Abstract The immiscible fluid displacement pattern, controlled by the balance of viscous and capillary forces has a significant effect on the recovery or storage efficiency in subsurface processes. The phase diagram of displacement patterns has been extensively studied for the two-dimensional (2D) micromodel; however, that of the three-dimensional (3D) porous media has received little attention. This work experimentally studied the immiscible drainage displacement in an unconsolidated packed bed at the pore scale with a wide range of capillary number Ca and viscosity ratio M using X-ray micro-tomography. Three typical displacement patterns, namely viscous fingering, capillary fingering, and stable displacement, were observed in 3D porous media. The rough location of three displacement patterns on the Ca–M diagram was consistent with previous studies in 2D micromodel. The boundaries for three regimes were determined based on the quantitative analyses of the saturation distribution as functions of Ca and M. Compared with the result in 2D micromodel, a broader transition zone between different regimes was found in 3D porous media. The characterizations of finger structures (e.g. fractal dimension and finger width) were applied to reveal the mechanism of how the injected fluid invades the pores and throats inside porous media for different displacement patterns. The average fractal dimension of capillary fingerings was 2.58 ± 0.05, which agrees with the 2.55 defined by the invasion percolation theory. For the viscous fingering, where the viscous force dominates the invasion process, the invading fluid follows a several preferential flow paths in the same direction as the injection and the finger width was only 1 to 2 pore bodies. Besides, the invasion dynamics under continuous injection conditions were compared for typical viscous and capillary fingerings. This study may improve our understanding of the dynamics of displacement processes jointly governed by the viscous/capillary forces in 3D porous media. Furthermore, the phase diagram under various conditions (i.e. a wide range of Ca and M) can help to find a suitable reservoir conditions for subsurface processes.

中文翻译：

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三维多孔介质中非混相流体驱替模式及相图的实验研究

摘要 由粘性力和毛细力平衡控制的不混溶流体驱替模式对地下过程中的回收或储存效率有显着影响。对于二维 (2D) 微模型，位移模式的相图已被广泛研究；然而，三维（3D）多孔介质的研究很少受到关注。这项工作使用 X 射线显微断层扫描实验研究了松散填充床在孔隙尺度下具有宽范围的毛细管数 Ca 和粘度比 M 的不混相排水位移。在 3D 多孔介质中观察到三种典型的位移模式，即粘性指法、毛细管指法和稳定位移。Ca-M 图上三种位移模式的粗略位置与先前在 2D 微模型中的研究一致。基于饱和度分布作为 Ca 和 M 的函数的定量分析，确定了三种状态的边界。与 2D 微模型中的结果相比，在 3D 多孔介质中发现了不同状态之间更宽的过渡区。应用指状结构的特征（例如分形维数和指状宽度）来揭示注入流体如何侵入多孔介质内部孔隙和喉道的机制，以实现不同的置换模式。毛细管指法的平均分形维数为 2.58 ± 0.05，与入侵渗透理论定义的 2.55 一致。对于粘性指法，粘性力在入侵过程中占主导地位，侵入流体沿与注入方向相同的几个优先流动路径，指状宽度仅为1至2个孔体。此外，比较了典型的粘性和毛细管指法在连续注入条件下的侵入动力学。这项研究可能会提高我们对由 3D 多孔介质中的粘性/毛细管力共同控制的位移过程动力学的理解。此外，各种条件下的相图（即宽范围的 Ca 和 M）可以帮助找到适合地下过程的储层条件。比较了典型粘性和毛细管指法在连续注入条件下的侵入动力学。这项研究可能会提高我们对由 3D 多孔介质中的粘性/毛细管力共同控制的位移过程动力学的理解。此外，各种条件下的相图（即宽范围的 Ca 和 M）可以帮助找到适合地下过程的储层条件。比较了典型粘性和毛细管指法在连续注入条件下的侵入动力学。这项研究可能会提高我们对由 3D 多孔介质中的粘性/毛细管力共同控制的位移过程动力学的理解。此外，各种条件下的相图（即宽范围的 Ca 和 M）可以帮助找到适合地下过程的储层条件。