CO ₂ /Brine Foaming Enhances the Transport of Cellulose Nanocrystals and Cocoalkylamine in Mimicked Deep Saline Aquifer Conditions

The application of nanoparticles in CO2 sequestration through foam stabilization holds the potential for enhancing the security of carbon storage. In this study, cellulose nanocrystals (CNCs) and the surfactant bis (2-hydroxyethyl) cocoalkylamine (CAA) were used to encapsulate CO2 in a foam structure, effectively retaining it within a saline environment for over 24 h. All studies were done at 60 °C and 1500 psi to mimic underground reservoir conditions. A key finding reveals that a higher foam quality (75%) was achieved by optimizing the ratio of carbon dioxide and CNC dispersion, allowing an increased amount of CO2 captured compared to lower foam quality (50%), which required more CNCs but encapsulated less CO2. Observations in the view cell confirmed CO2 foams formation and stability of CO2 foams, with phase separation evident when CNCs or CAA were used alone, as lighter foam layers settled atop denser brine layers. However, no brine drainage occurred over a 24 h period when the foams were prepared with CAA and CNC mixture. This phenomenon resulted from the low interfacial tension obtained in the presence of CO2 and CAA and the ability of CNCs to stabilize the foams. Furthermore, CNCs dispersed in brine failed to penetrate rock pores, suggesting a pore-blocking effect. On the contrary, in the presence of CO2, the CNC-stabilized foams improved the mobility of the CNCs through Berea sandstone cores, with the best results obtained when CAA and CNC were used in tandem, underscoring the potential of CNC foams for safe and efficient CO2 sequestration in subsurface saline aquifers.