Objective Carbon capture, utilization, and storage (CCUS) technology serves as a key method for carbon neutrality. However, large-scale engineering applications of CCUS are still confronted with serious challenges of environmental risks. Therefore, systematic environmental risk assessment plays an essential role in ensuring the environmental safety and social acceptability of CO₂ geological storage projects.

Methods Targeting the CO₂ geological storage project combined with overlying coal mining in Zhengning County, Gansu Province, this study performed the environmental risk assessment of CO₂ leakage based on the requirements of the Technical Guideline on Environmental Risk Assessment for Carbon Dioxide Capture, Utilization, and Storage (on Trial) (hereinafter referred to as the Guideline). Initially, this study identified the environmental risks associated with the project using the features, events, and processes (FEP) method. Then, based on the risk identification results, this study, through expert workshops, assessed the risks of CO₂ leakage to environmental media and beings using the risk matrix-based assessment method recommended in the Guideline. Finally, targeted recommendations for risk management were proposed according to the assessment results.

Results and Conclusions The results reveal low to ultra-low, acceptable environmental risks to receptors, except for the medium to high, unacceptable risk of blowout events to the surface atmosphere. The medium risk was reduced to a low, acceptable risk level after the implementation of targeted prevention and control measures such as enhancing wellbore integrity, installing wellhead devices matched with formation pressure, and space-atmosphere-surface-underground intelligent collaborative responses. Based on the environmental risk assessment results, this study constructed a phased prevention and control system, including strengthening wellbore integrity before CO₂ injection, implementing dynamic regulation and response during CO₂ injection, and establishing atmosphere-surface coordinated monitoring during CO₂ storage. This will provide risk management and control for the safe operation of CO₂ geological storage projects.