Various energy recovery, storage, conversion and environmental operations may involve repetitive fluid injection and thus, cyclic drainage–imbibition processes. We conducted an experimental study for which polydimethylsiloxane (PDMS)-based micromodels were fabricated with three different levels of pore-space heterogeneity (coefficient of variation, where COV = 0, 0.25 and 0.5) to represent consolidated and/or partially consolidated sandstones. A total of 10 injection-withdrawal cycles were applied to each micromodel at two different flow rates (0.01 and 0.1 ml min^–1). The experimental results were analysed in terms of flow morphology, sweep efficiency, residual saturation, the connection of fluids and the pressure gradient. The pattern of the invasion and displacement of the non-wetting fluid converged more readily in the homogeneous model (COV = 0) as the repetitive drainage–imbibition process continued. The overall sweep efficiency converged between 0.4 and 0.6 at all tested flow rates, regardless of different flow rates and COV in this study. In contrast, the effective sweep efficiency was observed to increase with higher COV at the lower flow rate, while that trend became reversed at the higher flow rate. Similarly, the residual saturation of the non-wetting fluid was largest at COV = 0 for the lower flow rate, but it was the opposite for the higher flow-rate case. However, the Minkowski functionals for the boundary length and connectedness of the non-wetting fluid remained quite constant during repetitive fluid flow. Implications of the study results for porous media-compressed air energy storage (PM-CAES) are discussed as a complementary analysis at the end of this paper.

Supplementary material: Figures showing the distribution of water (Fig. S1) and oil (Fig. S2) at the end of each drainage and imbibition step in different microfluidic pore-network models are available at https://doi.org/10.6084/m9.figshare.c.5276814

Thematic collection: This article is part of the Energy Geoscience Series available at: https://www.lyellcollection.org/cc/energy-geoscience-series

各种能量回收，存储，转换和环境操作可能涉及重复的流体注入，因此涉及循环排水-吸水过程。我们进行了一项实验研究，针对该模型制作了聚二甲基硅氧烷（PDMS）微观模型，该模型具有三种不同水平的孔隙空间非均质性（变化系数，其中COV = 0、0.25和0.5）来表示固结和/或部分固结的砂岩。以两种不同的流速（0.01和0.1 ml min ^–1）对每个微模型总共进行了10个注射-退出循环）。从流动形态，波及效率，残余饱和度，流体的连通性和压力梯度等方面对实验结果进行了分析。随着重复的排水-吸水过程的继续，在均质模型（COV = 0）中，非润湿性流体的侵入和驱替模式更容易收敛。在所有测试的流速下，总吹扫效率都在0.4到0.6之间收敛，而与本研究中不同的流速和COV无关。相反，观察到有效吹扫效率在较低流速下随COV越高而增加，而在较高流速下则相反。同样，对于较低的流量，在COV = 0时，非润湿性流体的残留饱和度最大，而对于较高的流量情况，则相反。然而，非重复流体的边界长度和连通性的Minkowski泛函在重复流体流动过程中保持相当恒定。本文末尾将对多孔介质压缩空气储能（PM-CAES）研究结果的含义进行补充讨论。

补充材料： https：//doi.org/10.6084/上提供了显示不同微流孔网络模型中每个排水和吸水步骤结束时水（图S1）和油（图S2）的分布的图。 m9.figshare.c.5276814

专题收藏：本文是《能源地球科学丛书》的一部分，可从以下网站获得：https：//www.lyellcollection.org/cc/energy-geoscience-series