Production behaviors and heat transfer characteristics of methane hydrate dissociation by depressurization in conjunction with warm water stimulation with dual horizontal wells

To investigate into the synergistic effect of depressurization and heat stimulation on hydrate dissociation and the three-dimensional heat transfer characteristics during hydrate dissociation in the porous media, a series of the hydrate dissociation experimental runs by the depressurization in conjunction with warm water injection with DWDH (dual horizontal wells) and single depressurization have been carried out in a three-dimensional CHS (cubic hydrate simulator). The results indicate that the gas production process can be divided into the free gas release stage, the mixed gas release stage, and the dissociated gas release stage. In the first two stages, the gas production is mainly controlled by the depressurizing rate. In the third stage, the duration of the hydrate dissociation with the DWDH method (water injection temperature equals to environmental temperature) is much shorter than that by the single depressurization. It is due to the fact that water injection enhances the heat convection and further increases the rate of the hydrate dissociation. The analysis of three-dimensional heat transfer shows that the heat transfer rate along the injection well is the fastest. Energy analysis indicates that the sensible heat of the hydrate reservoir is insufficient for the hydrate dissociation, and the heat for the hydrate dissociation mainly originates from the boundaries.