Permeation of semi-dilute polymer solutions in porous micromodels

In civil engineering, it is common practice 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. Here, we study the permeation of polymer fluids through porous micromodels to develop qualitative and quantitative insight into their flow through the pore space and their interactions with the solid skeleton. Our micromodels consist of custom microfluidic devices in a range of different geometries and complexities. We use a custom microscopy setup and a method of machine learning-assisted particle tracking velocimetry to explore transient 3D flow fields at the pore scale. Our working fluid is a semidilute aqueous solution of partially hydrolyzed polyacrylamide (HPAM). We study the flow of fixed concentration fluids, examining the connection between transients observed in simple shear rheometey tests and the steady state pressure drop versus flow rate relationship in porous micromodels. We also explore the transient displacement of water with miscible HPAM solutions with direct relevance to support fluids.