Three-component detection technology of down-hole TEM for hidden geological anomalies in coal mines

To meet the geological requirements for detailed exploration of concealed anomalies in coal mines and to accurately delineate and interpret hidden water hazards around boreholes, a three-component geological anomaly localization technique using borehole transient electromagnetic methods is proposed. This technique detects geological anomalies around boreholes by transmitting high-power abnormal field signals from the surface and receiving secondary three-component field signals from the vertical borehole after shut-off. First, the Maxwell software is used to calculate the three-component responses of anomalies at various orientations around the borehole, showing that the transient electromagnetic method produces stronger three-component anomaly responses when the probe is closer to the anomaly, with different combined response patterns. This enables the qualitative determination of the anomaly’s orientation relative to the borehole. Additionally, numerical simulations of three-component responses are conducted for common anomalies in coal mines, such as water-bearing collapsed columns, water-bearing faults, and flooded goaf areas. The simulations reveal that the amplitude and shape of the three-component anomaly response curves differ due to the varying sizes and orientations of the anomaly bodies, allowing for the qualitative identification of the anomaly type. Next, the current loop inversion technique is applied to spatially localize the anomaly bodies in theoretical models of water-bearing collapsed columns, water-bearing faults, and flooded goaf areas. The results demonstrate that the three-component anomaly responses from borehole transient electromagnetic surveys can effectively localize water-bearing anomaly bodies around the borehole and provide information on their location, size, and orientation. Finally, borehole transient electromagnetic detection is conducted on a suspected collapsed column identified by three-dimensional seismic data at a mine in Inner Mongolia. Two transmitting sources at different orientations are used to excite the field, and the collected data undergoes three-component inversion. The spatial localization of the suspected collapsed column is successfully achieved, along with its size and orientation. The results of the detection are validated with advanced borehole detection during subsequent tunnel excavation. Both theoretical models and experimental data show that the borehole transient electromagnetic three-component anomaly localization technique is an effective method for detecting geological anomalies around boreholes in coal mines.