Detection method of coal-rock interface and low-resistivity anomalous body based on azimuth electromagnetic wave

A geological model related to coal-rock electromagnetic parameters is constructed in this work using coal-rock media and coal-rock interfaces as the research objects for electromagnetic wave propagation response. An in-depth analysis was conducted to examine the response characteristics of the electromagnetic wave detection technology for coal and rock geological orientations while drilling in coal mines. We also studied the detection and identification methods and applicability of coal and rock interfaces. Next, we simulated the response characteristics of the instrument in the coal seam and established a calculation method for the orientation of the interface between the roof and floor of the coal seam and the distance between the instrument and the coal seam’s interface. The quasi-Newton method was used to perform inversion calculations on the theoretical model of the response of the borehole-while-drilling azimuth electromagnetic wave resistivity tool, and the simulation data were inverted in real time, thereby reducing the number of calculations of the Jacobian matrix, improving the inversion speed, and decreasing the level of dependence on the initial value. Furthermore, we obtained the signal response law of electromagnetic wave detection in low-resistivity aquifers and abnormal geological bodies (e.g., collapse columns and gangue interlayers) based on forward and inversion numerical simulation. Finally, by investigating the directional electromotive force simulation imaging method of the orthogonal coil, we verified the feasibility of the application of azimuth electromagnetic wave resistivity in high-resistivity coal seams. In this way, we can provide the basis for the detection of coal seam interface, geological anomaly body, and geological guidance application.