Experimental study on the dynamic filtration characteristics of supercritical CO2 foam fracturing fluid in porous media

Supercritical CO₂ (SC-CO₂) foam fracturing fluids are increasingly used in unconventional reservoir stimulation due to their water-saving advantages and potential for CO₂ storage. However, the filtration loss of SC-CO₂ foam into porous media significantly limits its fracturing effectiveness. This study employed a self-developed dynamic filtration testing system to investigate the rheological behavior and dynamic filtration characteristics of SC-CO₂ foam. A series of controlled experiments were conducted to examine the effects of foam quality, temperature, pressure, core permeability, and CO₂ phase transition on filtration behavior and core damage. The results demonstrate that SC-CO₂ foam is a shear-thinning non-Newtonian fluid whose viscosity increases with foam quality and pressure but decreases with temperature and shear rate. Compared with conventional fracturing fluids, SC-CO₂ foam exhibits superior filtration control without forming a filter cake. The filtration coefficient decreases with increasing foam quality (up to 80 %), but increases when the foam becomes unstable at 90 %. Phase transition of CO₂ leads to collapse of foam structure and loss of filtration control capacity. Core permeability significantly influences filtration loss, with higher permeability leading to increased fluid leak-off. The permeability damage rate ranges from 10 % to 30 %, and is most severe in low-permeability cores with high liquid-phase content. The key findings of this study are expected to provide theoretical guidance for evaluating the effectiveness of SC-CO₂ foam fracturing.