Synthesis Of Viscoelastic Surfactant And Its Property Analysis In Acid Clean Fracturing Fluid As A Thickener

With the continuous development of low-permeability oil and gas reservoir，the viscoelastic surfactant fracturing fluid has caught more attention. The resultsof the simple use of the viscoelastic surfactant fracturing are not very ideal tosome special and complex oil and gas reservoir. Therefore, to develop a newkind of acid fracturing fluid system which can etch out "dissolution passes" inthe strata rock surface, carry proppant to improve the diverting capacity, andexpand the seepage area will be an effective way in improving the fracturedcomplex lithology reservoir.In this paper, two kinds of cationic viscoelastic surfactants weresynthesized to solve the problem. The acid cleaning fracturing fluid wasprepared by using the two surfactants, and the basic properties of the acidcleaning fracturing fluid were studied. The results showed that:（1）The best synthetic conditions: the amidation reaction KOH0.53%，themol ratio of DMAPA to stearic acid is1.10to1, reaction temperature140℃,reaction time7-8h；the quaterisation reaction the volume ratio of propyl alcoholto water is1.8to1，the mol ratio of3-chloro-2-hydroxyl sulfonic acid sodiumto Alamine is1.10to1，reaction temperature70℃, reaction time6h；（2）The performance of the acid surfactant fracturing fluid: It has goodtemperature resistance ability. The viscosity of fracturing fluid is more than30.0mPa s and has good proppant suspension under different temperature anddifferent acid concentration. It also has excellence shear resistance capacity. Thedifference of the apparent viscosity is not very huge under different shear timein50℃and80℃, respectively. The viscosity of fracturing fluid reducedgradually with the increase of the shear rate. When the shearing actiondisappeared, the viscosity of the fracturing fluid increased gradually; it hasbetter performance of suspending sand and the velocity of sand settling is slow; the gel could break when it mixed with kerosene, and the viscosity of gelbreaking liquid is less than5mPa s; its leak-off coefficient is3.93×10^-4whichis below the standard of conventional fracturing fluid and gel; it has goodperformance of inhibitors, and the concentrations of the acid is still high after60min.（3） Microfoam acid clean fracturing fluid: the formulation of this system is3%XD-Y+0.5%corrosion inhibitor ATMP+3.6%ammonium chloride+1%glacial acetic acid+0.5%NaHCO₃. The fracturing fluid also has goodtemperature resistance and its apparent viscosity is108mPa s under90℃；theperformance of its shear resistance is good. The apparent viscosity is about70mPa s when it is sheared after60min; the performance of its proppantsuspension is also good，and the velocity of microfoam acid fracturing fluid islow to the conventional surfactant fracturing fluid when the temperature is60℃；the fracturing fluid is breaked when it is mixed with crude oil，and theviscosity of gel breaking liquid all can meet the requirements （less than5mPa s）; the Filter Loss of microfoam acid fracturing fluid is0.37mL/min and its leak-off coefficient is3.17×10^-4m/min^1/2，which are lower than surfactant fracturingfluid；the surface-interfacial tension of this fracturing fluid is very low. Thesurface tension is25.6mN/m and the interfacial tension is0.92mN/m, so theycould increase the flowback ability of the gel breaking liquids.（4）Acid fracturing fluid can improve the efficiency and effect of thefracturing by unifying acidification and fracturing together, which can addproppants as well as acidification; The microfoam acid fracturing fluid whichcombine the acid fracturing fluid and CO₂foam fracturing fluid effectively willimprove the proppant suspension of fracturing fluid, reduce the shearingresistance of fracturing fluid, and help the flowback of the gel breaking liquids.