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2. Evaluation of Different Perfortaing 
Techniques 
2.1. Through –Tubing Gun Perforating
System 
The through-tubing gun perforating approach has 
been used, with through-tubing perforators run on 
wire line, to overcome the perforating damage with 
adequate differential pressure to the wellbore. The 
basic technique involves establishment of suitable 
underbalanced condition (by adjusting the bottom-
hole pressure of the existing fluid in the tubing and 
casing), running and firing the gun. Then, the well 
will be allowed to flow and the spent perforator will 
be withdrawn.
The most important advantage of though-tubing gun 
perforating technique6 is its economical feasibility, 
especially in remedial operations and short zones. 
This system
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is not always a good solution of 
perforation/formation damage, especially problems 
of compaction and perforation plugging. The 
drawbacks of this system can be summarized as 
follows: 
1.
Smaller guns are underpowered, especially 
with damaged wellbores. In addition, gun 
length is limited by the required 
underbalanced pressure control and 
sometimes not feasible.
2.
This system is not suitable for long 
producing intervals, which require more than 
one gun run.
3.
Consistent performance requires good 
positioning of through-tubing guns to control 
the clearance.
4.
Gun debris remains in the well and requires a 
fishing job. In addition, the uncontained 
charges may cause casing deformation.
5.
Performing this system under high-
underbalanced pressures may cause blowing 
gun/cable up the hole, and 
6.
Using small perforation hole size and limited 
differential pressure for wire line operations 
induce a lower permeability zone and debris 
clogged perforations. The resulting low flow 
area can cause an excessive fluid velocity 
and finally provides water coning/sand 
production problems. 

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SPE 114793 
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