Experimental Study Of Enhanced Oil Recovery Under Heterogeneous Conditions By Polymer/surface Binary Flooding

Polymer-surfactant(PS)binary compound flooding has both the function of enlarging swept volume of polymer flooding and the effect of improving oil displacement efficiency of asp compound flooding,which helps to increase the capillary number so as to improve oil recovery.In recent years,polymer-surfactant(PS)binary flooding has been successfully used in Shengli and Daqing oilfield.In terms of traditional capillary number theory,with the increasing viscosity of displacing phase and decreasing oil-water interfacial tension,oil displacement system has stronger swept ability and oil displacement capability,as well as higher degree of enhanced oil recovery in oil reservoir.Therefore,when employed in most reservoir exploitation,binary compound flooding system obtains both relatively high viscosity and ultra-low interfacial tension at the same time either through improving concentration of polymer and surfactant,or via research and development of new polymer and surfactant.Considering the high cost of polymer-surfactant(PS)flooding technology,if polymer-surfactant flooding of high viscosity and low interfacial tension is used under different degree of reservoir heterogeneity,economic benefit would be certainly not good.Besides,binary compound flooding under different degree of reservoir heterogeneity has their optimal viscosity ratio and interfacial tension.In order to find specific ways to solve the problems,the paper conducts careful research on the influence of four parameters of variation coefficient,viscosity ratio(system/oil),interfacial tension and capillary number on improving oil recovery in polymer-surfactant flooding.Taking Es 2 of Shengtuo Oilfield as the experimental background,interfacial tension of eight representative surfactants(altogether four types)of good oilfield adaptability are measured,so as to optimize gemini surfactant HY-100A which can reduce oil/water interfacial tension to ultra-low(10-3 mN/m)after compounded with polymer HJ-NJ.After respectively discussing the influence of adding amount of polymer and surfactant on the interfacial activity and apparent viscosity of binary system;formula of polymer/surfactant compound system is thus screened according to meet the requirements of designed viscosity ratio and interfacial tension.Finally,"indoor heterogeneous model" is used to study effect of oil displacement rules and capillary number on oil displacement efficiency under the heterogeneous condition.The experimental results show that:?Critical viscosity ratio varies according to different degrees of oil heterogeneity.And the stronger the heterogeneity degree is,the larger critical viscosity ratio becomes;?Under the heterogeneity condition,the effect of surfactant increases with the rise of viscosity ratio,because the full play of synergy effect in polymer/surfactant binary system is on the premise of reasonable viscosity ratio of polymer;? When the heterogeneity degree is small(variation coefficient Vk?0.3),surfactant plays a main role in enhancing oil recovery,and oil recovery increases linearly with the decreasing interfacial tension.When the heterogeneity degree gradually increases,surfactant contributes less to improving the oil recovery.Instead,expanding swept effect of polymer becomes the main influencing factor to EOR.With the drop of the interfacial tension,enhanced oil recovery increases in a lower degree.And interfacial tension declines from 10-2 mN/m to 10-3 mN/m at the variation coefficient of 0.7,which cannot effectively enhance oil recovery.In addition,neither raising viscosity of displacing phase nor reducing the interfacial tension can effectively improve oil recovery at the variation coefficient of 0.9.?When the viscosity ratio of system is 0.1,EOR in polymer/surfactant compound system becomes poorer with the increasing variation coefficient.When the viscosity ratio is between 0.3 and 1.2,the change tendency of EOR in binary system is a downwards parabola with the increase of variation coefficient.When viscosity ratio reaches 0.3,oil recovery efficiency in binary system is the largest at the variation coefficient of 0.5.And when the variation coefficient is 0.7,EOR is the largest when the viscosity ratio is no less than 0.5.With the reduction of interfacial tension,the influence of variation coefficient on EOR in binary system weakens at the variation coefficient of no more than 0.7.?Under homogenization condition,increasing capillary number of binary flooding can effectively improve the oil recovery and reduce the residual oil saturation.However,under the heterogeneity condition,the change tendency of the capillary number,oil displacement efficiency and residual oil saturation is not exactly the same.Besides,when the degree of reservoir heterogeneity becomes stronger,increasing the capillary number actually cannot improve the recovery efficiency or reduce residual oil saturation.