A composite bridge plug is chosen for two reasons: it holds pressure, and it comes out of the hole quickly. In a high-temperature, high-pressure well those two requirements pull against each other, because the materials that survive 120 degrees C are usually the materials that are harder to mill. The Ultron composite bridge plug is built for that balance, with a full composite body that holds 15,000 psi differential and still drills out with conventional tools. That combination is what makes the plug usable in a well where a metal plug would either corrode or take a day to mill.
What a Composite Bridge Plug Has to Hold
The plug isolates a zone during fracturing, so it sees the treating pressure from above and, on some stages, from below. It also has to survive the thermal cycle of the treatment and the produced fluids that follow. A metal plug handles the pressure easily and then corrodes in a sour well; a composite plug handles the corrosion and has to be designed for the pressure. The full composite construction is what removes the metal-to-rubber sealing interface that usually fails first. On a composite body the element and the body expand together, so the seal is not dependent on a bonded interface holding through a thermal cycle.
Pressure and Temperature Ratings
The 4-1/2 inch plug is rated to 15,000 psi (105 MPa) differential at 120 degrees C (250 degrees F), with a maximum outside diameter of 89 mm and a minimum inside diameter of 25 mm. The 5-1/2 inch version holds the same pressure and temperature with a 110 mm body and a 33 mm bore. Both are rated for full differential from above and below, which matters on a well where the pressure direction changes between the frac and the flowback. A plug rated in one direction only is a plug that has to be oriented, and orientation is one more thing for the crew to get wrong at 3 a.m.
Drillout Time and Cutting Returns
Composite material is lower in hardness and more brittle than steel, so a tricone or junk mill cuts it faster. Field experience puts the saving at 30 to 50 percent of the drillout time compared with a metal plug, and the cuttings are lighter, so they lift more easily to surface. That matters on a long lateral where the mill-out is the operation that decides whether the well gets cleaned to total depth. On a pad with twenty stages, a 30 percent saving in mill-out time is measured in days of rig time rather than hours.
Setting Force and Casing Range
Setting force is 12 tons on the 4-1/2 inch plug and 17 tons on the 5-1/2 inch plug, applied through a standard setting tool and adapter. The applicable casing inside diameter is 97.18 to 101.6 mm for the smaller size and 118.62 to 124.26 mm for the larger, which covers the common weights in each size. The plug is 525 or 600 mm long, so it passes a tight kickoff without becoming a steering problem. A short, light plug also reduces the shock load on the setting tool when the string is run in through a build section.
Confirm the casing inside diameter against the plug range before the stage.
Check the setting tool and adapter match the plug body.
Record the setting force and the overpull on the stage report.
Composite Bridge Plug Selection for Old Wells
The other common use is a workover well that needs a zone isolated and then re-opened. A composite plug can be drilled out underbalanced, which protects a sensitive formation, and the lightweight cuttings reduce the load on the surface equipment. On an old well with scale and an irregular bore, the plug has to be selected against the actual drift rather than the nominal casing size, and the setting depth has to be clear of perforations that could take the setting force. On a well with an old gravel pack or a patch, the plug is set above the damaged interval rather than across it.
A composite bridge plug is a temporary barrier with a removal plan built in. Match the rating to the treatment, the body to the casing, and the drillout to the bit on the rig, and the plug does its job and leaves.
For more information, please contact China Vigor at info@vigorpetroleum.com or call +0086 29 81161513.
