Accurate and precise predictions of the temperature and pressure (P-T) conditions for the methane hydrate stability field have been shown to be an essential component of a variety of geochemical efforts. Careful correction of all measurements to absolute pressure is essential if a precision equivalent to a few meters depth is required. While linear interpolation of gas hydrate stability data works well in limited cases, second-order equations do a better job with regards to interpolating between existing data points. Our current inventory of geochemically relevant determinations of the dissociation temperatures and pressures of gas hydrates is very limited. Only one data set for seawater exists, and this is limited to pure methane gas measurements. Depending upon the form of the equation chosen to fit this data set, extrapolations to higher P-T conditions can be quite risky and lead to false interpretations. Adjustment of high pressure freshwater measurements can help extend the database, but these measurements are limited to pure methane gases as well.
The use of computer routines based upon various Gibbs Free Energy minimization algorithms to estimate the P-T stability conditions of gas hydrates has helped to expand the range of the predictions, but data to verify these estimates is quite scarce. Agreement between the computer predictions and the existing data is quite good, suggesting that the programs are accurate within reasonable limits. Their greatest utility will be with problems involving mixed gas compositions or at different salinities and ionic strengths not found in the data sets.
Was this article helpful?