Investigation of the formation characteristics of methane hydrate in frozen porous media

Abstract

The replacement technique of CO2–CH4 hydrate in naturally occurring gas hydrates is a promising method for achieving CO2 storage and CH4 recovery in permafrost regions. Revealing the formation characteristics of CH4 hydrate becomes an urgent need in porous medium below the freezing point. For this purpose, the formation experiment was carried out under different conditions and the formation characteristics were systematically investigated. The result indicated that the initial pressure was the key factor affecting the formation process of CH4 hydrate. And the final pressure drop was greater at higher initial pressure conditions. The final pressure drop reached to 0.92 MPa when the initial pressure was 9 MPa under the same temperature conditions. The results also illustrated that, the formation rate of hydrate was the fastest when the temperatures were closely to the freezing point. The average formation rate of CH4 hydrate reached to 0.646 mmol/h when the temperature was 273.15 K. Moreover, the smaller the particle size was, the higher the final conversion rate of ice. The final conversion rate reached to 56.5% when the initial pressure was 9 MPa. The results are of significance for exploiting natural gas hydrate in the permafrost regions. Highlights The formation characteristics of methane were studied in porous media below the freezing point. The higher initial pressure could enhance the final conversion rates of ice. The formation rate of methane was the fastest when the temperature was closely to the freezing point. The pressure disturbance could improve the formed amount of methane hydrate in porous media.