(649e) Modeling Densities and Equilibria of Ice and Gas Hydrate Phases

The general warming of land and oceans around the world has generated interest in understanding long term environmental impacts associated with the melting of ice sheets and thawing of permafrost regions. In this talk extensions of the multi-scale Gibbs-Helmholtz Constrained (GHC) equation of state to modeling the phase densities and equilibrium behavior of hexagonal ice and gas hydrates are described. A number of numerical results for mixtures of N₂, O₂, CH₄, CO₂, water, and NaCl for permafrost conditions are presented to illustrate the predictive capabilities of the multi-scale GHC equation. In particular, it is shown that the GHC equation correctly predicts

1)     The density of 1h ice and methane hydrate to within 1%.

2)     The melting curve for hexagonal ice.

3)     The heat of fusion of 1h ice at high pressure.

4)     The hydrate-gas phase co-existence curve.

5)     Various phase equilibrium involving ice and hydrate phases.

We also show that the GHC equation approach can be readily incorporated into subsurface flow simulation programs like FEHM to predict the behavior of permafrost and other reservoirs where ice and/or hydrates are present. Many geometric illustrations are used to elucidate key concepts.