Characterization of N2 foam flow with in-situ capillarypressure measurements in a high-permeability homogeneous sandpack: effect of surfactant concentration and flowrate.

Determining the capillary pressure during foam flow in porous media is important because bubbles are thought to coalesce by lamella rupture as the "limiting capillary pressure" is approached. In this study, the role of surfactant concentration on capillary pressure and apparent viscosity of a foam flowing, at different flowrates, through porous media was explored. An in-house capillary-pressure probe was constructed, and it was utilized to characterize the capillary pressure of a foam flowing in a 145-Darcy homogenous sandpack. In-situ capillary pressures were determined for seven foam-quality-scan experiments with different gas velocities and surfactant concentrations. By comparing the test results, collected under different flowrates and surfactant concentrations, the apparent viscosity and the capillary pressure decreased for a quality greater than the transition foam quality, at the peak of apparent viscosity. The transition foam quality increases with increasing surfactant concentration and flow rate. For the slowest velocity, a minimum surfactant concentration is required to generate strong foam. While above this minimum surfactant concentration, foam-apparent viscosity is similar for different surfactant concentrations at the same velocity.