Abstract A series of micro-scale core-flooding experiments were conducted in a miniature water-wet Berea sandstone sample to examine how changes in the desaturation (water-displacing-oil) protocol impact the non-wetting phase recovery and to provide, to the best of our knowledge, the first pore-scale evidences of the associated displacement subtleties. We studied (i) the continuous displacement mode (CDM), which consisted of a series of imbibition tests with increasing capillary numbers and similar initially connected oil, and (ii) the discontinuous displacement mode (DDM), which included a drainage followed by a multi-rate imbibition test. During all experiments, a cutting-edge imaging platform was employed to visualize the fluid occupancies in the pore space. The in-situ saturation measurements showed that, at a given capillary number, the non-wetting phase recovery was more efficient under the continuous mode during which the oil phase was connected prior to each imbibition. This is attributed to the changes in the order by which the pore-scale displacement events take place before entrapment. For the DDM, however, the entrainment of oil clusters is the governing recovery mechanism, and the desaturation process was observed only when a threshold capillary number was reached. These findings are supported by pore-scale fluid occupancy maps demonstrating piston-like and snap-off events during the capillary-driven flow processes as well as trapped cluster entrainment during the viscous-dominated flow tests. Moreover, this investigation presents previously unidentified pore-scale displacement events in natural porous media, such as fragmentation and coalescence of trapped non-wetting phase globules prior to entrainment.These mechanisms took place at intermediate capillary numbers and mostly under the discontinuous displacement mode before the threshold of mobilization was reached. The capillary desaturation process under CDM was found to be gradual and more pronounced compared to that under the DDM mode. It is also demonstrated that even though the pore-scale displacement mechanisms responsible for oil recovery are different for CDM and DDM, the viscous-dominated imbibition tests produce similar distributions of trapped oil clusters under both cases.

中文翻译：

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工艺相关毛细管去饱和的孔隙尺度实验研究

摘要 在微型水湿 Berea 砂岩样品中进行了一系列微型岩心驱油实验，以研究去饱和（水驱油）协议的变化如何影响非润湿相采收率，并提供给据我们所知，这是相关位移微妙性的第一个孔隙尺度证据。我们研究了 (i) 连续驱替模式 (CDM)，包括一系列具有增加毛细管数量和类似的初始连接油的渗吸测试，以及 (ii) 不连续驱替模式 (DDM)，其中包括排水，然后是多速率渗吸试验。在所有实验中，都采用了尖端的成像平台来可视化孔隙空间中的流体占有率。原位饱和度测量表明，在给定的毛细管数下，在连续模式下，非润湿相的回收效率更高，在此模式下，油相在每次渗吸之前连接。这是由于孔隙尺度位移事件在被截留之前发生的顺序发生了变化。然而，对于 DDM，油簇的夹带是控制恢复机制，只有当达到阈值毛细管数时才观察到去饱和过程。这些发现得到了孔隙尺度流体占据图的支持，这些图显示了毛细管驱动流动过程中的活塞状和折断事件，以及粘性主导流动测试期间的捕获簇夹带。此外，这项研究还展示了天然多孔介质中先前未识别的孔隙尺度置换事件，例如夹带之前捕获的非润湿相小球的碎裂和聚结。这些机制发生在中等毛细管数下，并且在达到动员阈值之前主要在不连续置换模式下发生。与 DDM 模式相比，CDM 下的毛细管去饱和过程是渐进的，更明显。还表明，即使 CDM 和 DDM 负责石油采收率的孔隙尺度置换机制不同，但粘性主导的渗吸测试在两种情况下产生相似的被困油簇分布。与 DDM 模式相比，CDM 下的毛细管去饱和过程是渐进的，更明显。还表明，即使 CDM 和 DDM 负责石油采收率的孔隙尺度置换机制不同，但粘性主导的渗吸测试在两种情况下产生相似的被困油簇分布。与 DDM 模式相比，CDM 下的毛细管去饱和过程是渐进的，更明显。还表明，即使 CDM 和 DDM 负责石油采收率的孔隙尺度置换机制不同，但粘性主导的渗吸测试在两种情况下产生相似的被困油簇分布。