They say every tool tells a story—if you know how to read it. For me, one of the most underrated tools in the wireline logging arsenal is the Casing Collar Locator, or CCL. It’s not flashy like a perforating gun, and it doesn’t give you beautiful caliper log curves or deep formation evaluation insights. But when you’re miles down a cased hole well, trying to land a wireline perforating job right in the “pay zone,” the CCL becomes your compass.
I was running a cased hole logging job in a high-pressure gas well—tight window, critical depth control, and the client wanted wireline and perforating done with no room for error. They were lining up a pump down perforating sequence right after we logged, so precision mattered.
Correlation Is Everything
This well had three separate logging runs planned: first, a gamma ray and CBL log combo for cement bond analysis; second, a production logging pass to track flow; and finally, a perforation run with CCL and gamma for final depth correlation.
That’s where the CCL came in.
Our wireline tools were calibrated, the wireline truck prepped, and the logging cable freshly tested. I connected the CCL between the gamma ray and the rest of the toolstring and powered up the system. The coils inside the CCL were ready to catch every collar along the way.
The Physics That Saves Jobs
Faraday’s Law of Induction—that’s the science behind the magic. As the CCL moves past a change in mass, like a casing joint, the magnetic flux around its coil shifts and induces a small voltage. That signal pops up on the log like a heartbeat—telling me, “Here’s a collar.” Smooth casing shows flat, 0V. But a collar? That’s your landmark.
Without that signal, I’d be relying on guesswork to line up the logs. And in cased hole well services, guessing is a good way to miss the zone and waste a perforation service.
I’ve worked enough wireline services oil and gas jobs to know: collars are your best friends when it comes to depth control.
Know Your Tool: Titan vs. Applied
On this job, we used a generic firing system, so I ran a Titan CCL—1500 ohm coil resistance and a quad diode setup. I always check diode voltages with a multimeter—1.2V in both polarities told me everything was working perfectly.
In other jobs, especially with addressable switches, I’ve used an Applied CCL with higher coil resistance (2500 ohms) and dual diodes. Lower voltage firing means the CCL design needs to conserve every bit of electrical integrity. If you’re running an addressable system and your CCL is bleeding voltage, you’re asking for a misfire.
That’s why electrical checks are sacred in this business. No shortcuts.
Maintenance: The Unseen Discipline
I’ve seen too many wireline companies lose jobs due to poor tool maintenance. Every time I crack open a CCL for rebuild, I check the o-rings, the bowsprings, the diode seating, and coil continuity. Loose connectors, damaged threads, or poor grounding? Those will kill your signal before you even reach the perforation depth.
In my years running wireline oilfield jobs, especially those involving wireline control systems, pipe recovery, or wireline perforating, I’ve learned this: consistent preventive maintenance turns tools into trusted partners.
The Payoff
We logged down, and every collar registered clean. The CCL response was crisp, spaced just like we expected based on the casing tally. When we hit the correlation zone, the gamma matched perfectly with our prior logs. Confidence locked in.
We set the depth. The perforating gun fired exactly where it needed to. Well integrity stayed intact. Job success.
Not because of high-tech wizardry—but because the CCL log put us right where we needed to be.
Why It Matters
Whether you’re new to the wireline business or a veteran running eline services, understanding how something as “simple” as a CCL works can make or break a job. From perforation wells to production logging services, the ability to correlate logs with precision is a core competency in cased hole solutions.
If you’re getting into wireline courses, pay attention when the CCL module comes up. Because while tools like the downhole camera, tracer tech, or pipe caliper tool are flashier, the CCL is what quietly keeps everything aligned.
And when you’re thousands of feet below surface, trust me—you’ll be glad it’s on your side.