二氧化碳干法加砂压裂增黏剂研制

用于干法加砂压裂的二氧化碳黏度低，致使携砂困难，进而压裂造缝效果不理想。提高二氧化碳黏度是二氧化碳干法加砂压裂的关键技术之一。根据路易斯酸碱作用机理，选用具有路易斯碱属性的油酸甘油酯与环己烷和氯仿按照（2.6~4.3） （1.0~2.3） （1.6~2.6）比例混合，得到一种新型不含氟两亲性脂肪族液态二氧化碳增黏剂ZNJ。采用德国MARS Ⅱ型流变仪进行黏度测试，20~25℃、18~20 MPa下，体积分数为7%的ZNJ可使液态二氧化碳黏度提高至8.82mPa·s；通过手摇泵控制加压，控制压力为10~20 MPa，在温度为7~18℃、剪切速率为170 s-1下，体系黏度变化不超过13%。在苏里格气田试验5井6层次，ZNJ体积分数为3%时，使用支撑剂为40/70目陶粒，最大单层加砂量10 m3，平均砂比6.1%，压裂施工压力平稳，裂缝延伸方位与常规压裂监测结果基本一致。以油酸甘油酯、环己烷和氯仿复配的增黏剂可以解决二氧化碳增黏问题。 

Development of Viscosifier Used in CO2 Fracturing Fluid with Sand

Sand carrying in CO2 fracturing fluid has been a problem because of the low viscosity of liquid CO2 which always results in poor fracturedevelopment in fractured formations. One of the key factors in the successful use of CO2 in reservoir fracturing is to increase the viscosity of CO2 used. According to the working mechanisms of Lewis acids and Lewis bases, an olein with Lewis base characteristics was chosen to mix with cyclohexane and chloroform in a ratio of (2.6-4.3) (1.0-2.3) (1.6-2.6) to form a liquid fluorine-free amphiphilic fatty compound, ZNJ, a viscosifier used to enhance the viscosity of CO2. At 20-25℃ and 18-20 MPa, liquid CO2 treated with 7% (vol.%) ZNJ had viscosity of 8.82 mPa·s, as measured on an MARS Ⅱ rheometer. At 10-20 MPa (controlled with a hand pump), 7-18℃, and shearing rate of 170 s-1, percent change in the viscosity of CO2 did not exceed 13%. The viscosifier has been used on 5 wells for 6 times. In the field applications, the concentration of ZNJ was 3%, the proppant used was haydite of 40-70 mesh, the maximum sand volume added in the fracturing fluid for a single fracturing zone was 10 m3, and the average ratio of sand to liquid was 6.1%. The fracturing job was smoothly performed, and the orientation of the fractures developed in the formations was in agreement with the orientation monitored in conventional fracturing jobs. It is concluded that liquid CO2 can be viscosified with olein, cyclohexane and chloroform.