Fast synchrotron tomography is used to study the impact of capillary number, $\text{Ca}$, on fluid configurations in steady-state two-phase flow in porous media. Brine and $n$-decane were co-injected at fixed fractional flow, $f_w=0.5$, in a cylindrical Bentheimer sandstone sample for a range of capillary numbers $2.1\times {10}^{-7}\le \text{Ca}\le 4.2\times {10}^{-5}$, while monitoring the pressure differential. As we have demonstrated in Gao et al. [Phys. Rev. Fluids 5, 013801 (2020)], dependent on $\text{Ca}$, different flow regimes have been identified: at low $\text{Ca}$ only fixed flow pathways exist, while after a certain threshold dynamic effects are observed resulting in intermittent fluctuations in fluid distribution which alter fluid connectivity. Additionally, the flow paths, for each capillary number, were imaged multiple times to quantify the less frequent changes in fluid occupancy, happening over timescales longer than the duration of our scans (40 s). In this paper we demonstrate how dynamic connectivity results from the interaction between oil ganglia populations. At low $\text{Ca}$ connected pathways of ganglia are fixed with time-independent small, medium, and large ganglia populations. However, with an increase in $\text{Ca}$ we see fluctuations in the size and numbers of the larger ganglia. With the onset of intermittency, fluctuations occur mainly in pores and throats of intermediate size. When $\text{Ca}$ is further increased, we see rapid changes in occupancy in pores of all size. By combining observations on pressure fluctuations and flow regimes at various capillary numbers, we summarize a phase diagram over a range of capillary numbers for the wetting and nonwetting phases, ${\text{Ca}}_w$ and ${\text{Ca}}_{nw}$, respectively, to quantify the degree of intermittent flow. These different regimes are controlled by a competition between viscous forces on the flowing fluids and the capillary forces acting in the complex pore space. Furthermore, we plot the phase diagrams of the transition from Darcy flow to intermittent flow over a range of Reynolds and Weber numbers for the wetting and nonwetting phases to evaluate the balance among capillary, viscous, and inertial forces, incorporating data from the literature. We demonstrate that pore geometry has a significant control on flow regime.

中文翻译：

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Bentheimer砂岩稳态两相流中的动态流体构造

快速同步加速器层析成像技术用于研究毛细管数的影响， $\text{钙}$，关于多孔介质中稳态两相流中的流体构造。盐水和$ñ$-癸烷以固定的分流共注入， $F_w=0.5$，在圆柱状Bentheimer砂岩样品中获得一定范围的毛细管数 $2.1\times {10}^{-7}\le \text{钙}\le 4.2\times {10}^{-5}$，同时监控压差。正如我们在Gao等人中所证明的那样。[物理 修订版液 5，013801（2020）]，依赖于$\text{钙}$，已经确定了不同的流动方式： $\text{钙}$仅存在固定的流动路径，而在观察到一定的阈值后，会观察到动态影响，导致流体分布的间歇性波动，从而改变了流体的连通性。此外，对每个毛细管数的流路进行了多次成像，以量化在比我们的扫描持续时间（40 s）更长的时间范围内发生的流体占用变化的频率。在本文中，我们展示了石油神经节种群之间的相互作用如何产生动态连通性。在低$\text{钙}$神经节的相互连接的路径由与时间无关的小，中和大神经节群体固定。但是，随着$\text{钙}$我们看到较大神经节的大小和数量都有波动。随着间歇的开始，波动主要发生在中等大小的孔和喉中。什么时候$\text{钙}$进一步增加，我们看到各种尺寸的毛孔中的占有率迅速变化。通过结合对各种毛细管数的压力波动和流动状态的观察，我们总结了润湿和非润湿相的一系列毛细管数的相图，${\text{钙}}_w$ 和 ${\text{钙}}_{ñw}$分别量化间歇流量的程度。通过在流动流体上的粘性力与作用在复杂孔隙空间中的毛细作用力之间的竞争来控制这些不同的状态。此外，我们结合了来自文献的数据，在润湿和非润湿阶段的一系列雷诺数和韦伯数之间绘制了从达西流到间歇流过渡的相图，以评估毛细管力，粘性力和惯性力之间的平衡。我们证明，孔的几何形状对流动状态有重要的控制。