Experimental research on injection of liquid CO2 for exploiting natural gas hydrates
Injection of liquid CO2 for exploiting natural gas hydrates can safely produce CH4 while sequestering carbon in situ.To reveal the influence of CO2 phase states on hydrate reservoirs during extraction,a triaxial hydrate penetration experimental apparatus was used.In a NaCl system,quartz sand served as the porous medium,CH4 gas was injected to form methane hydrate,simulating natural gas hydrate reservoirs.Under a pore pressure stress of 4.5 MPa,the effects of liquid CO2 injection on the decomposition behavior of methane hydrate,the impact of reaction temperature on methane hydrate extraction by liquid CO2 injection,and the influence of reaction temperature on the post-extraction hydrate saturation of the reservoir were studied,respectively.The results show that injection of liquid CO2 promotes the decomposition of methane hydrate.At the reaction temperature of 8.0℃and the reaction pressure of 4.5 MPa,compared with the depressurization method,injection of liquid CO2 increases CH4 production by 22.81%and the recovery rate by 13.66%.In a liquid CO2 environment,higher reaction temperatures are favorable for the decomposition of methane hydrate.Compared to 6.0℃,the CH4 production increases by 40.41%at 10.0℃.Higher reaction temperatures play a dominant role in promoting hydrate decomposition,compared to the heat released during CO2 hydrate formation.As the reaction temperature increases,CO2 sequestration amount,conversion rate,and post-extraction reservoir hydrate saturation all decrease.At reaction temperatures of 6.0℃and 10.0℃,CO2 sequestration amounts are 0.1962 mol and 0.1034 mol,CO2 conversion rates are 22.08%and 11.86%,and post-extraction reservoir hydrate saturations are 57.91%and 34.21%,respectively,which increases by 38.81%and decreases by 18.01%,compared to the average initial saturation(41.72%).Injection of liquid CO2 for exploiting natural gas hydrates has a positive effect on increasing CH4 production and recovery rates,as well as promoting CO2 sequestration.
liquid CO2hydrate extractionnatural gas hydratesCO2 sequestration
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