Adsorption Performance Of Coking Shale In The Sichuan Basin And Carbon Dioxide Displacement Behavior Of Shale Gas

Shale gas,mainly consisting of methane,is a typical and burgeoning unconyentional natural gas.The reserve of shale gas resources in china is abundant.Thus,the large-scale exploitation of shale gas is in favor of optimizing energy consumption structure and mitigating energy dependence on import.Recently,the carbon dioxide(CO2)injection in the deep shale reservoirs is not beneficial to enhance shale gas recovery,but also to reduce the major anthropogenic greenhouse gas CO2 emissions.In consideration of the above background,shale samples were collected from Jiaoshiba area of Sichuan basin to conduct related research.The main contents incorporate the physical and chemical properties of shales in Jiaoshiba area,the characteristics and regularity of the adsorption behaviors of pure CH4 and CO2 on shales,and the displacement behaviors of CH4 adsorbed on shales by CO2 injection.The detailed results are summarized as follows:(1)Study on the physical and chemical properties of shale samples in Jiaoshiba area shows that:?The TOC content of shale samples is lower,and the minerals are more complex mainly including quartz and clay minerals.The pore system mainly including the meso/macro pores of shale samples is relatively underdeveloped.?The relationship between the pore structure parameters and the TOC content depends on the range of TOC.The pore structure parameters of shale samples show negative correlation with the quartz content,while this trend is reverse for the clay mineral content.?The fractal theory analysis based on the results of N2 adsorption/desorption characterization indicates that the heterogeneity of the pore structure is higher than that of the pore surface of shale.The U-shaped trend exists between thepore fractal dimension and the TOC content.The pore fractal dimension exhibits a positive correlation with the clay minerals content while shows a negative correlation with the quartz content.The fractal dimensions of both the pore surface and the pore structure are positively correlated with the pore surface area and the pore volume of shale samples,respectively.(2)The research on characteristics and regularity of the adsorption behaviors of pure CH4 and CO2 on shales indicates that:?The simplified Ono-Kondo Lattice model is of good predictive accuracy for both CH4 and CO2 adsorption equilibrium behaviors at high pressure on four shale samples.The fitting parameters of Ono-Kondo Lattice model confirm that the adsorption capacity of CO2 on all shale samples is stronger than that of CH4,and the adsorption of both CH4 and CO2 on shales mainly obeys the physisorption mechanism.?The maximum adsorption capacity of CH4 shows a significant linear positive correlation with the micropore parameters of shales,while this linear positive correlation is weak for the maximum adsorption capacity of CO2.?The superior adsorption ratio of CO2 to CH4 of all shale samples ranges between 2 and 4 under the same conditions.The above results indicate that the displacement of CH4 adsorbed on shale reservoirs by CO2 injection is feasible.(3)Investigation on the displacement behaviors of CH4 adsorbed on shales by CO2 injection includes that:?CO2 injection into the shale system with saturated CH4 can displace shale gas CH4.? The amounts of both the recovered CH4 and the stored CO2 increase with the injection pressure of CO2.?The conceptual model of displacement process established in this work indicates that the displacement process of CH4 adsorbed on shales by CO2 injection can be divided into two stages:the shale samples with lower microporous specific surface area and volume have higher CO2 storage capacity under the lower CO2 injection pressure;while the shale samples with higher microporous specific surface area and volume have stronger CO2 storage capacity under higher CO2 injection pressure.This work aims to investigate the physical and chemical properties of shales from Jiaoshiba area,the characteristics and regularity of.the adsorption behaviors of pure CH4 and CO2 on shales,and the displacement behaviors of CH4 adsorbed on shales by CO2 injection.The related results and conclusions drawn from this work is helpful to further examine the shale reservoir characteristics and shale gas enrichment in Jiaoshiba area,and is also of meaningful some theoretical and practical values for CO2 sequestration in shale reservoirs with enhanced shale gas recovery.