Microsoft Word spe114793. doc

 
 
3. Underbalanced Perforating Technique
with Sucker Rod Pump Installation 
Completing wells with artificial lift pumping usually 
prevents the application of conventional perforating 
techniques with respect to creating the underbalance 
and firing the tubing conveyed perforating guns 
witout rekilling the well for the purpose of run well 
completion. Killing the well after peforration can 
case formation damage especially for low pressure 
reservoirs.
Since sucker rod pumping wells completion 
installation is one of the most flexible installations 
among the different form of artifical lift systems, 
Schlumberger
6
developed and tested a custom made 
below tubing anchor completion and perforating 
assembly which overcomes all of the restrictions. 
The firing system consists of two separate sections, 
of which only the fill sub is part of the gun string. 
The trigger charge firing head with sinker bar but is 
via a release mechanism secured to the ported hanger 
and run together with the sucker rod down hole 
pump. This release mechanism can only be activated 
once the pressure differential across the release 
sleeve exceeds the selectable shear pin rating. 
 
Firing sequence 
The gun firing sequence is as follows. 
1.
Sucker rod pump unloads annulus until the 
desired underbalance has been established. 
2.
Tubing is pressured up to release trigger 
charge firing head, and 
3.
Firing heads lands into receptor booster 
cover, sinker bar forces firing pin into 
percussion detonator, guns fire. 
Since the firing head and gun string are run in the 
well separately, the detonation transfer components 
between the two must be sealed. To penetrate these 
pressure barriers, a ballistic transfer shaped charge is 
installed in the firing head. When detonated, the 
shaped charge jet “triggers” the firing of the guns 
through a receptor booster installed in the top of the 
gun string, hence the name “trigger charge”.