Effects of depressurizing rate on methane hydrate dissociation within large-scale experimental simulator

Methane hydrate is the world’s largest hydrocarbon reservoir, and can be performed as an important “bridging” fuel to help the transformation of current energy situation to low-carbon energy system. High efficient scenarios of hydrate dissociation at the in situ environment is the primary prerequisite for successfully harvesting natural gas from hydrate reservoir. This work investigates the influences of depressurizing rate on methane hydrate dissociation within a large-scale hydrate simulator. Experimental cases with different depressurizing rates to dissociate water-saturated hydrate sample, which is the typical marine hydrate type, have been carried out in this study. Results indicate that gas production rate decreases with the improvement of the depressurizing rate, and increasing depressurizing rate is feasible for hydrate reformation during this period, suggesting that the depressurizing rate should not be too fast before the inner pressure decreases to equilibrium pressure corresponding to the in situ temperature. When the pressure decreases below the equilibrium pressure, the gas production rate, recovery, and heat transfer rate decline with the rising of depressurizing rate, whereas the lowest depressurizing rate cannot gain the highest gas production rate and recovery as well, demonstrating the optimal depressurizing rate existed in the depressurization stage. Mechanism analysis showed that the optimal depressurizing rate can be obtained when the fluid velocity victories in accordance with the heat transfer vector in the hydrate reservoir.