Dynamic behavior of hydrate dissociation for gas production via depressurization and its influencing factors

Natural gas hydrate can be a potential energy resource to be developed in the near future. Gas production is feasible via depressurization, which has been applied for gas extraction from gas hydrate deposits in Messoyakha. Understanding the dynamic behavior of hydrate dissociation, i.e. the variations of pressure, temperature and gas production rate during the depressurization process, is important for process optimization and predications of geological hazards caused by hydrate dissociation. In this study, methane hydrate formation and dissociation experiments were conducted using a self-designed apparatus under different conditions in simulated porous media. Hydrate formation in sand packs with different hydrate saturations were simulated, and the dynamic behavior of hydrate dissociation process and its influencing factors were analyzed, illustrated by gas production rate, accumulated gas production, and the associated temperature and pressure changes in the gas production process. The experimental results show that hydrate dissociation can be inhibited in the early stage if the production pressure is low, which can cause a decrease of the local temperature in the dissociation zone and restabilize the hydrate, and the efficiency of gas production can be improved by reducing the production pressure gradually. High permeability of the sand packs is conductive to increase gas production rate, but it can also induce a fast decrease on temperature and pressure. The time for hydrate dissociation becomes longer in the case of a higher hydrate saturation, and depressurization along with other stimulation methods, such as thermal stimulation, may be required for efficient gas production. (C) 2016 Elsevier B.V. All rights reserved.