<p>This study presents a detailed probabilistic assessment of geologic carbon dioxide (CO₂) storage in the Janggi Basin, a potential onshore pilot site in Korea. A comprehensive three-dimensional (3D) geologic and lithology model was developed using geostatistical methods based on data from multiple deep boreholes. The lithological heterogeneity in the Janggi Conglomerate was modeled using 100 lithofacies realizations to capture the spatial variability in rock properties. Subsequently, large-scale numerical modeling was conducted to predict the behavior of injected CO₂, considering both lithological heterogeneity and cap rock continuity. The results indicate that CO₂ migration is primarily driven by buoyancy, with the plume spreading laterally through high-porosity and high-permeability conglomerate and sandstone formations, while vertical migration is affected by the discontinuity of the upper mudstone cap rock. Probabilistic modeling emphasizes the need to consider geological uncertainties when assessing CO₂ storage potential, with consistent results in high-probability zones and notable variability in low-probability zones. This study provides insights into the risks and feasibility of geological CO₂ storage in complex formations, contributing to the advancement of safe and efficient carbon sequestration strategies to mitigate climate change.</p>