TECHNOLOGICAL CHALLENGE AND RESEARCH STATUS OF MINE WATER DEEP RE-INJECTION IN COAL MINING AREAS OF CHINA

Partial coal mining areas in China are confronted with the contradiction problem including a huge amount of mine water drainage,high treatment cost,and severe environmental protection pressure. It is necessary to ensure the safe mining of coal resources through mine water drainage and urgent to optimize the mine water treatment technology and cost. The quality of drained water should meet the requirements of environmental management. Therefore,how to treat mine water effectively and achieve a win-win situation for coordinated mining of coal and groundwater resources is one of the problems that need to be solved urgently. The authors' team,on the basis of systematic research on mine water deep re-injection,firstly defined the concept and then proposed the selection method and principles referring to geological structure,medium lithology of the deep re-injection target layer,hydrogeological structure characteristics,and groundwater quality compatibility. Secondly,in terms of basic theory,the focus of future basic research was summarized and clarified around eight aspects: regional deep hydrogeological conditions study,hydrogeological parameters calculation for weakly permeable formations,mechanism of multi-field coupling,enhanced permeability by hydraulic fracturing for low-porosity,low-permeability sandstone,evaluation of hydraulic fracturing in limestone,multi-medium of fracture-hole-dissolved-fissure-matrix & depiction of complex hydrodynamic fields,classification,control and prevention system of induced seismic risks,and technical standards and industry norms for the pollution prevention and control of mine water deep re-injection. Then,the authors expounded on six critical technologies focused on the development and utilization,including suitable areas & potential area screening for mine water deep re-injection,deep well construction-cementation-sampling & hydrogeological test equipment under extreme conditions,dynamic real-time monitoring & early warning technology for the process of mine water deep re-injection,quantitative characterization technology of fracture networks,collaborative storage of mine water and CO₂,environmental impact assessment of mine water re-injection & risk prevention and control. In terms of key equipment,software,and solutions,the technical direction of joint research was proposed based on the weaknesses and strengths of indoor test devices,on-site high-pressure re-injection equipment & intelligent systems,and an all-in-one software system. Finally,the authors proposed systematically the methodology of mine water re-injection,including floor sandstone and limestone mine water re-injection,roof sandstone and unconsolidated aquifer re-injection,as well as abandoned zone re-injection. The related technical requirements were clarified. Based on the above basic theoretical and critical technology framework,the authors discuss the "bottleneck" problem and the breakthrough direction for basic theory of mine water re-injection in the coal mining areas of China. The relevant basic and applied research directions are clarified. The authors hope to find a sustainable research and exploration path for the highly controversial practice of mine water deep re-injection.