Mud Pulse Telemetry: MWD Data Transmission with Pressure Sensors

Mud Pulse Telemetry: MWD Data Transmission with Pressure Sensors

Hydraulic data transmission requires sensitive pressure sensors capable of enduring high pressures. This is particularly true when used in measurement while drilling (MWD) applications.

MWD has become a standard application, especially for offshore directional drilling. Real-time data collection is essential for measuring the trajectory of the hole as it is drilled. For this purpose, various sensors are mounted on the drill head to provide information about the drilling environment in real time. Inclination, temperature, ultrasound and also radiation sensors are used. These various sensors are physically or digitally connected to a logic unit that converts the information into binary digits. The downhole data are transmitted to the surface via mud pulse telemetry. In addition to monitoring and controlling the drilling process, the data are used for further aspects, including:

  • Information about the condition of the drill bit
  • Records of the geological formations penetrated by the borehole
  • Creation of performance statistics to identify possible improvements
  • Risk analysis for future drilling

Mud pulse telemetry is a binary coding transmission system used with liquids. This is achieved by a valve that varies the pressure of the drilling mud within the drill string and thus converts the recordings of the sensors mounted on the drill head into pressure pulses. The pulsations reach the surface via the drilling mud. The pressure pulses are measured on the surface by a pressure transmitter and converted into an electrical signal. This signal is transmitted to a computer and digitized.

STS provides offshore directional drilling companies with analog pressure transmitters optimized for mud pulse telemetry. The sensors have to meet high demands: They must be extremely sensitive in order to reliably register even the smallest pressure differences. At the same time, the sensors must withstand pressures of up to 1,000 bar. Very high pressures are required to power the drill head in very deep drill holes. The pressure transmitters used for mud pulse telemetry on the surface are also exposed to these forces.

In addition to the high sensitivity, very fast response times are required to ensure good data communication in real time. In order to exclude falsified measurement results, the measuring instrument should be low-noise. The mud pumps in particular can cause the most signal noise in drilling applications. The drive of the drill is another source of interference. For this reason, analogue sensors with a 4 – 20 mA output signal are the best solution for mud pulse telemetry.