(599a) Solutions of Nonionic Surfactants in CO2 to Improve Unconventional CO2-EOR Via Wettability Alteration
AIChE Annual Meeting
Thursday, November 17, 2022 - 8:00am to 8:15am
CO2 huff nâ puff is a promising method for enhanced oil recovery (EOR) in unconventional shale formations. In this work, we postulate that CO2-EOR may be improved by the dissolution of surfactants into CO2 if both oil-rich and CO2-rich phases are present. A complete pressure-composition phase behavior diagram of CO2-dead Eagle Ford crude mixtures indicates that at 80 oC and pressures as high as 62 MPa, two such phases co-exist for CO2-rich mixtures. Therefore the dissolution of a surfactant in CO2 has the potential to improve oil recovery via wettability alteration from oil-wet to CO2-wet and/or CO2-oil interfacial tension (IFT) reduction. Three nonionic surfactants (linear dodecyl ethoxylate Indorama SURFONICÂ® L12-6, branched nonyl ethoxylate Indorama SURFONICÂ®TDA-9, and branched nonylphenol ethoxylate Indorama SURFONICÂ® N-100) were evaluated for CO2 solubility, shale wettability alteration, ability to increase oil recovery during laboratory huff nâ puff experiments, and effect on CO2-oil interfacial tension (IFT). Each surfactant exhibited CO2-solubility at temperatures up to 100 oC of roughly 1 wt% at pressures commensurate with CO2-EOR. The presence of surfactant in CO2 did not have a significant effect on CO2-oil IFT. High-pressure, high-temperature contact angle experiments demonstrated that the (CO2+surfactant) solutions can shift the wettability of oil-wet shale toward CO2-wet and water-wet. CO2 and (CO2+surfactant) huff nâ puff experiments for oil-saturated Eagle Ford, Mancos, and Bakken shale cores immersed in CO2 showed that CO2 solutions containing the branched nonyl ethoxylated alcohol gave highest cumulative oil recoveries of 72% and 75% (at 0.01 wt% and 0.1 wt% of TDA-9, respectively) compared to 71% recovery for the core immersed in pure CO2. Analysis of oil produced during confined-core huff nâ puff experiments indicated that heavier oil components were produced when the surfactant was added to CO2. These results suggest that CO2-soluble surfactants may increase oil recovery by wettability alteration rather than IFT reduction.