Parameter Inverse Studies Of Chemical Flood In Cores Based On EnKF

Chemical flood which can enhance effectively the oil recovery is widely used.However,the higher heterogeneity of reservoirs and the complicated displacement mechanism of chemical flood make it impossible to do quantitative research in flooding mechanism and influencing factors of chemical flood by core flooding experiments and numerical simulation techniques.In this paper,ensemble Kalman filter?EnKF?is used to inverse the model parameters of chemical flood by assimilating the observation data of surfactant/polymer flood in cores.On this basis the numerical model of chemical flood is established.At the same time,effects of injection-production parameters on oil recovery are analyzed.The specific content and results are as follows:?1?According to the displacement mechanisms of polymer flood and surfactant flood,the quantitative equations between viscosity and concentration of polymer is established.The calculation formula between oil-water interfacial tension and concentration of surfactant is proposed and the adsorption of chemicals is given.The model parameters of chemical flood in cores are determined,including porosity,permeability,relative permeability curve,chemical flood mechanism model parameters etc.?2?The observation data of surfactant/polymer flood in cores are assimilated by using the automatic inversion method based on EnKF,then the 3D heterogeneity model of porosity and permeability,the relative permeability curves and characteristic curves of chemicals are obtained to constitute the chemical flood model.On this basis,the numerical simulation result of chemical flood model is in agreement with experimental result of core flooding.The 3D fields of porosity and permeability reflect the characteristic of heterogeneous and the statistical average values are in good agreement with the conventional measurement results,which the relative deviation is about 10%between them.The curve of polymer viscosity and the curve of oil-water interfacial tension are in line with the laboratory experiments and theoretical data.The viscosity of polymer solution is 40mPa·s when the concentration is1500mg/L,and the oil-water interfacial tension is to a minimum of 1.5×10^-3mN/m at the critical micelle concentration of 0.3wt%.?3?The numerical simulations of surfactant/polymer flood in cores are carried out.The effects of flood method,injection pattern,slug size and injection concentration on recovery are discussed and the flood program of surfactant/polymer flood in cores is optimized.The results show that the optimum injection pattern of surfactant/polymer flood is slug injection,the slug size is 0.3PV,the injection concentration of polymer is 1500mg/L and the injection concentration of surfactant is 0.3wt%.It can increase oil recovery by about 19%compared to water flood.