Characteristics of water-bearing media in Jurassic strata and groundwater occurrence and migration law in Yili Mining Area, Xinjiang

Taking the Yili mining area in Xinjiang as an example, combined with the typical hydrogeological characteristics of the Tianshan Mountains, such as strong snowmelt runoff and uneven permeability of Jurassic coal-rich strata, the macroscopic hydrogeological conditions, microscopic water-bearing media characteristics and water-rich law of the main aquifers (aquicludes) layers in the mining area were systematically studied by means of field sampling, electron microscope scanning, mercury injection experiment, X-ray diffraction and pumping test. The hydrodynamic characteristics and migration law of aquifers under special stratigraphic and geomorphological conditions are revealed. The results show that the effective porosity range of the sandstone aquifer in the roof and floor of the Jurassic main coal seam in the study area is 17.1%-29.5%, and the effective porosity range of the Neogene and Jurassic aquiclude is 17.6%-29.0%. The aquifers (aquicludes) layer contains high clay minerals, which are expanded and argillized in water. The special microstructure and mineral composition make the aquifers (aquicludes) layer show the characteristics of high porosity and poor permeability. In the study area, the water abundance of the Quaternary pore aquifer and the Jurassic main coal seam roof and floor sandstone aquifer is weak, and some areas show moderate water abundance, mainly static reserves, with block characteristics. The hydrodynamic characteristics and migration law of the main aquifers (aquicludes) are systematically studied. The Quaternary system is affected by the macro-geomorphology and hydrogeological conditions of the piedmont, showing the dynamic characteristics of ‘slope transit flow’ in the form of pore phreatic water with high intensity flow. At the same time, it is blocked by the lower Neogene mudstone aquifuge and has no hydraulic connection with the sandstone aquifer of the roof of the coal measures. The sandstone aquifer of the 5# coal seam floor mainly affects the coal seam mining, in view of this layer, the “factory” shape of “lateral closure and lateral cover” was constructed in a large range and the dredging effect was remarkable, which created good hydrogeological conditions for underground mining. The relevant research results reveal the characteristics of special water-bearing media and the law of water storage and water control formed by the Jurassic coal-rich strata in the study area under the influence of sedimentary environment, which can provide certain theoretical and engineering basis for water prevention and control under similar mining conditions in the study area and western mining area.