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PETR 4314 Fall 2015

M. Y. Soliman, PhD, PE, NAI

Lecture 5

PETR 4314 Fall 2015, M. Y. Soliman, PhD, PE, NAI - Lecture 5

PETR 4314

Nodal AnalysisM. Y. Soliman, PhD, PE, NAI

Lecture 5 - The Near-Wellbore Condition; Skin Effects


Sources of Damage

Drilling

Completion

Production

Injection

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Lecture 5

PETR 4314 Fall 2015, M. Y. Soliman, PhD, PE, NAI - Lecture

5

The Near Well Condition

Damage Characterization

Skin Effects


Zone of Altered Permeability

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Lecture 5


Hawkins formula

w

s

s rr

kks ln1

sk

k

wr

srDamagepenetration

distance


Hawkins Formula

w

sidealwfs

r

r

kh

qpp ln

2,

w

s

s

idealwfsr

r

hk

qpp ln

2,

w

s

w

s

s r

r

kh

q

r

r

hk

qs

kh

qln

2ln

22

w

s

s r

r

k

ks ln1

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Lecture 5


Example 6-1

rw=0.328 ft

Penetration damage = 3ft

What is the skin ifk/ks=5 and 10.

Ifk/ks= 10. What would be the required

penetration damage to provide the same

skin effect as the latter case withk/ks=5?0.328

3.328


Example 6-1

w

s

s rr

kks ln1

27.9328.0

328.3ln15

s

85.20328.0

328.3ln110

s

0

5

10

15

20

25

0 1 2 3 4

Penetration of Damage, ft

Skin

K/Ks=2

K/Ks=5

K/Ks=10

ftr

er

r

r

s

s

s

s

60

328.0

21.5328.0

ln

328.0ln1585.20

21.5

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Lecture 5


Example 6-1

w

s

s r

r

k

ks ln1

0

10

20

30

40

50

60

70

80

90

100

0 1 2 3 4 5 6 7

skin

permeability of damaged area

Effect of permeability damage


Example 6-1

w

s

s r

r

k

ks ln1

What is the dominant term in the above equation?

How high can skin get? When?

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Lecture 5


Example 6-2

With same skin effects calculated Ex. 6-1,

compare portion of pressure drop due to

damage within the near-wellbore zone vs.

the total pressure drop. AssumeA=640

acres (re=2980 ft)


Example 6-2

skh

qBpskin 2.141

s

r

r

kh

qBp

w

etotal ln2.141

sr

r

s

sr

r

kh

qB

skh

qB

p

p

w

e

w

etotal

skin

lnln2.141

2.141

504.0

27.9328.0

2980ln

27.9

total

skin

p

p

696.0

85.20328.0

2980ln

85.20

total

skin

p

p

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 5 10 15 20 25

skin

da

magepressuredropasfractionof

totalpressuredrop

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Lecture 5

Pressure Drop in the Near-Wellbore Zone versus in

the Reservoir

ln

ln


Example 6-3 Skin Factor for Concentric Radial

Damage Zones

ln

ln ln lnp f f

p w f p w

r r rk ks

k r k r r


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Lecture 5


Skin Components

pseudopcd sssss

skinEffectivetodueSkinSkin

typermeabiliinchangeactual

damage p.p. &

slant

perfs Rate and phase dependenttotal

PETR 4314 Fall 2015, M. Y. Soliman, PhD, PE, NAI - Lecture

5

Skin Components

Non-Darcy Skin

Dqss

Skin due to evolution of gas or condensate

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Lecture 5


Field Determination of Non-Darcy Skin

Dqss Which test do you use

to get this graph?

Well Completed Openhole in The Top of The Reservoir


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Lecture 5


Skin from Partial Completion and Slant

Papers to read

Cinco, Ramey, and Miller, SPE 5589

Papatzacos, SPERE, SPE 13956, May 1987

Kuchuk and Kirwan, SPE 11676

Besson, SPE 20965


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Lecture 5


Equation for Partial Penetration Skin

h

hh

k

k

z

rr

hhh

)/h/(hB)/h/(hA

B

A

h

h

hrh

s

D

H

v

w

wD

wwD

wDDwDD

wD

wD

wDDwD

p

11

2/1

11

2/1

/

431and41

where

1

1

2

ln1

2

ln11

From Papatzacos, SPERE, SPE 13956, May 1987

h

zw

hw

h1

Calculate skin using this equation



From Papatzacos, SPERE, SPE 13956, May 1987

Effect of vertical permeability

Effect of vertical permeability on skin factor

10

12

14

16

18

20

22

24

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

permeability anistropy, kv/kh

Skin

factor

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Lecture 5


Equation for Partial Penetration Skin(Kuchuk and Kirwan - SPE11676)

