Seismic Surveying Motor

Introduction

iNetic was tasked with designing a DC motor capable of operating in high-temperature environments for seismic surveying applications. This case study highlights our engineering excellence in meeting stringent requirements and delivering a reliable solution. Seismic surveying is an essential method in geophysical exploration, providing valuable insights into the subsurface characteristics of the Earth. This case study examines the use of a brushed DC motor designed for the actuation of locking arms in seismic receiver tools. The motor plays a critical role in ensuring the precise and reliable positioning of seismic receivers, which are crucial for the accuracy of seismic data collection.

Motor Specifications and Design Requirements

The brushed DC motor is designed to meet specific requirements outlined in the specification document. Key parameters include:

  • Operating Voltage: +/- 120 VDC
  • No Load Speed: 9000 RPM
  • Max No Load Current: 50mA
  • Terminal Resistance: 200 Ohms
  • Torque Constant at 20°C: 0.1 Nm/A
  • Torque Constant at 200°C: 0.09 Nm/A
  • Normal Maximum Current: 160mA
  • Max Current: 220mA
  • Electrical Insulation: >275 MOhm @ 250V
SEISMIC SURVEYING MOTOR

Technical Requirements

Application

The motor is mounted to a planetary gearbox within a borehole seismic tool. This tool is deployed in oil wells, where it endures temperatures up to 200°C. The motor actuates locking arms via a ball screw mechanism, which engages the borehole’s sides to secure the seismic receiver tool.

Duty Cycle Operations

  • Opening Cycle:
    • 20 seconds at ~50mA
    • 2 seconds ramp up to 160mA
    • Stationary for 5 minutes
  • Closing Cycle:
    • 1 second ramp down to ~50mA
    • 20 seconds at ~50mA
    • 1 second ramp up to 100mA
    • Stationary for 3 minutes

Required Life

  • Operational Life: 200 hours at 200°C
  • Static Life: 1000 hours at 200°C

Environmental and Mechanical Stress Considerations

The motor is designed to withstand harsh downhole conditions, including:

  • Temperature Range: -30°C to 200°C
  • Acceleration: 30g half sine shocks for 11ms in any axis
  • Vibration:
    • 5-25Hz: +/- 2mm displacement
    • 25-1000Hz: 5g acceleration

Materials and Maintenance

The front face of the motor unit, interfacing with the gearbox, is constructed from 416S21 corrosion-resistant steel. Connectors must adhere to 200°C specifications. The motor is designed for customer reparability, allowing the exchange of components like armatures, brushes, and brush blocks, facilitating maintenance and reducing downtime.

Compliance and Safety

The design minimizes hazardous substances to ensure health and safety. The supplier is responsible for highlighting any potential hazards associated with the equipment’s operation and maintenance.

Conclusion

The brushed DC motor is a critical component in seismic surveying tools, providing reliable and precise actuation of locking arms in extreme downhole environments. Its robust design and adherence to stringent specifications ensure the integrity and accuracy of seismic data collection, contributing significantly to the field of geophysical exploration. The motor’s durability, ease of maintenance, and compliance with safety standards make it an asset in the deployment of seismic receiver tools.