Effect of bubbles on the gas–water migration during gas hydrate dissociation by depressurization

Abstract

Permeability is the key to controlling the efficiency of hydrate exploitation, but the research on gas–water migration focusing on bubbles is scarce. In this study, a permeability model considering bubbles was developed and applied to the numerical simulation of hydrate dissociation by depressurization. It can be investigated by varying the bubble partition function (fb) that the effects of bubble generation on hydrate dissociation rate and gas–water migration. The results show that the bubble saturation after hydrate dissociation can reach 0.04–0.18 at fb of 0.04–0.16. And the bubbles occupy the pore space, resulting in the core permeability being 4.01–15.49 % lower than that without bubbles. Furthermore, gas–water migration, pressure drop and heat transfer are hindered by bubbles to reduce the hydrate dissociation rate in the core. Therefore, the water velocity peak of bubble generation is reduced by 0–11.47 % and delayed by 9–32 min. It can be concluded that the peak of gas (water) production rate and the final cumulative production of gas (water) are reduced by 13.33–53.43 % (7.02–29.96 %) and 1.54–9.57 % (1.68–11.73 %) compared with no bubble generation, respectively. In other words, with bubble generation, gas and water produce slowly to a 6–65 min longer gas production time and are eventually partially trapped in the core.