Abstract: During fracturing treatment for oil reservoirs with low temperature,shallow layer and high freezing point,it is difficult to overcome uncompleted breakdown of gel because of uncompleted clean-up of fracturing fluids and cold damage to formation by injecting cold fluid.It is suggested to adopt a new microencapsulated heat-generating hydraulic fracturing fluid system made of the common hydraulic fracturing fluid compounded with microencapsulated heat-generating agents.Three kinds of chemical heat-generating system were investigated,and the NH₄Cl-NaNO₂ heating system was determined.According to the reaction characteristics of the system,oxalic acid was chosen as the catalyst of the reaction and encapsulated using ethyl cellulose and paraffin as coating materials by phase separation method.The results show that the new hydraulic fracturing fluid containing microencapsulated heat-generating agents has a good stability and compatibility.When the fracturing fluid with NH₄Cl-NaNO₂ concentrtation of 2.0mol/L and the oxalic acid microcapsule fraction of 0.93% and the ammonium persulfate fraction of 0.08% was sheared at the rate of 170s^-1 for two hours,the peak of temperature can reach 78.0℃,and the viscosity of fracruring liquid was about 300 mPa·s.After gel breaking for four hours,the viscosity of residual liguid was 3.12 mPa·s.

Key words: water based fracturing fluid, microencapsulated technology, heatgener atingagents, compatibility, gelbreaking, fracturing technology

摘要： 在低温浅层油气井及高含蜡、高凝油油井的压裂中,由于低温下常规破胶剂活性太低而使破胶困难,同时也由于注入流体的“冷伤害”而使得压裂增产效果较差。为了避免这些问题的出现,可采用微胶囊包裹化学生热压裂液进行压裂作业。通过实验选定了NaNO₂-NH₄Cl生热体系,利用相分离法对该体系的催化剂-草酸进行微胶囊包裹。当NH₄Cl-NaNO₂草酸微胶囊与羟丙基瓜尔胶压裂液复配后,体系的稳定性及抗剪切性能都保持较好。当体系中NH₄Cl和NaNO₂浓度为2.0mol/L时,草酸微胶囊质量分数为0.93%,过硫酸铵质量分数为0.08%时,在170s^-1剪切速度下连续剪切2h后,压裂液粘度能保持在300 mPa·s左右,生热峰值温度能达到78℃,4h后破胶液粘度为3.12 mPa·s。

关键词: 水基压裂液, 微胶囊包裹技术, 化学生热体系, 配伍性, 破胶剂, 压裂工艺