Influence of intrinsic permeability of reservoir rocks on gas recovery from hydrate deposits via a combined depressurization and thermal stimulation approach

Abstract

Reservoir permeability is a crucial controlling factor for the successful exploitation of unconventional gas hydrate resources, which represent a vast natural gas reserve with substantial energy potential. Numerical simulations and analyses are essential tools for the prediction and evaluation of natural gas recovery from hydrate deposits. In this study, a two-dimensional axisymmetric model was developed and validated to investigate the effect of the intrinsic permeability of reservoir rocks on hydrate dissociation characteristics induced by a combined depressurization and thermal stimulation method. Simulation results indicate that the average gas production rate from hydrate deposits could be enhanced when thermal stimulation was additionally applied at the same production pressure, but the enhancement effect weakens as reservoir permeability increases. Pressure reduction propagates slowly from gas production wells into cores with low-permeability, and thermal stimulation dominates hydrate dissociation. However, depressurization can play a determining role for hydrate dissociation in high-permeability cores which benefit to the propagation of pressure reduction. Increased permeability promotes the characteristic shift from thermal-stimulation-governed radial hydrate dissociation to depressurization-determined uniform dissociation. To a certain extent, increased permeability enhances gas generation, but there is a threshold beyond which this effect is no longer felt as excessive consumption of sensible heat restricts further hydrate dissociation. Although there are many uncertainties in the hydrate dissociation process in porous media, numerical simulation can provide useful information for evaluating the feasibility of methodology for gas recovery from gas hydrate reservoirs.