Spatial Distribution and Phase Transition Characteristics of Methane Hydrate in the Water-Excess and Gas-Excess Deposits

Methane hydrate is considered as a new environmentally friendly energy to meet future society development. To achieve safe and efficient hydrate production, it is critical to understand the hydrate accumulation characteristics in different deposits, considering the geological feature differences. In this study, the hydrate distribution characteristics in the gas-excess and water-excess deposits were visually investigated by using magnetic resonance imaging technology. Moreover, the effect of the initial gas pressure on hydrate formation behaviors and stability was analyzed. The results showed that methane hydrate first formed in the water–gas interface for the water-excess deposit, and then, the hydrate formation front gradually expanded into the water phase accumulation area. Moreover, the methane hydrate distribution was mainly determined by the initial distribution of water and gas in the porous media. For the water-excess deposit, the spatial distribution of methane hydrate showed an obvious heterogeneity, and the mass hydrate accumulated at the bottom of the deposit. However, a uniform distribution of methane hydrate in the gas-excess deposit was observed. Furthermore, methane hydrate that formed in the higher initial gas pressure and the water-excess environment had good stability during the water flow process, which prolonged the duration of the hydrate decomposition process. The findings attempt to provide valuable information and guidelines for understanding the gas hydrate system.