estimation of skin factor by using pressure transient

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Prepared by : Muhammad .S. Amin

Estimation of Skin Factor by Using Pressure Transient Testing Results

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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

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Formation damage is an undesirable operational

and economic problem that can occur during the various phases of oil and gas recovery.

introduction

2

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. Formation damage indicators include

permeability impairment, skin damage, and decrease of well performance

Introduction

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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:

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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:

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Causes of damage

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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

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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

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Flow enhancement May result from:

Matrix stimulation (near-wellbore permeability exceeds the natural value)

Hydraulic fracturing Highly inclined wellbore

Negative Skin

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Effective wellbore radius

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Positive skin has the effect of

reducing wellbore radius. Negative skin has the effect of

increasing wellbore radius

Sw wr r e

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Radius distribution

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ΔΡskin = (ΔΡ2- ΔΡ1 ) = ( p3 – p2 ) - ( p3 – p1 )

ΔΡskin = ( p1 – p2 ) ………… (A)

Skin factor equations

141.2

2o o o

S

q BP S

kh

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No damage – no skin (ks = k) Ideal drawdown:

Damage (ks < k) Real drawdown:

,

141.2ln

2o o o s

S wf idealw

q B rP P

kh r

,

141.2ln

2o o o s

S wf realS w

q B rP P

k h r

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Flow efficiency

Ideal drawdown

Real drawdownF

,

,

S wf ideal s

S wf real

P P kF

kP P

F < 1: Damaged well (skin is positive)F = 1: No change (skin is zero)F > 1: Stimulated well (skin is negative)

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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

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• Pressure Drawdown • Pressure Build up• Multirate• Injection/fall-off• Interference • Pulse

Types of Well Tests

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shut in the well till pressure reaches static level & then flowing the well at a constant rate ,q & measuring Pwf.

Pressure Drawdown Tests

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Pressure Drawdown Tests

Semilog plot of pressure drawdown data

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Pressure Drawdown Tests

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

Pressure Drawdown Tests

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•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 inflowing

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•

Horner relationship on semi-log plot

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•Advantages: –Precise control of rate –P* can be determined •Disadvantages: –Loss of production due to shut in.

Pressure Build-up Tests

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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

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Execution remained testes PanSystem

Future catalogue

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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

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THANK YOU ANY QUESTION?