Dynamic CO2 Leakage Risk Assessment of the First Chinese CCUS-EGR Pilot Project in the Maokou Carbonate Gas Reservoir in the Wolonghe Gas Field

Existing CO2 leakage risk assessment frameworks for CO2 capture, geological storage and utilization (CCUS) projects face limitations due to subjective biases and poor adaptability to long-term scale sequestration. This study proposed a dynamic risk assessment method for CO2 leakage based on a timeliness analysis of different leakage paths and accurate time-dependent numerical simulations, and it was applied to the first CO2 enhanced gas recovery (CCUS-EGR) pilot project of China in the Maokou carbonate gas reservoir in the Wolonghe gas field. A 3D geological model of the Maokou gas reservoir was first developed and validated. The CO2 leakage risk under different scenarios including wellbore failure, caprock fracturing, and new fracture activation were evaluated. The dynamic CO2 leakage risk of the CCUS-EGR project was then quantified using the developed method and numerical simulations. The results revealed that the CO2 leakage risk was observed to be the most pronounced when the caprock integrity was damaged by faults or geologic activities. This was followed by leakage caused by wellbore failures. However, fracture activation in the reservoir plays a neglected role in CO2 leakage. The CO2 leakage risk and critical risk factors dynamically change with time. In the short term (at 5 years), the project has a low risk of CO2 leakage, and well stability and existing faults are the major risk factors. In the long term (at 30 years), special attention should be paid to the high permeable area due to its high CO2 leakage risk. Factors affecting the spatial distribution of CO2, such as the reservoir permeability and porosity, alternately dominate the leakage risk. This study established a method bridging gaps in the ability to accurately predict long-term CO2 leakage risks and provides a valuable reference for the security implementation of other similar CCUS-EGR projects.