(84ai) Effect of Water-Gas Seepage and Salt Ions on Hydrate Phase Transition in Porous Media

Natural gas hydrate is the one of the most potential energy sources to meet the future human development. During the hydrate exploitation process, the multiphase seepage and infiltration of overlying seawater will influent the gas production efficiency. Therefore, it is necessary to reveal the interaction mechanism between multiphase seepage and hydrate phase transition characteristics. In this study, the multiphase flow in hydrate reservoirs is simulated by controlling the seawater–gas flowrate, and the variations of pressure, temperature, and seawater production volume are monitored to during the seawater–gas flow process. The experimental results point out that the hydrate re-formation and accumulation will occur and cause the blockage of flow path. Compared to deionized water-gas flow process, the amount of hydrate re-formation will significantly reduce in the seawater-gas flow system, especially in case of the higher seawater-gas flowrate ratio. Moreover, hydrate re-formation induces the temperature and pressure following a three-stage trend in the continuous seawater-gas flow process: (I) stable stage without hydrate re-formation; (II) rapid increase stage due to mass hydrate reformation; (III) blockage stage where the temperature and pressure obviously decreased and finally kept stable. After blockage, water and gas were stored in pore to continuously re-form solid hydrate barrier to prevent gas overflow, finally a stability reservoirs pressure was obtained.