Abstract:Aiming at the problems of low sweep efficiency of CO2 flooding and poor performance of conventional foam profile control ability, a high stability supercritical CO2 foam system composed of amphoteric surfactant HSD and modified SiO2 nanoparticles is constructed. Low permeability reservoirs in Shengli Oilfield are buried deep and have high temperature.The system showed good high-temperature resistance. At 120 ℃, the concentration of 0.5% nanoparticles increased the half-life of foam from 17 minutes to 40 minutes, and the stability was improved by nearly 2.5 times. The increase of reservoir pressure can increase both bubble volume and foam stability. Based on the power law model, the effect of nanoparticles on the rheological properties of supercritical CO2 foam system was studied. The results showed that the apparent viscosity of the system increased with the increase of the concentration of nanoparticles under the same shear rate, and the consistency coefficient increased from 0.073 to 1.22. The change rule of apparent viscosity of supercritical CO2 foam in porous media is simulated through core displacement experiment. The steady-state apparent viscosity of foam in porous media increases with the increase of nanoparticles. The foam of supercritical CO2 foam is stacked and discharged in "granular" shape. The size of foam is about 10 ~ 20um. Finally, the mechanism of nano particles enhancing the stability of CO2 foam was confirmed through experiments. The hydrophilic nano silica had interfacial activity due to the adsorption of surfactant molecules, which was adsorbed from aqueous solution to the gas-liquid interface, thus improving the stability of foam.