Integrated structural screening of faults for CO₂ storage in the EM field, Bredasdorp Basin

Structural attributes characterize 51 normal faults in the EM Field, offshore Bredasdorp Basin, South Africa. Fault scale is represented by plan-view extent (L). Within-surface variation is quantified by the heave range (ΔFH), throw range (ΔFT), combined displacement range (ΔFD), and cross-fault thickness change range (ΔCFTC). Dip-direction dispersion, throw consistency, and throw variability describe heterogeneity. L spans 0.32–9.04 km; 11 major faults contain 46.26% of cumulative L. Ranked separately for each attribute, the ten highest-ranked faults contribute 89.23%, 37.99%, and 71.43% of summed ΔFH, ΔFT, and ΔFD, respectively. Dimensionless ΔCFTC spans 0.092–6.000 and correlates with ΔFD (Spearman’s ρ = 0.93). The integrated structural significance (ISI) index balances scale, displacement, local complexity, and stratigraphic response. F22, F38, F2, F29, and F25 rank highest; minor F47 enters the 17-fault high-priority group. High-priority faults span western, central, northeastern, and southern sectors. Across 85 weighting scenarios, rank correlations are 0.961–1.000, retaining 14–17 baseline priority faults. Two resolution-related throw-ranking tests each retain 16 of 17. Conditional Monte Carlo analysis comprises 600,000 realizations across 12 scenarios, assuming ± 5–30% relative bounds on displacement ranges and, selectively, L. Median rank correlations are 0.9831–0.9997; nine faults occupy the top 17 in at least 95% of realizations in every scenario. ΔCFTC and local-complexity attributes remain fixed, contributing half the ISI weight. These results quantify sensitivity to assumed errors rather than measured interpretation uncertainty. The framework prioritizes fault-seal, geomechanical, and dynamic-flow assessments without predicting sealing, leakage, or reactivation.