Modeling of hydrate dissociation surface area in porous media considering arrangements of sand grains and morphologies of hydrates

The volumetric surface area of hydrates (Ah) in porous media is a key factor involved in hydrate kinetics as it determines the dissociation rate and gas production behavior. Oversimplification of the pore structure and morphologies of hydrates in porous media can cause large errors when modeling Ah. In this study, considering the multiple packing arrangements of sand grains and the structural morphologies of hydrates in porous media, a unified estimation model was developed to describe the evolution of Ah with hydrate dynamic dissociation. An average error of 4.03% was observed between the model and experimental results quoted in literature. Two evolution trends of Ah with hydrate saturation were found because of the change in the structural morphologies of the hydrates. Under the premise of the same porosity, compared with the cubic arrangement of sand grains, the Ah of the orthorhombic, tetragonal-sphenoidal, and rhombohedral arrangements were reduced by approximately 5.61%, 10.37%, and 12.15%, respectively. An increase in porosity due to the change in the packing arrangement of sand grains, and the distance between the adjacent sand grains led to a reduction in Ah by approximately 7.71% and 2.79%, respectively. Ah decreased exponentially with the size of the sand grains, which seemed to be the most critical factor in Ah estimation, and a fourfold increase in sand grain size (from 100 mu m to 400 mu m) reduced Ah by approximately 74.45%. These findings could help to reveal the evolution mechanism of Ah with hydrate dynamic dissociation and provide a more accurate estimation of the hydrate dissociation kinetics.