8204SPERamey,andGringartenbycomputed

point,pressureaveragetheis

log003745.0log05499.009069.0

cossin12

*

2*

*

1

D

wDwDD

v

h

w

wD

w

w

oD

n

pp

z

hhz

k

k

r

hh

h

hb

Dh

bnKbznbn

nbS


30

25

20

10

15

5

00.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Penetration Ratio; b

P

artialPenetrationSkin;pp

hwD= 50

hwD= 100hwD= 250

hwD= 500

hwD= 1000

hwD= 2500

hwD= 5000

hwD= 10000


(Kuchuk and Kirwan, SPE11676)

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Lecture 5Deviated Well Skin Effect for Isotropic and

Anisotropic Reservoirs (Besson)

= ln 4cos + cos ln 4 cos = ln 1

4 cos + cos ln211

4cos

= 12 co21 12

is angle from vertical



History of perforation

Bullet Guns

Shaped charges

Explosives

Primary detonators

Secondary -

30,000 ft/sec

2-5 million psi

Jet tip is up to 15 million psi

Hydrajetting

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Lecture 5


Perforation Skin Effect

Perforating Gun


The Perforation Process

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Lecture 5


Shaped-Charge Perforator

Explosive

Liner

Case


Events in Perforation Cleanup

Cement

Jet

Crushed Sandstone

Undamaged Sandstone, k

Debris

Crushed Zone, kpd

Berea SandstoneCasing

Conical LinerExplosive

Shaped Charge

Explosion

After

Perforating,

Before Flow

After Flow

A

B

C

D

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Lecture 5


Schematic of Sources of Damage Around Wellbore and Perforation

Cement

Casing

Charge and Core Debris

Pulveration Zone

Grain Fracturing Zone

Compacted

Zone

Undamaged

Permeability k

Wellbore Damaged

Permeability k d


Deep-Penetrating (DP) Charge(1 of 5)

A

Formation

t = 0

Casing

Fluid Gap

Carrier

Conical Liner

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Lecture 5



B

Liner Collapsesto Form Jet

t = 6 x 10-6t = 6 x 10-6 secsec



C

Jet PenetratesCarrier

Later Stages of LinerCollapse Produce

Slower-Moving Slug

t = 9 x 10-6

sec

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Lecture 5



Jet

Slug

t = 1.1 x 10-5

sec

DD



E

Stretching Jet

Penetrates

Formation

t = 2 x 10-5

sec

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Lecture 5


Deep-Penetrating Charges (DP)

Liner geometry isconical; a long, thin, stretching jet is

formed.

Penetration is relatively deep and the hole diameter is small.

Peak collapse pressure at the centerline reaches

approximately29 million psi.

Jet tip velocity can be as high as 26,000 ft/s.

20% of the liner forms the fast-moving jet; the

remaining 80% constitutes a slower-moving slug.


Big-Hole (BH) Charge(1 of 5)

AA

Formation

t = 0

Casing

Fluid Gap

Carrier

Parabolic Liner

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Lecture 5



BB

Liner CollapseLiner Collapse

and Inversionand Inversion

t = 1 x 10t = 1 x 10-5

secsec



CC

Relatively

Slow-Moving Jet

Concentration

of Material

t = 1.5 x 10-5

sec

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Lecture 5



t = 2.3 x 10-5

sec

Jet

Expansion

Slug

Slowly

StretchingJet

D



E

Large Hole

in Casing

Small Holein Carrier

t = 5 x 10-5

sec

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Lecture 5


Big-Hole Charges (BH)

Liner geometry isparabolic or hemispherical; a massive,

slower-moving jet is formed. Penetration is relatively shallow, but a large entrance hole is

created in the casing.

Jet tip velocities are around 13 to 20,000 ft/s.

The jet represents 60 to 80% of the liner mass; the

remaining 20 to 40% constitute the slug.

The annular gap between gun and casing is especially

important for jet development with BH charges, thusgun

centralization isrecommended.


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Lecture 5



Perforations Created using shaped charges

TCP or wireline

Skin factor / well productivity depends on:

Number of perforations

Length and diameter of the perforations

Phase angle (distribution)

Underbalance, overbalance or extreme overbalance

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Lecture 5


Types of Perforation

Underbalanced

Balanced Slightly Overbalanced

Extreme Overbalance Perforation


Underbalanced PerforatingUnderbalanced Perforating

Perforating with the pressure in the wellbore lower

than formation pressure.

At the instant of perforating, the pressure differential

causes fluid to flow, which helps clear the tunnel wall

from crushed rock, debris, and explosive gases.

The amount of underbalance required depends upon

the formation fluid type and reservoir permeability.

Higher underbalance is required in gas wells.

A few hundred psi may be sufficient for high-

permeability formations such as Berea. Optimized underbalance is necessary to avoid formation

collapse or stuck pipe.

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Lecture 5


Formation Permeability vs. Minimum Underbalance (Oil Zone)

Total Underbalance, psi

100

1000

100

10

1

0.1

0.01

1000 10,000

Acid d id not imp rov e pro duc tion

Acid d id i mpr ove p roduc tion

FormationPermeability,md


Formation Permeability vs. Minimum Underbalance (Gas Zone)

100

1000

Total Underbalance, psi

100

10

1

0.1

0.01

1000 10,000

Acid Did Not Im prove Produ ct ionAcid Did Improve Produc tion

Problems

Stuck

Packer

Casing

Collapse

Fo

rmationPermeability,md

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Lecture 5


Extreme Over-Balance

A near-wellbore stimulation technique in whichtubing is pressurized to high overbalance levelsusing compressible gases, usually Nitrogen (over asmall pad of liquid).

