Coupled processes in fractured media: a key to the energy transition

Abstract Fractured media in the subsurface are geological formations involved in various geoenergy technologies essential to decarbonisation, including geothermal energy, carbon sequestration, hydrogen storage, nuclear waste disposal, and critical mineral extraction. The presence of fractures both enable and threaten these applications, providing permeability pathways and storage space while also posing risks of leakage, induced seismicity, and long-term instability. Their behaviour is governed by coupled thermo-hydro-mechanical-chemical-biological (THMCB) processes due to interplay among these five effects. These coupled processes evolve dynamically across scales, creating major challenges for prediction and management. In this Perspective, we highlight the understanding of coupled processes in fractured media as key to geoenergy solutions for energy transition, review their historical and emerging roles, and outline key challenges such as upscaling, uncertainty quantification, system integrity, and seismic risk. We also identify opportunities in digital twins, physics-informed machine learning, advanced sensing, exascale simulation, and underground pilot projects, to address these issues. Ultimately, progress will require integration across disciplines and transparent engagement with society, transforming fractured media from a source of uncertainty into a foundation for safe and scalable subsurface energy systems.