The influences of composition and pore structure on the adsorption behavior of CH_(4) and CO_(2) on shale

CO_(2) enhanced shale gas recovery(CO_(2)-ESGR)has attracted extensive attention as it can improve the shale gas recovery efficiency and sequestrate CO_(2) simultaneously.In this study,the relationship between mineral composition,pore structure,CH_(4) and CO_(2) adsorption behavior as well as selective adsorption coefficient of CO_(2) over CH_(4)(αCO_(2)/CH_(4))in marine and continental shales at different temperatures was investigated.The results illustrated that shale with higher total organic carbon(TOC),higher clay minerals and lower brittle mineral contents has a larger micropores and mesopores volume and specific surface area.TOC content was positively correlated with fractal dimension Df.Both CH_(4) and CO_(2) adsorption capacity in shale have positive correlations with TOC and clay mineral content.CO_(2) adsorption capacity of the all the tested shale samples were greater than CH_(4),and theαCO_(2)/CH_(4) of shale were larger than 1.00,which indicated that using CO_(2)-ESGR technology to improve the gas recovery is feasible in these shale gas reservoirs.A higher TOC content and in shale corresponding to a lowerαCO_(2)/CH_(4) due to the organic matters show stronger affinity on CH_(4) than that on CO_(2).Shale with a higher brittle mineral content corresponding to a higherαCO_(2)/CH_(4),and no obvious correlation betweenαCO_(2)/CH_(4) and clay mineral content in shale was observed due to the complexity of the clay minerals.TheαCO_(2)/CH_(4) of shale were decreased with increasing temperature for most cases,which indicated that a lower temperature is more favorable for the application of CO_(2)-ESGR technique.