FLOW OF FOAM THROUGH POROUS MICROMODELS

This study focuses on the pore level behavior of foam in porous media. Air was injected into porous micromodels which had previously been filled with an aqueous solution of surfactant. The micromodels consist of an etched silicon wafer anodically bonded to a glass plate. The model simulates a monolayer of porous matrix. Three homogenous models of different pore dimensions and one heterogeneous model were used. Visual observations were made to determine the flow characteristics of "foam" under varying air injection rates, pore dimensions and surfactant concentration. Foam flow mechanisms, as observed in the micromodels, were recorded on video tapes. These tapes are available at the Stanford University Petroleum Research Institute, Stanford, California.;In the homogeneous micromodels, the wetting phase (surfactant solution) formed a continuous liquid network around the matrix. The air was found to propagate as tubular bubbles moving and extending over several pores. The flow mechanism was only slightly affected when different air injection rates, pore dimensions and surfactant concentrations were used.;Foam was found to be generated in the heterogeneous model. Air and liquid were propagated by a combination of channel flow (with liquid confined to small pores) and a bubble "break and reform" process. The break and reform process was caused by snap-off actions at pore constrictions.;A considerable reduction of effective mobility was observed in the presence of foam, compared to air-water systems without surfactant. Effective air mobility decreased with an increase in surfactant concentration in both the homogeneous and heterogeneous porous media. At a specific concentration, below the critical micelle concentration, mobility reduction converged to one value regardless of concentration changes. In the heterogeneous porous medium, surfactant concentration affected the flow mechanism. Foam bubbles produced at high surfactant concentrations were smaller than those generated at low surfactant concentrations.;The observed mechanisms can be broadly classified into two: membrane and foam bubble propagation. Propagation of membranes, air-liquid interfaces, occurred in the homogeneous porous media at both low and high surfactant concentrations, and in the heterogeneous model at low surfactant concentration. Foam bubble propagation occurred only in the heterogeneous model at high surfactant concentrations.