12-petrophysics basics [compatibility mode]

8/20/2019 12-Petrophysics Basics [Compatibility Mode]

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Geology

Chapter 12

Basics of Wireline Logging & Interpretation

Copyright 2009, NExT, All rights reserved


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Geology

What you will learn

What logging means


Different measurements we makeBasic wireline tools…and what they measure

Simple log analysis


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The Early Years—1912–1927

1912: Conrad conceives the

idea for electrical

measurements


: arce o ns s

brother–first work in

Normandy

1921: Office opens in Paris,

rue Saint–Dominique1927: First electrical

downhole log in

Pechelbronn, France


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Geology

First well logs recorded in 1927

The recording system


The cable winchThe stationary point-

by-point log


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GeologyModern Logging Truck

Modern Surface equipment :

High powered computers

Controls downhole logging

Changes signal configuration to


Includes surface database to

optimise results and for well-to-well

correlations

Used also for forward-modelling

Includes also all the well

configurations- depth, casing,

formations, etc..


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Logging Tools Modern Tools

Sensors used in modern logging:

Electrical

Electromagnetic

Magnetic Flux Induction


coust cUltrasonic

Nuclear: Neutron

Nuclear: γ- Rays

Nuclear: Nuclear Magnetic

Resonance Imaging (MRI)

Every potential signal source have been used in modern-day logging


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16001600

Modern logs have more

measurements but theprinciple is the same

Shading is often added to

Modern Logs


Gamma Ray (GR)

0 (G A P I) 150

S P ( S P )

0 (M V) 200

FXND

50 (P U ) 0

1:220 Ft Pa d

-180 180

Rt f rom HALS

RX18

1 1000

1 1000

Rt from AITH

1 (O HM M ) 1000

Mud Resist ivity from HALS

1 1000

Mud Resist ivity from AITH

1 (O HM M) 1000

AHTPR

5.007.75

12.0118.6228.8544.7269.81

107.43166.51258.08400.00

90 0 90

1700

Gamma Ray (GR)

0 (G A P I) 150

S P ( S P )

0 (M V) 200

FXND

50 (P U ) 0

1:220 Ft Pa d

-180 180

Rt f rom HALS

RX18

1 1000

1 1000

Rt from AITH

1 (O HM M ) 1000


1 1000


1 (O HM M) 1000

AHTPR

5.007.75

12.0118.6228.8544.7269.81

107.43166.51258.08400.00

90 0 90

1700

Gamma Ray (GR)

0 (G A P I) 150

S P ( S P )

0 (M V) 200

FXND

50 (P U ) 0

1:220 Ft Pa d

-180 180

Rt f rom HALS

RX18

1 1000

1 1000

Rt from AITH

1 (O HM M ) 1000


1 1000


1 (O HM M) 1000

AHTPR

5.007.75

12.0118.6228.8544.7269.81

107.43166.51258.08400.00

90 0 90

1700

ma e e og curves eas erto read.

Additional outputs can be

made:

Invasion ProfilesFacies

Layering

L

a y e r i n g

F

a c i e s

I n v

a s i o n P r o f i l e


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Open Hole Measurements :Wireline Logging.

LWD (Logging While Drilling)Logging on Drill Pipe (TLC) Wireline


LWD

TLC


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Why we log ?

• Lithology (reservoir rock?)• Resistivity (HC,water,both?)• Porosity (how much HC?)•


• Formation mech. properties• Permeability / cap pressure• Shape of the structure

• Geological information• Geothermal• Unconventional applications


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Review of Basic Logging Tools


• Spontaneous Potential (SP) and Gamma Ray (GR)• Resistivity• Neutron• Sonic

• Density


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Log Measurements

Type log Direct

Measurement

Indirect

MeasurementSelf-Potential (SP) mV Shaliness

Gamma-Ray (GR) API units Shaliness


Caliper Hole diameter Variouscorrections

Acoustic Travel time Porosity

Density Bulk density Porosity

Neutron Hydrogen index Porosity

Induction/laterolog Resistivity Watersaturation


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• Measures the electrical potential in the formation causedby the salinity difference between the drilling mud and theformation water

• SP is generally an indicator of permeability

Spontaneous Potential (SP)


The SP log measures the electricalpotential in the formation. This is arelative measurement. The deflectionon the SP log is measured from theshale to the sand. The amount ofdeflection that you see between the

shale and the sand is a relative amountof deflection. The log analyst does notread the value of the SP log directlyfrom the log. Rather, it is the differencebetween the shale reading and the sand

reading.


