Hydrogeophysical characterization of fractured rock through combined push-pull experimens and single-hole ground penetrating radar

Push-pull experiments are a popular method for investigating flow and transport properties of fractured rock systems. During the experiment, a tracer is injected and retrieved at the same location. By introducing a volume of chasing fluid between injection and retrieval, different scales of the system can be probed. By further allowing a resting period of the tracer non-reversible effects can be investigated. However, push-pull experiments are limited by ill-defined length scales, lack of information on fracture heterogeneity and the effect of ambient flow. To gain a deeper hydrogeophysical understanding of fractured rock we monitor push-pull experiments with single-hole ground penetrating radar (GPR). Through difference imaging we can clearly map the spatial evolution of the tracer in the system, as well as density driven and ambient flow effects. Furthermore, through a 3D modeling scheme that we have recently developed, we can simulate the propagation and scattering of GPR signals from millimeter-thin fractures in a domain of tens of meters, independent of fracture aperture and orientation. We are currently coupling the model with existing flow-and-transport solvers to allow simulation of the combined experiments.