Carbon dioxide/water foams stabilized with a zwitterionic surfactant at temperatures up to 150 °C in high salinity brine

Stabilization of CO2-in-water (C/W) foams with surfactants at high temperature and high salinity conditions is challenging given limitations in the solubility and thermal stability of surfactants, particularly for surfactants other than anionic ones. Here we show that a single zwitterionic surfactant, cetyl betaine (CH3(CH2)15N+(CH3)2CH2COO−), stabilizes viscous C/W foam (>15 cP) in crushed limestone (76-Darcy) at a temperature up to 150 °C and over a wide range in salinity up to 22% total dissolved solids (TDS) at superficial velocity of 940 ft/day. According to liquid chromatography mass spectrometry (LC/MS), cetyl betaine has high thermal stability with negligible chemical degradation after incubation at 135 °C for 30 days. Interfacial tension (IFT) at the C/W interface was reduced significantly from ∼37 mN/m to <5 mN/m with the addition of 0.08 mmol/L of cetyl betaine. Relative to ionic surfactants, the relatively weak electrostatic repulsion between the local charges in the headgroup is shown to produce strong adsorption at the C/W interface (∼134 Å2/molecule), resulting in generation of viscous foam (∼6 cP) even in pure water without added salt. At a low superficial velocity of 6 ft/day (shear rate 45 s−1) in a beadpack, foam was still formed with cetyl betaine. Static adsorption of cetyl betaine on carbonates was on the order of 1 mg/m2, and core flood test also proved that cetyl betaine could stabilize viscous C/W foam (>20 cP) within 6 pore volumes of injection at 120 °C. The surfactant stabilized viscous C/W foam at low oil fractions and broke in the presence of large fractions of oil, both of which are desirable in CO2 mobility control and oil displacement. The ability to form foams at high temperatures and over a wide range in salinity is important for various practical applications including CO2 enhanced oil recovery, fracturing with energized fluids and CO2 sequestration.