Gao Ying, Raeini Ali Q, Blunt Martin J, Bijeljic Branko
Qatar Carbonates and Carbon Storage Research Centre, Department of Earth Science and Engineering, Imperial College London, London SW7 2AZ, United Kingdom.
Phys Rev E. 2021 Jan;103(1-1):013110. doi: 10.1103/PhysRevE.103.013110.
Fast synchrotron tomography is used to study the impact of capillary number, 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 2.1×10^{-7}≤Ca≤4.2×10^{-5}, while monitoring the pressure differential. As we have demonstrated in Gao et al. [Phys. Rev. Fluids 5, 013801 (2020)2469-990X10.1103/PhysRevFluids.5.013801], dependent on Ca, different flow regimes have been identified: at low 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 Ca connected pathways of ganglia are fixed with time-independent small, medium, and large ganglia populations. However, with an increase in 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 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, Ca_{w} and 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.
快速同步加速器断层扫描技术用于研究毛细管数Ca对多孔介质中稳态两相流中流体构型的影响。在固定分流比fw = 0.5的情况下，将盐水和正癸烷共注入圆柱形的本特海默砂岩样品中，毛细管数范围为2.1×10−7≤Ca≤4.2×10−5，同时监测压差。正如我们在Gao等人的论文[《物理评论流体》5, 013801 (2020)2469 - 990X10.1103/PhysRevFluids.5.013801]中所证明的，根据Ca的不同，已识别出不同的流动状态：在低Ca时仅存在固定的流动路径，而在某个阈值之后会观察到动态效应，导致流体分布出现间歇性波动，从而改变流体连通性。此外，对于每个毛细管数，对流动路径进行多次成像，以量化流体占有率中较不频繁的变化，这些变化发生的时间尺度比我们扫描的持续时间（40秒）更长。在本文中，我们展示了动态连通性是如何由油团簇群体之间的相互作用产生的。在低Ca时，团簇的连通路径是固定的，存在与时间无关的小、中、大团簇群体。然而，随着Ca的增加，我们看到较大团簇的大小和数量出现波动。随着间歇性的开始，波动主要发生在中等尺寸的孔隙和喉道中。当Ca进一步增加时，我们看到所有尺寸孔隙中的占有率都出现快速变化。通过结合在不同毛细管数下对压力波动和流动状态的观测结果，我们总结了一个分别针对润湿相和非润湿相的毛细管数范围的相图，即Ca_w和Ca_nw，以量化间歇流动的程度。这些不同的状态由流动流体上的粘性力与作用在复杂孔隙空间中的毛细管力之间的竞争控制。此外，我们绘制了在一系列雷诺数和韦伯数下从达西流到间歇流的转变的相图，分别针对润湿相和非润湿相，以评估毛细管力、粘性力和惯性力之间的平衡，并纳入了文献数据。我们证明孔隙几何形状对流动状态有显著影响。
