New Method of Polyacrylamide Crosslinked Acid Gel-Breaking

Polyacrylamide crosslinked acid has been widely used in the acid fracturing in deep high temperture wells.The gel-breaking is to reduce the strata damage and to improve the effects of stimulation.Through laboratory tests,acid amount,temperature and gel breaker amount were analyzed for their effects on crosslinked acid gel breaking.Using the method of complexing metal ion in chelating agent,the crosslinked acid gel breaking effect was optimized.The results showed that no gel breaking occurred when temperature was less than 60 ℃,the acid amount was greater than 15%,and crosslinked acid viscosity was higher than 400 mPa·s;gel-breaking performance was not affected significantly when the acid amount was 20% and the mass fraction of ammonium persulfate increased from 0.1% to 0.6%,gel-breaking was uneven when the temperature was 90 ℃,crosslinked acid viscosity dropped to 5 mPa·s after 10 min,and the residue content was 1,470 mg/L.It indicated that the viscosity of crosslinked acid fell to 8 mPa·s after 60 min when 0.1% EDTA and 0.1% capsule breaker were added and the residue content was 387 mg/L,which led to improved gel breaking effect.The results showed that the combination of capsule breaker and EDTA(chelating agent)in the crosslinked acid system could delay the release rate of effective components in the gel-breaker and reduce the crosslinked acid viscosity,and finally improve effect of crosslinked acid gel-breaking.