In the past, the process of monitoring down hole well conditions was unreliable and expensive. The earliest types of down hole sensors employed what is referred to as “PHD sensor technology". COSCO does not produce or sell the older technology, as more advanced alternatives are now available. 

Electronics can now perform much better in extreme environments. Today’s technology is not only more accurate, but more efficient and reliable as well. The following discussion compares the ELECTRONIC sensor technology to the PHD sensor technology:

PHD type sensors have the following characteristics:

  • A bourdon tube is used to measure pressure. This is a mechanical device prone to failure and particularly prone to damage from impact that is commonly experienced while running in the hole.
  • By varying the resistance of the motor star point to ground, down hole parameter values can be determined by calculations based on resistance measurements at the surface. A relay is used to switch between pressure and temperature measurements. Being a mechanical device, a relay is rated for a limited number of switching operations. The most common failure occurs when the relay eventually seizes in one position and only one of the parameters can be measured.
  • Latch and de-latch features are required so the insulation resistance of the system can be measured accurately with a meg-ohmmeter.

Electronic sensors are significantly different as follows:

  • Mechanical devices have been replaced with more robust solid-state electronics that do not rely on moving parts. This increases reliability and accuracy and decreases the chances of damage during installation.
  • Data is transmitted to the surface via the main ESP power cable by means of a digital signal that is superimposed on the motor supply voltage. A surface choke filters the waveform to isolate the signal from the high voltage and a surface RTU measures, interprets and stores the data.
  • The use of a digital signal allows more than two readings to be transmitted simultaneously.
  • Data logging devices are used at surface to record readings in electronic memory. Down hole readings in addition to power supply and motor load readings can all be logged and stored together. This allows for a better understanding of the reservoir and ESP system conditions as a whole.
  • Resistance to ground values are not manipulated, hence the latch and de-latch functions are not required.
  • The RTU firmware (software program resident in both the down hole sensor and the surface interface panel) can be updated as new versions become available.
  • Repairs to the down hole tool can be easily accomplished by changing pre-calibrated circuit boards in the field.

 

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