CO2/N2 replacement-enhanced extraction of natural gas hydrate by pressure reduction
The substitution of CO2 hydrate for CH4 in natural gas hydrate is an innovative method for future energy production and greenhouse gas control.However,the replacement efficiency of CH4 in hydrate by CO2 is low under normal conditions,so the mining method of gas mixture combined with depressurization and enhanced replacement is proposed.The effects of depressurization enhanced replacement on gas phase composition,CH4 recovery rate,and CO2storage rate were investigated by simulating(seabed hydrostatic pressure)under triaxial stress constraint and injecting a fixed ratio of n(CO2)∶n(N2)=4∶1 replacement gas.The results.show that CO2+N2 combined with depressurization improves the replacement efficiency of CH4 hydrate,and the replacement rate of CH4 increases to 35.22％c ompared with 15.2％of traditional replacement method,in which the direct contribution rate of N2 is 8.66％.The gas diffusion effect in the later stage of decomposition is significantly enhanced by depressurizing and strengthening,and the methane recovery rate and CO2 storage rate are improved,which has a good application prospect for improving hydrate conversion recovery.
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