Wireline logging requires accuracy, attention, and repetition. But even with the best wireline tools, advanced logging cable, and seasoned wireline control systems, human error still finds a way in if you let your guard down.
It happened on a horizontal well, during a routine pump down perforating run. Everything looked fine at first. The wireline truck was prepped, pressure control equipment checked, and the gunstring was ready. The task seemed simple: correlate to the marker joint (MJ), set the plug, and fire the guns.
What could possibly go wrong?
The Mistake That Cost Us Depth
The mistake wasn’t in the equipment. It wasn’t even in the wireline tools. It was in the data entry.
While correlating to the MJ, the engineer typed the wrong depth into the wireline software. Just 10 feet off. But in a horizontal well, even that small of an off-depth perforation (ODP) can result in major complications. Plug set. Guns fired. Stage completed. It wasn’t until we returned to the marker joint that we saw the depth discrepancy.
Once we reviewed the correlation pass and compared it to the CBL log and the collar log, it was clear: we had made the mistake at the correlation point. And the guns had already been fired.
What Is Wireline Without Precision?
In the world of cased hole logging and wireline perforating, precision isn’t a bonus—it’s a requirement. Whether you’re performing formation evaluation, running a cement bond log, or setting plugs in a multi-stage perforation well, a 10-foot mistake is a costly one.
Our process needed to change, and fast. So, we implemented a few new steps, turning this incident into a lesson that would help shape future wireline services and reduce risk for every perforation stage.
Creating A Double-Confirmation Protocol
To prevent another off-depth perforation, we implemented a mandatory depth verification system before any plug is set or gun is fired. This procedure is now part of our complete wireline solutions:
- Client Verification: A signature line is now added to the shoot sheet after correlation. Before the engineer can proceed to set the plug, the client must review the marker joint depth and visually confirm the corrected depth.
- Correlation Plot Logging: On the first run in a new well, the collars above and below the MJ are logged and plotted. The engineer handwrites the MJ depth and depth correction on the plot. This is presented to the client before setting the plug.
- Depth Correction Logging: If a depth correction is made, the engineer logs a new correlation strip, runs it across the MJ, and visually confirms the corrected depth on screen.
These changes have now been baked into our SOPs for all cased hole wireline and pump down perforating jobs.
Why Depth Correlation Is Non-Negotiable
Wireline services oil and gas work demands efficiency, but never at the cost of depth accuracy. A 10-foot ODP could result in:
- Frac stage inefficiencies
- Misaligned perforating systems
- Missed formation targets during production logging
- Disruptions to cement bond integrity
- Delays in wireline well logging analysis
We all know the value of proper depth correlation in horizontal wireline operations. It makes or breaks the success of a well perforation. If you’re in the wireline business, running wireline trucks day in and day out, then you’ve probably seen what happens when you don’t take the time to triple-check the MJ.
Building a Culture of Accountability
This incident pushed us to emphasize correlation in our wireline courses. We teach engineers and operators how to verify depths using multiple tools, including the cement bond log, collar logs, and wireline software calibration. We stress the importance of depth correction logging, handwriting MJ depths, and requiring client sign-off.
If you’re working in the wireline services market and looking to strengthen your crew’s consistency, these are the practices that separate seasoned wireline providers from the rest. Downhole tools are only as accurate as the depths we give them. And wireline equipment is only as useful as the crew running it.
From Mistake to Standard
In wireline well logging, mistakes aren’t always avoidable—but how we respond defines our success. The 10-foot error became the basis for a process that now saves us from future off-depth perforations.
If you’re operating in cased hole logging service markets or managing wireline control systems on tight multi-stage schedules, take a lesson from this job. Implement dual verification, use plots, and make correlation something that requires more than just a glance.
Every wireline company talks about safety, but depth accuracy is a form of safety, too. It protects your reputation, your client’s production, and the success of every run.