The seven-inch casing string is where a lot of plug-and-perf work happens, and it is also where a mill-out costs the most. A 7 inch dissolvable frac plug is built for that string: short, light, and made from material that degrades in the well fluid so the lateral does not have to be cleaned out with coil. The design question is not whether the plug dissolves, but whether it holds long enough and leaves a bore big enough to produce through. On a long lateral the alternative is a coiled tubing mill-out that may not reach the toe, so the plug choice can set the lateral length limit for the whole pad.
What a 7-Inch Dissolvable Frac Plug Replaces
A conventional composite plug has to be drilled out, and the mill-out is a coiled tubing job with a fixed reach limit. A dissolvable plug is set, fracs the stage, and then degrades, so the well can be put on production without a mechanical cleanout. The body and the element both dissolve, which means no rubber residue and no debris to circulate out. The part count is 60 to 70 percent lower than a conventional plug, so there is less material in the hole to begin with.
Length, Bore and Ball Size in the Casing
The plug is 384 mm (15.1 inches) long, with a maximum outside diameter of 146 mm (5.75 inches) and a minimum inside diameter of 62 mm (2.44 inches). The dissolvable ball is 82 mm (3.23 inches). It fits casing with an inside diameter between 161.7 and 154.78 mm, which covers the common 7 inch weights. That bore is what the well produces through after the frac, so a restriction here becomes a restriction on the whole completion. Heavier 7 inch weights sit at the tight end of that range, which is why the casing tally has to be checked before the stage rather than after the plug is on the wire.
Temperature Window and Pressure Differential
The rating is 10,000 psi (105 MPa) differential across a temperature window of 90 to 120 degrees C (190 to 250 degrees F). That window is the operating envelope, not a suggestion: below it the dissolution chemistry slows down, and above it the reaction runs faster than the stage schedule can tolerate. The pressure rating has to be compared with the treating pressure at the plug, not with the surface pressure on the chart. The dissolution timing also has to be planned against the frac schedule: a plug that breaks down before the next stage is pumped is a communication path, not a barrier.
Setting Force and Adapter Compatibility
Setting force is 24 tons, delivered by a standard wireline setting tool through an adapter kit. The plug is short enough to pass a tight kickoff and light enough at 5.5 kg to handle on the floor without a cart. The adapter has to match both the plug and the setting tool, and the setting sleeve stroke has to be long enough to fully compress the element; a partial stroke will set the slips and leave the element short. The setting tool itself is checked at surface for charge and circuit continuity, because a misfire at depth leaves a plug in the hole and a decision to make.
Confirm the casing inside diameter against the plug range before the stage.
Verify the adapter kit and setting force before the plug goes in the lubricator.
Record the set pressure and the overpull on the stage report.
Dissolvable Frac Plug Run-in Practice
Run-in is where these plugs are damaged. Keep the wireline speed controlled through the vertical section and slow down approaching fluid level, pump the plug through the lateral at a rate the line tension allows, and keep the weight of the gun string off the plug while it is being stabbed. After setting, do not run back in to check it; confirm the set with pressure when the ball is pumped to seat. Keep the plug inventory matched to the stage list, since a plug that is one size out will either not pass the casing or not seal against it.
A dissolvable plug is a schedule decision as much as a completion component. Match the size to the casing, the rating to the treating pressure, and the run-in to the well trajectory, and the stage ends without a mill-out on the plan.
For more information, please contact China Vigor at info@vigorpetroleum.com or call +0086 29 81161513.
