Well Testing

Network of Excellence in Training

Dominique Bourdet

Introduction to Well Testing and Interpretation

WCP1 Course

2Network of Excellence in Training

• Introduction

• Well Testing Procedures and Hardware

• Examples of Typical Flow regimes

• Conclusions

Well Testing and InterpretationWell Testing and Interpretation


Description of a Well TestDescription of a Well Test

Time, t

Ra

te,

q

P

ress

ure

, p

t BU

t Dd

p Ddp BU

p i

p(t=0)

drawdown build-up

Drawdown :

Build-up : p p t p t ( ) ( )0

p p p ti ( )


Well Test ObjectivesWell Test Objectives

• EXPLORATION WELL

• APPRAISAL WELL

• DEVELOPMENT WELL



• EXPLORATION

– Nature and rate of produced fluid

– Initial pressure

– Reservoir properties




• permeability

• heterogeneity

• reservoir boundaries

– Well productivity

– Fluid properties (sampling)

• APPRAISAL




• drainage mechanism (permanent gauges)

• communication between wells

– Well productivity

– Average pressure

• DEVELOPMENT


Information obtained from Well TestingInformation obtained from Well Testing

– Reservoir responses• Reservoir in dynamic condition (flow lines are

established)

• Large volume investigated (averaging)

p

– Results

• Permeability (horizontal k and vertical kv)

• Reservoir heterogeneities– natural fractures,

– layering,

– change of characteristics.

• Pressure (initial pi and average )

• Boundaries (distance and shape)

• RESERVOIR DESCRIPTION


Information obtained from Well TestingInformation obtained from Well Testing

• WELL DESCRIPTION– Results

• Production potential

– productivity index PI,

– skin factor S

• Well geometry

10 Network of Excellence in Training

I S O

input system output

Inverse problem : O / I = S

Direct problem : I * S = O

Interpretation MethodologyInterpretation Methodology


Input Data required for Well Test AnalysisInput Data required for Well Test Analysis

• TEST DATA

– Flow rate (sequence of event)

– Bottom hole pressure

• WELL DATA

– Wellbore radius rw and geometry

– Depths (formation, gauges)


Input Data required for Well Test AnalysisInput Data required for Well Test Analysis

• RESERVOIR AND FLUID PARAMETER

– Formation thickness h (net)

– Porosity – Formation volume factor B

– Oil viscosity

– Compressibility of oil co, water cw and formation cf, water saturation Sw

fwwwot cScScc 1


Types of Well TestsTypes of Well Tests

– Drawdown test

– Build-up test

– Injection test / fall-off test

– Interference test and pulse test

– Gas well test

• Flow after flow test,

• Isochronal test,

• Modified isochronal test

• PROCEDURE


Types of Well TestsTypes of Well Tests

• COMPLETION

– Production test

– Drill stem test (DST)


Test Sequence (oil well)Test Sequence (oil well)

– Clean-up period (drilling and completion fluids, no measurement)

– Initial shut-in (pressure gauge at depth, initial pressure pi)

– Variable rate (start of rate measurement)

– Stabilized rate (main flow)

– Shut-in: build-up period

Time, t

Cleanup

Initialshut-in

Variablerate

Stabilizedrate

Build-up

Time, t

Rat

e, q

Pre

ssu

re, p

Cleanup

Initialshut-in

Variablerate

Stabilizedrate

Build-up


Drill Stem TestDrill Stem Test

Flowhead

BOP Stack

Casing

Tubing

Test toolPacker

Flowhead

BOP Stack

Casing

Tubing

Test toolPacker

• ONSHORE TESTING



• OFFSHORE TESTING

Fixed Rig (100 m maximum)

Fixed point at Packer

Fixed Rig (100 m maximum)

