Effect of Surface Hydrophobicity of Fluorescent Nanopolymer Microspheres on the Stability of CO2 Foam

Nanopolymer microspheres have been widely studied in the development of low-permeability reservoirs as an effective material to improve foam stability. However, there are few studies on the foam stability mechanism of nanopolymer microspheres. In this work, the effect of surface hydrophobicity of fluorescent nanopolymer microspheres PARC(Flu-Ac) on the stability of CO2 foam was investigated by using foam performance as an evaluation index. The mechanism of foam stabilization by PARC(Flu-Ac) with different degrees of hydrophobicity was clarified by studying the drainage rate, micromorphology, interfacial rheology of foam, and adsorption behavior of microspheres on the foam liquid film. The results show that PARC(Flu-Ac)-5 microspheres with neutral wettability have the best foam stabilization effect. At 94 °C, the foam volume of CO2 foam is 630 mL and the foam half-life is 30.12 min. PARC(Flu-Ac)-5 microspheres have a high desorption energy and can stably adsorb at the gas–liquid interface to form a solid layer. The microspheres improve the mechanical strength of the foam and reduce the direct contact of the fluid, thus providing space resistance for thinning the liquid film and the diffusion of gas between bubbles. In addition, the microspheres can slow the thinning rate of the liquid film through the release of free water. The stability of the foam is significantly improved. This study further clarifies the enhancement mechanism of nanopolymer microspheres on the stability of CO2 foam, which has excellent guiding significance for the application of CO2 foam in low-permeability oil fields.