Nanomaterials as CO2 foam stabilizers: A comprehensive review

The advances of nanotechnology and the need to develop strategies and new opportunities for utilizing CO 2 have motivated intense research efforts on CO 2 utilization as a foaming agent to improve the efficiency of oil extraction, carbon sequestration, and reservoir applications. This review critically examines advances in various CO 2 foam formulations modified by nanostructured materials. Silica, carbonaceous, fly ash - based, metal oxides, boron nitride and polyelectrolyte complex nanomaterials among others have been shown to enhance the stability and performance of CO 2 foams, thereby enabling more effective utilization of CO 2 in subsurface applications such as enhanced oil recovery (EOR), and advancing strategies for carbon management and resource valorization. Employment of various nanomaterials in non-functionalized and functionalized forms, as well as hybrid combinations with various chemical agents such as surfactants and polymers in flooding formulations of CO 2 foam is reviewed and compared, with an emphasis on surface functionality, compatibility with chemical agents, interfacial interactions and stability. Critical evaluation and comparisons are performed with respect to nanomaterials efficacy in improving foamability and foam stability by minimizing foam bubble coalescence and collapse, modifying reservoir rock wettability, decreasing interfacial tension, increasing sweep efficiency, altering rheological properties, improving mechanical properties, integrating electrostatic forces and thermal properties, and empowering other mechanisms. Furthermore, the effect of challenging reservoir conditions including salinity, temperature, pressure, permeability, oil and other reservoir fluid composition, as well as surface and structural characteristics, particle size and shape of nanostructured materials, surface modification methodologies, attached moieties, various chemical additives, dispersibility and stability, surface chemistry and related modifications for wettability optimization, and hybrid system synergies on the performance of nanomaterial-stabilized CO 2 foam formulations, are reviewed so as to determine structure-property-performance relationships and practical design strategies. Based on the retrieved comparisons, we propose optimal systems while also defining future trends and directions for nanomaterial-stabilized CO 2 foam formulations with significant potential for advancing the efficiency, sustainability, and environmental responsibility of the relevant CO 2 utilization processes by leveraging the unique properties of nanomaterials.