Characterizing Foam Flow in Fractures for Enhanced Oil Recovery

Gas is very efficient in displacing oil for enhanced-oil-recovery projects because of its high microscopicdisplacement efficiency. However, the process at the reservoir scale suffers from poor sweep efficiency due to density and viscosity differences compared to in-situ fluids. Foam substantially reduces the viscosity of injected gas and hence improves the sweep. Foam rheology in 3D geological porous media has been characterized both theoretically and experimentally. In contrast, the knowledge of foam flow in fractured porous media is far less complete. We study foam rheology in a fully characterized model fracture. This investigation is conducted by varying superficial velocities of gas and surfactant solution. We find in this model fracture the same two foam-flow regimes central to the understanding of foam in 3D porous media: a low-quality regime where pressure gradient is independent of liquid velocity and a high-quality regime where pressure gradient is independent of gas velocity. The transition between regimes is less abrupt than in 3D porous media. Direct observation of bubble size, bubble trapping and mobilization, and foam stability as functions of superficial velocities allows comparison with our understanding of the mechanisms behind the two flow regimes in 3D porous media. Additionally, foam is shear-thinning in both regimes. But in other important respects the mechanisms thought to be behind the two flow regimes in 3D media do not appear in our model fracture. Foam is not at the limit of stability in the high-quality regime. Mobility in the high-quality regime instead reflects reduced and fluctuating foam generation at high foam quality.