Pore-Scale Mechanism Research Of Imbibition In Porous Media

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.In this study,the Navier-Stokes equation coupled with volume of fluid method has been employed to build a pore-scale two-phase flow model and the mechanism and influencing factors of porous media at pore-scale are revealed through the quantitative characterization of the front morphology.Firstly,two-dimensional porous media models with different disorders were established.Based on these models,effects of poresize disorder and wettability on forced imbibition in porous media under different capillary numbers were studied.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.With the decrease of the wettability,the recovery efficiency decreases.At intermediate capillary number,only the largest disorder has obvious influence on the displacement process due to the highest entry pressure.At this time,the wettability still has a significant impact on the imbibition process.With the decrease of the wettability,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.As the disorder number increases,more unstable phase interface and lower recovery efficiency are observed.Secondly,we studied the effect of viscosity ratio and capillary number on the imbibition process,and found that a higher oil-water viscosity ratio has an important impact on stabilizing the oilwater interface and improving oil recovery.We compared the simulation results with the traditional displacement phase diagram.The analysis shows that as the disorder of the porous media increases,the simulation results deviate from the phase diagram due to the decrease of the critical capillary number.In addition,we calculated the energy capillary number according to the law of energy dissipation,divided the different imbibition areas and analyzed the characteristics of each area.Thirdly,we conducted imbibition simulations study on the threedimensional digital core based on the VOF method to study the influence of viscosity ratio,wettability and other factors on the imbibition process.Then we analyzed the influence of the heterogeneity of porous media by constructing three-dimensional homogeneous and heterogeneous porous media models.It was observed that larger wetting angle,lower oil-water viscosity ratio and the heterogeneous porous mediua will lead to more fingers,less stable displacement front and lower imbibition efficiency.Finally,we analyzed the influence of factors such as wettability and heterogeneity of porous media on the relative permeability of oil and water.This paper studies the microscopic imbibition mechanism at the pore-scale based on the Navier-Stokes equation and analyzes effects of different factors on the front morphology,phase distribution and recovery efficiency,which can provide theoretical guidance for tight reservoir development and related reservoir engineering methods.