(270d) Improving CO2-EOR in Shale Using Dilute Amounts of CO2-Soluble, Wettability-Altering Surfactants
AIChE Annual Meeting
Wednesday, November 18, 2020 - 8:45am to 9:00am
The solubility of several nonionic surfactant (which also exhibit water-solubility) was determined at concentrations between 0.1 â 1.0 wt% in CO2. The cloud point curves for several surfactants were determined at temperatures representative of unconventional formations.
Contact angle measurements were performed on Bakken and Eagle Ford rock samples using dead oil from both formations and synthetic brine. Shale samples were first aged in oil at high temperature and pressure to restore oil-wet characteristics to the rock. The contact angles of water and oil droplets on these samples were determined. Then, shale samples were immersed in water (control test) or an aqueous nonionic surfactant solution containing 0.1 â 1.0 wt% surfactant to verify that the previously reported shifts toward water-wetness occur. Oil-wet shale samples were also immersed in high pressure, single phase CO2-nonionic surfactant solutions containing 0.1 â 1.0 wt% surfactant, after which contact angles of oil and water droplets on the rocks were determined.
After assessing the change in wettability attributable to the addition of surfactant, lab-scale CO2 huff ân puff EOR experiments were conducted on cylindrical, oil-saturated, oil-wet cores immersed in either pure CO2 or CO2-surfactant solution. The amount of additional oil recovery attributable to the introduction of dilute amounts of CO2-soluble surfactants was assessed.
To the best of the authorsâ knowledge, this is the first attempt to dissolve dilute concentrations of wettability-altering chemicals in CO2 for EOR in unconventional liquid reservoirs. Although dilute amounts of water-soluble/CO2-soluble surfactants have been previously dissolved in CO2 for improved mobility control in conventional formations via the in situ generation of CO2-in-water foams as the surfactant partitions into the brine, this study focuses on the addition of nonionic surfactants to CO2 with the sole objective of having the surfactant adsorb onto the rock and favorably alter wettability.