High Temperature Ultradry Carbon Dioxide-in-Water Foam Stabilized with Viscoelastic Surfactants

Ultradry carbon dioxide- in-water (C/W) foams with gas phase volume fractions () above 0.95 tend to be inherently unstable, as the large capillary pressure between the foam bubbles accelerates coalescence. Herein, we demonstrate that these ultradry C/W foams may be stabilized with viscoelastic aqueous phases formed with a single surfactant at a concentration of only 1% (w/v). The C/W foams are stable in DI water and over a wide range of salinity. Moreover, they are stable even for temperatures up to 120oC and with  up to 0.99. The properties of the foams and the aqueous viscoelastic solutions are examined for a series of surfactants. For our surfactants, the relaxation times from complex rheology indicate the formation of viscoelastic wormlike micelles over a wide range in salinity and pH, given the high surfactant packing fraction. At 90 oC and above 0.9, the foam morphology was composed of ~ 35 m diameter bubbles with a polyhedral texture. The apparent viscosities of these ultradry foams reached more than 120 cP with stabilities more than 30-fold over those for foams formed with the non-viscoelastic surfactants. The highly viscous lamellae remain thicker, due to the slower drainage rate, therefore resulting in slower Ostwald ripening relative to foams with non-viscoelastic lamellae. This is shown by measuring the change in bubble diameter with time via optical microscopy. Ultradry C/W foam at elevated temperatures could potentially be useful for CO2 sequestration, improved oil recovery or for hydraulic fracturing with minimal use of water to reduce the requirements for wastewater disposal.