Application of coupled hydrodynamic and thermal Lattice–Boltzmann simulation on permeability estimation of hydrate-bearing sediment during hydrate dissociation processes

Abstract

Natural gas hydrates, which are plentifully distributed in ocean floor sediments and permafrost regions, are considered a promising unconventional energy resource. The current hydrate production approaches aim at breaking the thermodynamic equilibrium state to stimulate hydrate dissociation that releases methane and water molecules, which causes formation porosity and permeability alteration. Efficient estimation of permeability during hydrate dissociation is essential to evaluate the economic feasibility for gas production from hydrate-bearing sediment. In this paper, we developed a coupled hydrodynamic and thermal Lattice–Boltzmann (LB) method to rigorously model the coupled processes of mass transfer, conjugate heat transfer, and fluid flow during the hydrate dissociation. We then carried out numerical simulation on the dissociation processes of hydrate formation with the three most common hydrate distribution morphologies, pore-filling, grain-coating and dispersed, under two production approaches that are depressurization, and depressurization with thermal intervention. Our simulation results indicated that the coupling of gas transport and heat transfer has significant impact on pore geometry evolution, especially pore connectivity, during hydrate dissociation processes due to the endothermic nature of the dissociation processes. Therefore, it is vital to consider the coupling effects for estimation of hydrate formation permeability through numerical simulations.