The Micro-Flow Mechanism Study On Polymer Flooding Considering The Elastic Turbulence

In the chemical flooding enhanced oil recovery(EOR)methods,polymer flooding still plays an important role and has acquired a good effect in industrial applications of oilfields.Micro flow mechanism of polymer solution under laminar condition has been studied by experiments and theoretical studies,additionally,experimental and field data suggest that the elasticity of polymer improves displacement efficiency as well.Recently,in the micro oil displacement experiments,it is found that the polymer solution with low Reynolds number(Re)and high Weissenberg number(We)can induce elastic turbulence in the porous media,which could reduce the residual oil saturation.However,there are few studies in micro flow mechanism of polymer solution considering turbulence condition,especially at quantitative description.Therefore,in this work,the computational fluid dynamics(CFD)method was applied to carry out the theoretical research of the micro flow mechanism of viscoelastic polymer flooding with elastic turbulence,based on micro flow mechanism of viscoelastic polymer solution under laminar flow.Firstly,we established the single phase flow mathematical model of polymer solution considering elastic turbulence,and it was transformed into mathematical model by the log-conformation reformulation method.Then the finite volume method was used for the discretization of mathematical model,thus forming a numerical simulation method to describe the elastic turbulence of viscoelastic polymer solution,which improved the We of viscoelastic polymer solution.The flow characteristics of viscoelastic polymer solution in the dead end channel and expansion–contraction channel were studied further,and the onset of elastic turbulence was identified by velocity fluctuation and turbulence intensity.The changes of micro flow characteristics about viscoelastic polymer solution in porous media before and after the elastic turbulence were discussed through the behaviors of streamline,velocity contours,stress and pressure,and then the influence of elastic turbulence on the micro flow characteristics and micro sweep efficiency of viscoelastic polymer solution were revealed.The results show that in lower Re condition,the elastic turbulence critical Weissenberg number(We_c)of high elastic polymer solution was 5~10 in the porous media.Elastic turbulence changed the size of vortex and the position of vortex center in the dead end and convex corner,and increased the micro sweep area of polymer solution.Moreover,elastic turbulence increased the stress of the dead end and convex corner,and the pressure contours in dead area became denser,forming higher additional pressure drop,and increased pressure drop across the micro channel,which provided dynamic source for the residual oil.Before the occurrence of turbulence,the micro sweep efficiency increases significantly with the increase of Re,however,after the occurrence of turbulence,since the elastic effect of the polymer solution dominates,Re has little effect on micro sweep efficiency.When the elastic turbulence occurred,the micro sweep efficiency in the dead end channel was 21%~38%higher than that of We=0 and the micro sweep efficiency in the contraction-expansion channel was 8%~16%higher than that of We=0,therefore,the elastic turbulence contributes a lot to the micro sweep efficiency of the residual oil in the porous media.The study results provide important theoretical support for the design,screening and injection of polymer solution in oilfield,simultaneously,they are beneficial to the expansion and enrichment of micro flow mechanism of viscoelastic polymer solution.