Drainage displacement at unfavorable viscosity ratios is often encountered in oil recovery, CO₂ sequestration, and NAPL remediation, which significantly limits recovery of fluids from porous media. Surfactants have been extensively used as wettability modifiers to improve hydrocarbon recovery from rock matrix by imbibition. But little attention has been paid to the effect of surfactant-assisted wettability alteration on displacement in non-fractured porous media. In this study, we investigate surfactant-assisted immiscible displacement in NAPL-wet microfluidic chips. We find that the change of advancing contact angle by surfactant is velocity dependent. A stable displacement can be achieved at low velocity when wettability-altering surfactant solution is used as injection fluid. In comparison, fingering occurs at all capillary numbers for water injection, resulting in low NAPL recovery. The generation of NAPL ganglion during waterflooding is significantly different from that during wettability-altering surfactant flooding. The generation of NAPL ganglion during wettability-altering surfactant flooding is related to velocity and saturation due to the wettability alteration and interfacial tension reduction. In contrast, the production of NAPL ganglion during waterflooding is only saturation dependent. NAPL ganglia generated during wettability-altering surfactant flooding are primarily within the pore-size range and can be easily recovered in subsequent recovery processes. To the best of our knowledge, this study reveals for the first time the pore-scale mechanism of surfactant-assisted wettability on the immiscible displacement, which is important for highly efficient NAPL remediation.

中文翻译：

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表面活性剂辅助润湿性改变对不混溶位移的影响：微流体研究

在采油、CO _{2 中}经常遇到在不利的粘度比下的排水驱替封存和 NAPL 修复，这显着限制了从多孔介质中回收流体。表面活性剂已被广泛用作润湿性改性剂，以通过渗吸提高岩石基质中的烃采收率。但很少关注表面活性剂辅助润湿性改变对非破裂多孔介质中置换的影响。在这项研究中，我们研究了 NAPL 湿微流控芯片中表面活性剂辅助的不混溶置换。我们发现表面活性剂对前进接触角的变化与速度有关。当使用改变润湿性的表面活性剂溶液作为注入流体时，可以在低速下实现稳定的驱替。相比之下，在注水的所有毛细管数量处都会发生指状，导致 NAPL 回收率低。水驱过程中NAPL神经节的产生与改变润湿性的表面活性剂驱过程中的产生显着不同。由于润湿性改变和界面张力降低，在改变润湿性的表面活性剂驱替过程中NAPL神经节的产生与速度和饱和度有关。相比之下，注水期间 NAPL 神经节的产生仅依赖于饱和度。在润湿性改变表面活性剂驱替过程中产生的 NAPL 神经节主要在孔径范围内，并且可以在随后的回收过程中轻松回收。据我们所知，这项研究首次揭示了表面活性剂辅助润湿性对不混溶置换的孔隙尺度机制，这对于高效 NAPL 修复非常重要。