Effects of Flow Pattern and Pore Size on Immiscible Continuous Three-Phase Displacement

A single cylindrical capillary is often employed to construct a simplified system for multiphase flow in porous media, which is particularly important to numerous applications such as oil recovery and contaminated land and groundwater remediation. Herein, systematic experimental investigations were conducted on spontaneous and controlled displacement containing three phases (water, oil, and gas) in capillaries of various radii from 2 to 10 μm. It was demonstrated that the three-phase flow pattern was a dominating factor influencing displacement behaviors. For spontaneous displacement, the measured static contact angles could be adopted to predict motion rates and the total capillary pressures for the water–oil–gas flow satisfactorily, while it failed in predicting those of the oil–water–gas flow. The discrepancy in the latter case is attributed to the significant decrease of receding water–oil–solid three-phase contact angle, which could be strongly related to the retained water layer and be consistent with our prior simulation findings. For controlled three-phase displacement processes involving displacement of oil by water, results of the relationship between flow rate and external pressure drop and the variations of total capillary pressure with displacing phase saturation together imply underlying differences between the two kinds of flow patterns from the aspects of forces, energy, work, and pore size. The relationship between pressure gradient and displacement rate shows a clear linear correlation, which agrees with the expression of pressure gradient of liquid phase that established simultaneously.