Application Research of Seismic Prediction Technology for Disastrous Aquifers in Coal Seam Roof and Floor
Supervisor:wang yan chun duan zhong hui
Coal mine water accident is an important cause of deaths and injuries in coal mines.It is necessary to find out the existence of water sources by means of geological prospecting technology and carry out comprehensive water control measures.Predicting abnormal areas of aquifer strata on coal seam roof and floor by using three-dimensional seismic information is based on predicting spatial distribution of water sources on coal seam roof and floor,and provides hydrogeological basis for water control in coal mines.The sandstone fissure aquifer on the roof of No.5 coal seam and the limestone karst fissure aquifer under the floor are the main sources of mine water inrush in Chenghe mining area.Because the difference of wave impedance between target aquifer and surrounding rock is relatively small,the energy of seismic reflection wave is weak and the prediction is difficult.In order to improve the imaging effect and prediction accuracy of target aquifer,based on the analysis of the interference factors affecting the reflection wave quality of target aquifer in Chenghe mining area,this paper discusses the problems found from three aspects of acquisition,processing and interpretation of three-dimensional seismic data,and puts forward corresponding solutions.The main results are as follows:(1)Considering the surface geological conditions of the huge thick loess in Chenghe mining area,the explosion mode of combined multiple wells in the high-speed layer(below the diving surface)is proposed.(2)Through theoretical analysis and comparative analysis of experiments,it is found that the 60 Hz natural frequency geophone currently used in the mainstream of coalfield exploration will lead to distortion of seismic low-frequency effective signal.It was proposed earlier that 28 Hz or lower natural frequency geophone should be used for wide-band high-resolution seismic acquisition.(3)Aiming at the problems of large panel,low coverage times and limited azimuth angle of the three-dimensional observation system used in the past structural exploration in Chenghe mining area,a new lithologic exploration observation system with small panel,high folds and wide azimuth is optimized.(4)A six-step iterative velocity analysis process is designed for the residual static correction of the target data processing.The time-varying adjustment of the velocity spectrum effectively improves the picking accuracy of the aquifer’s weak reflected wave velocity.(5)In order to eliminate the shielding effect of coal seam on the reflection signal of the bottom limestone interface,a post-stack data coal removal technology is proposed,which can effectively suppress the strong axis of the coal seam and enhance the weak signal of the coal seam floor limestone formation.(6)Based on the post-stack inversion results of wave impedance,natural gamma ray and resistivity,a lithofacies probability analysis technique is developed,and lithologic data bodies reflecting the spatial distribution characteristics of rock formations are obtained.(7)Optimum RMS amplitude,spectrum imaging,waveform classification seismic attribute analysis technology and sparse pulse,logging constraints,multi-parameter neural network,geostatistics inversion method,with attribute analysis as the supplement,post-stack inversion as the main method,overlapping delineation of aquifer sand distribution of coal seam roof and limestone karst area of coal seam floor.Through the application of the integrated forecasting technology of acquisition,processing and interpretation in Wangcun Coal Mine of Chenghe Mining Area,the imaging effect and forecasting accuracy of aquifer target are significantly improved.The predicted thickness of sand body on the roof of coal seam can reach more than 5 m,and the identified limestone fissure karst development zone has been confirmed by the excavation of later roadways,which shows that this prediction technology can provide effective geological basis for the prediction and prevention of water inrush from roof and floor,and can be popularized and used.