Exploring geological parameters sensitive to underground coal gasification

Compared to ground coal chemical plants, underground coal gasification (UCG) requires gasifiers as geological bodies. Accurately understanding geological conditions is a critical prerequisite for UCG. To minimize the geological risks involved in UCG siting, this study systematically explored the geological parameters sensitive to UCG based on the intricate geological conditions of Guizhou Province, China. By collecting and organizing the exploration data of coal resources in Guizhou, this study established mathematical models for normalized, graded parameter value assignment, the algorithm of parameter weight vectors, and the algorithm of parameter weight product, with the purpose of obtaining the accurate quantitative data of geological parameters of the study area. Building on the geological parameter set comprising 26 geological parameters, this study identified the cross effects of critical geological risk factors on the feasibility of UCG in coal seams of a complex structural area using a mathematical statistics method. Finally, this study determined the geological risk sources sensitive to four indices: the feasibility of gasifier construction, process-related easy controllability, gasification safety, and the economy of development. The results show that the geological parameters of the four indices exhibit different sensitivities, which gradually weaken in the order of the feasibility of gasifier construction, process-related easy controllability, gasification safety, and the economy of development. The feasibility of UCG manifests the greatest dependence on the feasibility of gasifier construction, succeeded by process-related easy controllability. In contrast, the remaining two indices exhibit significantly reduced sensitivity due to their relatively high discreteness. Regarding the degree of sensitivity, the most sensitive parameter among 26 geological is the firmness coefficient of coal seams, with other eight dominant geological parameters including coal seam thickness, coal seam dip angle, coefficient of coal thickness variation, gangue thickness coefficient, fault index, coal seam burial depth, Audibert–Arnu dilatation, and bond index. These major parameters affect the feasibility of gasifier construction and process-related easy controllability. For the geological parameters sensitive to UCG in Guizhou, the key to the success of UCG projects lies in the feasibility of gasifier construction, and gasifier siting should first consider structural characteristics and their effects on coal seam conditions. To continuously promote the UCG industry, it is feasible to establish unified assessment criteria for the geological risks of UCG based on the abovementioned four indices, as well as the actual features and occurrence conditions of coal resources in China. Accordingly, a scientific basis can be provided for the siting of pilot test areas with typical geological conditions.