硼交联羟丙基瓜尔胶压裂液回收再用可行性研究

Feasibility of Reusing Boron/Hydroxyperopyl Guar Gelled Fracturing Fluid

探讨了羟丙基瓜尔胶／硼冻胶压裂液回收再用的可行性。分析了谊压裂液冻胶在无通用破胶荆情况下的非降解性破胶机理，控制因素为pH值和温度，破胶液黏度最低可达基液水平。基于一种有机硼交联HPG冻胶压裂液的实验数据及文献资料，讨论了升温，使用缓释酸及稀释3种非降解性破胶方法。①根据压裂过程中裂缝附近温度场分布设计压裂液，携砂液耐温性只需达到裂缝内的较低温度．地层温度恢复后其黏度将大幅降低；使用产气生热荆可提高裂缝温度。②加入设定量未指明组成的缓释酸使实验压裂液120℃黏度降至〈40mPa·s。补加NaOH后黏度维持〉200mPa·s近3小时。③压裂液与地层水等量混合后破胶，黏度～20mPa·s，复合清水压裂工艺即基于此原理。不同泵注阶段示踪剂产出曲线表明．影响压裂液返排的因素不只是黏度，某些未破胶压裂液的返排率反而很高；如使用方法适当，缓释酸破胶的返排率可以达到通用氧化型破胶剂破胶的相同水平。国外实践表明．重复使用低分子量瓜尔胶压裂液可提高压裂效果。图7参9。

The feasibility of recycling and reusing B/HPG gelled fracturing fluid is investigated. The non-degradlng breakdown mechanisms for this fluid without any standard breaker introduced are discussed, pH value and temperature are shown to be the controlling factors and the viscosity of a broken fluid is limited to that of the base fluid. Based on experiment,at data of a B/HPG gelling system as well as on published in literature data, three non-degradlng ways of gel breakdown are discussed, namely： raising temperature, using slowly releasing acids （SRAs）, and dilution. （1） The fluids are designed, taken into consideration of the temperature field distribution around a fracture during a fracturing operation, so that a proppant carrying fluid resistant to the lowered temperature in the fracture is used, its viscosity will drop significantly when the formation temperature recovered; a gas-producing/ heat-generating chemical agent can be used also. （2） The viscosity of an experimental fluid at 120℃ decreases down to 〈 40 mPa＇s with a SRA introduced and recovers and keeps 〉 200 mPa·s in nearly 3 hrs after NaOH added to the broken fluid. （3） An experimental fluid breaks down to viscosity -20 mPa·s when mixed with equal volume of a formation water and from this dilution concept a ＂slick water and hybrid fracs＂ technology is originated. Tracers production curves at different fracturing stages show that the viscosity is not the only factor controlling backflow of a fracturing fluid and very high backflow rates are observed for some fluids. With a SPA used properly, the back flow rate is similar to that with common oxidizing breakers. The practice abroad shows that reuse of low molar mass guar fluid results in better fracturing effects.