Abstract Fluid displacement experiments were performed with immiscible fluids in a packed bed of glass spheres. The three-dimensional (3D) structure of the fingering pattern was visualized by computer tomography (CT) for a range of capillary numbers (Ca) between 5.22 × 10−7 and 1.04 × 10−4 at the viscosity ratio of log M = −2.203 in the absence of the influence of buoyancy force. Based on the 3D CT images, the characteristics of the fingering pattern at the crossover from viscous fingering (VF) to capillary fingering (CF) were investigated quantitatively. The structure of the fingering pattern changed gradually from streak-like for VF to more compact for CF with a decrease in Ca. Associated with the crossover from VF to CF, saturation of the invading phase (IP) and the fractal number of the structure both increased. The invaded pore size and invaded throat size distributions were also estimated for all values of Ca. The invaded pore size distribution was similar for all Ca values, but a clear shift in the throat size distribution was observed with the crossover from VF to CF.

中文翻译：

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从粘性指法到毛细指法的交叉处不混溶流中的三维指法结构

摘要 流体置换实验是在玻璃球填充床中用不混溶流体进行的。指法模式的三维（3D）结构通过计算机断层扫描（CT）在5.22×10-7和1.04×10-4之间的毛细管数（Ca）范围内可视化，粘度比为log M = - 2.203 在没有浮力的影响下。基于3D CT图像，定量研究了从粘性指法（VF）到毛细指法（CF）交叉处的指法特征。随着 Ca 的减少，指法模式的结构逐渐从 VF 的条纹状变为 CF 的更紧凑。与从 VF 到 CF 的交叉相关，侵入相 (IP) 的饱和度和结构的分形数都增加了。还估计了所有 Ca 值的侵入孔径和侵入喉道尺寸分布。所有 Ca 值的侵入孔径分布相似，但观察到喉道尺寸分布在从 VF 到 CF 的交叉时发生明显变化。