Sedimentary Controlling Groundwater In Luohe Formation And The Water Flow Field Response Regularity After Mining Disturbance In Binchang Mining Area

Most of the Jurassic coal seams are covered with thick sandstone aquifers on the roof,which cause the mine water inflow larger and makes it difficult to prevent and control water hazards in Northwest China.Identifying the hydrogeological conditions of the roof aquifer and revealing the seepage law of the aquifer under the disturbance conditions of coal mining is the basis for studying a series of mine groundwater problems such as roof water hazards and water resource protection.The Binchang mining area is a very typical mining area affected by the Luohe Formation sandstone aquifer(very thick sandstone aquifer),the mine water inflow in the whole mining area is generally large,and this phenomenon is relatively rare in China.Due to the vertical heterogeneity of the Luohe Formation aquifer,the response law of the flow field to the aquifer after coal seam mining disturbance is not clear,this paper studies the sedimentary environment and microstructure of Luohe Formation,analyzes the vertical hydrogeological conditions of Luohe Formation,and reveals the response law of flow field after mining disturbance.The following main results were achieved:1)By analyzing the petrological characteristics,sedimentary characteristics and electrofacies of the Luohe Formation,it is determined that the Luohe Formation in the Binchang mining area is the sedimentary facies of “alluvial fan-braided river-alluvial fan” from bottom to top,revealing the variation law of the sedimentary environment of the Luohe Formation in different periods;Using porosity and permeability testing,SEM and other testing methods,and establishing a method for fine interpretation of porosity through well logging,it is concluded that the porosity of alluvial fans is relatively low,and the pores of braided river sedimentary facies are relatively developed;2)The hydrogeological conditions of the Luohe Formation sandstone aquifer at different depths were investigated by layered water pumping with double packers,and an analytical algorithm for layered water pumping in bounded aquifers was established based on the incomplete well flow model.Based on the hydrogeological parameters,water level,water temperature,hydrochemistry and other indicators of each layer,the Luohe Formation aquifer can be divided into three sections in the vertical direction: the upper and lower sections are poor water yield property,and the middle section is relatively good water yield property;3)Based on the vertical depositional environment,microstructure and hydrogeological characteristics of Luohe Formation,the sedimentary water control mode of Luohe Formation was revealed: the braided river sedimentary facies is poor water yield property,and the alluvial fan sedimentary facies is relatively good water yield property;The sedimentary subfacies overlap and cover each other,forming the vertical heterogeneity structure of the Luohe Formation aquifer.Then sedimentary hydrogeological boundaries and across stratigraphic hydrogeological boundaries control the thickness of each layer.Finally,two types of sedimentary controlling groundwater modes were generalized: sedimentary hydrogeological boundary groundwater control mode and sedimentary-across stratigraphic hydrogeological boundary groundwater control mode;4)Developed a comprehensive measurement method for the height of the waterflowing fractured zone in the whole process of coal seam mining,which is “background condition exploration before mining,water level monitoring during mining,and comprehensive test after mining”.Based on the tests of a large number of water-flowing fractured zone in the coal mining area,an empirical formula for calculating the height of water-flowing fractured zone of different parameters mined panels in the Binchang mining area is established.It is generalized that the water inflow of typical mine is mainly the bedding seepage and vertical infiltration of the lower section of Luohe formation aquifer;5)The three-dimensional numerical groundwater model of the typical mine was established to analyze the aquifer flow field and water level variation under different mining conditions,and finally revealed the flow field response characteristics after coal seam mining disturbed the Luohe Formation aquifer: In the mining disturbance zone,the lower section of the Luohe Formation aquifer,which affected by the water-flowing fractured zone,the lower section of the Luohe Formation was basically dredged,thus forming a vertical hydraulic gradient,driving the groundwater in the middle section of Luohe Formation aquifer to infiltration downwards;Outside the mining disturbance zone,groundwater flows along the strata driven by the horizontal hydraulic gradient.Finally,it shows the seepage characteristics of groundwater flows along the strata in the lower section and vertical infiltration in the middle section;6)Optimize the design of the underground water drainage engineering of the Luohe Formation aquifer,form the local drainage method of the aquifer,determine the main drainage layer is the lower part of the Luohe Formation,and the drainage time is based on the time when the flow field can reach a stable level,and determined the key technical requirements such as drilling structure and exploration tests.Through field engineering,the local drainage method can effectively delay the water discharge time of the working face and reduce the water inflow in the early stage of mining,providing technical support for the prevention and control of water hazards in the Luohe Formation aquifer.