The Effect of Trapped Gas on Foam Flow in a Model Porous Medium

Abstract

Foams for enhanced oil recovery can increase sweep efficiency, as they decrease the gas relative permeability, mainly due to gas trapping. However, gas trapping mechanisms are poorly understood. Some studies have been performed during corefloods, but little work has been carried out to describe the bubble trapping behaviour at the pore scale. Microfluidic experiments are a useful tool for studying the foam flow behavior at the pore scale. We have carried out foam flow tests in a model porous media glass micromodel. Image analysis of the foam flow allowed local velocities to be obtained. The quantity of trapped gas was measured both by considering the fraction of bubbles that were trapped (via velocity thresholding) and by measuring the area fraction containing immobile gas (via image analysis). A decrease in the trapped gas fraction was observed both for increasing total velocity and for increasing foam quality. Calculations of the gas relative permeability were made with the Brooks Corey equation, using the measured trapped gas saturations. The results showed a decrease in gas relative permeabilities for increasing fractions of trapped gas. It is suggested that the shear thinning behaviour of foam could be coupled to the saturation of trapped gas.