Balancing foam generation and stability in rough fractures for effective CO2 mobility control

CO2 channeling severely undermines sweep efficiency in fractured, low-permeability reservoirs, posing a critical challenge to enhanced oil recovery (EOR) and geological carbon sequestration. While foam injection is a proven method for CO2 mobility control in porous media, its performance in rough fracture systems remains insufficiently understood. This study systematically investigated the in-situ generation and transport behavior of three tailored supercritical CO2 foams using a novel high-temperature, high-pressure rough-fracture model under varying surface roughness coefficients (Rs) and injection conditions. Results indicate that increased roughness promotes foam generation through shear-induced disturbances but also accelerates film rupture due to excessive deformation. In low-roughness fractures (Rs ≤ 1.01), sufficient foam generation is essential, whereas in high-roughness fractures (Rs ≥ 1.05), maintaining foam stability becomes equally important. A synergistic formulation combining hydrocarbon/fluorocarbon surfactants, xanthan gum, and nano-SiO2 enhances interfacial adsorption, increases bulk viscosity, and improves wall friction, achieving a balance between foam generation and stability. These effects are further amplified by optimizing foam quality and exploiting shear-thinning behavior. The findings deepen understanding of foam-fracture interactions and provide practical guidance for improving CO2-EOR and geological sequestration strategies in fractured, low-permeability reservoirs.