DDHub-Semantic-Interoperability

Rotary torque

Authors:

• Author 1
• Author 2

Modifications

• 15.04.2021: creation

Signal definition

Quantity

• The torque quantity is .
• SI unit is .
• Common units are
  • mN in metric system

Data representation

Top-drive torque is a scalar value and is therefore represented as such.

Information

The reported torque is as a rule the sum of the following effects:

• torque applied to the drillstring
• torque required to overcome inertia of the device
• torque required to overcome internal friction of the device
• torque associated to externally applied forces.

For downhole monitoring purposes, mainly the first contribution is of interest.

AC Electric top-drive

• Sensor type:
  • the signal is derived from the current consumed by the electric driving system (typically a vfd).
  • The current is measured by hall effect sensors.
  • It is assumed that torque is proportional to this current.
  • Two main equations can be used for the torque

    • where $I$ is the moment of inertia

    • 

  • Possible forms:
    • continuous 4mA - 20mA: calibration of end-points and linear interpolation thereafter
    • discrete (calculation by drive based on pre-set parameters)
• Accuracy / uncertainty:
• Physical location:
• Logical location:
  • To pumping system:
    • Wash-pipe -> Kelly Hose -> Stand-pipe -> Pump manifold -> Mud pumps
  • To drillstring
    • Quill -> Pipe -> BHA -> Bit
  • To hoisting system:
    • Hook -> Travelling block -> Fast line -> Drawworks
  • To rig structure:
    • Top-drive frame -> track -> derrick
    • travelling block -> deadline -> dealine anchor
• Validity:
• Maintenance / calibration:
• Refresh-rate:
• Dependencies: several factors can affect the measure
  • gearbox intrinsic properties: moment of intertia. Moment of intertia should be measured across a range of operation RPMs and RPM differentials
  • gearbox extrinsic properties:
    • wear
    • gear mesh
    • oil viscosisty and lubricity
    • gearbox temperature (changes mesh and oil properties)
  • fluid passthrough properties:
    • pressure, rate, density can cause itnernal components to buckle or experience forces
  • block height: can affect the orientationof the pipe axis to the quill from buckling or eccentric rotation
  • block weight: will affect buckling
  • temperatures:
    • drive system
    • motor internal temperature
• Processing: the following data flow are possible:
  • AC motor -> AC input -> AC Transmission Line -> Variable Frequency Drive (VFD) -> DCS
  • VFD -> PLC -> 4-20mA output -> ADC -> Preprocessing -> Aggregation
  • VFD -> PLC -> COMS -> Aggregation
  • VFD -> Various -> DCS -> COMS -> Aggregation
• Comments:
  • the considered top-drive is an AC electric top drive. The considerations here may not be applicable fo rDC, Hydraulic, 4-Quadrant drive types.
  • measured moment of intertia vary significantly (up to 50%) from CAD model
  • Signal to noise ratios low
  • resistance of primary power cable not constant, can add “ghost” loads to torque calculations
  • torque often less accurate at low RPM
  • fluids are non-newtonians (drilling and gear): RPM and temperature should be required for torque calculations.

Relevant Vocabulary

Use-cases

Comments

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