Study On Crude Oil Emulsification Characteristics Of Weak Alkali ASP Flooding

As a chemical oil displacement agent,weak alkali ASP flooding integrates the advantages of polymer/surfactant/alkali.It can reduce the interfacial tension between oil and water while making the mobility ratio to be more favorable.However,for different oil production blocks,the crude oil emulsification characteristics are different during weak alkali ASP flooding.Study on the crude oil emulsification characteristics of weak alkali ASP flooding in the target block is of great significance to further improve the EOR effect of ASP flooding and to guide oilfield development.This paper first analyzes the reservoir geology of the target block and the development status of ASP flooding in typical wells.Then,the emulsification procedure is optimized in lab to obtain similar emulsions as formed in the field.Taking the water resolution rate and stability coefficient to evaluate the emulsion stability,the effects of five influencing factors on the stability of emulsion in the target block are studied:polymer concentration,surfactant concentration,alkali concentration,salinity and temperature.Finally,the loss of chemical agent and the dynamic change process of emulsion droplets at different positions on long core are analyzed,and the migration law and emulsification of weak alkali ASP flooding system in porous media are studied.The research results show that block a of C oilfield is suitable for weak alkali ASP flooding EOR technology.The produced fluid of typical wells in the target block is emjlsified to varying degrees.The high-speed shear emulsification method was selected to prepare emulsions and the emulsions made by shearing at 2500r/min for 10 min is close to the emulsion morphology on field.When the polymer concentration is2000 ppm,the surfactant concentration is 0.4% and the alkali concentration is 1.0%,the prepared emulsion has good stability with the formation water salinity of 4409.4mg/L and temperature of 45℃.The long core experiment shows that the chemical agent of weak alkali ASP flooding system is continuously lost during their migration.The concentration and viscosity of chemical agent at different positions increase first and then decrease with the increase of total injection chemicals,and the migration distance of surfactant is shorter than that of polymer.In the whole displacement process,four emulsification stages will occur at each sampling spot,which are medium emulsification stage,strong emulsification stage,weak emulsification stage and unobvious emulsification stage.Emulsification occurs at 50 cm from the injection end when the injection volume of the system is 0.2PV,and the strong emulsification stage occurs at 0.3-0.6PV.Emulsification occurs at 350 cm from the injection end when the injection volume of the system is 0.6PV,and the strong emulsification stage occurs only at 0.9PV.The farther away from the injection end,the later the emulsification occurs and the shorter the time occupied by the strong emulsification stage.Besides,the particle size of emulsion drops at different sampling points decreases first and then increases.For the same emulsification stage,the closer sampling spot to the injection end,the smaller the average droplet size is.