将天然气水合物中的CH4置换为CO2水合物是未来能源生产和温室气体控制的一种创新方法,但通常条件下CO2对水合物中CH4的置换效率较低,因此采用混合气联合降压强化置换的开采方法被提出.模拟(海底静水压力)在三轴应力约束状态下,通过注入固定比例[n(CO2):n(N2)=4:1]的置换气体,研究降压强化置换过程中储层气相组分、CH4开采率与CO2封存率的变化.结果表明:CO2+N2联合降压强化置换法大幅度提高CH4水合物置换效率,CH4置换率相较于传统置换法的15.2%提升至35.22%,其中N2直接贡献率占8.66%.通过降压强化,显著增强分解后期阶段气体扩散效果,提高CH4开采率与CO2封存率,对提高水合物转换开采具有良好的应用前景.
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.