The Wrong Det Cord: A Wireline Engineer’s Lesson in Perforation Failures

Posted on by Crissa Fel Tawadan

In wireline perforating, choosing the right detonating cord is just as important as selecting the right charges or switches. A small miscalculation in cord selection can lead to failed perforations, misfires, or downhole safety risks.

I once learned this the hard way during a plug and perf job that didn’t go as planned.

The Setup: A Standard Plug and Perforating Operation

We were running a plug and perf (PNP) job on a high-pressure oil well. The operation required:

  • A-140S blasting caps
  • Perforating guns loaded with 80-grain RDX detonating cord
  • Multiple stages of pump-down perforating

The det cord we used was Low Shrink (LS) detonating cord—a decision that would almost cost us the job.

The Problem: Misfires Due to Poor Detonating Cord Selection

When we fired the first stage, half of the perforating guns didn’t go off.

We immediately ran through potential issues:

  • Electrical failure? No—our continuity check was good.
  • Blasting cap misfire? No—some of the guns fired correctly.
  • Shot density problem? No—standard 4 shots per foot (SPF) configuration.

After pulling the string back out, we found the real issue. The LS detonating cord had failed to transfer detonation in certain points.

What Went Wrong?

  • LS detonating cord is harder to side-detonate when using A-140S caps.
  • The Kevlar jacket on LS cord reduced energy transfer, resulting in a partial misfire.
  • Low wellbore temperatures meant LS cord wasn’t necessary.

We had used the wrong det cord for the job.

Fixing the Issue: Choosing the Right Detonating Cord for Plug and Perf

To correct the problem, we reloaded the perforating guns using the recommended FireLine 17/80 RDX det cord and followed these best practices:

  • Used standard 80-grain RDX det cord instead of LS cord.
  • Kept prima cord runs clean and properly secured, preventing overlap.
  • Ensured proper alignment with A-140S blasting caps, improving detonation transfer.

The second run? Flawless perforations.

Key Takeaways for Wireline Engineers

  • Low Shrink (LS) det cord is not recommended for plug and perf.
    • It’s harder to detonate with standard blasting caps.
  • Use FireLine 17/80 RDX or DETOTEC 80 RDX for most plug and perf operations.
    • They offer reliable detonation transfer without unnecessary shrinkage.
  • High shot density (6 SPF or greater) may require Extra High Velocity (XHV) cord.
    • More shot points require more reliable detonation transfer.
  • Consider well temperature when selecting det cord.
    • LS cord is only necessary when temperatures exceed 190°F for over an hour.

Final Thoughts: The Right Det Cord Prevents Costly Failures

In wireline perforating, det cord selection is not one-size-fits-all. That day, we learned that cutting corners on cord selection can lead to serious operational delays.

So, next time you’re preparing a plug and perf job, double-check your detonating cord specs—because the wrong choice can cost you time, money, and efficiency.