Analysis of 3D ground-borehole TEM response characteristics and rapid positioning method for anomalous bodies

Through systematic forward modeling and analysis of a 3D geoelectric model containing anomalous bodies, this study proposed a rapid positioning method of anomalous bodies based on the ground-borehole transient electromagnetic (TEM) method. The analysis of the forward modeling response laws of the 3D geoelectric model containing anomalous bodies shows that the zero points of the X and Y component curves and the extreme points of the Z component curve of a pure anomaly field correspond well to the depths of the anomalous bodies; the morphologies of the X and Y component curves are basically unchanged when the sizes, resistivity, and burial depths of the anomalous bodies change but change when the orientations of anomalous bodies change. On this basis, this study proposed the following method to rapidly position anomalous bodies using the ground-borehole TEM method. First, determine the depths of anomalous bodies according to the zero points of the X and Y curves. Next, determine the quadrants (within 90°) of anomalous bodies according to the morphologies of the X and Y component curves. Finally, position anomalous bodies within 45° of boreholes according to the morphologies of the X+Y or X-Y component curves. Numerical experiments show that the positioning results of models of anomalous bodies with different orientations are consistent with those of the model designed in this study. As further verified using the ground-borehole TEM measured data of a mining area in northern Shaanxi, the inference that there is a water-filled goaf to the northwest of the borehole obtained using the method proposed in this study well agrees with the actual situation.