Study On Chemical Crossflow Prediction Method Based On Interwell Dynamic Connectivity During SP Flooding

Currently,Surfactant-Polymer flooding has become an important method to further enhance oil recovery of oil fields with high water-cut in China.However,in the process of SP flooding,the chemical agent is prone to crossflow along the high-permeability area between injection and production wells,resulting in a large number of chemical agent ineffective production and low oil displacement efficiency.At present,the reservoir numerical simulation method is used to predict chemical agent production concentration,and then profile control measures are implemented to achieve the purpose of improving chemical flooding development effect.However,there are some shortcomings such as the complex of building models and timeconsuming simulations.Therefore,a set of SP flooding chemical crossflow prediction method based on interwell dynamic connectivity inversion theory is established in this paper,which can more accurately and easily evaluate the degree of chemical crossflow and provide a mean of profile control for oil fields.Based on the systematic analysis theory and superposition principle,considering connectivity degree,time lag and attenuation,a mathematical model of dynamic connectivity between injection and production wells is established.Injection-production data combined with Levenberg-Marquardt optimization algorithm are used to solve connectivity coefficients between wells by the multistage optimization.Typical reservoir inversion results show that the connectivity coefficient is consistent with the reservoir geological features.A calculation method for chemical agent production concentration is proposed based on the mass transfer diffusion seepage theory.An analytical model for chemical agent production concentration considering adsorption,chemical degradation,accessible pore volume,etc.is established which uses Laplace transform to obtain chemical concentration solution.The sensitivity analysis of the analytical model influencing factors is carried out by applying the Plackett-Burman test design.Compared with the reservoir numerical simulation method,the calculation method has the advantages like less input parameters and faster calculation speed.By analyzing the characteristics of chemical agent production concentration curve,a characterization model of SP flooding is established.The parameters of the characterization model have clear physical meaning,and there is a good matching relationship with the analysis model.Combined with the established models and flow tube method,a set of SP flooding chemical crossflow prediction method is proposed.Firstly,the interwell single flow pipe parameters are obtained based on the dynamic connectivity model and the characterization model.Secondly,based on the analysis model,the production concentration curve of chemical agent of each flow tube is calculated.After the concentration curve of tubes are superimposed,the subsequent chemical agent concentration of production wells are obtained,and then the crossflow degree of production wells are predicted.This method is applied to predict the chemical agent concentration and crossflow degree of production wells of SP flooding pilot test in Gudong Oil field.The results show that the method has good fitting accuracy with chemical agent concentration monitoring data and has good applicability.