POPFS: Permeation of Polymer Fluids in Soils (2024–2026)

EPSRC EP/X034437/1

In civil engineering, it is common practise to support the walls of an open excavation, such as a borehole or trench, by filling it with fluid. The traditional and most widely used support fluids are slurries of bentonite clay in water. Semidilute aqueous solutions of high-molecular-weight polymer ("polymer fluids") are known to have a variety of advantages over traditional bentonite slurries in terms of both cost and environmental impact, but they remain under-used because they are poorly understood. This multi-university, EPSRC-funded project is aimed at advancing our understanding of the permeation of polymer fluids in soils ("POPFS") by combining macroscopic permeameter testing, rheometry, microfluidic flow characterisation, and computational fluid dynamics.

In the Poromechanics Lab, we are using microfluidic techniques to study the flow of polymer fluids in porous micromodels to develop qualitative and quantitative insight into their movement through the pore space and their interactions with the solid skeleton. Our micromodels consist of custom microfluidic and millifluidic devices in a range of different geometries, complexities, and scales. We are using a custom microscopy setup and a variety of imaging methods, including machine learning-assisted particle tracking velocimetry, to explore network-scale flow in 2D and pore-scale flow in 3D. Our working fluid is a semidilute aqueous solution of partially hydrolyzed polyacrylamide (HPAM). Dilute HPAM solutions have been widely studied in porous micromodels due to their well characterized shear-thinning rheology and relevance to many practical applications. At higher, semidilute concentrations, entanglement and elasticity lead to hysteresis, transient effects, and a macroscopic pressure-drop-versus-flow-rate response that cannot be captured by simple shear rheology.

Featured: Oxford Engineering Science, Ground Engineering

DEFTPORE: Deformation Control on Flow and Transport in Soft Porous Media (2019–2024)

ERC Starting Grant 805469

Fluid flows through soft porous media are ubiquitous in biology, medicine, and the earth sciences, and they play a key role in a variety of industrial and manufacturing processes. The defining feature of soft porous media is that they are highly deformable, enabling a strong two-way coupling between flow and pore structure. This coupling has profound implications for the transport and mixing of solutes and the interaction of multiple fluid phases, all of which are strongly coupled to pore structure. However, flow and transport in these systems are at the frontier of our ability to measure and model.

This ambitious project, funded by the European Research Council, combined high-resolution experiments with theoretical modelling across a series of classical flow problems to revolutionize our fundamental physical understanding of, and predictive modelling capabilities for, flow and transport in soft systems.

FRIICFLOW: Frictional Flow Patterns Shaped by Viscous and Capillary Forces (2019–2022)

EPSRC EP/S034587/1

Pattern formation during fluid-fluid displacement in rigid porous media has been studied extensively, and is now relatively well understood. This problem features three phases, two of which are mobile (the fluids) and one of which is immobile (the solid). In a granular packing, however, a sufficiently strong fluid flow can also mobilise the solid grains. We refer to the resulting three-phase flow problem as a multiphase frictional flow because granular friction and jamming become governing forces in the mechanics. These flows occur in a wide range of natural and industrial systems, including soil and mud flows, methane venting from sediments, degassing of volatiles from magma, multiphase oil/gas/sand/proppant flows during the recovery of hydrocarbons, fluidised bed chemical reactors, and the processing of granular and particulate systems in numerous industries. These systems are inherently difficult to predict and control because of their complexity, which manifests itself through the self-organization of a wide variety of intricate macroscopic displacement patterns. These patterns are shaped by small-scale interactions at the interfaces where the invading fluid, the defending fluid, and the grains meet. Relevant physical mechanisms include frictional stress in the grains, viscous dissipation in both fluids, and capillarity (including both interfacial tension and wetting).

The FRIICFLOW project was a collaboration with Dr. Bjornar Sandnes at Swansea University. The goal of the project was to uncover the roles of viscous and capillary forces in the shaping of flow patterns in multiphase frictional flows. The Oxford team led the development of continuum-mechanical models for these systems, informed by an extensive experimental program conducted by the Swansea team in parallel with the modelling efforts.