on CH4 h
ydrate stability conditions in the marine environment can be evaluated
by determining how these processes affect lna(w) of pore water.