Experimental observation of methane hydrate dissociation via different depressurization modes under water phase flow

As one of the most potential unconventional fossil fuels, the safe and efficient production of natural gas hydrates (NGHs) has become a prominent research area worldwide. Water flow erosion, which has been proven to be a powerful methane hydrate dissociation method recently, may be an effective way to mitigate the challenging ice generation problems urgently needed to be solved for depressurization production. In this study, we visually studied the effects of the three depressurization modes combined with water flow erosion on MH decomposition using in-situ magnetic resonance imaging. The time and spatial characteristics of the three-phase water-gas-hydrate during the MH production process are indirectly determined in sediment. Three stages of the energy recovery process are directly observed: the MH stable existing stage, the free gas production stage, and the MH decomposition stage. Our work indicates that all three combination modes effectively eliminate ice generated during the MH production process. Compared with the sudden depressurization method, radial extension appears on one side or two sides of the decomposition trends. In addition, the results denote that the higher water flow rate can efficiently enhance the effect of depressurization on hydrate dissociation. Meanwhile, the MH decomposition rate and formation stability benefit more from a faster water flow rate and depressurization rate.