The Study On Microscopic Porous Flow Behavior Of Polymer Solutions

During water displacement, the residual oil in the porous medium is difficult to displace, but the effect of displacement will be better with the polymer solution. Many researchers through the experiments have confirmed that the viscoelastic nature of the displacing polymer fluids can in general improve the displacement efficiency in pores. In this thesis, a great deal of work is reviewed including the status of basic theories on polymer flooding, model for viscoelastic fluid, model of porous media, and general research on the flow of viscoelastic fluid through complex channels. It is shown that research on the mechanism of microscopic displacement commonly bases on laboratory studies, for some oil displacement phenomena, it can only explained qualitatively, the theoretical research needs further on. So that, besides choosing proper model for viscoelastic fluid and geometric model characterizing reservoir pores, effective numerical methods should be used to solve mathematical model, so as to theoretically study viscoelasticity of polymer solution how to affect the microscopic displacement efficiency quantitatively. Therefore, we have done the following work mainly:The constitutive equations describing polymer rheology are analyzed by combing the typical rheology of polymer solutions. Lots of constitutive equations are studied according the rheology of the polymer solutions. In this paper the PTT model which can more accurately describe the rheology of polymer is selected.The mathematical model concluding the continuity equation, momentum equation and PTT constitutive equation is established. The governing equations are discreted adopting the staggered grid finite volume method numerically, the momentum equations are solved by power format and the constitutive equations are solved by first-order upwind scheme. Finally, the problem of high We number is solved, the stream function contours, velocity contours and the first normal stress difference contours are drawn under the condition of same quality and the condition of same pressure difference. In order to calculate the microscopic sweep efficiency in pore models, we define sweep boundary of displacement fluid, determine it by velocity method and finally analyze the microscopic displacement efficiency of polymer solution quantitatively.Numerical results show the viscoelasticity of polymer solutions is the main factor influencing sweep efficiency. With increasing elasticity, the flowing area in the corner is enlarged significantly, thus the area with immobile zones becomes smaller. Flow velocity is larger than that for a Newtonian fluid, the sweep area and displacement efficiency increase as the elasticity increases. The viscoelastic behavior of the displacing polymer fluids can in general improve the displacement efficiency in pores compared to using Newtonian fluids. This conclusion should be useful in selecting polymer fluids and designing polymer flooding operations.