Abstract
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 flow in the
interacting fracture and porous media. 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 (LED) panel and a charge-coupled-device
(CCD) 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.