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SP Log

GRC

0 150

SPC

MV-160 40

ACAL

6 16

ILDC

0.2 200

SNC

0.2 200

MLLCF

0.2 200

RHOC

1.95 2.95

CNLLC

0.45 -0.15

DT

us/f150 50

001) BONANZA 1

10700


10800

10900

Log


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The GR Log

GR is the measurement of the natural radioactivity of the

formation

GR – Gamma Ray


In sedimentary formation; this reflects the presence of shaleRadioactive elements tend to concentrate in shales.

Clean (Shale-free) formations usually have low level of

radiation


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Gamma Rays are bursts of

high-energy electromagnetic

waves that are emittedspontaneously by some

radioactive elements. Nearly all

GR – Gamma Ray


Potassium (K)

Thorium (Th)Uranium (U)

e amma a a on

encountered on Earth is emitted

by:


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GR – Gamma Ray



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Resistivity Theory

Current can only passthrough the water in the

formation, hence the

Resistivity


Resistivity of the formation

water (RW )

Amount of water present (Øand SW)

Pore structure (F) This definesthe tortuousity and throat radii

of the current path.


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I n c r e

a s i n g O i l S

Resistivity


Effect ofdecreasing

Sw on the

measured

Resistivity

t u r a t i o n


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GeologyBonanza #2

09/13/2003 3:57:45 PM

DEPTH

FT

1:500

GR(GAPI)0. 150.

SPC1 (MV)-100. 0.

CALI (INCH)6. 16.

ILD(OHMM)0.2 2000.

SN(OHMM)0.2 2000.

MLL (OHMM)0.2 2000.

RHOB (GC3)1.7 2.7

NPHILS (dec)0.6 0.

DT2 (US/F)150. 50.

10700

The Resistivity Log

Resistivity Logs can be of two types:

1. Induction Logs (shown here)2. Laterologs

Both measure resistivity, but use

Copyright 2009, NExT, All rights reserved 25

10800

10900

different physical methods.

Laterologs cannot be used in Oil-Based Muds

Three measurements usually made:1. Shallow (mud filtrate)2. Medium3. Deep (true resistivity)


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Porosity

3 porosity logs - acoustic, density, neutron

• All read the same if:

– litholo known


– shale free – 100% water

• Porosity calculation is complex - must take into accountlithology, shale, and fluid type

• Calibrate with core data - note scale difference

A li d


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The density logging tool measures the

formation density and formation

lithology.

The effects of borehole, mud, poor

-

FDC – Density Log


for digitally.Gamma rays lose their energy when

they collide with electrons (Compton

Scattering)

By measuring the number of gamma

rays and their energy levels at a given

distance from the source, the electron

density of the formation can be

predicted.

A li d


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A li d


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Neutron tools emit high energy neutrons

and measure the response of theseneutrons as they interact with theformation, or in many cases, the fluidswithin the formation.

Neutron Tools: Principles

CNL – Neutron Log


This measured response is affected by the

quantity of neutrons at different energylevels and by the decay rate of theneutron population from one givenenergy level to another.

A neutron interacts with the formation in avariety of ways after leaving the source, itis the aftermath of these interactions thatis detected by the tool.

Applied


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STANDARD DISPLAY OF COMPENSATEDNEUTRON LOG (CNL)

- Basic Quality Control:

Neutron Porosity values should be taken with

care in front of bad hole - washout - values

CNL – Neutron Log


might read too high.

