Locking ring assembly Ring A
Drillpipe (closed string)
Pressure gauges Interference fit
Dual hydraulic-delay firing head (HDF)
Low-friction swivel Wave spring Ring B
Spacer Gun assembly
4.5-in. oriented perforating gun, low debris, 4 shots per foot, 10° /350°
Orienting weight
Sealed ballistic transfer
Locking screw Coupling device Gun assembly > Eliminating rotation at connections. Each gun is aligned and locked to the next with an interference-
t notched and keyed coupling device. During assembly, locking Ring A on the coupling device is forced into the female notches in the gun barrel and held in place by a wave spring and shoulder Ring B. The design eliminates play, or rotation, between gun sections. Achieving cumulative alignment errors of less than 10 minutes of a degree per gun assembly is not uncommon.
7-in. liner
OCD Orientation Confirmation Device
Bottom nose
independent of tortuosity in highly deviated well- bores. The new OrientXact tubing-conveyed oriented perforating system depends on several key components to attain the required orienta- tion accuracy, including a combination of guns, gun-section
locking adapters, orienting
weights and swivels (left). Special aligning and locking adapters assure
> Design of the OrientXact tool tubing-conveyed oriented perforating system. The OrientXact design directs all perforations in a vertical direction with 10° /350° gun phasing. Pressure gauges may be used to record pressure changes during discharge. One or more low-friction swivels support the gun string. Two OCD Orientation Con rmation Device units are located at opposite ends of each swivel-supported section. The need for orienting weights is determined based on rotational torque requirements.
a minimum buildup of alignment error within the gun-string sections. Each gun tube connects to the next with interlocking rings (above). Tight manufacturing tolerances virtually eliminate alignment errors caused by the small clockwise gun-string spiral inherent in the old threaded design. The average alignment error is reduced to 10 minutes, or 0.167° per gun assembly, satis- fying the demanding requirements of the Visund perforation project.
The compressional and tensional load on swivels in long perforating strings can be as high as 55,000 lbf in horizontal sections and 250,000 lbf [1,112 kN] in vertical sections.7
Schlumberger
developed special low-friction swivels to with- stand high loads while maintaining perforation accuracy. Under typical wellbore operating con- ditions, the new roller-bearing swivels produced a tenfold decrease in rotational friction. Tests conducted at the Schlumberger Reservoir Com- pletions (SRC) Center in Rosharon, Texas, USA, verified that the new gun string could develop sufficient torque to overcome swivel resistance with tensional and compressional loads to 55,000 lbf with simultaneous bending to 10° per 100 ft [30 m] (next page, left). Orientation accu- racy within ±10° can be achieved with sections longer than 1,600 ft [488 m] between swivels.
32
Oilfi eld Review
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