Fixed point at Packer



• Cased hole

DST STRINGS

– Open hole packer

– Barefoot

– Zonal Isolation

• Open hole


Surface EquipmentSurface Equipment

• FLOW HEAD: flowing, killing, wireline

• CHOKE MANIFOLD: positive & adjustable

• HEATER: hydrates, high viscosity

• SEPARATOR: metering of three phases

• TANK: oil rate

• BURNER


Surface EquipmentSurface EquipmentSURFACE SETUP

Burner

Burner

Heater

Separator

Surge

tank

Air

compressor

Water

pump

Rig HP

pump

Gas

OilWater

Choke maniflod

Flowhead

Transfer pump

Oil manifold

Gas

manifold


Test SeparatorTest Separator

• RATE MEASUREMENT– Oil and water: positive displacement– Gas: orifice meter

Effluent

Water Oil

Gas

Effluent

Water OilWater Oil

Gas

• THREE PHASES: oil, water and gas


Down Hole EquipmentDown Hole Equipment

• PRESSURE GAUGES: memory or surface read out

• DOWN HOLE VALVE: DST, sampling

• BOTTOM HOLE SAMPLER: PVT analysis

• RFT, MDT: initial pressure, gradient & contacts,

permeability


SafetySafety

• EQUIPMENT: pressure, temperature, sour gas

• PROCEDURE: pressure test, emergency shut-down,

day / night, safe area

• ENVIRONMENT: burning, oil drop out


Wellbore StorageWellbore Storage

rrw

pi

pw



•

Time, t

Rat

e, q

Pre

ssu

re, p

q Surface

q Sand Face

tDd

pDd

tBU

pBU



gV

C u

non-eruptive well:

woVcpV

C

C : wellbore storage coefficient

(Bbl/psi)

with

co : fluid compressibility

Vw : wellbore volume



tC

qBp

24

• Straight line on linear scale (at the beginning of the response)

Elapsed time, t

Pre

ssu

re c

han

ge,

p

Elapsed time, t

Pre

ssu

re c

han

ge,

p


Radial Flow Regime Radial Flow Regime (infinite

homogeneous behavior)

pwf

rw rrip

pi

S = 0

pwf

rw rrip

pi

S = 0


Radial Flow RegimeRadial Flow Regime (infinite homogeneous behavior)

rw r

pwf(S=0)

pwf(S>0)

ri

p skin

p

pi

S > 0

rw r

pwf(S=0)

pwf(S>0)

ri

p skin

p

pi

rw r

pwf(S=0)

pwf(S>0)

ri

p skin

p

pi

S > 0

Pwf(S<0)

p skin

pi

Pwf(S=0)

S < 0



SkinpqB

khS

2.141• SKIN:

• DAMAGED WELL (S > 0): poor contact between the well and the reservoir (mud-cake, insufficient perforation density, partial penetration) or invaded zone

• STIMULATED WELL (S < 0): surface of contact between the well and the reservoir increased (fracture, horizontal well) or stimulated zone



Equivalent wellbore radius: Serr wwe

w

S

w

S

SSwSw r

rkh

qBrr

hkqB

pp ln2.141

ln2.141

0,,

w

S

SSwSw r

rkk

ppqB

khS ln1

2.141 0,,

Radial steady state flow:

rwrs

ks

k



S

rc

kt

khqB

pwt

87.023.3loglog6.162 2

• Semi-log straight line



• RESULTS:

1. the semi-log straight line slope m : the permeability k

mqB

kh

6.162

23.3log151.1 2

hr 1

wtrc

kmp

S

2. the straight line intercept: the skin factor S



- Low

permeability

- High

permeability

0

2000

4000

6000

0 10 20 30 40

time, hours

pre

ssu

re,

psi

no skin

moderate skin

0

2000

4000

6000

0 10 20 30 40

time, hours

pre

ssu

re,

psi high skin

very high skin



- Low

permeability

0

1000

2000

3000

0.001 0.01 0.1 1 10 100

time, hours

pres

sure

cha

nge,

psi

no skin

moderate skin

p skin

- High

permeability

0

1000

2000

3000

0.001 0.01 0.1 1 10 100

time, hours

pres

sure

cha

nge,

psi

high skin

very high skin

p skin


Fractured Well: Linear Flow RegimeFractured Well: Linear Flow Regime

• INFINITE CONDUCTIVITY FRACTURE

xf


Fractured Well: Linear Flow RegimeFractured Well: Linear Flow Regime

tkchx

qBp

tf

06.4

Pre

ssu

re c

han

ge,

p

t

Pre

ssu

re c

han

ge,

p

t

• Straight line with the pressure versus the square root of time


ExampleExample• SEMI-LOG ANALYSIS

0

500

1000

1500

2000

2500

3000

1.00E-03 1.00E-02 1.00E-01 1.00E+00 1.00E+01 1.00E+02

time, hours

pre

ssu

re c

han

ge

, psi

Flow rate : 1000 BOPD

Fluid Volume-Factor : 1.2000 vol/volFluid Viscosity :0.500E+00 CPporosity : 25.0000 %

net thickness : 30.000 FEETwell-bore radius :0.300E+00 FEETTotal Compres:0.185E-04 1/psi

Straight line slope : m = psi/cycleStraight line pressure at 1 hour : Dp(1hr)= psiPermeability thickness : kh = md.ft

Skin factor S =


• SEMI-LOG ANALYSIS

10 -3 10 -2 10 -1 10 0 10 1

3000

.35

00.

