Depressurization method is regarded as a promising gas production technique from methane hydrate reservoirs. There are three major factors that determine gas production rate by depressurization : kinetics of hydrate dissociation, gas flow through the reservoir, and heat transfer to the dissociating zone. As the gas productivity of methane hydrate wells significantly changes depending on the factors that determine the rate, it is important to find the most governing factor. To find such rate-determining factors, we developed a new method by introducing formulations of three potential methane fluxes generated by kinetics of hydrate dissociation, gas flow and heat transfer.
The proposed method was applied to the analysis of hydrate dissociation and gas production behaviors in laboratory scale depressurization experiments on artificial methane hydrate cores. From the calculation and comparison of those rate-determining factors, we concluded that gas productions in those experiment cases were mainly limited by heat transfer. Hydrate dissociation rates during the experiments were well matched with the methane fluxes calculated by heat transfer, which increased in proportion to the heat flux into the core. According to the core experiment results, gas production rate from depressurization of high-permeability hydrate cores is probably limited by heat transfer. Future application of this method to the analysis for hydrate reservoir performance should give us a clue to finding a best production method.
