Method and application on 2D pseudo-seismic inversion of Roadway-Borehole transient electromagnetic detection in coal mine

Goaf roadway poses a vital threat to coal mine safety and miner’s life. The scale of the goaf roadway volume is relatively small,therefore,the ordinary geophysical prospecting method can hardly detect it accurately. Also, the drilling method can rarely hit the target precisely. For the purpose of detecting the goaf roadway more precisely,a road- way-borehole transient electromagnetic method(TEM),belonging to a 2D operating method with fixed source and dy- namic reception device,was proposed. This method, by arranging a fixed transmission cable over the borehole and shifting a receiving probe along the borehole to implement three-component observation,realized a high-precision de- tection for the borehole radial geological anomalous bodies. The device,with more complex observation curve,had har- der inversion difficulties. By analyzing the data characteristics adopting asynchronous parallel GPU plus CPU finite-dif- ferent time-domain 3D numerical simulation method,this paper presented a related sliding time window wave-field inverse transformation algorithm,combined the both advantages of time segmentation and full time wave-field transforma- tion algorithm,to transform data with higher accuracy. By studying the characteristics of time-distance curve of 2D transient electromagnetic virtual wave field data,a corresponding dynamic correction algorithm was derived. By adop- ting equivalent conductive plane method,initial velocity model was constructed. Ultimately,based on virtual acoustic medium hypothesis,the roadway-borehole TEM data pseudo-seismic inversion was realized by the means of conjugate gradient full-waveform inversion technique. The inversion results of 3D numerical simulation,flume simulation experi- ment and coalmine on-site simulation data showed that it had acquired favorable effect in exploring small-scale anoma- lous body on the radial direction of the borehole. In order to test the practicability and availability of this operating method in detecting water-logged goaf roadway’ s shape,characteristics and scale,the author’ s research group has conducted an case study in Shanxi’s coal mine. The research showed that the roadway-borehole TEM detection method is a great combination to underground geophysical exploration technology and drilling technology,and to make them supplement to each other. It is an effective application in goaf roadway with water detection.