(353e) Study of CO2-Soluble and Brine-Soluble Surfactants for CO2 Mobility Control

The effectiveness of (CO₂-soluble/brine-soluble) and (CO₂ –insoluble/brine-soluble) surfactants for CO₂ foam mobility control was studied for the recovery of oil from the pores of subterranean layers of porous sandstone or carbonate.  These surfactants enable the in-situ generation of CO₂-in-brine foams within porous media.  These foams increase the apparent viscosity of the CO₂, thereby inhibiting the formation of viscous fingers and early CO₂ breakthrough. There are several advantages for using CO₂-soluble surfactants, especially for operators that inject only CO₂, but it is also possible to dissolve the surfactant in slugs of brine that can be injected alternately with pure CO₂ (SAG process), or to add surfactant to both the CO₂ and the brine.

Brine, oil and core samples were obtained from an oilfield in a southern state.  The feasibility of using both CO₂ and/or brine to deliver the surfactant to the oil reservoir was examined.  CO₂-soluble alkylethoxylate and alkylphenol nonionic surfactants have limited solubility in CO₂ (< 0.10 wt %) at reservoir conditions.  CO₂-insoluble, brine-soluble ionic surfactants are up to ~1 wt % soluble in the reservoir produced brine (which would be used to prepare the surfactant solution that is injected) at reservoir conditions. 

Laboratory experiments with our high-pressure cell indicate that for this particular oilfield, the higher surfactant concentrations that can be achieved in brine yield foams that are far more durable and “viscous” than foams generated by dissolving surfactant only in the CO₂.  Further, these foams are resilient in the presence of crude oil.  We will present results for the adsorption of the surfactant by the reservoir rock; one of the major causes of foam degradation.  The foam mobility (apparent viscosity) will be determined by injecting CO₂ into a field core saturated with aqueous surfactant solution.  Finally, CT images of the foam being generated within and propagated through field cores will also be presented.