skin factor

8/10/2019 Skin Factor

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APPROPRIATE SKIN FACTOR FOROPTIMAL WELL PRODUCTIVITY

By

WILLIAMS ACHESE

DE.2008/1223


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INTRODUCTION

The formation can be damaged during drilling, casing and cementing,

completion, well servicing, well stimulation and production operations.

The skin due to damage can be defined as the additional pressure drop inthe near wellbore area that results from the drilling, completion and

production practices used (Van Everdingen, 1953).

Formation Damage can be defined as any near wellbore alteration thataffects permeability due to well operations (Byrne et al, 2007).


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Damage Caused by

Drilling Fluid

Mud filtrateinvasion Damage Caused by

Production

p < pbp > pb

Damage CausInjection

dirtywater


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Reservoir Model of Skin Effect

Bulk

formation

h

rw

ka

ra

k

Altered

zone

R i P P fil


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Reservoir Pressure Profile

500

1000

1500

2000

1 10 100 1000 10000Distance from center of wellbore, ft

Pressur

e,psi

ps

skh

qB2.141ps

Skin and Pressure Drop


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Skin and Pressure Drop

spqB

hk00708.0s D

Skin Factor and

Propertiesof the Altered Zone

w

a

a r

rln1

k

ks


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Effective Wellbore Radius

w

wa

r

rlns

s

wwa err

Productivity Index

wfpp

qJ

Flow Efficiency

w

ideal

actualf

p

pp

J

JE


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ANALYSIS OF A BUILD-UP CURVE

In a buildup test, a well which is already flowing (ideally at

constant rate) is shut in and the downhole pressure measured

as the pressure builds up. Ever since van Everdingen and Hurst

(1953) introduced the concept of a skin factor, the primary

focus of research has been on evaluation and minimization of

formation impairment.

The skin effect and its influence on the productive capacitive of

a well is illustrated more efficiently in well before and after

perforation as illustrated in the table 1


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Before After

Perforated interval 6258-70ft 6258-70ft

h, producing interval 548cm 548cm

Cumulative production 3956 B/D 5500 B/D

Production rate 96 B/D 60 B/D

Production time 41.21 days 91.67 days

t, production time 3561000 sec 7920000 sec

Shrinkage factor 0.795 0.795

q at reservoir conditions 222 cc/sec 139 cc/sec

Pressure increase per cycle 6 psi 4 psipr , flowing pressure 2060 psi 2502 psi

, viscosity 0.65 cp 0.65 cp

, porosity 0.219 0.219

c, fluid compressibility 0.00017/atm 0.00017/atm

rw,well raduis 6.3 cm 6.3 cm

Reperforating Job


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PRESSURE BUILD-UP TEST BEFORE REPERFORATION PRESSURE BUILD-UP TEST BEFORE R


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Before Reperforation After Reperforati

Reservoir pressure, PR 2554 psi 2554 psi

Pressure drop, PRPf 494 psi 52 psi

Pressure drop due to skin, ps 441 psi 16 psi

Skin, s 84.8 4.6

Permeability, k 118 md 111md

Effective well bore radius, rwa 9.35 x 10-37cm 6.33 x 10-2 cm

Production Index 0.194B/D-psi 1.154B/D-psiFlow Efficiency 0.107 0.692

TABLE 2RESERVOIR PRESSURE GOTTEN FROM THE BUILDUP

CURVE INTERPRETATION

The result show that the first perforation job was not efficient a

that the reperforation essentially removed a large resistance wh

existed near the well bore


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CONCLUSION

It is always possible to reduce the damage skin in the vicinity of a we

stimulation techniques such as fracturing, so both damage and

improvement can occur. The appropriate skin factor for optimal wel

productivity can be achieved and control during well testing. In the

reperforation of the well as describe in this paper. After reperforatio

resulting skin factor is lesser when compared after reperforation.


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THANK YOU

skin factor

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