Formulation and performance evaluation of polymer-thickened supercritical CO2 fracturing fluid

Compared with conventional water-based fracturing fluid, supercritical CO2 fracturing fluid has the characteristics of inhibiting water sensitive damage and improving flowback efficiency. In view of the problems of low viscosity, poor sand-carrying performance and large filtration loss capacity of pure supercritical CO2, a supercritical CO2 fracturing fluid system had been prepared: 5% polydimethylsiloxane +5% kerosene +90% supercritical CO2. The rheological property, sand-carrying property, filtration loss property, core damage property and wetting inversion property of the system were systematically studied through performance evaluation experiments. At 325 K, the viscosity of the system can reach 4.67 mPa s, which was 54.26 times higher than that of pure supercritical CO2. The performance evaluation showed that the system had a good rheological property. The sand-carrying capacity was improved by 38.17%, and the filtration loss coefficient was decreased by 71.71% at most. The interaction results between CO2 and reservoir showed that the system could effectively increase the porosity and permeability of the core. For ultra-low permeability sandstone core, the porosity was increased by 7.71%, the permeability was increased by 115.20%. While for shale core, the porosity was increased by 6.99%, permeability was increased by 102.44%. At the same time, the system can change the core wetted by water phase into a neutral wetted one which was favorable for oil and gas flow. This system is expected to be further studied in oilfield applications.