(599a) Solutions of Nonionic Surfactants in CO2 to Improve Unconventional CO2-EOR Via Wettability Alteration | AIChE

(599a) Solutions of Nonionic Surfactants in CO2 to Improve Unconventional CO2-EOR Via Wettability Alteration


Enick, R. M. - Presenter, University og
Burrows, L., 1National Energy Technology Laboratory
Haeri, F., National Energy Technology Laboratory
Tapriyal, D., National Energy Technology Laboratory
Crandall, D., NETL
Goodman, A., National Energy Technology Laboratory
CO2 huff n’ 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 SURFONIC® L12-6, branched nonyl ethoxylate Indorama SURFONIC®TDA-9, and branched nonylphenol ethoxylate Indorama SURFONIC® N-100) were evaluated for CO2 solubility, shale wettability alteration, ability to increase oil recovery during laboratory huff n’ 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 n’ 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 n’ 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.