Quantitative Visualization of Two-Phase Flow in a Fractured Porous Medium

Two-phase fluid flow in fractured porous media impacts many natural and industrial processes but our understanding of flow dynamics in these systems is constrained by difficulties measuring the exchange of water between fracture and adjacent porous matrix. We present a novel experimental system that allows quantitative visualization of the air and water phases in a single analog fractured porous medium. The fracture system consists of a sintered-glass porous plate in contact with an impermeable glass plate. A reservoir connected to the porous plate allows control of pore pressure within the porous medium. The fracture fills and drains through the porous matrix and flow manifolds along two edges of the fracture. The fracture is mounted in an imaging system that includes a controlled light-emitting diode panel and a charge-coupled-device camera. Flow and pressure are controlled and monitored by a computer during experiments. To demonstrate this system, we carried out a series of cyclic drainage and imbibition experiments in fractures bounded by porous media with different pore-size distributions in the porous matrix. Images of the drainage process demonstrate that the air-water distribution within the fracture evolves differently than has been observed in non-porous fractured systems. Specifically, we observed limited trapping of water within the fracture during drainage. Conversely, during imbibition, because air cannot exit through the porous matrix, significant regions of air became entrapped once pathways to the fracture boundaries became water filled. The differences in phase evolution led to substantial differences in the evolution of estimated relative permeability with saturation. Developed a novel experimental method to visualize two-phase flow in a fracture bounded by a porous matrix The evolution of the air-water distribution within the fracture was measured during sequential drainage and imbibition experiments Capillary head versus saturation curves are sensitive to the pore-size distribution of the bounding porous matrix