Objective and Method To determine the boundary detection capability of logging-while-drilling (LWD) electromagnetic azimuthal measurements for high-resistivity coal mines, this study simulated geosignal responses under varying operating frequencies, transmitter-receiver coil spacing conditions, and formation resistivity values. Then, key parameters for boundary detection for high-resistivity coal seams were optimized. Accordingly, this study proposed design schemes for LWD instruments with short (< 80 inches) and long (approximately 240 inches) transmitter-receiver coil spacing for short-distance (2.032 m) and long-distance (6.096 m) detection, respectively.

Results and Conclusions LWD electromagnetic azimuthal measurements exhibit a significantly decreased depth of detection (DOD) in high-resistivity coal seams compared to that in low-resistivity hydrocarbon reservoirs. Consequently, the existing methods for selecting the operating frequency and transmitter-receiver coil spacing are no longer applicable. In high-resistivity coal seams, increasing the operating frequency and transmitter-receiver coil spacing appropriately can enhance the strength and DOD of geosignals. Under transmitter-receiver coil spacing of 50‒85 inches (1.270‒2.159 m) and an operating frequency of (2‒5) MHz, the DOD can reach 3 m, meeting the need for roof and floor detection. When the transmitter-receiver coil spacing increases to 5 m and the operating frequency decreases to 200‒400 kHz, the DOD of electromagnetic signals in high-resistivity coal seams can extend to 10 m, offering a foundation for long-distance detection of low-resistivity anomalies.