Effect of reservoir temperatures on the stabilization and flowback of CO2 foam fracturing fluid containing nano-SiO2 particles: An experimental study

CO2 foam fracturing technology shows promise concerning enhancing coalbed methane (CBM) recovery and realizing CO2 geo-sequestration in deep un-mineable coal seams. However, one of the main challenges for successful CO2 foam fracturing is the foam destabilization and rupture that are caused by reservoir temperatures. The application of nanotechnology can improve foam stability. This paper aims to investigate the mechanism of CO2 foam stabilization by nano-SiO2 particles and the effect on fracturing fluid flowback at different reservoir temperatures. The foaming performance, interfacial rheological properties, and wettability of sodium dodecyl sulfate (SDS) and SDS/SiO2 dispersions in distilled water were examined using the foam scanner and interfacial rheometer. The results show that the foaming capacity of a CO2 foam fracturing fluid is found to increase with increases in temperature while the foam half-life is decreased. With an increase in the 0.2 mass% SDS + 0.3 mass% nano-SiO2 solution temperature from 20 °C to 60 °C, the foaming capacity increases by 24.42%, from 0.86 to 1.07, while the foam half-life decreases by 94.14%, from 7254 s to 425 s. The addition of nano-SiO2 particles reduces the foaming capacity of the SDS solution but substantially increases the foam half-life. When the temperature is 30 °C, the foaming capacity of 0.2 mass% SDS + 0.3 mass% nano-SiO2 solution is 8.33% lower than that of 0.2% SDS solution, but the foam half-life increases by 100.29%. The adsorption of nano-SiO2 particles at the gas-liquid interfaces increases both the viscoelastic and elastic moduli, which in turn enhances the ability of the foam to resist external disturbances. The viscoelastic and elastic moduli of the foam are both observed to decrease with increasing temperature, while both high temperatures and the presence of nano-SiO2 particles increase the capillary resistance of the fluid, which will degrade flowback. This study provides basic theoretical support for the application of CO2 foam fracturing technology to CBM production enhancement.