Analysis of Foam Mobility and Foam Texture in Heterogeneous Microfluidic Porous Media

Foams are essential in applications ranging from enhanced oil recovery in the oil industry to carbon sequestration in hydraulic fracking sites. Thus, there is a great interest in understanding the fundamental physicochemical processes associated with foam to predict its behavior in natural porous media environments. Microfluidics have been proven to be effective in visualizing small-scale events and processes that would otherwise be difficult to observe in natural confined systems. In this study, a microfluidic device designed to mimic natural heterogeneous sandstone porous media is employed to investigate the effects of gas types on gas trapping, foam texture, foam stability, and phase mobility in quasi-steady-state flowing foam. Nitrogen foam of varied surfactant concentrations is evaluated in this work. Phenomena such as foam bubble trapping and lamellar division are directly observed in microfluidic devices and compared among different foam qualities and surfactant concentrations. In these cases, foam was characterized by pressure drops, apparent viscosities, foam mobility, and variations in foam texture. An in-depth comprehension of foam texture, in relation to foam quality and flow, is possible by combining high-speed imaging and image processing. A foam population balance model and the relationship between the trapped foam texture and trapped fraction were evaluated with experimental results. It was found that trapped foam directly contributes to its apparent viscosity, while the sizes of flowing foam bubbles also play an important role. We also probed the role of pore size in foam bubble generation and found that bubbles smaller than the average pore size could be an indicator of foam strength. Gas population balance was also evaluated using results from image analysis.