Perfect placement isn’t as easy as you might think. You’re pumping a 40-foot tool string down thousands of feet, for several miles along a horizontal well, hanging it from a line that stretches under load. All those variables, and you still expect the string to land within a foot or two of where the completion design specifies. That’s a lot of faith in a lot of variables.
Why is depth control so difficult?
A 2026 DarkVision Technologies paper, “Frac Optimization: Analyzing Operational Metrics That Matter,” used high-resolution acoustic imaging data to look at how accurately the industry is executing several completion KPIs. Depth control was one of the biggest takeaways: the average combined cluster and plug depth offset over the previous two years was 7.9 feet.
That might not sound like much across a 10,000-foot lateral. But downhole, it can be the difference between A) putting a plug where it was designed to work, and B) setting it somewhere it was never supposed to be. There are lots of reasons why that can happen, but the big one is damn simple: wireline stretches. The amount of stretch changes with line type, tension, tool weight, well geometry, friction, and how much line is in the hole.
DarkVision showed an example where depth control was generally well managed, but wireline stretch wasn’t properly accounted for. The result was a large discrepancy at the toe that progressively decreased toward the heel. At another well, day and night crews zeroed their strings differently, creating repeatable stage-to-stage depth errors. Differences in pump-down, plug-setting, and pull-out procedures were also identified as potential causes.
How far off depth are we talking about?
DarkVision’s aggregate perforation data found an average absolute cluster depth offset of 8.5 feet per well, with a 7-foot standard deviation. The maximum average offset observed on a well was 27 feet. The data also showed a tendency to shoot deeper than intended, with depths that varied significantly. The paper’s plug data tells a similar story.
Most concerning, a plug was set below the top cluster of the previous downhole stage in approximately 32% of wells. Where this happened at least once, the affected wells averaged 2.2 plugs downhole of a top cluster. Some wells had more than 60% of their plugs set in that position. So if you’re thinking depth control is an isolated issue, it’s not; it's showing up in almost a third of the wells surveyed, and in some cases for up to two-thirds of plugs set.
What happens when a frac plug is set off depth?
Frac plugs are built to provide a pressure barrier between stages. But the plug still needs suitable casing and the right relationship to the perforations around it. Set it somewhere with eroded perforation at the plug set depth or just above the plug, and you’ve changed the conditions the plug was designed for.
DarkVision notes that off-depth placement can contribute to poor isolation when plugs land in areas with unfavorable casing geometry. The nastiest case is putting the plug below the top cluster of the previous stage. In fact, DarkVision documented a Stage 48 plug that was actually set at Stage 47’s fourth perforation cluster. The next stage underperformed because the barrier was no longer separating the stages where the completion design intended it to.
That creates the potential to:
- Overstimulate the previous stage
- Understimulate the target stage
- Leave portions of the lateral untreated
- Lose isolation or struggle to pressure test
- Expose the plug to conditions outside its intended operating envelope
You may know immediately when a plug outright fails. You usually don’t know whether it’s set on location or if it’s 30 feet away unless somebody goes downhole and looks. It’s an important distinction when you’re diagnosing frac plug failures. Blaming the plug without confirming where it was set can hide the real root cause.
READ MORE: Frac plug forensics: what downhole imaging tells us about plug failure
Do perforations have the same problem?
Plugs aren’t the only downhole tools wandering away from the plan. Poor perforation depth control changes cluster spacing and can put shots in places the completion engineer never intended. Clusters spaced too far apart can leave reservoir behind. Put them too close together, and backside communication can contribute to uneven stimulation.
DarkVision’s data found operators perforated an average of 10.3 casing collars per 10,000 feet of lateral, while only 3.65% of wells in the analyzed dataset had zero collars shot. Performance varied dramatically between operators, from about one collar to as many as 25 per 10,000 feet. Shooting a connection can change perforation behavior and contribute to uneven stimulation.
This is the same basic lesson we’ve seen with oriented perforating: designing something correctly at surface doesn’t mean much if the downhole execution doesn’t match the design.
What’s the financial impact?
DarkVision’s paper puts a price tag on the problem. Their researchers estimate that missing just 10 feet of pay can represent up to $60,000 in lost net present value and $20,000 in wasted capital expenditures.
On one well, perforations were placed within 11 feet of their intended depths. Several months later, the same crew averaged roughly 45 feet off depth on another well. DarkVision estimated the resulting discrepancy left as much as 22% of the lateral unstimulated. Same basin, same crew, different result.
Can quality control address depth issues?
Completion engineers spend a lot of time reviewing isolation, plug erosion, perforation design, pressure response, and stimulation uniformity. But plug depth and perforation depth are inputs to everything that follows. If that input is wrong, you can spend a lot of time optimizing to fix the wrong problem.
DarkVision argues for routine depth-control quality control rather than assuming deployment went according to plan. For example, their Wireline Scorecard compares cluster-to-cluster spacing, cluster-to-plug spacing, and measured plug and cluster positions against their intended depths.
That doesn’t mean every operator needs to image every well. Downhole studies aren’t cheap, and nobody needs another diagnostic program just for the sake of collecting data. But when you do run one, use it to question the assumptions everybody normally takes for granted. Ask questions like:
- Did the plugs set where we thought?
- Did the guns fire at the designed depths?
- Are different crews following the same depth-correlation procedure?
- Are we properly accounting for wireline stretch?
- Does a plug failure line up with where that plug was actually set?
- Are recurring depth discrepancies showing up stage after stage or pad after pad?
What should you do now?
We spend plenty of time talking about plug design, sealing performance, erosion, drillout, and materials. But a plug can only perform in the conditions you give it. Before blaming the hardware, make sure it was placed where the completion design said it belonged.
DarkVision’s dataset shows that off-depth plugs and perforations aren’t rare exceptions. It’s happening in nearly a third of all wells, with a wide range of off-depth positions. The industry-wide combined depth discrepancy improved from 10.5 feet to 7.9 feet over the periods analyzed, but there’s still plenty of room to tighten up that number. Treat depth control like every other critical completion parameter, using measurements and quality control to check values.
At Repeat Precision, we build downhole tools to run fast, set reliably, and hold isolation under real-world loads. But good equipment still needs good execution. Want to tighten up your completion and eliminate uncertainty downhole? Let’s talk.
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