P(VAc-AM)核壳微球型压裂液破胶剂延迟破胶效果评价

在压裂施工中，破胶时间的控制对压裂增产效果有巨大影响。利用反相乳液聚合制备了包覆过硫酸铵（（NH₄）₂S₂O₈）的聚（乙酸乙烯酯-丙烯酰胺）的核壳型微球，对比了该微球和直接加入过硫酸铵作为破胶剂时聚丙烯酰胺溶液的黏度和pH值变化。结果表明，该微球使溶液黏度半衰期由直接加入（NH₄）₂S₂O₈时的几分钟延长至1 h；同时，pH值下降速度减缓和下降幅度变小，说明微球的包覆抑制了溶液中聚丙烯酰胺氧化降解产生氢离子的速率。由此可知，该微球能通过延迟溶胀作用缓释过硫酸铵，降低聚丙烯酰胺在水溶液中的自由基氧化降解速率。 

Evaluating the Effect of Delayed Gel Breaking by P(Vac-AA) Core-Shell Microsphere Fracturing Fluid Gel Breaker

In fracturing operations, timingof gel breaking plays a great role in the enhancement of oil recovery. A poly(vinyl acetateacrylamide) (P(Vac-AA))core-shell microsphere coated with ammonium persulfate ((NH4)2S2O8) has been synthesized as a gel breaker through inverse emulsion polymerization. Laboratory experiments have been done to compare the changes of the viscosity and pH value of polyacrylamide solution when the microsphere and ammonium persulfate were used as gel breaker respectively. Experimental results showed that the viscosity half-life of polyacrylamide solution, which was only several minutes when ammonium persulfate was directly used as gel breaker, was extended to 1 h when the microsphere was used as gel breaker. Meanwhile, the use of the P(Vac-AA) microsphere also slowed down the pH decrease of the polyacrylamide solution and reduced the magnitude of the pH decrease, indicating that the core-shell structure inhibited the rate of hydrogen ion generation by oxidative degradation of polyacrylamide in the solution. It is thus understood that by delaying its swelling action, the microsphere slowly releases ammonium persulfate, reducing the free radical oxidative degradation rate of polyacrylamide in aqueous solution.