Experimental study of strong imbibition in microcapillaries representing pore/throat characteristics of tight rocks

Imbibition pervasively exists in many industrial processes and is fundamental in developing unconventional resources in tight formations. Micromodels have been widely used as powerful tools for real-time observations of imbibition dynamics to support numerical modeling developments and understanding of macroscopic patterns. However, the inherent limitation of 2D micromodels in presenting 3D features in the pores/throats of tight rocks may reduce the reliability of the microfluidic results. Here, we quantitively investigate imbibition dynamics in single pore geometries that consider 2D pore-scale characteristics of tight rocks with an etching depth higher than the critical geometric criteria for including 3D features. We discuss the experimental data based on varying parameters, such as five pore shapes, a wide range of pore-throat aspect ratios (6.25 to 100), two typical throat widths (3 and 8 μm), and local capillary numbers (10-6 to 10-4). The results show that the wetting phase saturations increase linearly with the increasing inlet flow rate, consistent with previous findings in cores and 2.5D micromodels, but only in macropores. Snap-offs are found when the moved meniscus front pressure is higher than the critical capillary pressure of snap-off. An etching depth higher than the critical geometric criteria is necessary but insufficient to mimic imbibition dynamics in tight rocks by 2D micromodels with a pattern that the most pore-throat aspect ratios are less than 30 at a strong imbibition condition.