Connectivity Analysis of Fault Damage Zones for CCS Using Graph Theory

Assessing the potential for fault-related leakage is critical for the safe and long-term storage of CO₂ in Carbon Capture and Storage (CCS) projects. Fault permeability, particularly along the Fault Damage Zone (FDZ), is a key uncertainty because direct in-situ measurements are rarely available. Current workflows estimate FDZ permeability using seismic-scale fault attributes combined with outcrop analogues, often relying on fracture network statistics including orientation, density and intersection distributions. While these methods provide a first-order approximation, they do not fully capture the spatial complexity of natural fracture networks, leading to potential inaccuracies in leakage risk assessments. This study introduces a Graph Theory-based approach to quantify FDZ connectivity in the context of CCS leakage risk assessments. By representing fracture networks as graphs and applying metrics such as the Largest Component Ratio (LCR), we provide a robust and spatially sensitive measure of connectivity. The methodology is tested on both synthetic Discrete Fracture Network (DFN) models and outcrop-derived networks. Results demonstrate that LCR correlates strongly with the percolation probability and better accounts for network heterogeneity compared to traditional topology-based methods. This approach supports fault risk assessments for CCS as a first screening step, contributing to improved site selection and long-term containment strategies.