Review of Research Progress on UCG Technology in 2023-2024

【Background】The industrialization of underground coal gasification (UCG) technology is a possible solution to ensure the security of clean energy supply, and a new round of UCG technology research is booming currently. 【Methods】By systematically perusing domestic and international literature, the research progress of UCG technology from 2023 to 2024 is reviewed, the main challenges faced by UCG technology development are analyzed, and future key exploration aspects are proposed. 【Advances】Recent research has proposed transformative technologies for the development and utilization of coal energy based on UCG. It is believed that the development of the collaborative and efficient UCG-CBM-CCUS joint production technology is the key to promoting the industrialization of UCG technology. The research scope for dynamics and process control of UCG production has been expanded, and the UCG heat and mass transfer model and simulation method have been improved. A mathematical model of the main parameters of UCG cavity growth process has been established, and the responses and variations of UCG production behavior to furnace temperature, operating pressure, gasification agent formula, and gas injection process have been explored. The natural and cost advantages of hydrogen-rich gas production from UCG have been demonstrated, and potential multiple functions of acoustic emission positioning technology in dynamic monitoring of UCG production have been revealed. The focus of UCG safety research is on four aspects, including the operational safety, groundwater safety, surface subsidence prevention and control, and carbon emission reduction. The characteristics of UCG syngas explosion, wellbore spray cooling measures, and hydrogen corrosion resistance of pipes have been studied. A high-temperature resistant backfill material has been preliminarily developed, and various UCG groundwater pollution prevention and control technologies have been proposed. Multiple methods for the prediction of UCG ground and residual subsidence have been formed, and basic strategy for the UCG carbon emission reduction and an active emission reduction carbon, named as the Carbon Regulation and Reduction, have been proposed. Significant progress has been made in the research of UCG geological constraints and site-selection evaluation, underground key equipment and tools, and technical and economic evaluation. Geological evaluation is highly focused on the response of UCG engineering behavior to geological conditions, and new ideas have been proposed and demonstrated such as the catalyst injection process, new ignition method, the stimulation heating with external electromagnetic field, the improvement of gasification agent injection method and process. Key equipment tools such as combustible casing and continuous pipe have been successfully developed, and various new process and technology ideas are innovative and have potential practical value. The economic competitiveness of UCG syngas production and utilization is studied and demonstrated. The on-site technical verification of new high-efficiency joint UCG-ECBM (enhancing coalbed methane) process has been successfully implemented for the first time. 【Prospects】In view of the significant issues revealed in recent UCG field tests, three future key research aspects have been proposed, i.e, geological evaluation and UCG engineering integration, construction technology improvement and key equipment and tool research and development.