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

Chen, Yunshen, Elhag, Amro S., Cui, Leyu, Worthen, Andrew J., Reddy, Prathima P., Noguera, Jose A., Ou, Anne Marie, Ma, Kun, Puerto, Maura, Hirasaki, George J., Nguyen, Quoc P., Biswal, Sibani L., Johnston, Keith P.
Industrial & Engineering Chemistry Research 2015 v.54 no.16 pp. 4252-4263
adsorption, carbon dioxide, dolomite, engineering, ethoxylation, foams, glass, nonionic surfactants, oils, permeability, porous media, salinity, sand, sodium chloride, solubility, surface tension, temperature, viscosity
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.