Control mechanism of regional structure on geothermal water chemistry, geothermal field and thermal hazard in a coal mine

Abstract

The coalfields of eastern China possess a great potential for hydrothermal geothermal resources. Rapid exploration and development of these geothermal resources are vital for achieving carbon emission reductions and promoting the green transformation of the mining sector. In this work, we analyze the chemistry of geothermal water and borehole temperature data from the Ordovician limestone thermal reservoir in the Xinhu coal mine, Huaibei Coalfield. The results indicate that the deep geothermal water is predominantly characterized by a Na·Ca-HCO₃·SO₄ composition, representing a mixture of shallow and deep groundwater. The horizontal average temperature of the thermal reservoir in the Ordovician limestone of this region is 50.5 °C, with the average circulation depth of geothermal water in the Ordovician limestone being 1267 m. The Xinhu coal mine has an average geothermal heat flow value of 61.93 mW/m² and an average geothermal gradient of 26.2 °C/km, and the geothermal gradient is controlled by faults and syncline structures. The drilling temperature curve indicates that the geothermal gradient in the study area is stable, with heat transfer primarily occurring through heat conduction. The dual tectonic heat accumulation model consisting of the Xinhu syncline and the deep large-scale faults determines the occurrence environment of the hydrothermal system of the Xinhu coal mine. Consequently, the combined influence of the F₁, F₂ and F₉ fault systems, and geothermal water migration formed the second-level thermal hazard in the coal mine.