Research On The Mechanism Of Underground Thermal Environment Regulated By Geothermal Mining In Deep High-temperature Mines

As mining engineering proceeds to increasingly greater depths,higher rock temperatures and thermal stress pose a major challenge for the safe and efficient exploitation of deep resources.Synergetic mining of mineral resources and geothermal resources in deep mines can not only play a crucial role in heat hazard control with low cost and high efficiency,but also provide considerable geothermal energy.It is a win-win situation of resource exploitation and energy utilization and an important measure to convert harm into profit and waste into treasure.In recent years,the utilization of mine geothermal energy has gradually been a concern and attention,and some ideas of mine geothermal exploitation have been put forward.However,at present,there is still a lack of systematic research on the synergetic mining of mine geothermal energy to heat hazard control.The interaction mechanism of geothermal mining on underground thermal environment is still unclear in deep mine.In addition,there is no scientific theoretical basis on how to design a reasonable mine geothermal exploitation process for heat hazard control.Accordingly,this paper proposed the co-operation pattern and method of geothermal control and exploitation based on the heat and mass transfer characteristics of roadway.A numerical model and similar simulation experiment platform of synergetic mining of mine geothermal energy to heat hazard control were established to study the law of fluid flow and heat transfer in the process of geothermal exploitation of rock stratum.The critical factors affecting the heat transfer of roadway and heat recovery performance of the geothermal system are analyzed,which provides theoretical guidance for the design of reasonable technology and methods for geothermal exploitation in strata to heat hazard control.This research is dedicated to the management and resource utilization of high geotemperature in mines,the guarantee of safe,green,efficient and energy-saving production of deep mines,as well as the development of mine geothermal mining and energy structure system in deep mines.The main research contents and results of this paper are as follows:（1）A fully coupled multi-physical field numerical model was established to describe the groundwater migration,unsteady heat transfer of surrounding rock,non-isothermal flow of airflow and dynamic heat transfer on roadway wall.The dynamic change law of airflow temperature field and surrounding rock temperature field in both radial and longitudinal directions of roadway were analyzed.The buoyancy effect induced by airflow temperature difference will enhance the heat transfer in airflow and promote the surrounding rock to release heat into the airflow of roadway.When the magnitude of groundwater flow is larger than 0.01 m/d,the neglect of groundwater flow in surrounding rock will lead to a large deviation in the airflow temperature prediction.The orthogonal experiment results show that the surrounding rock temperature and airflow temperature are the key factors influencing the heat exchange of roadway.（2）A robust numerical calculation method is proposed that the ventilation roadway is approximated as a one-dimensional line element and the dynamic heat transfer between the one-dimensional roadway and three-dimensional surrounding rock in the radial direction was calculated by equivalent heat transfer coefficient equation,which can solve the heat transfer in large-scale ventilation network fastly with satisfactory accuracy.The accuracy of the proposed 1D roadway model is verified from three aspects:the airflow distribution in ventilation network,heat conduction and convection within roadway wall,and heat transfer in surrounding rock.Based on a field case analysis,it is found that the periodic change of underground air temperature is lagged behind the change in atmospheric temperature due to the heat storage/heat release of roadway surrounding rock.The heat release from air self-compression is an important heat source for underground airflow heating in summer.The airflow temperature in the roadway linearly increases with increasing geothermal temperature and average annual ambient temperature.Increasing the ventilation volume promotes heat dissipation of roadway surrounding rock in winter,and the underground airflow temperature will reduce in summer.（3）A novel synergetic mining approach is proposed that controls heat hazards at low cost and simultaneously exploits mineral and geothermal energy.The cooling effect of mine geothermal mining on the heat recovery performance of geothermal system and airflow temperature of ventilation network are preliminarily analyzed by numerical simulation.The characteristics of geothermal resources in deep high-temperature mines were analyzed,the conception and method of synergetic mining of mine geothermal energy as a solution to heat hazard control was put forward.A numerical model of synergetic mining of mine geothermal energy controlling heat hazard is established to analyze three typical mine geothermal mining methods.It is found that when the injection well is arranged horizontally under the main air intake roadway,the cooling range and cooling effect of water injection on the ventilation roadway are the best.The cooling rate of roadway and heat production performance of geothermal system are optimal simultaneously,when the cold water is injected above the rock strata near the roadway and heat water is extracted from deep high-temperature rock strata.In that case,a single heat production well can produce 1.68×10¹⁵ J.（4）A similar experimental platform was designed and established,which provides a new research method for synergetic mining of geothermal energy.Experiments on ventilation and heat transfer of roadway and water injection and extraction in rock formation were carried out.Based on the similarity theory,the similarity criteria for the simulation experiment of synergetic mining of geothermal energy to heat hazard control were deduced,and the matching scales of parameters between reduced-scale model and full-scale model were obtained.According to the 1:100geometric scale,a simulation experiment system was designed and built.The results of similarity simulation show that the influence of water injection and heat recovery on the heat transfer of ventilation roadway can be divided into three phases:cooling by ventilation and heat exchange,rapid cooling of surrounding rock,steady of ventilation and heat transfer.Lowering the injection water temperature or increasing the water injection time can improve the cooling rate and cooling effect of roadway,but it will result in a lower temperature of production water in production well.A high water injection rate facilitates the cooling rate of the roadway and increases the range of heat recovery in formation resulting in a higher production water temperature.（5）A multi-physical field（airflow field-concentration field-seepage field-temperature field）mathematical model is established to describe the non-isothermal heat transfer of gas-liquid two-phase seepage in porous media coupled with unsteady heat transfer of airflow and surrounding rock.The accuracy of the numerical model was verified by the results of indoor similar simulation experiments.And the influence of the layout of injection well and production well,initial condition of rock formation on heat transfer of roadway and water injection and heat production under initial unsaturated formation are analyzed.The simulation results show that the cooling of surrounding rock with injected water lags behind the change of its water content.The increase of distance between injection well and roadway,rock porosity and initial rock temperature will lead to an increase of cooling response time for roadway.When the airflow temperature in the roadway changes periodically with the seasons,the surrounding rock cooled by water injection can regulate the underground thermal environment by absorbing heat from airflow in summer.180 pictures,20 tables,216 references...