Characteristic Evaluation And Injection Parameters Optimization Of Alkali-free Binary Composite System

With the rapid development of the world economy,the demand for oil and gas was increasing year by year.As exploration and development of new oilfields have become more and more difficult,it was more necessary to enhanced the recovery of old oilfields.Polymer flooding was the most effective and widely used technology to enhanced oil recovery,which could increase oil recovery by more than 10%.However,with the extension of development time,some problems gradually emerged,resulting in 40%~50% of crude oil remaining underground after polymer flooding.In order to further enhanced oil recovery,the new polymer-based chemical flooding method was more worthy of exploration,especially the alkali-free binary flooding technology,due to the removal of alkali in the formulation can not only play a synergistic role between polymer and surfactant,but also avoid scaling problem.Therefore,the characteristics of binary composite system were studied,and the theoretical model of binary system flooding was established,the injection parameters were optimized,which has great significance to guide the development of alkali-free binary flooding in oilfields.Taking Sazhong development zone of Daqing Oilfield as the research object,based on indoor physical experiments,the characteristics of alkali-free binary composite system were evaluated,including relative permeability curve measurement,rheological property measurement and interfacial tension measurement.The effects of polymer concentration and surfactant concentration on seepage characteristics,rheological characteristics and interfacial tension reduction of binary system were analyzed.The percolation mathematical model binary system was established,especially considering adsorption,inaccessible pore volume,shear dilution,polymer elasticity and capillary number and so on.Finally,based on the mathematical model,20 simulation schemes were designed,and the injection parameters,such as polymer pre-slug,main slug,sub-slug,injection rate,polymer concentration and surfactant concentration were compared,and the optimal injection scheme for the block was obtained.Moreover,the simulation results of the prediction model were compared with those of indoor oil displacement experiments.The results showed that the influence of polymer concentration on the percolation characteristics and rheology of binary composite system was more obvious than that of surfactant concentration.Surfactant can reduce the interfacial tension between oil and water,but after reaching ultra-low interfacial tension,the degree of reduction was slowed down and gradually stabilized.The optimal injection parameters of binary system for Sazhong development zone were optimized: the pre-slug injected PV was 0.03,the main slug injected PV was 0.3,the sub-slug injected PV was 0.2,the injected rate was 0.12PV/a,and the concentration of polymer and surfactant were 1800mg/L and 0.3wt% respectively.In addition,the results of prediction model and indoor experiments were compared;the accuracy was more than 96%.