Owing to the excess of carbon dioxide emissions in the atmosphere, a transition to a neutral carbon economy is needed. In this framework, Carbon Capture and Storage (CCS), and Carbon Capture Utilization and Storage (CCUS) become essential areas of development. Sequestering CO2 into different geological media such as deep saline aquifers and hydrocarbon reservoirs reduces the net anthropogenic gas emissions. In 2020, the global CO2 emissions corresponded to 31.5 gigatons. In the case of Saudi Arabia, the Riyadh province emitted 45.8 megatons. This study aims to evaluate for the first time the CO2 storage potential of the Unayzah Formation in Saudi Arabia, identify the primary trapping mechanisms, and capture the effects of the highly heterogeneous reservoir. CO2 injection in geological media is challenging because of the complexity of the geological properties and the CO2 phase behavior at super-critical conditions. In the present evaluation, we constructed a geological model only with public domain data. Similarly, we obtained different scenarios of the model on account of the uncertainty in the geological parameters. Later on, we selected a base model representing a conservative scenario to perform high-resolution simulations to determine the dominant mechanisms influencing the storage efficiency. In the main analysis, we simulated continuous injection of CO2 for forty years followed by twenty years of monitoring. We tested the injectivity of the reservoir showing it is possible to inject 1 and 2 megatons in vertical and horizontal wells, respectively. Likewise, lower injection rates improved solubility and residual trapping. Residual trapping is dominant, and it could reach fifty percent, while solubility could reach up to fifteen percent of the total CO2 injected. Along with these scenarios, we performed an Uncertainty Analysis based on porosity and permeability multipliers, salinity, and hysteresis effect. Finally, we demonstrated the effectiveness of the seal, and the structural and stratigraphic trapping. Until the development of the current analysis, there is no evidence of public domain studies assessing the storage potential into saline aquifers in Saudi Arabia. This contribution is essential for developing CCUS and promoting a circular carbon economy in line with the Vision of the Kingdom for the future.