For CO2 enhanced oil recovery, it is challenging to design stable surfactant for foams at high temperatures. Switchable amine surfactants were designed for CO2 to form CO2/water foams for mobility control for temperatures up to 120 °C and a salinity of 22% total dissolved solids (TDS) in carbonate reservoirs. These surfactants can reversibly switch from a CO2 soluble nonionic state to a water soluble cationic state with a decrease in pH. Below pH 6.5, these surfactants are highly protonated and cloud points are greater than 120 °C. In this cationic state, they exhibited low oil/water partition coefficients on the order of 0.1 which suggests that losses of surfactant to oil phases in EOR will be small. Also, these surfactants were effective in lowering the interfacial tension between water and CO2 at high temperature and high salinity from ~30 mN/m to 5 mN/m. For the proper choice of hydrophilic/lipophilic balance between the amine head group and length of surfactant tail, the surfactants stabilized CO2 foams over a wide range of salinities from 3% to 22% TDS brine. The foam was generated when the surfactants were injected from either the brine or CO2 phase with similar viscosities of ~30 cP which indicates that surfactants can readily undergo transport to the interface in each case. The foam generated exhibited shear thinning behavior which is beneficial for high injectivity near the well bore and high viscosity deep in the reservoir.

Switchable amine surfactants for CO2 foams in high temperature enhanced oil recovery

249th National Meeting (2015)

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