CO₂-in-Water Foam at Elevated Temperature and Salinity Stabilized with a Nonionic Surfactant with a High Degree of Ethoxylation

Abstract

The utilization of nonionic surfactants for stabilization of CO2 foams has been limited by low aqueous solubilities at elevated temperatures and salinities. In this work, a nonionic surfactant C12–14(EO)22 with a high degree of ethoxylation resulted in a high cloud point temperature of 83 °C even in 90 g/L NaCl brine. Despite the relatively high hydrophilic–CO2-philic balance, the surfactant adsorption at the C–W interface lowered the interfacial tension to ∼7 mN/m at a CO2 density of ∼0.85 g/mL, as determined with captive bubble tensiometry. The adsorption was sufficient to stabilize a CO2-in-water (C/W) foam with an apparent viscosity of ∼7 cP at 80 °C, essentially up to the cloud point temperature, in the presence of 90 g/L NaCl brine in a 30 darcy sand pack. In a 1.2 darcy glass bead pack, the apparent viscosity of the foam in the presence of 0.8% total dissolved solids (TDS) brine reached the highest viscosity of ∼350 cP at 60% foam quality (volume percent CO2) at a low superficial velocity of 6 ft/day. Shear-thinning behavior was observed in both the glass bead pack and the sand pack irrespective of the permeability difference. In addition, C12–14(EO)22 stabilized C/W foam with an apparent viscosity of 80–100 cP in a 49 mdarcy dolomite core formed through a coinjection and a surfactant-alternating-gas process. The dodecane–0.8% TDS brine partition coefficient for C12–14(EO)22 was below 0.1 at 40 °C and 1 atm. The formation of strong foam in the porous media and the low oil–brine partition coefficient indicate C12–14(EO)22 has potential for CO2-enhanced oil recovery.