Research progress and key challenges in product regulation of deep coal underground gasification and CO₂ sequestration in gasification chamber

Underground Coal Gasification (UCG) is a chemical mining method that converts underground coal into combustible gases such as H₂, CH₄, and CO through controlled combustion. UCG is an important technical means for achieving clean and efficient utilization of deep coal resources. A large number of gasification chambers are formed after the completion of UCG, which serve as high-quality natural spaces for the geological storage of carbon dioxide. However, the current UCG technology faces challenges such as difficult reaction process control, poor gas production quality and stability, uncertain gasification chamber stability, and inadequate long-term sealing of the cover layer, which hinder its widespread application. The work focuses on the development prospects of deep underground coal gasification coupled with carbon dioxide storage (UCG-CCS), systematically reviewing the research progress at home and abroad in three aspects: first, the generation laws and regulation methods of underground gasification products; second, three dimensional evolution characteristics of gasification chambers under multi-field coupling conditions; third, the dynamic evolution mechanism of the sealing properties of the surrounding rock under the thermal effect of CO₂ sequestration in the gasification chambers. On this basis, three core scientific challenges that urgently need to be addressed at present are summarized: ① Unclear mechanism for efficient gas production regulation under the thermal and mass transport conditions of native dense coal; ② Unclear mechanism for secondary weak surface formation in the surrounding rock of underground gasification chambers under multi field coupling conditions; ③ Unclear dynamic evolution mechanism of gasification chamber sealing under chemical mechanical coupling. Furthermore, three major research challenges have been summarized: how to achieve long-term stable and efficient gas production in UCG, how to control the stability of gasification cavity structure under high recovery rate conditions, and how to achieve long-term safe CO₂ storage in gasification chambers of UCG. Finally, the key research directions for future work are prospected, which provides references for the clean and efficient utilization of deep coal resources and the safe sequestration of CO₂.