Study On The Prediction Method Of Water Inflow Of Drainage Boreholes And Working Faces In Compound Aquifers

Ordos Basin is rich in coal resources,and its Jurassic Yan 'an Formation coal seam mining is generally threatened by roof water disasters.The "three maps-double prediction method" is a quantitative evaluation method for effectively solving the roof water disaster of the coal seam.The water-rich zoning map of the direct water-filled aquifer on the coal seam roof in the "three maps" is the key and the basis for determining the key "target area" of the water drainage project.The "double prediction" of water inflow from working face and pre-drainage boreholes is the foundation of drainage engineering and drainage system design.Therefore,scientific and reasonable evaluation of the water-rich of the direct water-filled aquifer,and accurate prediction of the water inflow from the drainage borehole before mining and the water inflow from the mining work face have important guiding function and practical engineering value for safe and efficient production in mines.According to the compound water-filled aquifer affecting coal seam mining in Hujierte mining area having the water disasters characteristics of large water inflow per borehole,high water pressure and uneven water enrichment,the hydrogeological conditions were analyzed,the sedimentary facies and sandstone distribution law of Jurassic strata are determined,a water-rich evaluation model of compound water-filled aquifer was established,the methods for calculation of drainage boreholes water inflow and optimization design of the boreholes before mining were put forward,and the water inflow of the working face was predicted dynamically.The main conclusions of this paper are as follows:1)The main water filling channel of coal seam mining is the water flowing fractured zone.The direct water-filled aquifer is a sand-mudstone interbedded composite aquifer of Jurassic Yan 'an Formation Member 3,Zhiluo Formation Member 1 and Member 2,of which Zhiluo Formation aquifer has strong water-rich property and high water pressure.2)According to the analysis of petrology,paleontology and logging facies characteristics,it is found that the sedimentary facies of the third member of Yan 'an Formation are mainly delta plain deposits with four paleochannels from north east to south west.The first member of Zhiluo Formation and the second member of Zhiluo Formation are mainly meandering river deposits,and the riverbed is spread in the northwest-southeast direction.The plane distribution of sand body is basically consistent with the distribution of sedimentary facies.3)Taking aquifer recharge property,hydraulic conductivity coefficient,sandstone thickness,sand-ground ratio and sandstone layer number as rating indexes,a water-rich evaluation method of compound water-filled aquifer based on aquifer composition elements is proposed.Taking Hulusu coal mine as an example,the water-rich property of the compound water-filled aquifer is evaluated.The result shows that the water-rich zoning evaluated by this method is basically consistent with the results of water detection and drainage project.4)The hydrogeological parameters of the compound water-filled aquifer are calculated by using steady flow Dupuit,unsteady flow Theis and leaky formula respectively through dewatering tests.The results show that during the dewatering test of sand-mudstone interbedded aquifer,the leakage recharge of adjacent aquifer occurs.The calculation result of hydrogeological parameters using the Hantush formula of the Leaky Theory is more consistent with the actual results.Meanwhile,statistical analysis shows that the permeability coefficient of aquifer has a negative exponential correlation with the depth of aquifer,and the permeability has an exponential correlation with effective porosity.5)Based on the water quantity exchange between the aquifer and the boreholes,a coupling model of aquifer-borehole water quantity calculation is established.The model is used to reproduce the variation of the water quantity in the drain hole and the water level in observation well and the design parameters of drainage boreholes are optimized.The results show that the water inflow per unit length of the borehole increases first and then decreases with the increase of angle.With the increase of the number of boreholes,the total water inflow of boreholes keeps unchanged after increasing to a certain extent.The optimal elevation angle of drainage boreholes is 60°and the optimal number of boreholes in a single drill site is 5.The total cost of the scheme of small spacing between drilling sites is greater than that of the large spacing,while the total construction time of the large spacing is greater than that of the small spacing scheme.6)The Drain subpackage is used to describe the internal boundary conditions of continuous mining at multiple working faces,and the numerical method is used to calculate the water inflow of 9 working faces in the first mining area of Hulusu coal mine.The results show that the numerical method fully considers the sedimentary characteristics of strata in the hydrogeological parameter zoning and the influence of mining face on the next working face,and can realize the dynamic prediction of water inflow from working face based on the mining progress of the mine.The predicted results are basically consistent with the actual water inflow.