Study on Response Characteristics of Transient Electromagnetic Method in Complex Coal Mine Based on Numerical Simulation

In this paper, the response characteristics of complex coal mine transient electromagnetic method (TEM) based on numerical simulation are studied. In view of the complex and changeable geological environment and the challenge of coal mine detection technology, the application of TEM in coal mine and its response characteristics are deeply analyzed by numerical simulation method. A coal mine stratum model with a total thickness of 200 m is studied and designed, including sandy soil layer, coal seam and rock layer, and each layer has different resistivity. Three specific minedout areas with different shapes, sizes and resistivity are set in the model to simulate the complex geological conditions of coal mines. A square transmitting coil is set in the center of the model, Maxwell equations are solved by finite element method (FEM), and the grid is divided to accurately simulate the electromagnetic field distribution. It is found that the propagation of electromagnetic field in multi-layer stratum structure is significantly affected by the resistivity of each layer. The high resistivity stratum has little attenuation effect on electromagnetic field, while the low resistivity stratum leads to the rapid attenuation of electromagnetic field. The existence of mined-out areas has a significant impact on the distribution of electromagnetic fields. Mined-out areas with different shapes, sizes and resistivity lead to different abnormal responses of electromagnetic fields, which can be used to identify and locate mined-out areas. The intensity of electromagnetic field gradually decreases with time in the whole model, showing an exponential decline trend, and is affected by formation resistivity and goaf characteristics. Through numerical simulation, the response characteristics of TEM in complex coal mine environment are systematically studied, which provides technical support for improving the accuracy and reliability of coal mine detection. The influence laws of different geological conditions, goaf shapes and mine roadway interference on transient electromagnetic signals are analyzed, which provides a strong guarantee for coal mine safety production.