Investigation of permeability and growth habits in hydrate-bearing porous media considering pore irregularity

The permeability of hydrate-bearing sediments critically affects gas production rate and efficiency. Reported permeability from artificial and natural cores is widely scattered owing to porous media particle size, porosity and hydrate saturation (S-H), but pore irregularity was ignored. Therefore, analyzing the effects of pore irregularity on growth habits and permeability is crucial. In this study, we used glass beads (represent regular pores, well-rounded grain) and quartz sands (represent irregular pores, angular grain) with nearly the same particle size distribution (mean and median particle size is around 103 mu m and 100 mu m, respectively) and porosity (about 39%) as the porous media, to determine the hydrate growth habits and the permeability as a function of S-H. First, the hexagonal prism model (HP model) was proposed for well-rounded porous media with regular pores, and a fractal model was recommended for angular porous media with irregular pores. The fitting permeability reduction exponents (N) in these two models indicated that both pore-filling (5% < S-H < 25%, N = 30) and grain-coating (0 < S-H < 5%, N = 15) hydrates existed within glass beads, and only pore-filling (0 < S-H < 25%, N = 15) hydrates were dominant in quartz sands. The permeability values in glass beads were consistently higher than those in quartz sands due to more pore connections, smooth surfaces, and grain-coating hydrates in glass beads. This study provides the permeability reduction model based on pore irregularity.