Characterization of Fluid Flow and Energy Exchange in a Natural Rough-Walled Fracture

Quantitative studies of flow in fractured rock are important to engineering, hydrogeological, and geotechnical practices due to the ubiquitous nature of fractures in geothermal, water supply, and petroleum reservoirs. Importantly, fluid flow through fractured systems induces energy and chemical exchange with the host rock. The nature and magnitude of this exchange however, has been shown to be dependent upon several factors including flow path tortuousity and the geometry of fracture heterogeneities (Heinle 2017). Due to the difficulty of observing flow fields in a natural fracture system, many studies of single-fracture flow have used geometric simplifications such as the parallel plate model. These models however, lead to inaccuracies when predicting advection and diffusion in natural systems with complex asperity geometries. More recent studies (Heinle 2017) have used simplified artificial fracture asperities to introduce some of the complexity inherent to natural systems, however few studies have yet focused upon the effect of natural fracture surface roughness on fluid flow and energy exchange with the host rock matrix. Here we present work conducted to quantitatively model the effect of natural fracture roughness on fluid flow and energy exchange processes. The first phase of study involves the replication of natural granite fractures using white light interferometry and digital re-composition. Modeling of coupled heat diffusion and advection processes through the host fracture is then conducted using COMSOL Multiphysics 5.3^®. Preliminary results from flow modeling focus upon the relationship between fracture surface roughness and conjugate heat transfer efficiency in a series of synthetic apertures of variable surface roughness.