Working mechanism and experimental study of electromagnetic measurement while drilling systems based on a relay station

ABSTRACT Electromagnetic measurement while drilling systems transmit downhole data via an information channel composed of a drill string and formation; the formation has a strong attenuation effect on the signal. Signal attenuation during electromagnetic wave transmission through the formation limits the well depth at which this technique can be applied. This paper discusses several commonly used methods to improve the depth at which electromagnetic measurement while drilling applications can be conducted, including turbine power supplies, adaptive power outputs and transmitting antenna extensions. Based on both theory and practice, the characteristics of these methods are analysed, and a relay station‐infused electromagnetic measurement while drilling system is proposed. The relay station‐infused electromagnetic measurement while drilling system consists of a downhole instrument assembly, a relay station and a ground receiver assembly. The repeater receives the electromagnetic wave signal from the underground transmitter and, after amplification, decoding and other processing, re‐encodes the signal and forwards it to the ground receiver at different frequencies, so as to increase the underground electromagnetic wave signal relay transmission. The design of the relay station module is introduced in detail, and the influencing factors and rules of signal transmission are analysed. Signal transmission experiments show that the electromagnetic measurement while drilling system based on a relay station can reliably represent the relay of signals and can thus be used in deeper wells.