Influence of Hydrate Saturation on Methane Hydrate Dissociation by Depressurization in Conjunction with Warm Water Stimulation in the Silica Sand Reservoir

In this study, the different saturations of hydrate samples were formed in a cubic hydrate simulator (CHS) filled with silica sand. Subsequently, the hydrate was dissociated by depressurization in conjunction with warm water stimulation using dual horizontal wells. The hydrate dissociation process includes the depressurizing period and the injection period (the constant-pressure period). Hydrate was dissociated simultaneously in the whole reservoir during the depressurizing period. Meanwhile, gas production in the depressurizing period is mainly determined by the depressurizing rate, and it has little relation to the hydrate saturation (when the hydrate saturation ranges from 15.5% to 39.1%). During the injection period, more gas can be produced for the reservoir with the higher hydrate saturation, whereas the highest average gas production rate can be obtained for the reservoir with the middle-higher hydrate saturation. With respect to the gas production in the depressurizing period, gas production in the injection period is the dominant factor affecting the whole production efficiency in the experiment. In addition, the energy ratio only increases with the increase of the hydrate saturation in the prior stage of the constant-pressure period, and the final energy ratio with the middle-higher hydrate saturation is the maximum. Moreover, energy analysis indicates that heat injection plays the leading role for hydrate dissociation in the constant-pressure production period when the initial hydrate saturation is higher than 32.4%.