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

Abstract

Molecular dynamics method was used to establish composite wall/inorganic nanopores of three pore sizes, three shale oil systems, five CO2-cosolvent systems, and pure CO2 system. The process of CO2-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 CO2 and shale oil. The more the non-polar components of shale oil, the lower the mutual solubility of CO2 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 CO2. The CO2 inside the kerogen is not easy to diffuse and leak, thus allowing for a stable carbon storage. The highest CO2 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.