Underground coal gasification on the Thulin site: results of analysis from post-burn drillings

Abstract At the end of the coal gasification test in Thulin, three boreholes were drilled to provide information on the operating features of the gas generator by analysis of cores and cuttings. Petrological and mineralogical studies of the rocks adjacent to the coal seam provide information on the mineralogical and structural transformations that took place. In particular, analysis of the magmatic rocks indicates that the highest temperatures attained were above 1100 °C, whereas other rocks underwent rubefaction at temperatures of only 60–70 °C. Petrological studies of the coaly organic matter remaining within the samples show the presence of coke and anthracitic structures. The studies indicate that reaction temperatures of at least 900 °C were attained in some locations, and over 1000 °C (possibly 1100 °C) in others. The enrichment in 13 C and D of the coaly organic matter remaining in the cuttings enables zones to be located where combustion and gasification reactions progressed furthest. The information obtained has enabled assessments to be made of the extent of gasification and transformations undergone in each drilled area. The results indicate that steam gasification and methanation processes could predominate over pyrolysis.