Displacement Mechanism of Oil in Shale Inorganic Nanopores by Supercritical Carbon Dioxide from Molecular Dynamics Simulations

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• 作者：Bing LiuChao Wang ; Jun Zhang ; Senbo Xiao ; Zhiliang Zhang ; Yue Shen ; Baojiang Sun ; Jianying He
• 刊名：Energy & Fuels
• 出版年：2017
• 出版时间：January 19, 2017
• 年：2017
• 卷：31
• 期：1
• 页码：738-746
• 全文大小：777K
• ISSN：1520-5029

文摘

Supercritical COb>2b> (scCOb>2b>), as an effective displacing agent and clean fracturing fluid, exhibits a great potential in enhanced oil recovery (EOR) from unconventional reservoirs. However, the microscopic translocation behavior of oil in shale inorganic nanopores has not been well understood yet in the scCOb>2b> displacement process. Herein, nonequilibrium molecular dynamics (NEMD) simulations were performed to study adsorption and translocation of scCOb>2b>/dodecane in shale inorganic nanopores at different scCOb>2b> injection rates. The injected scCOb>2b> preferentially adsorbs in proximity of the surface and form layering structures due to hydrogen bonds interactions between COb>2b> and −OH groups. A part of scCOb>2b> molecules in the adsorption layer retain the mobility, due to the cooperation of slippage, Knudsen diffusion, and imbibition of scCOb>2b>. The adsorbed dodecane are separated partly from the surface by scCOb>2b>, as a result the competitive adsorption between scCOb>2b> and dodecane, and thus enhancing the mobility of oil and improving oil production. In the scCOb>2b> displacement front, interfacial tension (IFT) reduction and dodecane swelling enhance the mobilization of dodecane molecules, which plays the crucial role in the COb>2b> EOR process. The downstream dodecane, adjacent to the displacement front, is found to aggregate and pack tightly. The analysis of contact angle, meniscus, and interfacial width shows that the small scCOb>2b> injection rate with a large injection volume is favorable for COb>2b> EOR. The morphology of meniscus changes in the order convex–concave–COb>2b> entrainment with the increase of the injection rate. The microscopic insight provided in this study is helpful to understand and effectively design COb>2b> exploitation of shale resources.