CAREER: Solute Transport Coupled to Geomechanics and Convective Mixing

University Of Southern California, Los Angeles CA

Investigators

Abstract

The movement and dilution of fluids in a fractured aquifer is important because it affects the safe disposal and effective containment of industrial wastes leaching into the ground. Computer simulations to predict the position and shape of the moving plume of fluid are challenging because the fluid inside the fractures moves faster than the fluid outside. The fracture properties that control this behavior change with the fluid pressure and mechanical stress in the aquifer. In groundwater systems, the viscosity and density of the contaminant fluid often differ from that of the water saturating the aquifer, which causes the fluid to channel through the aquifer in the form of fingers. Although these fingering processes are known, the effects of their interaction on the spreading and mixing of a contaminant plume in a fractured aquifer are unknown. This project will use laboratory experiments and computer simulation modeling to study the interaction between fluid flow, rock deformation, and fracture processes that affect the spreading and dilution of aquifer plumes for radioactive waste disposal and carbon sequestration applications. Increasing our knowledge will lead to better selection of the waste disposal site and minimize errors in the forecast of plume position and plume size at a selected site, and help decrease the aquifer remediation cost and time. The project will generate publicly available datasets and modeling tools which will be shared with groundwater engineers, hydrogeologists, and environmental engineers through an industry-academia partnership. A Masters-to-PhD Bridge program with summer research experience will be created for students. The spreading and mixing of groundwater solutes in fractured rocks are multiphysics problems in hydrogeology due to the coupling between fluid flow, solute transport, and geomechanical processes. This project will improve our understanding of the physical mechanisms stemming from the two-way coupling between solute transport and geomechanical processes in stress-sensitive aquifers in the presence of fingering and convective mixing. How the coupling activates certain fracture and fingering directions while suppressing others and how the hydromechanical properties affect the spreading and mixing metrics are questions that will be addressed through high-resolution numerical simulations, fracture mechanics and hydrodynamic instability theory, and experiments of solute transport in rocks. A novel spectrofluorimetric tracer quantification method coupled with distributed strain sensing will be developed. Experimental and simulation results will be synthesized to define a transport-geomechanics coupling strength parameter based on the hydromechanical properties of the aquifer and the physical properties of the solute. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.