Dissolving Nonionic Surfactants in CO₂ to Improve Oil Recovery in Unconventional Reservoirs via Wettability Alteration

Abstract

CO2 injection is a promising method for enhanced oil recovery (EOR) in unconventional shale reservoirs. In this work, we postulate that CO2 EOR may be improved by the dissolution of surfactants into CO2. Although CO2 is a relatively good solvent for oil, we show that CO2 and Eagle Ford oil are immiscible at compositions above 70 wt % CO2, even at pressures as high as 62 MPa. The presence of a CO2–oil interface at reservoir conditions indicates that the addition of a surfactant has the potential to improve oil recoveryvia wettability alteration from oil-wet to CO2-wet, CO2–oil interfacial tension (IFT) reduction, or both. Three nonionic surfactants (branched tridecyl ethoxylate Indorama SURFONIC TDA-9, branched nonylphenol ethoxylate Indorama SURFONIC N-100, and linear dodecyl ethoxylate Indorama SURFONIC L12-6) were evaluated for CO2-solubility, shale wettability alteration, effect on CO2–oil IFT, ability to generate CO2–oil foams, and ability to increase oil extraction from Eagle Ford, Mancos, and Bakken shale cores. Each surfactant dissolved in CO2 up to 1 wt % at pressures and temperatures commensurate with CO2 EOR. CO2-dissolved surfactants did not significantly affect CO2–oil IFT or generate CO2–oil foams, but they did induce a dramatic change in the contact angle of an oil droplet on an oil-aged shale chip in CO2 from strongly oil-wet (11°) toward intermediate CO2–oil wettability (82°) (at 80 °C, 27.6 MPa). The branched tridecyl ethoxylated surfactant, SURFONIC TDA-9, afforded the highest oil recovery in core soaking experiments75%, compared to 71% by pure CO2. Analysis of oil extracts by gas chromatography revealed that heavier oil components were produced when the surfactant was added to CO2. These results indicate that CO2-dissolved surfactants may increase oil recovery from shale by wettability alteration from oil-wet toward CO2-wet.

CO2-Soluble Nonionic Surfactants for Enhanced CO2 Storage via In Situ Foam Generation

“…The solubilities of the surfactants in CO 2 were determined using a visual, isothermal, nonsampling method that is described in our previous publication. 35 The experiment was performed in a windowed, variable-volume view cell. The surfactant and liquid CO 2 were injected into a sampling cylinder above a sliding piston.…”

“…The stabilities of CO 2 −brine−surfactant foams were measured in the same windowed, variable-volume view cell as described in section 2.3, and our previous publication. 35 To the view cell were added equal volumes of CO 2 (based on CO 2 density at 46 °C and 20 MPa), brine, and surfactant (0.1 wt % relative to the mass of brine). The cell was sealed, the temperature increased to 46 °C and the pressure was increased to 20 MPa.…”

Water- and Surfactant-Based Huff-n-Puff Injection into Unconventional Liquid Hydrocarbon Reservoirs: Experimental and Modeling Study

“…The injection of wettability modifiers caused the oil recovery to increase by 25%. Besides that, projects that used systems of nonionic surfactants dissolved in CO 2 as wettability alteration agents in unconventional reservoirs are known. , Such solutions modify the rock surface from oil-wet to water-wet. The gas chromatography analysis conducted after soaking experiments showed that surfactant promoted extraction of heavier oil components.…”

Rough Surface Effect on CO2 Displacement at the Nanoscale

“…5,6 In light of these challenges, CO 2 injection shows great potential as a complementary energy source for shale formations. 7,8 CO 2 has a relatively high mobility in shale and can dissolve in shale oil to lower its viscosity. 9−11 Furthermore, CO 2 is preferentially adsorbed in kerogen, displacing light hydrocarbons.…”

“…Shale oil plays a crucial role in supplementing conventional oil resources . However, the primary production of shale oil is often hampered by a low recovery rate (typically at 3–10%). − The water injection method, commonly used to replenish conventional reservoir energy, becomes costly for improving shale oil recovery due to the nanometer pore sizes and low permeabilities (from nano- to microdarcy) of shale formations. , In light of these challenges, CO 2 injection shows great potential as a complementary energy source for shale formations. , CO 2 has a relatively high mobility in shale and can dissolve in shale oil to lower its viscosity. − Furthermore, CO 2 is preferentially adsorbed in kerogen, displacing light hydrocarbons . As the oil industry aims to meet the net-zero emission goal, CO 2 injection for shale oil recovery aligns with this purpose. , …”