Heterogeneous transport in porous media: from immiscible fluid displacement to cracking

Filtering water and brewing coffee are familiar processes that rely on transport in a porous medium. This process also underlies many technological applications, including oil recovery, groundwater remediation, carbon sequestration, and drying of granular materials. When sufficiently slow, transport is typically modeled using a simple continuum approach. However, while appealing, such an approach neglects heterogeneities in transport that can strongly impact bulk behavior. In this talk, I will describe two different examples of how we investigate heterogeneous transport, and its implications, in porous media. 

First, I will describe how we visualize the flow of multiple immiscible fluids within a disordered porous medium, in 3D, over length scales ranging from smaller than a pore to that of the entire medium. This capability enables us to elucidate the physics underlying immiscible fluid displacement. The disordered structure of the pore space typically leads to disordered finger-like displacement pathways; however, we show how a pore size gradient can either stabilize the flow, preventing fingering, or further destabilize the flow, exacerbating fingering. Our results thus provide a way to control fluid displacement pathways in porous media.

Second, I will describe how we investigate the drying of packings of shrinkable, porous grains. Using a combination of experiments, poroelasticity theory, discrete-element simulations, and continuum modeling, we show that the packings crack in diverse ways upon drying. We show that the cracking behavior can be predicted from four state variables that arise from the interplay between fluid transport, grain shrinkage, capillary cohesion, and substrate adhesion. Moreover, we demonstrate how crack evolution can be guided by tuning the spatial structure of the drying profile. Our results provide a way to control crack evolution and ultimately could pave a way to better manage drying-induced cracks in engineering applications. Ultimately, our research stimulates new findings and questions at the interface of Engineering, Physics, and Materials Science.