Structural and flow modelling of bedrock fractures - a software perspective
Authors: Ovaskainen Nikolas , Nordbäck Nicklas , Engström Jon , Nikkilä Kaisa 
Published: March 2024

Discontinuities of the bedrock, i.e. fractures, form the main pathways for fluid flow in crystalline rocks. For modelling purposes, fracture data can be gathered from e.g. bedrock outcrops and drillcores. Remote digitization of bedrock outcrops results in mostly two-dimensional fracture data while structural measurements in-situ and from drillcores results in three-dimensional data. The nowadays common digitized two-dimensional fracture trace data can be analysed for geometric (e.g. orientation and length) and topological properties (e.g. connectivity). For these purposes, specialized tools exist such as FracPaq (Healy et al., 2017), NetworkGT (Nyberg et al., 2018) and fractopo (Ovaskainen, 2023).For three-dimensional fracture data analysis, the options become more sparse because as the data gains complexity through the addition of a dimension, so does the software required for analysis. This is especially the case for software that, rather than analysing fracture data, (also) generates it such as with discrete fracture network (DFN) modelling. DFN-modelling is required when fluid flow, reactive flow, geothermal flow, or contaminant transport properties of the fracture network need to be assessed at a scale larger than it is feasible to collect fracture data. Due to the added complexity, the available software for these purposes is varied and require specialized knowledge to use them effectively. In hydrocarbon exploration, geothermal exploitation and nuclear waste disposal, software such as FracMan (WSP trademark) is used for DFN-modelling and subsequent flow modelling. Although free and open-source options for DFN-modelling exist, they often lack user-friendly interfaces and lack the necessary manpower for further development outside of research purposes.&#160;In FLOP (FLOw Pathways within faults and associated fracture systems in crystalline bedrock) -project we gather knowledge of the available free and open-source software for three-dimensional fracture data analysis and modelling. We integrate the found solutions with macro- and microscale fracture data from outcrops and X-ray CT-imaging, respectively, to investigate flow channeling. We also apply the more mature tools available for two-dimensional fracture trace analysis, such as fractopo (Ovaskainen, 2023), to characterize varied sampling locations where flow properties of field analogues will be studied.&#160;The FLOP-project is funded by SAFER2028, a Finnish research programme on nuclear energy research, and the Geological Survey of Finland. The project is conducted in collaboration with the Deep-HEAT-Flows geothermal energy project.&#160;ReferencesHealy, D., Rizzo, R.E., Cornwell, D.G., Farrell, N.J.C., Watkins, H., Timms, N.E., Gomez-Rivas, E., Smith, M., 2017. FracPaQ: A MATLAB&#8482; toolbox for the quantification of fracture patterns. Journal of Structural Geology 95, 1&#8211;16. https://doi.org/10.1016/j.jsg.2016.12.003Nyberg, B., Nixon, C.W., Sanderson, D.J., 2018. NetworkGT: A GIS tool for geometric and topological analysis of two-dimensional fracture networks. Geosphere 14, 1618&#8211;1634. https://doi.org/10.1130/GES01595.1Ovaskainen, N., 2023. fractopo: A Python package for fracture network analysis. JOSS 8, 5300. https://doi.org/10.21105/joss.053