A Story from the Field: The Importance of Stray Voltage Checks

Working in wireline services oil and gas, I’ve learned that the smallest details can make or break a job. One such detail that often gets overlooked is the presence of stray voltage at the wellsite. The first time I encountered this issue, it nearly caused a major delay in our wireline well logging operation. Since then, I’ve made it a strict habit to conduct thorough stray voltage checks before setting up our cased hole wireline equipment.

Why Stray Voltage Checks Matter

Stray voltage is an invisible but dangerous issue that can affect wireline control systems and lead to equipment failures, safety hazards, and potential damage to downhole tools. When handling wireline perforating or formation evaluation tools, any unexpected electrical interference can compromise the integrity of the operation.

By ensuring the grounding circuit is functional before attaching logging cables and wireline equipment, we can avoid unnecessary risks and ensure well integrity throughout the job.

How to Perform a Stray Voltage Check

Through experience and best practices aligned with API RP-67, here’s how I conduct a proper stray voltage test before any cased hole logging job:

• Gather the Required Equipment 
  • Digital Multimeter
  • File and emery cloth
  • Grounding cables
  • Ensure the safety key is in the “SAFE” position

• Verify the Grounding Circuit 
  • Clean a spot on the wireline logging cable and check resistance between that spot and the grounding clamps.
  • The resistance must be less than 1 ohm to confirm a functional ground.

• Check for Voltage at Key Connection Points 
  • Spool off the wireline cable and position it near the wellhead.
  • Clean bare metal points on the cable, wellhead, and rig or crane.
  • Using a digital multimeter, measure voltage between:
    • The cable and wellhead
    • The rig/crane and the cable
    • The rig/crane and the wellhead
  • If voltage is over 0.25 volts, identify and eliminate the source before proceeding.

• Attach Grounding Cables 
  • Once voltage is below 0.25 volts, attach the grounding cables securely.
  • Recheck voltage between the clamps—it should read near zero volts.

• Ongoing Monitoring 
  • On 24-hour operations, repeat this check every 24 hours.
  • On multi-well pads, recheck the voltage each time the wellhead connection is broken.

Key Takeaways for Wireline Companies

• Never ignore stray voltage. Even minor electrical disturbances can impact wireline perforating, downhole pipe recovery, and perforation well integrity.
• Always check for both AC and DC voltages starting from the highest scale and working lower.
• Grounding cables should never be used to eliminate voltage over 0.25 volts—the source must be identified and resolved first.
• Routine checks help ensure compliance with wireline service standards and improve cased hole logging service market safety.

By making stray voltage checks a part of our standard operating procedures, we can protect our teams, our wireline equipment, and the wellsite itself. The smallest details, like ensuring proper grounding, are what separate reliable wireline providers from the rest.