Numerical evaluation of fault reactivation and leakage risk in CO2 geological storage

Abstract The injection and long-term storage of CO₂ can alter pore pressure in fault zones, potentially reactivating faults and significantly increasing leakage risks. Current research on CO₂ leakage along faults primarily relies on 2D models, which fail to fully account for fluid flow and diffusion in 3D porous media or accurately represent the impact of 3D features on pore pressure. Using the Ordos Basin onshore saline aquifer project as a case study, this research establishes a model to analyze CO₂ leakage and fault reactivation risks by incorporating actual engineering and geological parameters. The study investigates the dynamic pressure response in fault zones during long-term CO₂ storage, calculates leakage rates under varying injection and fault property conditions, and identifies primary and secondary factors influencing fault reactivation. Results indicate that early CO₂ injection leads to pressure buildup in the fault zone, peaking with continued injection before gradually declining as CO₂ migrates and dissolves, with pressure dropping rapidly post-injection. Under baseline conditions, CO₂ leakage rates along faults range between 0.1% and 1%, with sensitivity to parameters ranked as follows: distance from injection point > fault zone thickness > fault zone permeability > fault dip angle > injection rate. Fault reactivation risk peaks at a 60° dip angle, while other key influencing factors include injection rate, distance from injection point, fault zone permeability, and thickness. The distance from the injection point emerges as the most critical parameter, capable of driving leakage rates beyond safe thresholds and pushing fault reactivation coefficients to critical levels. These findings offer valuable guidance for China’s upcoming large-scale geological CO₂ storage initiatives.