Geological carbon storage (GCS) in depleted U.S. oil and gas reservoirs offers a strategically important pathway for large-scale carbon dioxide (CO₂) mitigation by leveraging existing subsurface data, infrastructure, and proven trap systems. However, long-term storage security depends on comprehensive geological risk assessment that integrates reservoir characterization, leakage pathway evaluation, geomechanical stability analysis, monitoring technologies, probabilistic modeling, and governance frameworks. This study synthesizes current scientific evidence to evaluate the principal geological controls governing storage integrity. Findings indicate that containment performance is primarily influenced by caprock continuity, structural architecture, reservoir heterogeneity, legacy well integrity, and injection-induced stress redistribution. Wellbore degradation and fault reactivation emerge as dominant risk factors, particularly in reservoirs with high historical well density and complex structural settings. Coupled hydro-mechanical modeling demonstrates that pressure perturbations may extend beyond the injected plume, emphasizing the importance of controlled injection strategies and stress-field analysis. Advances in time-lapse seismic monitoring, probabilistic risk quantification, deep learning-based simulation, and digital twin technologies enhance predictive capability and enable adaptive injection management. Effective regulatory oversight and long-term stewardship frameworks further strengthen containment reliability. Depleted reservoirs represent viable long-term CO₂ storage options when supported by integrated, multidisciplinary risk assessment frameworks and continuous monitoring systems that proactively manage geological uncertainty and maintain sustained storage integrity.