Objective Underground coal gasification (UCG) is an innovation in traditional coal mining technology. The prerequisites for successful UCG include developing a systematic geological evaluation system and scientifically selecting the optimal coal seam.
Methods Using mathematical analysis methods such as analytic hierarchy process (AHP), coefficient of variation method, and technique for order preference by similarity to ideal solution (TOPSIS), this study systematically analyzed the coal quality, coal seam occurrence, hydrology, surrounding rocks, geological structures, hazardous elements, and geological exploration degree of coal reservoirs in the Aidinghu mining area, Turpan-Hami coalfield. Accordingly, this study deeply explored the feasibility of UCG in the Aidinghu mining area, constructed the resource evaluation system for selecting the optimal coal seam for UCG, and determined gasifier sites.
Results and Conclusions The results indicate that the study area exhibits coals with low ranks and simple structures. The coal seams in the area display low moisture and ash contents, moderate volatile constituents, substantial quantity, simple geological structures, and moderate burial depths. The roofs and floors of the coal seams consist largely of mudstones, siltstones, and fine-grained sandstones, with faults being underdeveloped. Furthermore, the study area boasts abundant coal reserves, low hazardous element contents in the coal seams, and a high geological exploration degree. All these render the study area suitable for UCG. The second-level evaluation indices consist of 23 geological factors such as coal type, the burial depth of coal seams, the lithology of coal seam roofs and floors, and coal reserves. Using reasonable mathematical statistics and scientific quantitative transformation, this study determined the comprehensive weight and grades of these indices and established a multi-level resource evaluation system for selecting the optimal coal seam for UCG applicable to the study area. Using this evaluation system, as well as the weighted sum method and TOPSIS, this study determined that the top three coal seams favorable for UCG in the Aidinghu mining area are the upper part of the No. 8 coal seam, the No. 11 coal seam, and the No. 7-3 coal seam sequentially. Finally, the upper part of the No. 8 coal seam was identified as the most favorable coal seam for UCG in the study area. The results of this study provide a scientific basis for the subsequent UCG implementation in the study area and serve as a reference for selecting the optimal coal seam for UCG in other areas.
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