Study On Transmission Seismic Wave Field And Its 3D Imaging Technology In Coal Mining Face

Accurate prediction of geological conditions in mine is the prerequisite to ensure safe and efficient mining.Transmission seismic tomography between two or more roadway is an effective geophysical exploration method.It is difficult to meet the requirements of the interpretation accuracy of the geological anomaly by using the two-dimensional transmission seismic tomography technique in the coal mining face.It is an important direction to improve the precision of geostructure detection in coal mining face by studying the data acquisition and inversion imaging technology of 3D transmission seismic wave field in undulating coal seam.Firstly,taking the geological structure anomaly in the coal face as the research object,three-dimensional numerical models are established in this paper,and the 3-D transmitted seismic wave field is simulated by using the high-order staggered grid finite difference method.By using three components simulated signals and 3D snapshots,the 3D seismic wave field response characteristics of geological structural anomalies such as coal seam dip angle,fold and fault are analyzed.Nineteen three-dimensional numerical models were calculated by 3-D ray tracing method.Based on the calculation results,the transmissive body wave velocity characteristics of the faults,folds and thickness changes in horizontal and inclined seam are analyzed and discussed.It is concluded that the high velocity strata of the roof and floor are the fast and convenient passage for transmitting seismic body wave,and its fluctuation is an important factor influencing the inversion result of seismic wave velocity tomography.Secondly,aiming at the existent problems of 2D seismic wave tomography in coal mining face,the elevation coordinates are creatively added to this method,and the two-dimensional inversion plane model is improved to three-dimensional plate model.The pseudo 3D transmission seismic velocity inversion technique does not aggravate the underdetermination of the velocity equation with adding the height information of the roadway and greatly reduces the disturbance of the roadway undulation.The pseudo-3D ray tracing technique and time-frequency analysis technology are combined to carry out the spectrum analysis and the dispersion curve extraction of the Love-type channel wave signals.The iterative matching calculation of the extracted dispersion curve and inversion model is carried out by using the genetic algorithm,the thickness of the undulating coal seam and the shear wave velocity distribution in the depth direction are obtained,combined with the above imaging methods and 3D backprojection technology,the 3D transmission seismic imaging of the coal mining face with undulating coal seam is realized.The three dimensional spatial distribution characteristics of shear wave velocities and thickness of coal and surrounding rocks with different depths are obtained.Finally,three groups of 3D numerical simulation and two groups of 3D physical simulation experiments are carried out to obtain the transmission seismic data of the known model.The feasibility and effectiveness of this imaging technique are verified by comparing and analyzing the 3D transmission seismic imaging results and known models.The result of seismic tomography imaging is expanded from two dimensional to three dimensional spaces,which improves the imaging accuracy and the visualization degree of the geological anomaly,and provides the theoretical basis and technical innovation for the accurate interpretation of the geostructural anomaly in the coal mining face.In the field application,the imaging technique can realize 3D velocity imaging in a certain range of coal seam,and well describes the geological structure and the characteristics of roof and floor strata in the undulating coal mining face.But it was also found that,the complex geological conditions of coal seam and low velocity mudstone will have great influence on the imaging result.The adaptability of the imaging method in field application needs to be continuously verified and summarized.