18-PSEUDOSKINS

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Copyright 2007, , All rights reserved

PSEUDO SKINS




COMPONENTS OF THE SKIN FACTOR

S = Sd + Spp + Sperf + Sturb+ Ssw + Sgp

where:

– Sd = skin due to near wellbore formation damage

– Spp = skin due to partial completion

– Sperf = skin due to perforations

– Sturb = skin due to turbulence

– Ssw = skin due to slanted well

– Sgp = skin due to gravel pack




PERFORATING AND SKIN EFFECT

SHAPED CHARGE

CASE

LINER

EXPLOSIVE

DETONATING CORD

PRIMER CHARGE

CHARGE

DETONATION

WIRELINE

COLLAR LOCATOR

CONTROLLED WEAK

POINT HEAD

SHAPED CHARGES

(HELICAL PATTERN)

DETONATION WAVE

(initiated by electric current)

JET

LINER COLLAPSE AND JET FORMATION

LINER-STRETCHING PHENOMENON

REAR JET (SLUG))

VELOCITY 3000 Ft/secJET TAIL

VELOCITY 3000-7000 Ft/sec

JET TIP

VELOCITY 25000-30000 Ft/sec

LINEAR VELOCITY GRADIENT

JET TIP PRESSURE: 15x106 psi




PERFORATED TUNNEL PERFORATIONS PHASING ANGLE


CASING

CEMENT

PERFORATED TUNNEL

FORMATION

DAMAGE

UNDAMAGED ZONE

CRUSHED ZONE




CasingCement

CompactedZone

PerforatingDebris

MudFiltrateZone

Virgin Formation

Undamaged Zone

DebrisCrushed

Zone

Damaged

Zone

Cement Casing


PERFORATED TUNNEL




K R

rw

rd

Damaged Zone Thickness

K D

rprdp

Lp

FLOW INTO A PERFORATION

K DP

CEMENT

CASING


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LOCKE’S NOMOGRAPH FOR SP CALCULATION

6”

12”



Calculation of the eff ect of f low through the compacted zone

of the perforated tunnel (S dp ).

h = total formation thickness

k R = unaltered reservoir permeability

k d = damage zone permeability

k dp = compacted or crushed zone permeability

rdp = compacted zone radius

rp = perforated tunnel radius

N = total number of perforations

Lp = perforation length

Sdp =h

k dp k d

k R k R

NLp

rdp

rp

ln( )



SKIN DUE TO PARTIAL COMPLETION (Spp)

skin due to partial penetration of the producing zone (vertical well)

hh p

= 2

-

k k

r h

ln

1

-

h h

S

v h

w p pp



Skin due to slanted well

Ssw = -(q/41) 2.06 - (q/56) 1.865 Log(h/100 r w)

q = well inclination angle

h = total formation thickness



An oil well is producing from a consolidated sand.

From a build-up test analysis the following data was obtained:

Reservoir Permeability (K R )=100 mD

Skin effect (S)=14

Average Reservoir Pressure (Pr)=2085 psi; qo=202 STB/day; Pwf=1765 psi

Horizontal to vertical permeability (Kh/Kv)=1.0 (from core analysis)

PVT Data: Bo=1.2 bbl/STB; µo= 1.15 cps (assume constant)

Completion Data:

Wellbore diameter =12 in. (rw=6 in.=0.5 ft)

Formation thickness=60 ft.

Casing ID= 8.921 in.

Perforation diameter= 0.5 in.(rdp=0.25 in)

Perforation length= 9 in.

Perforated interval= 30ft. Number of shots per foot =4; (90º phasing angle).

Permeability of the crushed zone of the perforations =10 mD

Radius of crushed zone of perforation tunnel (rp) = 0.75 in.

Permeability of damaged zone (Kd)=10 mD;

Radius of damaged zone (rd)=12 in (thickness of damaged zone=6 in)

A) Calculate the formation damage skin effect (Sd).

K dp= 0.1K R

solution

EXERCISE

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18-PSEUDOSKINS