Summary of underground coal gasification field tests and suggestions for industrial development

China's underground coal gasification has entered a new historical development opportunity period, driven by the dual requirements of realizing the "carbon peaking and carbon neutrality goals" and ensuring national energy security. This paper analyzes the history of underground coal gasification in chronological order in order to scientifically formulate a technological breakthrough route and promote industrial development. The history is divided into three stages of development: mine type gasification, straight/directional well type gasification, and horizontal well type gasification. The underlying logic of promoting gasification technology innovation at different stages is explored. The reasons for the failure of industrialization are analyzed from the two aspects of technology and non-technology, and the countermeasures for industrialization are proposed. The findings of the study are as follows： (1)Horizontal well & controlled retracting injection point gasification process can not only effectively avoid the risks of shallow gasification in terms of surface subsidence and freshwater pollution, but also has the advantages of expanding the scope of vertical coal resource development, increasing the amount of coal control within two wells, improving the quality of crude gas, and ensuring continuous gasification. In the current and future period, this method is the mainstream technical route.(2)China has the longest field test period and has been in the stage of mine-type gasification for a long time. Although China's underground gasification of medium-deep coal test research is in the early stage, but due to the difficulty and low maturity of technology research, the major coal-rich countries in the medium-deep coal gasification technology research and development basically falls into the same pace. This technology has the potential to become a new track for China's drilling-type gasification technology to overtake the other countries. (3)Analysis shows that the poor applicability of technology is the main technical reason for the difficulty in industrialization of mine and vertical well gasification, and the low maturity of technology is the main technical reason that restricts the industrialization of horizontal well gasification. The long-term safety and high production issues have not been completely solved.(4)The low-cost development of conventional natural gas and the impact of the shale gas revolution, public concerns about environmental pollution caused by shallow gasification, and the government's policy shift towards underground coal gasification are the main non-technical reasons for the termination of foreign experiments; The long-term lack of development planning, relatively single scientific research and experimental subjects, insufficient scientific research investment, lack of industrial support policies, and lack of establishment of joint innovation mechanisms are non-technical reasons that hinder China's industrialization. The industrialization suggestion of UCG in China is put forward: it is necessary to fully understand the complexity and challenges of underground coal gasification technology in the new period. According to the two levels of “full accomplishment” and “high-quality accomplishment”， the core issues of "longterm stable production" and "high yield and excellent production" should be solved. Through synchronous promotion of scientific research and on-site experiments, the technological maturity should be continuously improved. On the production side, the cascade development method of "physical gas extraction followed by chemical gasification" should be adopted to avoid competition with the development of coalbed methane. On the utilization side, actively exploring the integration development mode with oil and gas, new energy and coal chemical industries to improve economic benefits.⑥As a subversive “artificial gas reservoir” development method, the success of underground coal gasification can provide technical reference for fluidization development of other mineral resources, and push China's unconventional fossil energy development technology to a new level.