UpsFrac v1.0: an open-source software for integrating modelling and upscaling permeability for fractured porous rocks

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Abstract. The efficient and accurate simulation of fluid flow and heat transport underground plays an important role in groundwater migration and geothermal resource prediction. Rock fractures are complex in geological settings, exhibiting multiple-scale properties with varied patterns under different geological conditions. Modelling and upscaling the permeability of fractured porous rocks are both important and sophisticated processes in numerical simulations. While existing tools like MRST offer upscaling capabilities, they often lack integrated workflows for automated uncertainty quantification and direct coupling between fractal-based DFM generation and flow-based upscaling within a single framework. In this study, we propose an integrated methodology for modelling and upscaling the permeability of fractured porous rocks and develop an open-source software, UpsFrac, to implement this approach. The software considers complex fracture geometries in discrete fracture models (DFM) that are created deterministically and stochastically. UpsFrac employs conforming grid-based DFM with explicit matrix-fracture coupling, ensuring higher accuracy for complex fracture networks. The software can characterize the complexity of fractured porous rocks, including power law (fractal) length distribution, correlations between fracture length and aperture, and the effects of rock matrix properties. The state-of-the-art upscaling method, the multiple-boundary fracture upscaling (MFU) method, is applied to calculate equivalent fracture permeability, which links the fine-scale discrete fracture model to the coarse-scale equivalent fracture model. The current implementation is 2D and MATLAB-based, built upon fracture modelling code ADFNE and reservoir simulation code MRST, which can easily run DFM ensembles for uncertainty analysis. The code is available in open repositories to encourage modelling and upscaling of complex fractured porous rocks, allowing users to develop their own routines within the current framework and benefiting a broader community.

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