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Coiled Tubing Perforating
Coiled tubing provides additional perforating capability and flexibility over other conveyance systems. The rigidity and strength of coiled tubing allows enduring greater tensile and compressive forces, which is a major operational advantage when perforating in highly deviated and horizontal wells or with longer gun strings.
Coiled tubing perforating is ideal for live wells; pressure control techniques are used to run long gun strings and either drop off or retrieve the guns without having to kill the well.
In subsea wells, the subsea lubricator defines the length of gun that can be run. With other wells, the surface riser or surface lubricator valve determines the length of gun. The CIRP deployment system can be used in conjunction with coiled tubing to deploy and retrieve guns under pressure.
In depleted wells where drawdown is insufficient, nitrogen can be circulated at convenience to lighten the overall fluid column, increasing the drawdown at the zone of interest. The resulting pressure differential is similar to that produced by gas lift systems.
For accurate depth control, coiled tubing wired with integrated electrical cable is run in combination with a casing collar locator and a gamma ray detector. Optional real-time and memory sensors for pressure and temperature are used to monitor the required underbalance.
There are several ways to activate guns run with coiled tubing: hydraulic delay firing heads; drop ball firing heads; eFire-CT firing system using circulation rates; or electrically using "stiff-wire" coiled tubing, where an electric line cable is run through the coiled tubing to enable firing the guns in a similar manner to a wireline job.
Stiff-wire coiled tubing allows the use of standard wireline correlation tools. Hydraulic coiled tubing allows stimulation fluids to be pumped without the risk of damaging a wireline cable.
An additional specialty gun is the pump-over gun. This gun allows circulation through a special sleeve on the outside of the gun to the bottom of the string. The pump-over gun is used during frac operations in horizontal wells to save a cleanout trip between fracturing and perforating the next interval.
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