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The article discusses research which assessed the behavior of downhole electromagnetic telemetry (EMT) in deep subsurface prospecting and the characteristics of uphole EMT with repeater system. Topics covered include the performance of downhole EMT during sudden water influx into adjacent formation during directional drilling, the characteristics of downhole EMT in deep horizontal well, and the behaviors of the EMT system with oil based mud (OBM) and water based mud (WBM).

Electromagnetic telemetry is bi‐directional transmission of borehole data for effective drilling, especially in unconventional wells. In this study, numerical simulations was used to investigate the possibility of applying EM telemetry for measurement while drilling (MWD) in an ultra‐deep borehole in the Tahe region of the Tarim basin, using the drill string as an antenna excited as a gaped dipole source to quantify spatial variations of the electromagnetic field from subsurface to the surface. Results confirm that the distribution of the electric field along the drill string is sensitive to vertical variations of electric conductivity in the host rock. The simulated results show a high attenuation within the conductive formations, thereby limiting the effectiveness of EM telemetry in data transfer to the surface. In addition, the changes in thickness and resistivity of the target region affects the amplitude of the desired response. [ABSTRACT FROM AUTHOR]