EXPERIMENTAL STUDY ON GAS HYDRATE SYSTEM STATE EVOLVING DURING DEPRESSURIZATION

Natural gas hydrate has been treated as a potential energy resource for decades. Depressurization is currently the most promising method for hydrate production. However, its efficiency is far from the commercial need. Hydrate production involves heat transfer, multi-phase seepage, phase transition, and reservoir deformation. A thorough understanding of how multiple physical processes evolve during depressurization is of great significance for efficiency enhancement of hydrate production. An experiment was carried out to simulate depressurization induced evolution of the multiple physical processes. Methane hydrate was formed by using the gas excess method under a heterogeneous temperature condition. Evolutions of pore pressures and temperatures were analyzed. A comparison between gas production process and heat transfer process was discussed. Main conclusions are drawn as follow: temperature distribution is parabola-like after hydrate formation, which has higher temperatures in two sides of the sample. In addition, hydrate distribution is inhomogeneous. Pore pressures decrease completely from the outlet to the inlet, and temperatures increase from the two sides into the middle part. The gas production process related to the heat transfer process well, and the stable stage for gas production is controlled by the heat transfer process. It is a feasible way to replace heat conduction by heat convection or choose a slow depressurization strategy to enhance production efficiency for the commercial need.