CT studies of surfactant-induced CO₂ mobility control

Foam mobility control for CO₂ was studied by Computerized pornography (CT) in tertiary first-contact miscible corefloods. The CT images show that injection of 0.05 wt% Neodol 25-12 Ethoxy Glycerol Sulfonate (NEGS 25-12S) in brine prevents gravity and viscous instabilities, and enables CO₂ to displace all the oil from cores in a piston-like manner. Surfactant screening tests, designed to test the debilitating effect of temperature, salinity, and crude oils on foam performance, are described. NEGS is both temperature and salinity tolerant: it forms stable foams with CO₂ in the presence of oil to at least 76 deg C with hard brines containing at least 18 wt% TDS. CT studies revealed a combination of factors contributing to effective CO₂ mobility control. These include both increases in apparent CO₂ viscosity and capillary pressure changes which produce a high-saturation brine bank insitu. This brine bank separating the CO₂ and oil banks further reduces CO₂ mobility through relative permeability effects but does not impair oil recovery efficiency by brineshielding mechanisms.