Risk analysis and production safety design of supercritical carbon dioxide storage in gasification combustion cavity

The storage of supercritical carbon dioxide in the coal underground gasification combustion cavity can not only reduce greenhouse gas emissions, help control global climate change, but also avoid potential geological hazards caused by the long-term existence of coal-burning holes. It is an important innovative development direction for the global coal industry. However, currently, there is insufficient examination of the practicality and hazards of UCG-CCS through industrial trials, which considerably restricts the spread and use of UCG-CCS. This study employs theoretical analysis and numerical simulation to examine the geological feasibility of UCG-CCS. It finds that the risk of carbon dioxide leakage in UCG-CCS is predominantly due to overlying rock fractures being diffused by the integrity of the cover layer and the parameters of the gasification furnace. It has also been found that the development height of cap rock fractures is closely related to CO2 injection pressure and gasification furnace width. As CO2 injection pressure increases, the capping fracture exhibits a descending trend resembling a stair-step; as gasification furnace width decreases, the development height of cap rock fractures decreases. On this basis, the technical approach and design method of preventing carbon dioxide leakage in UCG-CCS are proposed. The research findings have significant theoretical and practical implications for site selection and risk assessment in UCG-CCS process engineering.