Modelling geological CO₂ leakage: Integrating fracture permeability and fault zone outcrop analysis

Geological carbon capture and storage (CCS) is a critical technology for mitigating greenhouse gas emissions, but the risk of leakage remains a significant concern. Fault and fracture networks across sealing intervals are potential pathways for CO₂ to escape from storage reservoirs, necessitating accurate assessment of their permeability and connectivity. Our study presents an integrated approach for modelling geological leakage in fault zones, combining single fracture stress-permeability laboratory measurements with detailed fracture outcrop data to simulate in-situ conditions for carbon storage. We studied caprock sequences cut by a normal fault in the Konusdalen West area (Svalbard, Norway), a regional seal for the reservoir of the Longyearbyen CO₂ Laboratory, and an analogue to Barents and North seas caprock formations. Digitising the outcropping fracture network, we explored the variations in fracture size distribution and their connectivity in different portions of the fault zone. These parameters are fundamental to establish if the fracture network provides permeable pathways. Integrating outcrop analysis with laboratory measurements allows us to create coupled hydromechanical models of the natural fracture network and to evaluate their upscaled permeability. We found that fracture network geometries vary across the fault zone, resulting in different upscaled permeability models, thus highlighting the importance of including detailed fracture network information into permeability simulations. Our study provides a framework for incorporating fracture permeability measurements and outcrop analysis into the modelling of geological leakage in fault zones, which can inform the design and operation of CCS projects and help mitigate the risks associated with geological storage of CO₂.