| Abstract: |
Starting in 1992 a high temperature MWD system was developed for geothermal well drilling through a NEDO (New Energy and Industrial Technology Development Organization in Japan) project. This system features both electronic and mechanical devices, and it can operate in a 200 degree centigrade environment. The electronic device consists of many kinds of components including resistors, condensers, transistors, diodes, ICs, relays also memories, A/D converters, multiplexers, crystal clocks, and operational amplifiers. The sensing devices are flux gate type azimuth sensors, servo accelerator type inclination sensors and a diode type temperature sensor. A rithium type battery is adapted to the power supply. These mechanical devices include a direct current motor to move a pulse generating valve, and a multi stage mechanical seal system. The main specifications are 50 hours operating time in a 200 degree centigrade environment and 5 hours survival time in a 220 degree centigrade environment. Because of the hard formation of geothermal well drilling, anti-vibration performance is 30G for 6 hours. Anti-shock performance is 1,000G in a half millisecond.Å@The sonde is the pressure barrel and includes all electronic and mechanical devices. The outer diameter is 44.4 mm (= 1.75 inch) and the length is 12 m. Acquisition data include azimuth, inclination, tool face and bore hole temperature. Sensors for weight on bit, bit torque and bore hole pressure will also be developed in the future. A pressure pulse device is utilized in order to transmit bore hole information data from the bottom to the surface by emitting a positive pulse up signal to the mud. Two prototypes have now been manufactured and their performances have been verified through field tests both in Japan and overseas. Those tests have been successfully carried out under normal temperature conditions. Another field test is planned under a high temperature condition in a geothermal well. |