Optimal survey parameters for the borehole-to-surface controlled source electromagnetic method

The Frequency-domain borehole-to-surface controlled source electromagnetic (FD-BSCSEM) method is a geophysical technique used to explore mineral resources and assess engineering geology. However, the optimal selection of operational parameters for borehole-to-surface measurements remains a topic of debate. Through three-dimensional numerical simulations, we investigate the propagation characteristics of current in the BSCSEM method and the impact of various operational parameters on the simulated responses. Using a high resistivity plate-shaped anomaly as a case study, we analyze the effects of offset, source position, and source length on the radial electric field component ( Er ). Our results show that for anomalies buried at a depth of 500 m, the offset should be limited to within 2000 m to ensure sufficient signal strength and resolution. Charge accumulation is primarily concentrated at the top and bottom surfaces of the anomaly. When the source is sufficiently close to the anomaly, a stronger anomalous response will occur at the surface. When the source length is significantly longer than the thickness of the anomaly, the anomalous signal experiences rapid attenuation; therefore, it is advisable to limit the source length to prevent excessive energy dispersion. Finally, we examined the response of low-resistivity bodies. Compared to high-resistivity anomalies, horizontal currents are more likely to dominate in low-resistivity bodies, leading to differences in parameter selection. • Innovative Approach: We conducted a study on the device parameters of the Borehole-to-Surface Controlled Source Electromagnetic Method (BSCSEM) and found that different parameters significantly affect resolution in practical exploration. • 3D Numerical Simulation: Through three-dimensional numerical simulations, we systematically analyzed the propagation characteristics of current within anomalies and their impact on exploration results, providing a scientific basis for optimizing device parameters. • Key Parameter Analysis: The study indicates that for anomalies buried at a depth of 500 m, the offset distance should be limited to within 2 km to ensure sufficient signal strength and resolution. • Electric Field Response Characteristics: Results show that the electric field response generated by vertical current sources is highly sensitive to high-resistivity bodies, exploring the distribution characteristics of the electric field and its relationship with anomalies. • Device Optimization Recommendations: It is suggested to limit the source length to prevent excessive energy dispersion, while emphasizing the influence of source depth and position on resolution capability.