助溶剂对二氧化碳置换页岩油及碳封存的影响

Effect of cosolvents on CO2 displacement of shale oil and carbon storage

利用分子动力学方法建立了3种孔隙尺寸的复合壁面纳米孔隙/无机纳米孔隙、3种页岩油体系、5种CO_(2)+助溶剂复合体系及纯CO_(2)体系,模拟了页岩纳米孔隙中CO_(2)+助溶剂对页岩油的置换及封存过程,分析了置换与封存的影响因素。研究表明:石英壁面对页岩油的吸引作用随羟基化程度增大而增强,石英羟基化程度越高,页岩油中极性组分的开采难度越大。纳米孔隙孔径对页岩油置换效率也有较大影响,孔径越大,页岩油置换效率越高。助溶剂分子与页岩油极性越接近,越有利于CO_(2)与页岩油互溶,加入强极性助溶剂时页岩油中非极性组分越多,越不利于CO_(2)与页岩油互溶。乙酸乙酯对极性相对较强的页岩油剥离效果较好,二甲醚则对极性相对较弱的页岩油剥离效果较好。干酪根具有较强的吸附性能,对CO_(2)具有更强的吸附能力,CO_(2)进入干酪根后不易发生扩散泄漏,碳封存稳定性好。二甲醚作为助溶剂时,CO_(2)的封存率最高,乙酸乙酯作为助溶剂时,封存稳定性最好。

Molecular dynamics method was used to establish composite wall/inorganic nanopores of three pore sizes,three shale oil systems,five CO_(2)-cosolvent systems,and pure CO_(2) system.The process of CO_(2)-cosolvent displacement of crude oil in shale nanopores and carbon storage was simulated and the influencing factors of displacement and storage were analyzed.It is shown that the attraction of the quartz wall to shale oil increases with the degree of hydroxylation.The higher the degree of quartz hydroxylation,the more difficult it is to extract the polar components of shale oil.Nanopore size also has a great impact on shale oil displacement efficiency.The larger the pore size,the higher the shale oil displacement efficiency.The closer the cosolvent molecules are to the polarity of the shale oil,the higher the mutual solubility of CO_(2) and shale oil.The more the non-polar components of shale oil,the lower the mutual solubility of CO_(2) and shale oil with highly polar cosolvent.Ethyl acetate is more effective in stripping relatively high polar shale oil,while dimethyl ether is more effective in stripping relatively low polar shale oil.Kerogen is highly adsorptive,especially to CO_(2).The CO_(2) inside the kerogen is not easy to diffuse and leak,thus allowing for a stable carbon storage.The highest CO_(2) storage rate is observed when dimethyl ether is used as a cosolvent,and the best storage stability is observed when ethyl acetate is used as a cosolvent.