CNL is usually run in combination with LDT.

Zones of poor density readings are usually

identical with poor neutron porosity readings.


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Clean Sand Formation Porosity:Neutron Matrix Correction (Chart)

CNL – Neutron Log


Applied


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Typical Neutron-Density Response

CNL – Neutron Log


Note:scale is LIMESTONEcompatible

Applied


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Basics of sonic tool

The sonic tools create an

acoustic signal and measure how

long it takes to pass through 1’ of

BHC – Sonic Log


.

By simply measuring this time we

get an indication of the formation

properties. The amplitude of the signal will

also give information about the

formation.

Applied


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Wyllie time-average equation

BHC – Sonic Log


Applied


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BHC – Sonic Log

Sonic Log measures

interval transit time.

The higher the number,the slower the time – and


formation (sound travelsquicker through moredense materials – porosity will slow it down)

Applied


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Applied


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Applied


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Applied


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Applied


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Applied


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Geologyshales Shale Distribution in a

reservoir Structural shale : where the shale

grains replace some of the sand

grains. In this case the matrix density

changes but the porosity does not


a er.

Laminar shale : Thin layers of shalein the matrix, replacing both matrix and

porosity. There are hence changes in

matrix density and the porosity.

Dispensed shale : The clay mineral

fills in the intergranular space i.e.. itchanges the porosity leaving the

matrix density untouched.

Applied


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Clean (Shale-Free) Formation

Water

Oil

Porosity

( φφφφ )

Matrix

Water / Hydrocarbon


Matrix

san ,

Limestone,

Dolomite,

Mixture)

Usually Good Permeability

Relatively: High Porosity

Easy to interpret and model

Applied


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GeologyShaly Formation

Oil

Porosity

( φφφφ )

MatrixWater

Shale

Shale

Water / Hydrocarbon


Usually Poor Permeability

Relatively: Lower PorosityDifficult to interpret and model

Shale disguises thin reservoir beds in shale beds

Plays a critical role in producing the reservoir

Matrix

,

Limestone,Dolomite,

Mixture)

Shale

Applied


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Why bother computing Vsh?

I n c r e a s i n

Sw= 25%

50 0hm-m


V s h

Effect of

Increasing

Vsh on the

measuredResistivity

Sw= 25%

Sw= 25%

AppliedShales and appearance on Logs


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Shales and appearance on Logs

Shales have properties that have important influences on logreadings: Shales have porosity- but no appreciable permeability.

The porosity is filled with conductive water.

Shales are often radioactive (Thorium and Potassium).

Resistivity logs show shales as low resistivity zones.


The Gamma Ray reads the high value in the shale (usually). Resistivity logsreact to the water filled porosity of the shale as well as the electrical propertiesof the rock. This gives a low resistivity value for this rock.

Applied

R i Sh l d L


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GeologyNeutron porosity logs exhibit shales as high porosity.

Density and sonic logs react to the porosity and matrix changes (grains).

Gamma ray logs react to shale radioactivity.



Applied

R i Shale Corrections


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Shale Corrections

The electrical properties of shales greatly influence the calculation of fluid

saturations.

A layer of water close to the clay surface is electrically charged.

Archie's equation assumes that the formation water is the only electrically-


conductive material in the formation.

The clay layer requires an additional term in the saturation equation.

Porosity tools can be corrected for the shale effect. An "effective porosity "

Фe

can be computed as compared to a "total porosity " Фtwhich includes

the shale effect.

