Progresses and revelation of underground coal gasification field test

To further understand the key scientific issues of the commercialization of underground coal gasification, based on analyzing underground coal gasification field tests at home and abroad, this paper summarizes the characteristics and relevant elements of underground coal gasification, including regional coal seam characteristics in gasification area, gasification process, crude gas components and calorific value, and so on. The result shows that environmental risk, geological conditions, coal grade and geomechanics-hydrogeological conditions are needed to take into account in the site selection for gasification; drilling has become the main gasification mode; gasification with oxygen enriched air in medium-deep depth has become an important breakthrough direction; controlled retracting injection point is the main gasification process. In the view of gasification coal seam burial depth and combustible gas composition in the crude gas, underground coal gasification can be divided into three types: shallow layer (formation pressure less than 4 MPa), middle deep layer (formation pressure between 4 and 18 MPa), deep and ultra-deep layer (formation pressure more than 18 MPa) underground coal gasification. The chemical reaction of underground coal gasification is mainly water-gas reaction, methanation reaction and supercritical reaction in shallow layer, middle deep layer and deep and ultra-deep layer differently, corresponding to that, the main combustible gas of produced crude gas is H2, CH4 and H2. It is an important way to achieve the commercialization goal of underground coal gasification under the carbon neutral goal that organically combines together the four aspects of favorable area evaluation, efficient gasification process, stable operation control and carbon capture and storage, which will be the main technology research and development direction of underground coal gasification in the future.