Heat transfer analysis of methane hydrate dissociation by depressurization and thermal stimulation

摘要

The dissociation of natural gas hydrate is an endothermic reaction closely related with the heat transfer characteristics in porous media. This study mainly focuses on the three-dimensional heat transfer behaviors during hydrate dissociation by depressurization and thermal stimulation based on the experiments in a Cuboid Pressure Vessel (CPV). The evolution of various heat flows (including the heat transferred from the boundariesQB, the injected heat from the wellQinj, the heat consumed by the hydrate dissociationQH, and the sensible heat change of the depositQS) and their relationships during hydrate dissociation are obtained through numerical simulation. The heat lossQLduring gas production is calculated and analyzed for the first time. It is found that the hydrate dissociation is mainly promoted by the driving forces of depressurization (Fdep) and thermal stimulation (Fths), which are dependent on the heat flows ofQBandQinj, respectively. The effect ofFdepwill be weakened under higherFths. Part ofQinjandQBare absorbed and stored asQSby the porous media and the fluids of the deposit. OnceQBbecomes negative, it starts to make contribution to the heat loss instead of the hydrate dissociation, resulting in a sharp increase ofQL. In addition, a proper thermal stimulation rateqand production pressurePWshould be selected so that the hydrate dissociation rate could be significantly enhanced while the thermal efficiency and energy efficiency are still favorable when compared with using single depressurization.