Deformation And Fracture Mechanism Of Residual Oil Adhering To Wall Surface

Polymer displacement has become one of the necessary recovery enhancement methods for old oil fields,but the mechanism of its polymer displacement in the subsurface is difficult to be clarified.The recovery rate of water displacement is generally not high,and there is still a large amount of residual oil left in the formation,so the study of the mechanism of polymer displacement after water displacement is of great significance to improve the recovery rate of crude oil.In the microscopic scale,we take the film-like residual oil adhering to the wall as an example to analyze its force deformation phenomenon under different working conditions,summarize the law and explore the conditions for the rupture of small oil droplets.In this paper,the rheological properties of viscoelastic polymer solution are described by upper-convected Maxwell constitutive equation,and the two-dimensional flow equation of viscoelastic fluid in microscale flow channel is established by combining the non-Newtonian fluid dynamics theory.The front tracking method is used to track the changes of the intersection between the displacing fluid and the residual oil,and the Crank-Nicolson algorithm is used to solve the discrete equations to ensure the accuracy,and then explore the mechanism of residual oil rupture to provide theoretical support for improving the recovery of crude oil.The main contents are:(1)Establishing the computational model and computational grid for the flow of displacing fluid in core micro-pore channels,and performing grid-independent verification.At the same time,the pressure distribution and stress distribution at the oil-displacing fluid interface during the flow of viscoelastic fluid displacing residual oil are calculated by numerical calculation software.Then the tensor analysis method is used to calculate and analyze the force acting on the residual oil film and compare and analyze the difference of pressure gradient changes in the flow field under different working conditions.(2)Combining physicochemical interface theory and finite element method,and using Front tracking interface tracking method for interface tracking solution.The influence of the rheological parameters of the displacing fluid on the deformation of the residual oil film is calculated and analyzed.The difference between the interface area between the displacing fluid and the oil film after deformation and the interface area before deformation is then divided by the interface area before deformation and defined as the "deformation rate",and the deformation rate is used to judge the degree of deformation of the oil film and summarize the factors and laws of the deformation of the residual oil film.(3)Based on the result of the residual oil deformation,the radius of curvature calculation formula is applied to determine the inflection point of the interface shape between the residual oil and the displacing fluid.The initial wetting angle of the oil film is taken into consideration to modify the formula of the capillary number,which is defined as the critical capillary number,to investigate the conditions of oil film deformation rupture.The calculation results show that the capillary number is a quasi-factor for determining the size of oil film deformation.For the same oil film,the higher the capillary number,the greater the deformation;the initial wetting angle of the oil film and the volume of the oil film itself affect the change in the capillary number;this in turn affects the degree of deformation of the oil film;for the same oil displacement system,the capillary number for determining oil film break-up and separation is not a constant value,but varies with the change in volume and initial wetting of the oil film.Oil film rupture is judged by a modified critical capillary number.When the flow field capillary number is greater than the critical capillary number,the oil film will continue to deform until it breaks up and separates.