Estimation of skin factor by using pressure transient

Prepared by :
Muhammad .S. Amin
Estimation of Skin Factor by Using
Pressure Transient Testing Results
4/21/2015 1

4/21/2015 2
Objectives
 Introducing skin factor and formation damage.
 Introducing well testing as a tool to describe the productivity
and future of a reservoir.
 Different methods of well testing such as Drawdown and
Build Up tests has been applied to determine Skin factor
 We will integrate the pressure analysis approach with the
pressure integral analysis approach and develop a consistent
and applicable method for the analysis of well test data to
evaluate skin factor.
 In this project, PanSystem program will also be applied to
evaluate the effect and value of skin factor


 Formation damage is an undesirable operational and
economic problem that
can occur during the
various phases of oil
and gas recovery.
introduction
4/21/2015 2


 . Formation damage indicators include permeability
impairment, skin
damage, and
decrease of well
performance
Introduction
4/21/2015 4


 Formation damage can occur at any time during a
well’s history from the initial drilling and completion
of a wellbore through depletion of a reservoir by
production. Operations
such as drilling,
completion,
workovers and
stimulations.
Formation Damage in Oil Wells:
4/21/2015 5


 1. Shallow damage is the most common and makes
the biggest impact on production.
 2. It may take significant damage to create large
drops in production
 3. The problem, however, is that the highest
permeability zones are the easiest to damage, and
that can have a major impact on productivity
Observations on Damage:
4/21/2015 6


Causes of damage
4/21/2015 7


 Skin factor denoted by the symbol S .
 What ever is the reason of the pressure loss or losses
in production (flow efficiency) there is a measure of
severity of for this reduction which is called skin
factor (S).
 Skin has no physical dimension.
 Skin can be zero (no effect), positive or negative.
Concept of Skin factor
4/21/2015 8


 A restriction to flow.
 A distortion of the flow lines from the perfectly
normal to the well direction.
 May result from:
Positive Skin
St = Sfm + Sc +Spp
4/21/2015 9


Flow enhancement
May result from:
 Matrix stimulation (near-wellbore permeability
exceeds the natural value)
 Hydraulic fracturing
 Highly inclined wellbore
Negative Skin
4/21/2015 10


Effective wellbore radius
4/21/2015 11


Positive skin has the effect of reducing
wellbore radius.
Negative skin has the effect of
increasing wellbore radius
S
w wr r e
 
4/21/2015 12


Radius distribution
4/21/2015 13


ΔΡskin = (ΔΡ2- ΔΡ1 ) = ( p3 – p2 ) - ( p3 – p1 )
ΔΡskin = ( p1 – p2 ) ………… (A)
Skin factor equations
141.2
2
o o o
S
q B
P S
kh


 
4/21/2015 14

No damage – no skin (ks = k)
Ideal drawdown:
Damage (ks < k)
Real drawdown:
,
141.2
ln
2
o o o s
S wf ideal
w
q B r
P P
kh r


 
   
 
,
141.2
ln
2
o o o s
S wf real
S w
q B r
P P
k h r


 
   
 
4/21/2015 15


Flow efficiency
Ideal drawdown
Real drawdown
F 
 
 
,
,
S wf ideal s
S wf real
P P k
F
kP P

 

F < 1: Damaged well
(skin is positive)
F = 1: No change (skin
is zero)
F > 1: Stimulated well
(skin is negative)4/21/2015 16


To determine the following parameters
 Initial pressure (p)
 Average pressure within the drainage boundary (p)
 Permeability thickness product(kh) and
permeability(k)
 Mechanical skin factor (S)
 Area drained (A)
Why test a well
4/21/2015 17


• Pressure Drawdown
• Pressure Build up
• Multirate
• Injection/fall-off
• Interference
• Pulse
Types of Well Tests
4/21/2015 18


shut in the well till pressure reaches static level & then
flowing the
well at a constant
rate ,q &
measuring Pwf.
Pressure Drawdown Tests
4/21/2015 19

Semilog plot of pressure drawdown data4/21/2015 20


4/21/2015 21


•Advantages:
–Suitable in new wells
–No need to lose production
– K, S, reservoir size can be determined
•Disadvantages:
–Difficult to maintain constant production rate.
4/21/2015 22


•Most preferred well testing technique
•The well is first produced at a constant rate till
pressure is stabilized
and then the well is
shut in
•Pressure is recorded
as a function of time
Pressure Build-up Tests
Shut in
flowing
4/21/2015 23

•
Horner relationship on semi-log plot
4/21/2015 24


•Advantages:
–Precise control of rate
–P* can be determined
•Disadvantages:
–Loss of production due to shut in.
Pressure Build-up Tests
4/21/2015 26

 Formation damage can be occurred in different stages of oil
well operations.
 Skin factors can be positive or negative .
 Well testing can help reservoir engineer as a formation
evaluation tool to describe the future performance of oil wells
in terms of pressure drop and flow efficiency.
 Different methods of well testing such as Build-up,
drawdown, injection, fall of, can be applied at different case
to determine skin factor of oil wells.
 Petroleum engineer need to monitor oil well timely, therefore
different action need to be don,
 Sometime formation damage can be due to partial penetration
. of the pay zone .
Conclusion
4/21/2015 27


Execution remained testes
PanSystem
4/21/2015 28
Future catalogue


 Clegg, J. D.: “Production Operations Engineering,”
Petroleum Engineering Handbook, Vol. IV, SPE,
2007.
 Economides, M. J., Hill, A. D., and Ehlig-
Economides, C.: “Petroleum Production Systems,”
Prentice Hall, PTR, 1994.
 Bellarby, J.: “Well Completion Design,” 1st Ed., Elsevier
B.V., 2009.
Refrences
4/21/2015 29

Estimation of skin factor by using pressure transient

More Related Content

What's hot (20)

Viewers also liked (20)

Similar to Estimation of skin factor by using pressure transient (20)

Estimation of skin factor by using pressure transient

Editor's Notes