Research on evaluation technology system of mid-deep underground coal gasification based on researchers from China

Underground coal gasification is of great strategic significance to the effective and clean development of coal resources and scale up production of natural gas worldwide. Selection evaluation is the foundation of the exploration and development of underground coal gasification. In this paper, the differences between mid-deep (500-2200 m) and shallow layer (<500 m) underground coal gasification are analyzed, the key parameters affecting underground coal gasification are clearly identified, and the selection evaluation technology system is established. The results show that there are great differences between mid-deep and shallow layer underground coal gasification in terms of furnace construction site selection, engineering process, gasification efficiency and gasification products, the former is the main development direction in the future considering the resource potential, gasification efficiency, environmental protection and technological progress. The research of mid-deep underground coal gasification selecting should be carried out step by step with "favorable area-favorable zone-favorable zone ranking-favorable target" evaluation system. In the early stage of exploration, the product of thickness and volatiles can be used as a rapid evaluation index. Within the suitable range, the larger the index is, the more favorable it is, and when the index is greater than 3, it is defined as the favorable area. Further, ten key geological parameters of coal seam geological conditions, coal-rock and coal-quality characteristics and structural hydrologic conditions are selected and graded during zone evaluation according to different threshold ranges. At the same time, a favorable zone queuing method based on the two-factor evaluation method is established. Additionally, the final target site selection is established with more detailed evaluation parameters, such as process performance parameters, gasification characteristics parameters, technical recoverable indicators, economic recoverable indicators. The study provides the siting selection technology for the middle deep coal underground gasification, which is of great significant for the development of coal underground gasification industry.