Drilling deeper – can position sensors take the heat?

Paul Boughton

Leila Briem reports on the latest developments in sensor technology

As the world strives to find and extract more oil to meet the increasing global demand, the technology challenges of drilling deeper wells intensify significantly. These deeper reserves require a new level of sophistication for oil and gas companies and the tools required for the job demand top performance and critical reliability in the harshest environments. The push to reach deeper oil reserves on both land and offshore means that downhole tools, especially those used for measurement while drilling (MWD) and logging while drilling (LWD) applications must operate dependably while subjected to extreme heat, pressure, shock and vibration.

Linear position sensors play a crucial role in MWD and LWD tools by providing linear feedback in tasks such as directional drilling and core sampling. Since tools can only be rated as high as their individual components’ capabilities, many manufacturers face the prospect of needing to de-rate tools because the sensors could not meet the high temperature and pressure requirements of the other parts. The harsh environmental conditions deep in a well operation drives engineering innovation to develop sensors to not only operate in temperatures of up to 200°C, pressures up to 30,000 psi and high shock and vibration but also to accurately relay position feedback information day after day in increasingly tough environments. A failure in the sensor would require the removal of the tool, which can take up to a day and cost potentially hundreds of thousands of dollars in downtime, making sensor reliability and service life critical to the tools’ operation. 

Advances in sensor technology

So how have downhole sensors risen to meet these challenges? Position sensors are being designed to take the heat, relying on strong (and often proprietary) conductive plastic resistive inks that are tough enough to withstand operating temperatures from -40° to +200°C, high linear velocities exceeding 2,000mm/second and aggregate mechanical travel exceeding one million metres. To accommodate pressure and the unique chemistries of the downhole environment, variations of linear position sensors feature nickel-plated aluminium housings that can be vented to operate in high pressures when immersed in fluids and are available with pressure or non-pressure headers. The constant vibration or ‘dither’ present in downhole applications poses an additional threat, causing ordinary materials to wear faster, leading to frequent repairs or replacements. To prevent or limit the potential damage caused by dither, tough, resilient materials are employed that stand up to vibrational wear and tear, provide longer life and lower maintenance costs for the tools.

Not only must sensors battle heat, pressure, shock and vibration, but they must also be compact enough to operate in the limited amount of space available for components in downhole tools. To save space, a series of thick film conductive plastic sensors has been designed to be internally mounted and fit snugly into cylinders or actuators. This allows them to provide highly accurate positioning information, while the internal construction protects the sensors from environmental hazards. Compact designs ranging from 3/8” diameters for small-diameter casings and cylindrical shafts up to 1” diameters with removable contact assemblies and rigid I-beam designs allow the sensors to fit into and operate reliably in confined spaces.  

These design innovations now give specialised position sensors the capability of reliable operation in deep well drilling. As wells continue to go deeper and push the limits of downhole components, it will be up to leading sensor manufacturers to continue advancing their designs to meet the ever harsher demands of high temperature, high pressure downhole drilling.

For more information visit www.beisensors.com/encoder-sensor-solutions-oil-gas-industry.html

Leila Briem is communication specialist at BEI Sensors, a brand of Custom Sensors & Technologies (CST), California, USA.

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