Stored energy in gas is released upon the perforatingevent, resulting in a formation fracture.

This methods used to bypass, rather than remove,perforation tunnel damage.

Creates short fractures during the perforation process

Propellant has been also used


Gas and/or Liquid Pumping

Compressed Gas

in Wellbore

TCP Gun

Liquid or Gas over

Perforation Interval

Pay Zone

Damaged Zone

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Lecture 5



Overbalance Pressure vs. Depth

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

1,000 3,000 5,000 7,000 9,000 11,000 13,000 15,000

Depth, ft

OverbalancePressure

Applied,pbh-

pres,psi

OverbalancePressureApplied,pbh

-pres,psi

Excess Overbalance Pressure vs. Depth

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Lecture 5


Applied Wellbore Pressure Gradient vs. Depth

0.5

0.75

1

1.25

1.5

1.75

2

2.25

2.5

1,000 3,000 5,000 7,000 9,000 11,000 13,000 15,000

Depth, ft

AppliedPressureGradient,pbh

/D

,psi/f

AppliedPressureGradient,pbh

/D,psi/ft


Perforation Skin Variables

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Lecture 5

PETR 4314 Fall 2015, M. Y. Soliman, PhD,

PE, NAI - Lecture 5

Effect of Shot Density and Perforation Length on Productivity Ratio

ProductivityRatio

Perforation Length ( in)

1.2

1.1

1.0

0.9

0.8

0.7

0.6

0.5

0 3 6 9 12 15

12-in. Wellbore

Diameter 0.4-in. Perf.

Diameter

No Crushed Zone

No Damaged Zone

No Turbulence

SPF

16

8

4

SPF

16

8

4

90Phasing

0 Phasing

Open Hole


Effect of Perforation Diameters and Length on Production Ratio

ProductivityRatio

Perforation Length ( in)

1.1

1.0

0.9

0.8

0.7

0.6

0.5

0 3 6 9 12 15

4 SPF

No Crushed Zone

No Damaged ZoneNo Turbulence

Perf. Diameter

0.55 in.

0.40 in.

0.15 in.

90Phasing

0Phasing

Perf. Diameter

0.55 in.

0.40 in.

0.15 in.

18

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Lecture 5


Effect of Wellbore Damage on Productivity Ratio

ProductivityRatio

Perforation Depth, inches

0

No PerforationDamage

Shots Per

Foot

8

4

2

1.2

1.0

0.8

0.6

0.4

0.2

0

2 4 6 8 10 12 14 16 18

8 Inch Deep Drilling

kDamage With = 0.2

kdd


Perforation Skin Components

wbVHp ssss

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Lecture 5


Calculation of SH

)(ln

w

wH

r

rs

perf

perf

4

lra

l

r

w

w

for 0

for 0

Usually negative why?


Calculation of SV

V

H

perf

perf

Dk

k

l

hh

H

V

perf

perf

Dk

k

h

rr 1

2

b

D

b

D

a

V rhs110

21 log araa D 21 brbb D

SPFhperf

1

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Lecture 5


Calculation of Swb

wperf

wwD

rl

rr

wDrc

wb ecs2

1


Near Well Damage and Perforations

ss

wwss

perfperf

wperfppppdsperf

sperfp

s

dp

w

s

s

pd

rk

krrr

k

kll

rlssssrl

rlsk

kss

r

r

k

ks

1and1

:andatevaluatediswhere,)(,For

for)(ln1)( 0

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Lecture 5


Discussion Topics

Effect of perforation length and diameter

Effect of SPF

Effect of phasing

Production

Fracturing

Effect of vertical permeability

Effect of centralization

Deep penetration or big hole?

Common Well Completion


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Lecture 5


Horizontal Well Damage


Horizontal Skin Effect

1

3

4

1

1ln1

max,

2

2

max,

w

H

w

H

anis

eqr

a

r

a

Ik

ks

v

hani

k

kI

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Lecture 5


Damaged Permeability

vHkkk

svsHs kkk ,,


Skin Effect and Well Performance Comparison with an

Undamaged Vertical Well

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Lecture 5


Horizontal Well Skin Effect Damage Penetration and

Severity of Damage

Why does it take a

significant damage to

seriously affect HW

performance?


Hydrajetting

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Lecture 5



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Lecture 5


Bernoulli's equation


02 2

sc

f

cc

dWDg

dLuf

g

ududz

g

gdp

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Lecture 5What does Hydrajetting do?

After creating a cavity; jet pump principle is applied

Jet creates a small vacuum pulling fluid into the cavity Applying momentum and mass balance equations one may

calculate the increase in pressure as fluid mix.


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