Research and test on CO2 dry fracturing fluid system

In order to increase the production of low pressure, low permeability, strong water locking or water sensitive damaged tight sandstone reservoir after fracturing, research was conducted on CO2 dry fracturing fluid system. The molecular simulation technique was used to study the microscopic configuration of molecules between liquid CO2 and viscosifier, to evaluate the viscosifying effect of various CO2 viscosifer on liquid CO2 , to optimize the viscosifiers, and to build the formula for CO2 fracturing fluid. Based on the research, it was found that, under the conditions of 62–63 ℃ and 15–20 MPa, the viscosity of CO2 dry fracturing fluid system was increased to 5–10 mPa·s, which is 240–490 times that of supercritical CO2. The average rate of damage to core permeability of gas wells was 2.75%, and the average rate of damage to core permeability of oil wells was 0.98%. This fracturing fluid system was successfully tested on the first domestic well with CO2 dry sand fracturing in Sulige Gas Field, and the production was increased remarkably.