A short offset transient electromagnetic method for long-distance exploration of boreholes

With an increase in the difficulty with the exploration of oil, gas, and mineral resources, conventional log and seismic methods fail to accurately evaluate the geological structures and transverse reservoir distribution far from boreholes. Therefore, this study proposed a transient electromagnetic (TEM) method for long-distance exploration of boreholes. Specifically, this study investigated the influence of key parameters of TEM devices for boreholes on the exploration distance. Based on the finite element analysis, this study calculated the responses of low- and high-resistivity geobodies under different receiver-transmitter distances, coil parameters, and exploration distances. The results showed that receiver-transmitter distances had little effect on the distance of electromagnetic exploration in the temporal domain. However, the results indicated that coil parameters had significant effects on the near-well detection distances. Under the transmitter coil parameters of 200 turns and 2A current, the TEM method for boreholes was more sensitive to low-resistivity geobodies, with near-well exploration distances reaching 40~50 m and 30 m for low- and high-resistivity geobodies, respectively. Therefore, it is feasible to conduct short-offset near-well long-distance exploration using TEM detectors with short transmitter coils for boreholes.