Geological consideration for site selection of underground coal gasifier

Underground coal gasification(UCG) is a revolution in traditional coal mining technology, and the site selection of underground coal gasifier is a prerequisite for a successful UCG project. Refining and analyzing the previous research results, the principle of UCG and the geological controls of site selection of underground coal gasifier were reviewed. The results show that lignite is the most suitable for UCG. UCG should choose thickness greater than 2 m, angle is less than 70° and buried depth of coal seam is 300 to 2 000 meters. At the same time, the UCG process may pollute the groundwater, and the influx of groundwater into the gasification zone will lead to the failure of gasification. UCG is liable to cause the breakage of surrounding rocks, resulting in the groundwater infiltration into the gasification zone and ground surface subsidence. In addition, UCG has strong selectivity for geological structure, and may affect the activity of microorganisms in nearby aquifers.