Signal processing in the microwave front-end radiolink for logging-while-drilling through the borehole pipes
Logging-while-drilling (LWD) telemetry systems have been designed relying on cable-based equipment or advanced signal processing techniques applied to the electromagnetic channel through ground. The main disadvantage of such systems consist in the fact that measurements can be actually carried out only when the drilling operation is stopped. In this paper, a dedicated X-band equipment for LWD telemetry along pipes regarded as dielectric waveguides is proposed. A hybrid-integrated power amplifier-transmitter for this purpose is described. This system represents a modern solution to geophysical applications where transitions from vertical to horizontal drilling are required. Drilling pipes provide a new communication channel for telemetry although the potential issues related to large attenuation in the soil and external disturbances are to be carefully assessed beforehand. In particular, great attention has to be put in such a way as to achieve an efficient excitation and reduced distortion of the radio signal propagating along the pipe. In the paper we put in details the simulated performances, transmitter design, and current-efficiently issues. The output power is up to 10–25 Wt in short-pulse mode, at central lobe of 9–10 GHz. This level of power is sufficient for the short boreholes. The proposed amplifier-transmitter is used to establish a new communication channel. It is link between surface and the drilling point. Some review explaining the great degree of interest in this topic is presented. Experimental measurement results are provided as well.