Laboratory experiment on a toluene-polydimethyl silicone thickened supercritical carbon dioxide fracturing fluid

Supercritical carbon dioxide (SCCO₂) fracturing fluid is an excellent application in CO₂ re-use. It has many advantages than water-based fracturing fluids. However, the low viscosity hinders its application in unconventional oil and gas reservoirs. Therefore, we tried to improve the property of SCCO₂ fracturing fluid by increasing the viscosity. A thickened SCCO₂ fracturing fluid was constructed and the fracturing property of the fracturing fluid was investigated. The fracturing fluid consisted of toluene (cosolvent), polydimethyl silicone (thickener) and SCCO₂. In SCCO₂, toluene and polydimethyl silicone obtain low miscible pressure at 42 °C. In addition, the constructed fracturing fluid system obtains higher viscosity value (as high as 1.5 mPa·s), which can be 40 times high than the viscosity of pure SCCO₂ at 42 °C and 20 MPa. These features match the viscosity requirement as a fracturing fluid. Molecular dynamics (MD) simulations were carried out to study the solubility parameter of the fracturing fluid system in molecular level. These MD simulation results show that, as a cosolvent, toluene helps polydimethyl silicon dissolve in SCCO₂, which is consistent with laboratory experiment results. Moreover, the studied fracturing fluid obtains good properties as a fracturing fluid in terms of high proppant carrying capability, low fluid leakoff coefficient, and low formation damage rate.