Microsoft Word spe114793. doc

 
Abstract 
Underbalanced tubing conveyed perofration (TCP) 
attained higher production and assured safety when 
applied with sucker-rod pump installation in wells in 
three different Egyptian oil fields. The TCP allowed 
more efficient operation because it does not require 
killing the well after perforation to run the downhole 
pump and sucker rod. The overbalanced perforation 
eliminates the risks of damaging the producing 
formation beyond the perforations.
The compared performance of wells using 
underbalanced TCP with that of other wells using 
tubing gun technique, casing gun technique eveals 
that the underbalanced TCP prevailed successful in 
all cases.
1. Introduction and Review 
Many thousands of depleted wells all over the world 
use sucker rod pump systems as artificial lift method. 
Application of conventional perforating techniques 
for sucker rod pumping system may cause formation 
damage for the well to be killed after perforation to 
run the downhole pump and the sucker rod. Since 
underbalanced perforating has been proven to 
provide much more production than either balanced 
or overbalanced perforating, it is recommended for 
application instead of sucker rod or along with them.
The major goal of any well completion is to obtain 
maximum oil production. The used perforating 
techniques and tools
1-5
have been proven to have a 
tremendous importance on determining the resulting 
production rate. It is always required to have such a 
program that would minimize the 
perforation/formation damage and maximize the well 
deliverability, hopefully reducing the total number of 
storage wells required. 
Naguib et al
1
reviewed and evaluated different 
artificial lift methods in Egyptian oil fields. Fig. 1 
shows the locations of these fields. The study 
indicated that Egyptian natural producing wells 
represent 15 %, while gas lifted wells are 24 %, and 
the pumped wells are 61 %.
The relationship between the well borehole pressure 
and the formation pressure at the time of perforation 
can be classified into (a) overbalanced, (b) balanced, 
or (c) underbalanced. Underbalanced perforating is 
perforating that is performed when the reservoir 
pressure (P
r
) is higher than the downhole wellbore 
pressure (P
wf
) Then, the underbalanced pressure (P
u
) 
= P
r
– P
wf
. 
In a consolidated formation, the jet perforating 
process causes a severe compaction surrounding 
mass as the penetrating an ultra-high speed “bullet” 
advances. Without further cleaning, the debris and 
compaction may form a definite permeability block 
to the extent that an open channel may not exist. This 
problem has not been appreciated for a long time. 
The resulting low flow rate may be considered 
adequate or incorrectly assumed to be the maximum 
flow potential, or the flow rate may be assumed 
coming from only a few well perforations. The 
general recommendation to overcome perforation 
damage has been to perforate with sufficiently high 
differential pressure toward the wellbore in order to 
flush out debris and compaction. 

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SPE 
114793 
Brieger and Stovall
1
showed that many field-
operating crews believe erroneously that such an 
ideal perforation occurs under typical downhole 
conditions. Their study showed that laboratory tests 
using limited differential pressure indicated that 
much higher energy is required to dislodge the zone 
of low permeability resulting from perforation, 
crushed rock where lining jet gun perforation 
channels. On the other hand, field tests indicate that 
the tubing conveyed perforating technique (also 
called Vannsystem) has high back-surge pressure, 
which may provide enough energy to produce almost 
ideal perforations and provide very positive results. 
Colle
2
developed a completion technique for 
overcoming formation damage. Basically, this 
technique suggested overcoming the formation 
damage of cementing, drilling, and perforating by 
perforating with deep penetrating shaped charges and 
immediately back-surging with maximum differential 
pressure to the wellbore. 
The sole objective of the production engineers is to 
have well perforations producing at minimum flow 
resistance at the reservoir/perforated-system 
interface. Bell et al
3
showed that this could be 
achieved by (a) establishing well conditions 
enhancing cleanup of the perforations, and (b) 
choosing perforators and techniques providing the 
best flow performance. They
3
also concluded that 
natural completions are always more productive 
when perforation is achieved under reverse pressure. 
The perforating equipment and techniques have a 
very important bearing on the determination of the 
resulting production. Bell
4
indicated that the best 
perforating techniques depend on the type of well 
completion. Furthermore, for a specific completion 
method, choices of techniques and equipment are 
constrained by the well configuration, fluid type of 
wellbore pressure, formation characteristics, and 
damage conditions. Bell also stated two main steps 
for obtaining minimum resistance to flow at the 
reservoir/perforated system interface: (a) establishing 
well conditions that enhance cleanup of the 
perforations, and (b) choosing perforators and 
techniques for best flow performance. 
It is imperative for the completion engineer to 
perforate a well such that the completion pressure 
loss is low, the production rate is high, the operation 
is safe, and the cost is low. Crawford
5
developed and 
presented a set of equations for a systematic 
estimation of a desirable downhole design guidelines 
for (1) the minimum underbalanced pressure 
necessary to provide clean perforations, (2) the 
maximum underbalanced pressure that can be 
tolerated without causing sand production, and (3) 
recommended underbalanced pressure.