A Laboratory-Validated, Graph-Based Flow and Transport Model for Naturally Fractured Media

Abstract

Fractures are a primary feature controlling flow, transport, and coupled processes in geologic systems. To date, experimental image-based observations of these processes have been challenging. Here, we use pulse-tracer experiments with a conservative radiotracer ([¹⁸F]-fludeoxyglucose) spanning multiple flow rates with simultaneous positron emission tomography imaging to characterize transport in a 5.08 cm fractured Sierra granite core. A graph-based, laboratory-validated flow and transport model is successfully demonstrated to describe the conservative solute transport in the natural fracture. Model network complexity, determined by the number of nodes and edges, significantly impacts model fit to observed data. Large graphs over-describe a fracture plane and act similarly to a porous medium while small graphs oversimplify the solute transport behavior. To our knowledge, this work provides the first validation of graph-based flow and transport models across a range of experimental conditions and sets the groundwork for upscaling to more complex and computationally efficient fracture models.