Enhanced Methane Hydrate Recovery through CO2/N2-Assisted Depressurization in Muddy Silt Sediments

Utilizing flue gas for CH4 replacement in natural gas hydrate reservoirs ensures formation stability and facilitates CO2 sequestration, offering an efficient and ecofriendly approach to energy extraction. However, research on the definitive mechanism and applicability of this mixed gas in extracting marine natural gas hydrates is currently lacking. In this study, we remodeled muddy silt sediment samples from the South China Sea and analyzed the characteristics of CH4 hydrate generation in the reservoir. Building upon this, we have identified the time-varying pattern of CH4 replacement by flue gases of the CO2 and N2 mixtures and unveiled the factors influencing CH4 extraction efficiency. During the progression of the replacement reaction, a mixed hydrate film forms on the hydrate surface, hindering the replacement process. Concurrently, the poor permeability of the muddy silt sand reservoir renders multiple depressurizations ineffective in enhancing CH4 production. Hence, enhancing the diffusion rate of CO2 in the reservoir is pivotal for improving both the CH4 extraction rate and the CO2 sequestration rate.