Unexpected restrictions in a wellbore, such as casing patches or deformation, create issues in all phases of a well’s life cycle. These challenges impact the completion significantly. There is only one option for Plug & Perf Completions: Extended Range Plugs.
While the frac itself may not be affected more than by a slight increase in friction pressure due to the restriction, the major effect is on the equipment needed to isolate each zone.
A typical frac plug will be roughly .3″ less than the drift of the casing. For instance, the drift diameter of 5.5″ 20# casing is 4.653,” and most plugs for this size have a 4.375″ OD. This clearance is the proven optimal mix of pump-down efficiency and risk mitigation.
A restriction in the well above uncompleted zones eliminates the ability to utilize standard plugs. Extended Range frac plugs become the only option. These plugs have a smaller OD but will anchor & seal in the same casing ID. The smaller OD enables the plug & perf operation to continue because the plug will pass through the restriction.
Extended Mechanical Challenge
Extended-range plugs are mechanically challenging because of how far the anchor and seal must travel. The WellBoss Company XRP Plugs for the same 5.5″ 20# casing above have a 3.75″ OD, resulting in a 1/2″ gap between the plug OD and the casing. To span this gap, the anchor (slips) must travel further to bite into the casing.
The large gap also affects the sealing element. At higher pressures, the expanded rubber element will extrude down the length of the plug, affecting its ability to hold pressure. Eliminating the extrusion & maintaining isolation requires an elaborate element backup system.
A restriction in the well also restricts the size of the bit/mill used to drill up the plugs. Using an undersized bit is challenging on any plug, but the large expansion gap on the extended-range plugs further increases the chance of getting larger pieces back during milling. Consulting with the mill-up company before the operation so they fully understand the equipment in the well and can adjust their procedures accordingly will go a long way toward a smooth mill out.
The leading technology for this scenario is the WellBoss XRP Extended Range composite plugs for 4.5″ and 5.5″ casing sizes.
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