Investigation into optimization condition of thermal stimulation for hydrate dissociation in the sandy reservoir

Investigation of the optimal injection temperature for the hydrate dissociation plays a significant role in the gas hydrate exploitation in the practical field. In this work, the experiments of hydrate dissociation by depressurization in conjunction with thermal stimulation (DT) with the different injection temperatures are carried out in a Cubic Hydrate Simulator (CHS). Evaluation of the entropy production minimization (EPM), the energy ratio and the thermal efficiency are employed to investigate into the optimized injection temperature for hydrate dissociation. The thermal efficiency decreases with the increase of the injection temperature. The optimal injection temperatures for the hydrate dissociation from the points of the maximization of the energy ratio and the minimization of the entropy production, which are equivalent to maximizing the energy production and minimizing the energy consumption, respectively, are 38.8°C and 37.9°C. The results of evaluations from the two aspects are in a quite good agreement. Thus, the warm water injection of approximately 38–39°C is suitable for hydrate dissociation with the DT method, and the hot water injection beyond 39°C is uneconomical for hydrate dissociation.