Image-based pore-network modeling of two-phase flow in hydrate-bearing porous media

Abstract

Natural gas hydrate (NGH) has been widely regarded as a future strategic alternative energy resource. Permeability is crucial to produce gas effectively from NGH reservoirs. Experimentally studying the hydraulic characteristics of hydrate-bearing porous media, especially for two-phase flow, is difficult due to the rigorous stable conditions of NGH. In this work, the 3D porous structure and NGH distributions of a synthetic sample with a hydrate saturation of 52.43% are first obtained by using μCT scanning. Then, the hydrate saturation is numerically increased and decreased to generate nine extra hydrate-bearing samples, which cover a wide saturation range from 5.53% to 67.26%. Finally, a quasi-static pore-network model is used to study the effects of hydrate saturation on the absolute permeability and gas–water relative permeabilities of hydrate-bearing porous samples. The numerical algorithm of generating hydrate-bearing samples can well mimic the realistic morphology and distributions of hydrate in porous media. Hydrate saturation remarkably influences the pore-size distribution and connectivity of pore spaces. The relationship of absolute permeability and hydrate saturation, which qualitatively matches experimental data, is fitted. Moreover, gas relative permeability decreases as hydrate saturation increases.