SYSTEM AND METHOD FOR DOWNHOLE TELEMETRY

摘要

A system and method are provided for providing electromagnetic (EM) measurement-while--drilling (MWD) telemetry capabilities using an existing m ud- pulse MWD tool. An EM tool intercepts the output from the mud-pulse tool and generates an EM signal tha t mimics a mud--pulse pressure signal. The EM signal is intercepted at the surface by a receiver module that conditions the signal and inputs the signal into the existing pulse tool receiver. Since the EM signal mimics a mud-pulse signal, the pulse tool receiver does not require software or hardware modifications in order to process an EM telemetry mode. The EM tool can be adapted to also provide dual telemetry by incorporating a conventional pressure pulser that would normally be used with the pulse tool. A gap sub assembly for isolating the drill string is also provided that includes a pair of subs whose shoulders are separated by a non-conductive ceramic material and whose threads are separated by an insulative material, preferably a Kevlar.T M. cloth.