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Understanding of wettability effects on multiphase displacement in porous media is very helpful for design and optimization of engineering applications. Microfluidic experiments on chips provide a powerful visible test platform to reveal mechanisms of such effects, however some laboratory tests have reported inconsistent wettability effects on displacement with the previous field or core tests. Therefore it is very important to revisit the designs of pore geometries and flow conditions and to perform the experiments carefully under consistent parameters with field tests, whose quantitative observations may help to reveal the mechanisms.
This work will report our unique geometrical design of porous microstructures, step by step approaching the real rock materials. The strategy of “reservoir chip” will be introduced based on stochastics-statistics. By performing the microfluidic experiments carefully under consistent Capillary numbers as the field tests, the non-monotonic wettability effects will be presented on displacement efficiency in heterogeneous porous structures, in contrast to the monotonic ones in the homogeneous porous structures. Experiments on designed microfluidic chips show that there exists a critical wettability to attain the highest efficiency of displacement in the porous matrix structure combined with a preferential flow pathway, while a stronger wettability of displacing fluid leads to a higher displacement efficiency on the same matrix structure only. Pore-scale mechanisms are identified to elucidate the formation of this non-monotonic wettability rule: balance between sweeping ability and carrying ability of the displacing fluid. A multi-etching fabrication technology is then designed to manufacture variable-depth microfluidic chips to study the 3D effects of pores. The experimental results, together with pore-scale numerical simulations, show that the interfacial instability enhanced by 3D geometries may sometimes dominate the invading process. A diagram is therefore obtained to illustrate such a process. The pore-scale findings may provide unique insights into the joint effects of both wettability and flow heterogeneity on fluid displacement in porous media.
| References | [1] W.H. Lei, X. Lu, W. Gong, M. Wang*. Triggering interfacial instabilities during forced imbibition by depth variation in microfluidic porous media. Proceedings of the National Academy of Sciences 120(50): e2310584120, 2023 [2] W.H. Lei, W. Gong, M. Wang*. Wettability effect on displacement in disordered media under preferential flow condition. Journal of Fluid Mechanics 975: A33, 2023 [3] W. Lei, X.K. Lu, F.L. Liu, and M. Wang*. Non-monotonic wettability effects on displacement in heterogeneous porous media. Journal of Fluid Mechanics –Rapids 942: R5, 2022 [4] F.L. Liu and M. Wang*. Wettability Effects on Mobilization of Ganglia During Displacement. International Journal of Mechanical Sciences 215: 106933, 2022 |
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| Country | China |
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