Effects of pore-size disorder and wettability on forced imbibition in porous media

Abstract

Imbibition is the process by which the wetting fluid displaces the non-wetting fluid driven by capillary force. It occurs in many natural and industrial processes, such as enhanced oil recovery and geological carbon sequestration. The imbibition process is highly affected by wettability, viscosity ratio and injection flow rate, and the competition between these factors becomes more complicated when pore-size disorder is involved. In this study, we systematically investigate forced imbibition in four two-dimensional (2D) porous media with different disorders over a broad range of wettability conditions and flow rates. We analyze the relationship between the interfacial length and the invading fluid saturation, and the relationship between displacement front and invading fluid saturation. Results show that disorder and wettability have different impacts on the imbibition process under different capillary numbers. At low capillary number, displacement process is not sensitive to disorder due to the contradicting effects and the imbibition process is governed by the wettability. At intermediate capillary number, only the largest disorder has obvious influence on the displacement process due to the highest entry pressure. The transition from capillary fingering to viscous fingering occurs leading to a higher displacement efficiency. At high capillary number, disorder has a great influence on the front morphology and displacement efficiency while the wettability has relatively weak impact. The pattern transition is also observed at strong imbibition because of the competing effects between the capillary force and the viscous force.