Abstract: Considering that conventional hydraulic fracturing fluid could cause damage to the shale, easy to produce water lock, not easy to flowback, and cause problems such as water consumption and environmental pollution, low damage carbon dioxide gel fracturing, the self-made F2EU and F4EU thickeners were added to the supercritical CO₂ base solution to research the effect of the dosage of the two thickeners on the viscosity of supercritical CO₂ gel fracturing fluid. Taking into account the cost and the efficiency, the optimum thickener was 2% F4EU, which could increase the viscosity of CO₂ to 15.4 mPa·s. The effects of temperature, pressure and shear rate on the viscosity of gel fracturing fluid system was studied. The experimental results showed that the system viscosity decreased with the increase of temperature, but there was a brief rising stage in the middle and the fracturing fluid system viscosity increases with the increase of pressure; but the fracturing fluid viscosity decreased with the increase of shear rate, which proved to be a typical shear thinning pseudoplastic fluid. The average damage rate of F4EU thickened supercritical CO₂ gel fracturing fluid was 1.39%, which was much less than the damage rate of conventional fracturing fluid. The researches showed the F4EU thickened supercritical CO₂ gel fracturing fluid would have a good application prospect in shale gas production.

Key words: supercritical CO₂, gel fracturing fluid, optimization, effect factor, low damage