Non-contact Signal Connector for Geothermal MWD Systems

Abstract

The Agency of Industrial Science and Technology is developing geothermal MWD system which detects thrust force, torque, etc. while drilling a geothermal energy well. The MWD system has a sensor-sub that offers sensors, and a sonde that processes sensor signal and sends information to the ground with mud-pulse. In order to detach the sonde as occasion demands, signal transmission between the sensor-sub and the sonde is carried through a non-contact connector. Mutual electromagnetic induction type connectors are made for the non-contact signal transmission. For high temperature use up to 250°C, the connectors consist of polyamide-imide coated copper coils and mild steel cores. To facilitate uniting the connector, the coil moves freely in the axial direction, and the gap of lmm is made in the radius direction. Effects of relative displacement due to vibration, electromagnetic induction noise, pressure, temperature and mud on the transmission efficiency are examined. In case of using facing coil type connector with coil length of 16mm, change of transmission efficiency is negligibly small while relative displacement being less than 4mm. Pressure, temperature and the mud slightly effect on the signal transmission efficiency. On the other hand, the connector is strongly affected by the electromagnetic induction noise.