Nan Yiling, Li Wenhui, Zhang Mingshan, Jin Zhehui
School of Mining and Petroleum Engineering, Department of Civil and Environmental Engineering, University of Alberta, Edmonton, Alberta T6G 1H9, Canada.
J Phys Chem B. 2021 Aug 26;125(33):9621-9628. doi: 10.1021/acs.jpcb.1c04869. Epub 2021 Aug 12.
Despite a great promise in the enhanced oil recovery in tight formations, CO flooding with surfactants is hindered due to the low surfactant solubility in supercritical CO (scCO). Alcohol blending can increase the sodium bis(2-ethylhexyl) sulfosuccinate (AOT) solubility in scCO. While this finding offers a promising solution to CO flooding in tight oil reservoirs, to the best of our knowledge, their working mechanism still remains elusive. Herein, we report a molecular dynamics simulation study to explore the working mechanism of alcohols in reverse micelle (RM) dispersity ("solubility") increment. The spontaneous aggregation process in two systems (System A consisting of AOT and scCO; System B consisting of AOT, scCO, and 10 wt % ethanol) are conducted under a typical tight oil reservoir condition (333 K and 200 bar). After 600 ns runs, the AOT molecules aggregate together and form rod-like RMs in System A, while form several small sphere-like RMs in System B. We observe that the aggregation process in System A occurs when two clusters approach each other end-to-end. More CO molecules are around the Na ion at the end of the clusters, which can be readily replaced by AOT molecules. On the other hand, the ethanol molecules can better solvate and surround Na ions, preventing the further aggregation of AOT clusters in System B. The potential of mean force calculations also reveal that while two small clusters formed by four AOT molecules attract each other in System A, they repel each other in System B. Our work should provide important insights into the design of scCO-soluble surfactant formulas.
尽管表面活性剂驱替二氧化碳在致密地层提高采收率方面前景广阔，但由于表面活性剂在超临界二氧化碳（scCO）中的低溶解度，限制了其应用。添加醇类可以提高双（2-乙基己基）磺基琥珀酸钠（AOT）在scCO中的溶解度。虽然这一发现为致密油藏的二氧化碳驱替提供了一个有前景的解决方案，但据我们所知，其作用机理仍不清楚。在此，我们通过分子动力学模拟研究来探索醇类在反胶束（RM）分散性（“溶解度”）增加方面的作用机理。在典型的致密油藏条件（333 K和200 bar）下，对两个体系（体系A由AOT和scCO组成；体系B由AOT、scCO和10 wt%乙醇组成）的自发聚集过程进行了模拟。经过600 ns的模拟运行，体系A中AOT分子聚集在一起形成棒状反胶束，而体系B中形成了几个小球状反胶束。我们观察到体系A中的聚集过程是在两个聚集体端对端相互靠近时发生的。在聚集体末端的Na离子周围有更多的CO分子，这些CO分子很容易被AOT分子取代。另一方面，乙醇分子可以更好地溶剂化并包围Na离子，从而防止体系B中AOT聚集体的进一步聚集。平均力势计算还表明，在体系A中由四个AOT分子形成的两个小聚集体相互吸引，而在体系B中它们相互排斥。我们的工作应为scCO可溶表面活性剂配方的设计提供重要的见解。
