Exploring fluid mechanics in energy processes: viscous flows, interfacial instabilities & elastohydrodynamics

Abstract

The displacement of fluids in porous media and fluid-structure interactions are major elements in upstream oil and gas processes. For instance, water flooding, which is an enhanced oil recovery process, consists of injecting water into petroleum reservoirs to displace and, hence, recover residual resources. This process is limited by flow instabilities since water cannot sweep the viscous oil efficiently. Moreover, hydraulic fracturing uses pressurized water to crack the tough, yet compliant, shale rock and release the trapped natural gas. In this thesis, we provide new insights on controlling interfacial instabilities that occur in two-phase fluid displacements by leveraging flow geometry.

When a flow passage is nonuniform, surface tension forces can either suppress or trigger interfacial instabilities in two-phase fluid displacements. We demonstrate this phenomenon experimentally and theoretically in a variety of geometrically varying configurations. In particular, we study two-phase flows confined to elastic boundaries. In this case, the flow geometry is provided by the subtle coupling between fluid flow and the compliant structure. Also in the spirit of fluid-structure interactions, we investigate boundary-layer flows, which are coupled to elastic and soft surfaces.

Beyond conventional energy sources, we shed light on the effect of fluid flow on the performance of microfluidic microbial fuel cells. These devices, which rely on bacteria to consume nutrients and generate electricity in return, exhibit a surprising dependence on fluid flow. We report the existence of an optimal flow rate range in which microfluidic microbial fuel cells achieve a maximum current production.