Applied

R i Shales and appearance on Logs


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GR (zone) - GR (clean)

GR (shale) - GR (clean)

Vsh =

Applied

Reservoir ShalesShalesShalesShales andandandand appearenceappearenceappearenceappearence on Logson Logson Logson Logs


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ShalesShalesShalesShales andandandand appearenceappearenceappearenceappearence on Logson Logson Logson Logs


Applied

Reservoir The Invasion process


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The Invasion process

Progressive invasion

Mudcake is formed from solids in mudThis creates an impermeable barrier

Although Phydraustatic > Pformation little no invasion will take place

Copyright 2009, NExT, All rights reservedProgressive filtrate invasion and mud-cake build-up

Applied

Reservoir



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BOREHOLE

Formation

Rxo t i v i t y



Mud

Borehole mud M u d c a k e

Invaded ZoneFiltrate filled

V i r g i n Z

o n e

T r a n s i t i o n Z o n e

Rt R e

s i

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Rt

Rs

Rm

Mud

hmc Flushedzone Zone of

Adjacent bed

Uninvadedzone

R

Resistivity of zone

Resistivity of the water in the zone

Water saturation in the zone

The invasion processcreates a zone where the

main water is filtrate

This invaded zone also



Rs

Rw

Sw

or

annulus

did j

Adjacent bed

∆r j

dhHole

diameter

h

dh(Bed

thickness)

(Invasion diameters)

Sxo

Rmf

RxoMudcake

has less HC than the

virgin zoneThis fluid displacement is

an indication of fluid

mobility

Applied

Reservoir Determination of Water Saturation


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Archie’s Equation (uninvaded formation)

m is the tortuousity factorcontrolling the passage of current

in the formation. This usually

varies in the range 1.2 to 6.0

Determination of Water Saturation

wn Ra


ome mes an a erm s use .

This is done indirectly to accountfor the variation in mn is the saturation exponent: thisis a function of Wettability (high

for oil-wet, lower for water-wet)Usually m = n = 2 is used

φφφφ tm R

Sw = Water SaturationRt = Formation Water Resistivity

o = Porosity

Applied

Reservoir Identifying Hidrocarbon zones


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Identifying Hidrocarbon zones


Applied

Reservoir Water Sample Analysis


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The water’s ability to conduct electricity is afunction two major factors:

Water SalinitySalinitySalinitySalinity

As salinity increases, more ions are

V

Formation

water or filtrate

Water Sample Analysis


available to conduct electricity so Rw

(water resistivity) decreases. Theresistivity, and hence the salinity, can be

measured at the surface if a water sample

is available.

Water TemperatureTemperatureTemperatureTemperatureAs water temperature is raised, ionic

mobility increases and resistivity

decreases.

I

Applied

Reservoir

Log Rt vs Log Porosity CrossPlot


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Rt

1

10

φ2Rt = . Sw2

Rw

Rt =Rw

Log Rt vs. Log Porosity Crossplot 5- Rw from Cross-plots

HC Direction

Log Rt vs Log Porosity CrossPlot


φ φφ φ

1 10 100

0.01

0.1

φm

Log Rt = Log Rw - m log φφφφ

A cross-plot of the above

equation, on a log-log scale willgive the following:

A slope= m

An intercept on the Rt axis is

equal to Rw (for100% porosity)

Rw= 0.021

Best fit lineIn the South-WestDirection

Applied

Reservoir Lithology


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Lithology could fall in

one of these categories:

Single Rock Lithology

Lithology


ng e o ogy +

ShaleTwo or more

Lithologies

Two or more

Lithologies with shale

shale

Applied

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Geology

This is a classical example

of using z-axis plot

The z-axis here is the

Cross plots and their Applications


amma ay, w c s an

indicator of shaliness.

Higher red-colour intensity

signifies a higher value of

GR on the z-axis, which inturn, indicates an increase in

the volume of shale (Vsh).

Applied

Reservoir Density-Neutron Cross Plot


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A Density-Neutron cross-plot in

a carbonate reservoir. The

matrix is a Ls-Dol mixture.

This example explains how to

com ute the orosit and then

Density Neutron Cross Plot


the lithology for every log point.

1. Draw equal porosity lines

between SST-LST-DOL

lines

2. Plot points3. Estimate for red points –

porosity and lithology %

Porosity= 24 pu

Lithology:Vdol= 80%

Vlim= 20%

Porosity= 17 puLithology:

Vdol= 30%

Vlim= 70%

Applied

Reservoir Steps to achieve a Quick evaluation


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