The influence of disjoining pressure on foam stability and flow in porous media

Abstract

Foam flowing in porous media can exhibit large flow resistances that make it an attractive fluid for improving underground oil recovery. To be an effective displacement fluid, however, the lamellae, which discretize the gas into foam bubbles, must remain stable. This work studies how the stability of single foam films, as gauged by the magnitude of their disjoining pressures, influences the flow resistance of foam in porous media. Steady state pressure gradients of flowing foam in 2.3 μm2 permeability glass beadpacks and disjoining pressure isotherms of single foam films are measured for 10−3 M and 0.017 M sodium dodecyl sulfate (SDS) solutions with and without NaCl. The constant-rate flow experiments show that the addition of salt to 10−3 M SDS increases the pressure gradient in the beadpacks from 0.1 to 4 MPa m−1 at 0.50 M NaCl. Surfactant solutions of 0.017 M SDS content exhibit pressure gradients of 22 MPa m−1, quite independent of salt concentration. Likewise addition of salt to the 10−3 M SDS solutions dramatically influences the disjoining pressure isotherms by raising the rupture pressure from 0.5 to above 15 kPa at 0.50 M NaCl. The 0.017 M SDS solutions display rupture pressures above 30 kPa, independent of salt concentration. We conclude that high repulsive disjoining pressures in single foam films lead to strong foam in porous media with large flow resistance. Further, we find that the limiting capillary pressure for rapid foam coalescence in porous media is close to the rupture pressure of foam lamellae as obtained from measured disjoining pressure isotherms.