(746j) A Model for Gas-Hydrate Equilibrium in Porous Media

Gas hydrates are crystalline inclusion-compounds with gas molecules trapped in a host lattice formed by water molecules in an ice-like hydrogen-bonded framework. Gas hydrates occur naturally in the permafrost region or as a dispersed phase in ocean-floor sediments at low temperatures and high pressures. It has been reported that the amount of methane trapped in marine sediments is about three orders of magnitude larger than the worldwide conventional natural-gas reserves combined. Gas hydrates are an untapped energy resource, but also a potential contributor to global warming. It is then important to know the exact location and zones of stability of the methane-hydrate regions within deposits, i.e., the conditions at which methane hydrate is thermodynamically stable. This information can guide the design of technologies for harvesting methane and natural gas from hydrate deposits, and, most importantly, predict destabilization of those deposits that may result in catastrophic gas release.
A new model for the prediction of gas-hydrate equilibrium in model cylindrical pores will be presented in this work. Pore-wall properties effects on hydrate equilibrium were captured in the model within the mechanical equilibrium condition. In agreement with visual observations of gas-hydrate cores, the model predicts the formation of hydrate concave-convex lenses within the pores. The proposed model was tested against experimental methane-hydrate equilibrium data reported in the literature. Model predictions show very good agreement with experimentally-measured equilibrium data, with absolute average deviations (AAD%) lower than 1%.