A dynamic pore-scale network model for two-phase imbibition

• A dynamic pore-scale network model is developed for imbibition in two-phase flow.
• The model accounts for the complex dynamics of wetting film swelling and snap off.
• A new method is proposed to solve the nonlinear system of equations for pressure.
• The selection strategies for scale factor and time-step size are discussed.
• The rate effects on relative permeabilities and residual saturation are studied.

Pore-scale network modeling serves as an efficient tool for the simulation of multiphase flow in porous media, like carbon dioxide sequestration, enhanced gas/oil recovery and transport in fuel cell. To overcome the limitations of existing dynamic networks, we develop an alternative model for imbibition that accounts for the complex physical process of frontal displacement, film swelling, and snap off. The novelty of this model is that the outlet boundary is permeable to both wetting and non-wetting fluids before all the displaced phase is trapped. Instead of solving the nonlinear system of film pressure equations with conventional algorithms, a scale factor is employed to iteratively adjust the solutions estimated independently by mass conservation and the Young–Laplace equation until they are consistent with each other. To guarantee the effectiveness and accuracy, we also provide strategies for the selection of two significant considerations: scale factor and time-step size. This method is employed to study the effects of displacement rate and contact angle on waterflooding performance, relative permeabilities, as well as residual saturation. We believe this model can be further used to describe the distribution of slickwater in shale gas systems after hydraulic fracturing and predict water saturation based on the pore-scale topology of reservoirs.