Effects of water-gas two-phase flow on methane hydrate dissociation in porous media

Abstract

Natural gas hydrates (NGHs) represent a rich new natural gas resource, offering tremendous potential due to their high energy density and abundant reserves. The safe and efficient exploitation of NGHs is a worldwide focus. The water-gas migration characteristics in sediment are a critical parameter for hydrate exploitation, and the promotion effect of water phase flow on NGHs exploitation has been confirmed. However, there is little research on the influence of water-gas flow on hydrate dissociation. The effects of different water-gas (H2O-CH4) flow rate ratios on methane hydrate (MH) dissociation were visually investigated in this study. The influences of temperature and pressure changes on MH dissociation were eliminated during the water-gas flow. The results showed that the water phase flow was the dominant factor for hydrate dissociation, while the gas phase flow has a negative effect. When the water-gas flow rate ratios were 1-1 (the water and gas flow rates were both 1 ml·min−1) and 1-2 (the water and gas flow rates were 1 and 2 ml·min−1, respectively), the phenomenon of MH reformation in the hydrate reservoir was apparent. Moreover, MH will dissociate with higher water-gas flow rate ratios, and there will also be a higher average MH dissociation rate and a shorter variation time in the flow channel with the high water-gas flow rate ratios. Furthermore, a suitable water-gas flow rate ratio of 2-1 (the water and gas flow rates were 2 and 1 ml·min−1, respectively) was determined for relative permeability measurements in the slow hydrate dissociation process.