Study On Risk Assessment Method Of Jurassic Coal Seam Mining Failure And Roof Water Inrush In Shanbei-longdong Area

Aiming at the problems of shallow water-resource losses and roof water-inrush accidents induced by the mining of shallow buried coal,I systematically study the prediction methods and technologies considering the influence factors of mining destruction and roof water inrush under the guidance of hydrogeology theory.The used data and technologies include logging data,3D seismic data,gassmann fluid substitution theory,well-log constrained impedance inversion,PNN inversion,genetic algorithm optimized BP neural network and analytic hierarchy process.Applying related methods and technologies to Shanbei and Longdong areaes,I found that the proposed method can predict the mining failure of N₂ laterite in Shanbei area and the water inrush risk of coal roof in Longdong area.The prediction results are highly consistent with true uncovered geological data.For the prediction of mining induced failure of shallow buried coal seam,I use Xiaobaodang No.2 mine in Shanbei area as the research area,where the predicted aquifer?The red clay layer of Neogene System Pliocene series Baode formation,N2laterite?is sandwitched between shallow water resources and the No.1 coal seam.The factors affecting the mining failure include:?1?internal factors such as thickness,strength and porosity of laterite;?2?external factors such as the interval between laterite and No.1 coal seam.During prediction,the thickness of N₂ laterite is calculated with Kriging interpolation using true 17 well data as inputs;the strength of N₂ laterite is calculated with inversed acoustic impedance and the positive correlation association between the Young's modulus and impedance;the porosity of N₂ laterite is calculated with PNN inversion from multiple seismic attributes;the interval distance between N₂ laterite and No.1 coal seam is calculated with 3D seismic interpreted horizons and seismic inversed interval velocity.Finally,the weight coefficient of each factor is calculated with analytic hierarchy process.In this way,I predicted the mining failure to N2 laterite in the study area.For the prediction of water inrush risk of coal roof,I use the roof of No.3 coal seam in Cuimu coal mine in Longdong area as the research target.The factors affecting the risk of water inrush mainly include four types,including water enrichment of main aquifer,water conductivity of water conducting stratum,water resistance of aquifuge and bed thickness of aquifuge.The water enrichment of main aquifer is affected by its thickness,water bearing property and porosity.The water conductivity of water conducting stratum is affected by its porosity.And the water resistance of aquifuge is affected by its sandy content.The porosity of main aquifers and water conducting stratum is calculated with PNN inversion using multiple seismic attributes as inputs.The thickness of main aquifer and aquifuge is calculatedwith 3D seismic interpreted horizons and seismic inversed interval velocity.The water resistance of aquifuge is calculated with seismic inversed acoustic impedanceand negative correlation association between water resistance and aquifuge impedance.The water bearing property of main aquifer is calculated with seismic inversed acoustic impedance and density and Gassmann fluid substitution theory.Finally,the weight coefficient of each factor is calculated with analytic hierarchy process.In this way,I predict the risk of water inrush from coal roof in the study area.The predicted results is in accordance with the actual observed water inrush points,verifing the accuracy and feasibility of the prediction method.Meanwhile,I use GA-BP neural network model inputted with the factors such as depth of coal seam,dip angle of coal seam,impedance of the overlying strata,length ofmining panel and mining thickness to predict the height of water conducting fissure zone in whole area.