Simulation of water self-imbibition in nanometer throat-pore structure filled with oil

Water self-imbibition potentially serves as a driving force for shale oil recovery due to the sizeable capillary pressure in the nanometer pores of shale. Understanding the water self-imbibition mechanism at the nanometer pore-scale helps promote shale oil recovery. In this work, we performed the direct numerical simulation using the phase-field model to study water self-imbibition dynamics in the nanometer throat-pore structure filled with oil. The effects of throat/pore morphologies (throat size, coordination number, and pore shape) and fluid properties (interfacial tension, contact angle, and viscosity) on the water imbibition dynamics were studied in detail. We distinguished two types of imbibition processes and found that the throat/pore morphologies significantly affect the final oil displacement ratio. Meanwhile, the interfacial tension and water contact angle mainly influence the imbibition rate (i.e., the oil displacement rate), while the water viscosity influences both the imbibition rate and the final oil displacement ratio. A qualitative correlation of the imbibition time and fluid properties is deduced by comparing classical theory predictions and simulation results. The quantitative deviations caused by local confinement are delineated as well.