A novel multi-level and multi-branch geothermal well system for synergetic geothermal energy exploitation and mine heat hazard prevention: numerical investigation

Abstract

With the increasing of mining depth, heat hazard faced by deep coal mines is increasingly prominent. The inability to carry out mining work in high-temperature environments limits the exploitation of high-quality coal resources in deep areas. In this research, the idea of a synergetic geothermal exploitation method and mine heat hazard prevention was proposed to liberate the high temperature coal resources. The key of this study is to exploit geothermal resources while achieving efficient cooling of coal seams and ensure the safety of water inrush in this process. Therefore, based on actual conditions of mines in eastern China, the multilevel directional branch layout modes of channels were proposed and the parametric range of water injection-endangering safety was determined. Numerical Fluid Mechanics and heat transfer models of underground mining areas were developed in COMSOL Multiphysics by taking single channels as examples. Thereafter, influences of pressure, temperature, and level spacing of water injection on the temperature reduction effect of the model and heat adsorption effect were revealed. The results showed that higher water injection pressure, lower water injection temperature, and small-interference level spacing in a safety range can well demonstrate the temperature reduction effect of the model. On this basis, the optimal scheme can be determined to help obtain the number of channel branches in a full range. The developed intact numerical model in the application zone has three channel branches and the average temperature of coal seams in the case of 1.8 years is reduced below 26 °C. The results proved that this scheme delivers efficient temperature-reduction performance.