(400c) An Improved Clapeyron Model for Predicting High - Pressure Gas Hydrate Phase Equilibria

Gas hydrates are a group of non-stoechiometric, ice-like crystalline compounds formed through a combination of water and suitably sized ?guest? molecules under low-temperature and elevated pressure conditions. Prediction of hydrate phase equilibria at high pressures is a real challenge, taking into account hydrate phase boundary at these conditions is sharp and strong function of temperature. The ice-vapor-hydrate (I-V-H), liquid water-vapor-hydrate (LW-V-H) and liquid water- liquid hydrocarbon- vapor- hydrate (LW-LHC-V-H) equilibria occur normally at relatively low and intermediate pressures. However, the LW- LHC-V-H and LW-V-H phase boundaries approach high pressures by increasing temperature. The liquid water- liquid hydrocarbon- hydrate (LW-LHC-H) phase boundary is however stronger function of the system temperature. At high pressures, many petroleum fluid systems are in single-phase conditions; a situation where almost all conventional methods for hydrate phase boundary modeling fail. At these conditions, the hydrate dissociation pressure exceeds the bubble point pressure of the system and the hydrate phase boundary is reduced to a three-phase line with only water, liquid hydrocarbon and hydrates in equilibrium (i.e., LW-LHC-H region). In this region, the Clapeyron model is normally and currently used for predicting high pressures hydrate phase behaviors. In this work, the conventional Clapeyron model is modified for predicting high pressure gas hydrates phase equilibria for three substances including CO2, H2S and C2H6. It is found that the presented modification improves the predictions of the original equation.