Alkyl Ethoxylate Surfactants With High Hydrophilic-Lipophilic Balance for Smart CO2-Water Foam in Enhanced Oil Recovery

The sweep efficiency for CO₂ enhanced oil recovery can be improved by forming CO₂/water (C/W) foams with nonionic alkyl ethoxylate surfactants with high Hydrophilic-Lipophilic Balance (HLB). With long ethylene oxide (EO) chains as hydrophilic heads, these alkyl ethoxylate surfactants have high cloud points (70 ^oC or higher) in the presence of brines with NaCl concentrations up to 120 g/L, which is of interest for foam stabilization in reservoirs with high temperatures and salinities. Due to their high HLB value, these alkyl ethoxylate surfactants partition strongly to low salinity brine phase versus a dodecane phase at moderate temperatures (24-40 ^oC). Moreover, they reduce the interfacial tension between CO₂ and low salinity brine (~1% Total dissolved solids (TDS)) at moderate tempeature. Thus, they form “smart” shear-thinning CO₂/water foams in sand packs with different permeabilities without stabilizing dodecane/brine emulsions, which is of interest in mobility control of C/W foam for CO₂ enhanced oil recovery.