Work

Variability of fracture surface roughness in crystalline host rocks: implications for transport model simplifications

Year: 2025

Type: article

Abstract: Variability in fracture geometry and its complex surface characteristics are major contributors to solute transport and retention effects in rocks such as granite. Understanding the effects of cross-scale fracture geometry on solute transport modeling is critical for reliable quantitative predictions in applications such as geothermal energy use and nuclear repository safety. Here, we systematically investigated the sensitivity of fracture surface topography variability to the flow field and solute transport behavior. Specifically, we investigated the role of multiscale fracture surface roughness in solute transport modeling. As a starting point, our study utilized a 3D fracture geometry derived from CT scans and employed COMSOL Multiphysics software for solute transport modeling. By introducing increasingly lower spatially resolved geometries, while maintaining a constant high resolution mesh for simulation calculations, we investigated the consequences for transport on surfaces composed of superimposed building blocks of different sizes and shapes. The results indicate that fracture geometry simplifications with reduced spatial frequency information of well-defined, specific domains do not have a clear trend to alter the BTCs tailing. Instead, this type of model simplification can cause both increased and decreased tracer residence times, leading to misleading interpretations. We explain this by a complex superposition of surface building blocks of different sizes, such as single crystal surface pits, grain boundaries between crystals, and fracture curvature. For model sensitivity analyses, we suggest the use of concentration difference and acceleration maps to identify local transport heterogeneities introduced by geometric simplifications. In addition, we conclude that power spectral density (PSD) analysis provides a means of defining a range of surface spatial frequencies that helps to avoid oversimplification in geometric models of reactive transport.

Source: Applied Geochemistry

DOI: 10.1016/j.apgeochem.2025.106401

Authors: Wenyu Zhou, Johannes Kulenkampff, Daniel Jara Heredia, Thorsten Schäfer, Cornelius Fischer

Institutions: University of Bremen, Helmholtz-Zentrum Dresden-Rossendorf, Friedrich Schiller University Jena, Leipzig University

Language: English

Topic: Groundwater flow and contamination studies

Subfield: Environmental Engineering

Field: Environmental Science

Domain: Physical Sciences

Open Access status: hybrid

Estimated APC paid: $3,490

Funder: Bundesministerium für Umwelt, Naturschutz, nukleare Sicherheit und Verbraucherschutz