Analytical modelling of gas production from hydrates in porous media

Gas hydrates are being considered as an alternative energy resource of the future since they exist in enormous quantities in permafrost and offshore environments. However, gas production potential from hydrate reservoirs through different production schemes has not been fully investigated yet. This work introduces a simple analytical model for simulating gas production from hydrate decomposition in porous media by a depressurization method. We consider the heat transfer to the decomposing zone, intrinsic kinetics of hydrate decomposition, and gas-water two-phase flow as the three primary mechanisms involved in hydrate decomposition in porous media. In this study, the relative importance of these mechanisms is compared over a realistic range of the physical properties. It is shown that for the cases studied, the effect of two-phase flow is significantly smaller than the heat transfer and the intrinsic kinetics of hydrate decomposition. Considering the rate-controlling mechanisms, an analytical model is developed to predict the performance of decomposition of gas hydrates in porous media. The model is used to perform sensitivity studies to investigate the feasibility of commercial gas production from hydrate reservoirs. The results suggest that significant quantities of gas can be produced from gas hydrate reservoirs where the hydrate overlies the gas zone. Such reservoirs have been found in the permafrost regions of Siberia, Alaska, and Canada.