CO₂-Switchable Surfactants for Foam Behavior Optimization: Experimental Insights for CO₂ Storage Applications

Water-flooded reservoirs and aquifers targeted for cross-border CO₂ storage can only reach full capacity if resident fluids are efficiently replaced by injected CO₂. We propose a novel technique for improving the efficiency of CO₂ storage by controlling the mobility of CO₂ using novel CO₂-switchable surfactants. We aim to investigate the effects of pH, surfactant-to-Polyethylene glycol (PEG) mole ratio, and aging time on the foam characteristics and performance of long-chain surfactants with different head groups. A systematic experimental design was employed using the Design of Experiments (DOE) framework to evaluate the impacts of pH, surfactant-to- PEG mole ratio, and aging time on foam behavior. The study incorporated 24 unique experimental configurations, with controlled variations of the independent variables. Each experiment was performed under two temperature settings (22°C and 70°C) and two gas atmospheres (CO₂ and N₂). Foam properties, including stability and formation dynamics, were meticulously analyzed using a foam scanner, enabling precise characterization of the influence of environmental and compositional factors. This study investigates the impact of surfactant head group chemistry on foam behavior under the controlled conditions mentioned before. For N,N- Dimethyltetradecylamine N-oxide (DTAO), increasing temperature amplified the effect of mole ratio on foam generation, while aging time inversely impacted foam stability and generation. pH was the dominant factor in the early stages of foam formation. DTAO exhibited the highest foam generation and stability across all conditions, outperforming other surfactants. For N,N-Dimethyltetradecylamine (DTA), low pH enhanced foam stability, but temperature rise negatively affected both foam generation and stability. Mole ratio effects became more significant at elevated temperatures and longer aging times. In the presence of N₂ gas, foam generation sharply decreased at both temperatures, while foam stability remained relatively unchanged. Cetylpyridinium Chloride (CPC) showed a similar trend, with higher temperatures leading to a marked reduction in foam generation and stability, further exacerbated by PEG polymer. Aging time amplified foam degradation, while pH and mole ratio effects were more pronounced at elevated temperatures. Using N₂, foam generation dropped sharply, but foam stability remained stable. These results underscore the influence of temperature, gas type, and surfactant head group on foam performance, with DTAO showing superior stability and generation.