Numerical simulation of drillhole transient electromagnetic response in mine roadway whole space using integral equation method

Borehole transient electromagnetic method (BHTEM) is operated in mine roadway. The source of BHTEM is laid in mine roadway and receiver is placed in drill hole, observation is carried out in turn from top to bottom. In order to study the response characteristics of BHTEM in roadway whole space, numerical simulation is carried out using integral equation method (IEM) based on 3D mathematical model in which the representative stratum of the coal seam floor under the threat of water hazard is selected as the research object and coal seam floor contains water bearing abnormal body. The transient electromagnetic (TEM) response characteristics are analyzed. The numerical simulation results show that the coal seam on both sides of the roadway has little influence on the vertical induction electromotive force response, when its resistivity is greater than that of coal roof and floor. While it has relatively great influence on the horizontal induction electromotive force responses of stations located in the shallow part within 30 meters and it has little influence on the horizontal responses of stations located in the deep. When coal seam floor contains horizontal low resistivity plate-like abnormal body, the horizontal component of the induction electromotive force is relatively superior to the vertical component in drill hole in terms of vertical resolution and the duration of the abnormal response of the abnormal body. While the amplitude of the vertical induction electromotive force is stronger than that of the horizontal induction electromotive force. So, not only the vertical component of the induced electromotive force in the borehole but also the horizontal component needs to be observed in actual observation.