The thing about wireline logging is that you can have the most advanced wireline tools, the sharpest crew, the most dialed-in wireline control systems—but if your base log isn’t accurate, everything that follows is built on sand.
I learned that lesson early in my career, during a cased hole logging job where we were prepping for a multi-stage wireline and perforating operation. The client gave us their “verified” base log depth from a previous run. Everything looked fine. The logging cable tension was good, wheels calibrated, gamma ray response aligned—until it didn’t.
We missed a perforation zone by 5 feet.
What caused it? A mismatch between the measuring wheel size and the cable in use. No one had double-checked the system setup. The base log was off—and every subsequent correlation tied to it was, too.
That mistake led to a full-depth review and some of the best field training I’ve ever received.
Why Base Log Correlation is a Wireline Foundation
In any cased hole wireline operation, the base log is more than a gamma ray record. It’s your primary reference for every future run—production logging services, perforating gun deployment, cement bond logs, even pipe recovery if things go south.
Get it wrong, and you’re chasing ghosts. Get it right, and every pass after becomes efficient and precise.
The Real-World Base Log Checklist I Follow Now
Here’s the depth control protocol I use, every job:
- Confirm well depth, KB (Kelly bushing), GL (ground level), float collar, shoe, liner top, DV tools, and marker joints before starting.
- Match Geo-Log measuring wheels and benchmark systems to the correct cable size.
- Cross-check the most recent line record book depth correction for the specific cable in use.
- Run only scintillation-type gamma ray detectors for base log recording.
- Use multiple tie-in points—marker joints, liner tops, casing changes—to validate correlation.
- Document any shift amounts and correlation points in the log header with direction and depth.
- Keep margin of error within 1’ per 1,000’—any more than that, and something’s off.
If we’re off by more than 1 foot per 1,000 feet, we stop. The measuring system gets checked and calibrated before going back in the hole.
When the Pipe Tally Lies
You’d be surprised how often pipe tallies get blamed for correlation problems. But when things are off-depth, you can’t just assume it’s the pipe. We’ve had cases where bad measuring wheels, uncalibrated encoders, or even a missed depth correction update caused the issue.
That’s why I log every discrepancy, and if the pipe tally ends up being wrong, I make a clear note under “Remarks” on the job header and include the correction.
Archiving: Protecting the Log for the Life of the Well
A base log doesn’t end when the toolstring is pulled. Every logging pass—on depth or not—gets recorded and archived. We file both the digital log file and hard copy with the job paperwork package.
That way, six months—or six years—down the road, when they’re calling you back for plug and abandon, wireline well logging, or another perforation service, you’re not starting over.
You’re building from a verified foundation.
Lessons for the Next Generation
If you’re taking wireline courses or learning to run your own wireline unit, don’t let your base log become a check-the-box task. It’s the bedrock for:
- Perforating gun targeting
- CBL and caliper logs
- Tracer tech validation
- Production logging interpretation
- Even holefinder tool reliability
In a world where wireline companies are expected to run faster, smarter, and safer, depth accuracy is still the gold standard.