Estimation of Methane Recovery Efficiency from Methane Hydrate by N2−CO2 Gas Mixture Injection Method

Methane hydrate (MH) is the best-known unconventional energy resource and has begun to open its promising future especially for Japan. In 2017, the second offshore gas hydrate field test was conducted in the Eastern Nankai Trough, Japan, where a depressurization technique was adopted for producing methane gas. Alongside the depressurization method, the replacement of CH4 from gas hydrates by N2−CO2 gas mixture was suggested and adopted to increase performance for both methane gas recovery and carbon dioxide sequestration. The amount of abundant methane hydrates is estimated to exist in the permafrost area; therefore, this method, which does not require any heat source, can be used as a standard method for recovering methane. In this study, experiments to continuously inject N2−CO2 gas mixture (59 mol% CO2) into hydrate-bearing cores with different methane hydrate saturations were conducted. Simultaneously, the numerical simulation model was constructed and in order to express the gas exchange phenomenon o...