Preparation Of Microemulsion Cleanup Additives And Research On The Mechanism Of Cleanup

With the complicating of the reservoir geological conditions increasingly and the increasing depth of the reservoir at the present,the requirements to flowback additive's performance are also improved.So the research on the microemulsion flowback additive with high efficiency and the mechanism of the cleanup has become very important,so as to adapt to the complex reservoir conditions and to increase the output of oil and gas field.Studies have shown that,in acid medium the betaine type amphoteric surfactant(CAB)can change the wettability of sandstone/mica surface and the zeta potential of sandstone core powder obviously.By atomic force microscopy observation,the adsorption model is set up to verify that,in low concentration,the CAB mainly occur monolayer adsorption,mica surface can be improved as the weak hydrophilic surface and core powder zeta potential increases gradually.In high concentration,double layer adsorption occurred,the weak hydrophilic mica surface recovery to hydrophilic surface and the core powder charge carried from negative to positive.Under high and low concentration,Gemini type cationic surfactant can make the hydrophilic sandstone surface occurred wettability reversal,and concentration had little impact;The zeta potential of core powder adsorped with Gemini change from negative to positive,and will no longer change increases to a certain value;By atomic force microscopy observation,the adsorption model is set up to verify that,Gemini in hydrophilic solid surface formation of monolayer adsorption,result in wettability reversation.And in high concentration,a small amount of double layer adsorption occurred.In low concentration,nonionic surfactant AEO mainly occur monolayer adsorption,in high concentration,double layer adsorption occurred mainly with a small amount of double layer adsorption,but whether single or double AEO cannot obviously improve hydrophilic sandstone core wettability,little change for the contact Angle.The strong-interaction and good synergistic effect exise between nonionic surfactant and other ionic surfactant.Microemulsion flowback additive with good cleanup effect is composed of different types of surfactant,and evaluate the performance for it.Study found that:the particle size distribution range of microemulsion is about 80 nm,conform to the definition of microemulsion;The surface tension can be reduced to 26.0 mN/m at lower concentrations,and the interfacial tension can be reduced to<0.1 mN/m,thus capillary force could be reduced effectively,help working fluid to flowback;Hydrophilic sandstone/mica surface contact Angle can be improved to 70 °,achieve neutral-weak hydrophilic(65 °<contact Angle<90 °);Through indoor physical model experiment,the flowback rate is improved up to 29.72%;Microemulsion's stability is good,also has certain antibacterial sterilization performance,and has good compatibility with fracturing fluid and its additives.Microemulsion flowback additive system is simple and convenient to prepared,and it's thermodynamic performance is stable,can significantly reduce the interfacial tension of the water,to improve the hydrophilic sandstone core wettability,has good compatibility with the fracturing fluid,has a good application prospect.