Numerical simulation response characteristics of down-hole TEM for advanced detection

In order to avoid the problems that the traditional underground electromagnetic transient detection,the elec- tromagnetic interference signal,anchor net and road header are affected by the roadway,an advanced detection method for measuring the three-component signal of transient electromagnetic field in the underground coal working face or the horizontal borehole of the working face was proposed. The method has the characteristics that the radial detection depth is large,the three-component receiving probe is close to the abnormal body,the ratio of the abnormal field to the total field is high,and the abnormal body is more easily found. Based on the transient electromagnetic three-dimensional time domain finite difference forward algorithm,the total field and the anomalous field of the uniform three-component model of the uniform hole in the uniform half-space model,the uniform half-space containing the isolated anomalous body model and the response characteristics of total field and anomalous field of abnormal body in different directions of the horizontal borehole were systematically studied. It is found that the three-component total field and the anoma- lous field is consistent with the smoke circle effect. The three-component attenuation curve of the total field and the a- nomalous field or the variation of the shape of the multi-track curve with time can be analyzed by the position of the in- duce current loop relative to the measuring point or the measuring line at different times. Without considering the mu- tual inductance phenomenon,the three-component response at different moments of underground reception can be re- garded as the superposition of the background current loop and the abnormal current loop,wherein the three-compo- nent form of the anomalous field can be modeled by the current loop of the same shape perpendicular to the first field direction. In addition,when the anomalous body is located at different orientations of the horizontal borehole,the X component of the anomalous field is S-shaped,the Y component and the Z component are unimodal anomalies,and the different quadrant anomalies. The three-component combination is different in shape,and the depth and orientation of the borehole where the abnormal body is located can be determined. Finally,the similarity test of the ground-hole tran- sient electromagnetic advanced detection method is carried out,which verifies the correctness of the response charac- teristics of the theoretical model.