Effects of asphaltene from residual crude oil on CO₂ foam stability

CO₂ foam stability in the presence of oil is crucial for CO₂ geo-storage in depleted hydrocarbon reservoirs. While previous studies have examined the impact of oil on foam stability, the understanding of how asphaltenes affect foam stability is limited. This study investigates the effects of asphaltene on CO₂ foam solutions in synthetic and crude oil samples. Spinning-drop interfacial tension (IFT) measurements showed that asphaltene significantly increased IFT across all oil types. Asphaltene hinders surfactant molecules from reducing IFT and improving surface activity. Foam half-life measurements showed that asphaltene concentrations of 1.6% and 8% decreased average foam stability by 80% and 85%, respectively. Without asphaltene, increasing the surfactant concentration from 0.1% to 1% reduced IFT and increased foam stability. However, in the presence of asphaltene, increasing the surfactant concentration from 0.1% to 0.5% improved foam stability and reduced IFT, whereas increasing it from 0.5% to 1% slightly decreased foam stability and raised IFT. Despite similar asphaltene content, foam stability was higher in crude oil than in synthetic oil, underscoring the influence of oil viscosity and asphaltene stability on foam performance. Image-based analysis further confirms that asphaltene accelerates bubble coalescence and promotes non-uniform bubble growth, leading to a faster decay in bubble number over time. This study sheds light on the application of CO₂ foam injection for underground CO₂ storage in depleted oil reservoirs, where the presence of oil residue and asphaltene precipitation may hinder CO2 containment.