4000

.45

00.

5000

.55

00.

Delta-T (hr)

P P

SI

SLOPE

Perm-Thickness = 380. MD-FEET permeability = 12.7 MD skin = 5.69 prod. time=0. hr at rate=1000.000 STB/D R(inv) at 22.63 hr = 356. FEET R(inv) at 1.188 hr = 81.7 FEET slope of the line = -256.673 PSI/cycle

1996/01/01-1000 : OIL

ExampleExample


Closed Reservoir: Pseudo Steady Closed Reservoir: Pseudo Steady State Regime State Regime

rrwpire

pw


Closed Reservoir: Pseudo Steady State RegimeClosed Reservoir: Pseudo Steady State Regime

rrwpi re

pw


rrwpi re

pw

Closed Reservoir: Pseudo Steady Closed Reservoir: Pseudo Steady State Regime State Regime


Time, t

Pre

ssu

re, p

pi

p-

slope m*

pseudo steady state

Closed Reservoir: Pseudo Steady Closed Reservoir: Pseudo Steady State Regime State Regime• Straight line on linear scale


Closed Reservoir: Pseudo Steady State RegimeClosed Reservoir: Pseudo Steady State Regime

– At late time,

SC

r

Akh

qBt

hAcqB

p

A

wt

87.0351.0log

log6.162234.0 2

*234.0

mcqB

hAt

– Result: the reservoir pore volume


Well ResponsesWell Responses

• FLOW REGIMES

– Geometry of the flow lines :

radial, linear, spherical, etc.

– Pressure : (t) =

etc.

ttt 1,,log

– Straight line on a specialized pressure versus time plot.


Well ResponsesWell Responses

• WELL RESPONSES

– Fractured well:

– Well in a channel:

1. Linear

2. Radial

1. Radial

2. Linear


Build-up analysisBuild-up analysis• Semi-log scale: Horner plot

Pre

ssu

re,

psi

a

(tp + t) / t

1 101 102 103 104

3000

3250

3500

3750

4000

slope m

Pre

ssu

re,

psi

a

(tp + t) / t

1 101 102 103 104

3000

3250

3500

3750

4000

slope m


Type Curve analysisType Curve analysis• Log-log Scale

Dimensionless time,tDCD

10-1 1 10 102 103 104

Dim

en

sio

nle

ss

Pre

ss

ure

, p

D

102

10

1

10-1

CDe2SStart of semi-log radial flow


Derivative AnalysisDerivative Analysis

1.0E+00

1.0E+01

1.0E+02

1.0E+03

1.0E-03 1.0E-02 1.0E-01 1.0E+00 1.0E+01 1.0E+02

t, hours

p a

nd

p',

psi

derivative

pressure

• Well with wellbore storage & skin in a homogeneous reservoir


Derivative AnalysisDerivative Analysis

Dim

ensi

onl

ess

pre

ssur

e, p

D

102

10

1

10-1

10-1 1 10 103 104 105

CD e 2S

103

3

1030

1020

1015

1010

106 104

0.3

102

Approximateend ofwellborestorage

DAMAGED

NORMAL

ACIDIZED

104010501060

108

101

103

104

106

108

1010

1015

1020

1030

1040

1050

1060

1030

1020

1015

1010

106

104

102

1060

1040

103

108

103

10.3

CD e 2S

1050

2

10

1

10-1

10-1 1 10 10 103 104 105

Dimensionless time, tD/CD

CD e 2S

103

3

1030

1020

1015

1010

106 104

0.3

102


DAMAGED

NORMAL

ACIDIZED

104010501060

108

101

103

104

106

108

1010

1015

1020

1030

1040

1050

1060

1030

1020

1015

1010

106

104

102

1060

1040

103

108

103

10.3

CD e 2S

1050

10

1

10-1

10-1 1 10 2 103 104 105

CD e 2S

103

3

1030

1020

1015

1010

106 104

0.3

102


DAMAGED

NORMAL

ACIDIZED

104010501060

108

101

103

104

106

108

1010

1015

1020

1030

1040

1050

1060

CD e 2S

103

3

1030

1020

1015

1010

106 104

0.3

102


DAMAGED

NORMAL

ACIDIZED

104010501060

108

101

103

104

106

108

1010

1015

1020

1030

1040

1050

1060

103

104

106

108

1010

1015

1020

1030

1040

1050

1060

1030

1020

1015

1010

106

104

102

1060

1040

103

108

103

10.3

CD e 2S

1050

• Well with wellbore storage & skin in a homogeneous reservoir

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Testing

End of Module

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Well Testing