Experimental Study of CO2 Foam Flow in Porous Media and Application of Fractional-Flow Method to Foam Flow

Foam flow in porous media is a complicated process. Recent research using N2 identified two distinct regimes for foam flow: a high- quality regime and a low-quality regime. Pressure gradient is independent of gas flow rate in the high-quality regime and independent of liquid flow rate in the low-quality regime. The purpose of this research is to see whether the two regimes exist for C02 foam. Previous studies with C02 have found one regime or the other, but not both. An apparatus was constructed to conduct high-pressure C02 foam core flooding experiments. The experiments were performed at room temperature of 740F and at pressures above 1500 psig. Surfactant solution and super-critical C02 were co-injected into Berea sandstone cores at various flow rates. Superficial velocities of surfactant solution and C02 ranged from 0.18-1.84 ft/d and 0.48-3.79 ft/d, respectively. The surfactant used was Chaser CD1045 at 0.25 wt % and 0.8 wt % concentration in a synthetic brine of 3 wt % NaCl and 0.01 wt % CaC12. Steady-state pressure drop along the core was recorded. In these results pressure gradient increases with increasing gas flow rate at constant liquid flow rate and decreases with increasing liquid flow rate at constant gas flow rate. The data from the experiments at different surfactant concentrations have the same trend of pressure gradient change with flow rates, but do not show the characters of either flow regime as seen with N2 foam or in other studies with C02. Fractional-flow methods were used to analyze and compare several foam models in the literature. Useful insights about the mechanisms controlling behaviors in these models are obtained from this analysis.