Fluid flow in complex porous media: a study of spatial correlation, disorder and deformation

Fluid flow through porous media is studied for its importance to natural and industrial systems, such as oil recovery and CO2 sequestration. In these scenarios, a fluid invades a porous medium and displaces or mixes with fluid that already exists there. This thesis focuses on how complexities arise in such processes when the connectivity of the pores is considered. In addition to the overall disorder in a system, the ways in which pores connect with each other have a significant effect on fluid invasion and mixing within a porous medium. Here, I develop and employ experimental techniques for exploring this connectivity in a variety of scenarios. First, spatial correlations in the pore-scale properties are introduced in the context of fluid-fluid displacement. Increasing the correlations' range leads to increasingly large areas of similarly-sized pore throats and more asymmetric invasion patterns with lower interfacial area and a lower fraction of trapped defending fluid. This work helps to show under what conditions spatial correlations will impact mixing and reactions in a porous medium. The second project investigates transport phenomena in disordered porous media. I inject a dyed fluid phase and observe how it mixes with a miscible, undyed defending fluid. A small level of disorder promotes mixing around the porous system. However, for higher disorders mixing is then restricted, as larger patches of obstacles collectively hinder flow. This work has significance in understanding how organisms will organise themselves to efficiently transport nutrients. Finally, I investigate the effect of a deformable porous medium. For elastic obstacles, the pressure drop of an interface trapped in a pore throat causes that throat to deform. I investigate this regime and explore how disorder restricts the appearance of fracture-like patterns. A group relating the change in pore shape due to elastic effects, relative to natural size variations, is shown to control the pattern selection. Fracture-like invasion patterns are found to be more strongly favoured when fluid is injected at a constant flow rate, as opposed to constant pressure