12-petrophysics basics [compatibility mode]
TRANSCRIPT
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Applied
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Geology
Chapter 12
Basics of Wireline Logging & Interpretation
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What you will learn
What logging means
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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
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: 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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First well logs recorded in 1927
The recording system
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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
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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
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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
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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
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
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
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
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LWD
TLC
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Geology
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Geology
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Geology
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Geology
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Geology
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Geology
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Why we log ?
• Lithology (reservoir rock?)• Resistivity (HC,water,both?)• Porosity (how much HC?)•
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• Formation mech. properties• Permeability / cap pressure• Shape of the structure
• Geological information• Geothermal• Unconventional applications
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Review of Basic Logging Tools
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• 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
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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)
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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
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10800
10900
Log
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The GR Log
GR is the measurement of the natural radioactivity of the
formation
GR – Gamma Ray
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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
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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
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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
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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
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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
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– 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
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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
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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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GeologyExample of standard CNL - NEUTRON LOG
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
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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
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Applied
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Typical Neutron-Density Response
CNL – Neutron Log
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Note:scale is LIMESTONEcompatible
Applied
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Geology
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
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.
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
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Applied
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BHC – Sonic Log
Sonic Log measures
interval transit time.
The higher the number,the slower the time – and
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formation (sound travelsquicker through moredense materials – porosity will slow it down)
Applied
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Applied
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Geology
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Applied
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Geology
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Applied
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Reservoir
Geology
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Applied
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Reservoir
Geology
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Applied
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Reservoir
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
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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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Reservoir
Geology
Clean (Shale-Free) Formation
Water
Oil
Porosity
( φφφφ )
Matrix
Water / Hydrocarbon
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Matrix
san ,
Limestone,
Dolomite,
Mixture)
Usually Good Permeability
Relatively: High Porosity
Easy to interpret and model
Applied
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Reservoir
GeologyShaly Formation
Oil
Porosity
( φφφφ )
MatrixWater
Shale
Shale
Water / Hydrocarbon
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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
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Reservoir
Geology
Why bother computing Vsh?
I n c r e a s i n
Sw= 25%
50 0hm-m
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V s h
Effect of
Increasing
Vsh on the
measuredResistivity
Sw= 25%
Sw= 25%
AppliedShales and appearance on Logs
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Reservoir
Geology
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.
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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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Reservoir
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.
Shales and appearance on Logs
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Applied
R i Shale Corrections
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Geology
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-
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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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Reservoir
Geology
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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Reservoir
Geology
ShalesShalesShalesShales andandandand appearenceappearenceappearenceappearence on Logson Logson Logson Logs
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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
The Invasion process
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ReservoirGeology
BOREHOLE
Formation
Rxo t i v i t y
The Invasion process
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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
Applied
Reservoir The Invasion process
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ReservoirGeology
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
The Invasion process
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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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ReservoirGeology
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
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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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ReservoirGeology
Identifying Hidrocarbon zones
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Applied
Reservoir Water Sample Analysis
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ReservoirGeology
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
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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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ReservoirGeology
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
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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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ReservoirGeology
Lithology could fall in
one of these categories:
Single Rock Lithology
Lithology
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ng e o ogy +
ShaleTwo or more
Lithologies
Two or more
Lithologies with shale
shale
Applied
Reservoir Cross-plots and their Applications
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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
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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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Geology
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
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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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Geologyp Q
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