Study On Low Temperature Gel Breaking Technology Of Water-based Fracturing Fluid

Gel breaking of fracturing fluid affects the fracturing operation.In order to solve the problems of not breaking in time and completely when APS is used in water-based fracturing fluid at 20⁵0℃,this paper started with reducing the concentration of thickener and searching for efficient gel breaker and accelerator,aimed at reducing the difficulty of gel breaking of fracturing fluid and the content of gel breaking residue,provided some solutions of gel breaking at low temperature.In this paper,we synthetized a crosslinking agent CL-3 which is suitable for low guar gum concentration according to the crosslinking mechanism of organic boron and the effects of different reaction conditions on the crosslinking properties.Finally,the optimum synthetic reaction temperature is 50⁶0℃,reaction time is 3-4 h,boric acid dosage is about 21%,ligand ratio is 2:1.The basic formula of fracturing fluid used for screening gel breaker is 0.18%HPG+0.1%Na₂CO₃+0.3%BLF-13 clay stabilizer+0.3%DL-12 drainage aid.The cross-linking ratio is 100:0.4,and the gel viscosity of fracturing fluid is kept at 90mPa·s at 50℃.The breaking effect of APS gel breaker is evaluated by the optimized low temperature fracturing fluid formula.The breaking time of APS is long at 20³0℃.It is necessary to add accelerator to promote the decomposition of APS.The order of accelerating ability of reducing accelerator is Fe（II）=RA>CuCl>Na₂SO₃,and finally APS/RA,APS/Fe（II）/SAC,APS/Fe（II）/EDTA gel breaker groups is selected,which meeting the requirements of rapid gel breaking within 4 hours at 20³0℃,and the content of residue in gel breaker is less than APS gel breaker.The gel breaking performance of BBT-2 was better than DY-3 when the concentration is 10-50 ppm,it could break in 4 hours.The residual content was265-337mg·L^-1.After compounding with the three groups of gel breakers,BBT-2 and APS/Fe（II）/SAC gel breaker group had synergistic effect.The viscosity of gel breaking solution was about 2mPa·s,and the residual content of breaking solution was 145-161mg·L^-1.