A green aqueous foam stabilized by cellulose nanofibrils and camellia saponin for geological CO2 sequestration

Geological carbon dioxide (CO2) sequestration in deep formations involves displacing resident fluids from porous media, and is considered an unstable process due to the unfavorable mobility ratio between the resident and displacing fluid. Although various chemicals have been added to improve the CO2 sweep efficiency, this often results in pollution to the environment and the formation. Here, a novel green foam was prepared to enhance CO2 sequestration. The stabilization mechanisms and rheological properties of the CO2 foam with cellulose nanofibrils (CNFs) and camellia oleifera saponin (COS) were explored. Furthermore, the pore-scale behaviors of the CO2 foams were investigated using a micromodel. The results demonstrated that the abundant hydrogen bonds between CNFs and COS molecules led to the formation of tight bubble film which could stably encapsulate CO2 and inhibit its diffusion. The interlacement and entanglement of CNFs endowed liquid phase with high viscosity, which restrained liquid drainage and improved the interfacial viscoelasticity. The pore-scale behaviors showed that the higher viscoelasticity and stability caused large numbers of small bubbles to group together, providing greater flow resistance to control the mobility of the foam. The CNF/COS foam significantly improved the CO2 saturation in aquifers and oil reservoirs.