The Modular Downhole Tractor (MDT) is used to transport passenger wireline tools into wells where standard wireline deployment is not possible or practical.
Description
The MDT is a wireline deployed system used to push passenger logging tools into difficult well profiles. It is modular enabling a number of sections – actuator and drive arms/wheels – to be connected together below the MDT electronics section to provide greater forces to push the tools along the well. The tractor is DC powered and can drive both up and downhole. The electronics cartridge for the MDT contains a highly efficient (97%) electric motor that controls the clutch and drive assembly of the tool; it also houses tool telemetry boards. Signals from the MDT and associated sensors are compressed downhole in the electronics cartridge for transmitting to surface enabling the logging engineer to monitor several tractor functions in real-time. There is also a surface-controlled switch mechanism (within the electronics cartridge) that isolates the tractor from its passenger tools during the logging survey.
The MDT drive arms and wheels are optimized to provide the maximum force to drive the MDT/passenger tool combination along the well. A self-adjusting mechanism to control traction ensures that the drive arms grip the casing wall with a force proportional to the tractor load. This, and the ability to adjust the gripping force from surface, prevents the tractor drive wheels from slipping. The drive arms open when power is applied to the clutch and close when it is switched off. A fail-safe mechanism automatically disengages the clutch if power is lost, completely closing the drive arms, so the MDT can safely be retrieved. The arms are available in various sizes to match the casing internal diameter. In complex completions each pair of arms can be of different lengths to suit casings of different sizes.
Low friction four arm centralisers and knuckle joints specifically designed to operate with the MDT can be included in the tool configuration to aid access in difficult areas of the well. CCL and head tension readings are provided for depth control and overpull indication respectively.
WEST software models the downhole forces and so can be used to plan MDT operations. The software can be used to identify many operational considerations such as optimum MDT configuration, the depth at which the MDT should be activated and to plot tractor and cable tension forces. WEST can be used both as part of the prejob planning and real-time during the logging operation. WEST can overlay real-time data on the modelled data during an operation.
Features
- Real-time log of CCL, Head Tension, Tractor Load, Tractor Speed and Arm Position.
- DC powered.
- Bi-directional drive.
- Self-adjusting traction control.
- Modular drive sections.
- WEST simulation software for pre-job planning.
- Helicopter transportable.
- Low cost alternative to coil tubing deployment.
