Intro_Logging.ppt

Conventional Well Log
Interpretation
By
Hayder A. Jumaah

2 Intro to Well Logging Restored
Basic Well Logging Tools
 Lithology Tools
– Spontaneous Potential
– Gamma Ray
 Fluids Identification Tools
– Resistivity
 Laterolog
 Induction
 Petrophysical Tools
– Porosity
 Neutron
 Density
 Sonic
 Auxiliary Tools
– Caliper

Caliper
 The Caliper log is a continuos
measure of the actual borehole
diameter
 Shows the condition of the well over
the footage where other tools are
being run (Washouts, bridges)
 Caliper is also used to calculate the
volume of cement needed behind
the casing
 Open hole log will give Volume of
the wellbore

Spontaneous Potential - SP
 Measures the electrical potential in the formation
caused by the salinity difference between the
drilling mud and the formation water
 Generally an indicator of permeability
 Generally mimics the GR curve

 SP:
– Membrane Potential -
Em
– Liquid Junction Potential
- Ej
 “The SP cannot be
recorded in holes with
nonconductive muds”

 If Rmf > Rw
– Shales will have a low SP
and clean sandstones will
have a higher SP.
 If Rmf < Rw
– Shales will have a high
SP and clean sandstones
will have a lower SP.
 If Rmf = Rw
– Little SP will be
developed and the SP log
will have very little
character.

 Shaliness indicator
– SPshale = -10 mV
– SPsand = -40 mV
– SPlog = SP reading from
the log = -25 mV
– The percentage of shale
will be :
 SPlog - SPshale / SPsand
- SPshale =
– 15/-30 = .5 or 50% shale
 Fresh and saltwater interface
 Correlation

SP Log Response
Shale
Impervious
nonshale
Impervious
nonshale
Reservoir
bed
Reservoir
bed
Shale
SP

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/f
150 50
001) BONANZA 1
10700
10800
10900
SP
Log

Gamma Ray
Gamma Ray Tools detect the naturally
occurring radiation within the rock
Radioactive elements tend to
concentrate in clays and shales
Potassium (K)
Uranium (U)
Thorium (Th)

Gamma Ray
 In sedimentary formations, the
GR log reflects the clay or
shale content
 Clean formations, such as
sandstones or limestones,
usually have a very low level of
radioactivity
 In general, the lower the
Gamma Ray reading, the
cleaner the sand
 Gamma Ray logs can be run in
cased holes, but the data will
be suppressed

Example GR 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/f
150 50
001) BONANZA 1
10700
10800
10900
GR
Log

Resistivity Tools
 Induction Tools
– Run in nonconductive or low-conductivity muds
– Dual Induction - DIL: Is the earlier version of induction tool
which read a Shallow (SFL) and deep measurement
– Phasor Induction - DIT-E: Is an enhanced Induction tool
giving Shallow, Medium, and Deep measurements
– Array Induction - AIT: Is the newer generation of Induction
tools giving 5 curves with set depths of investigation: 10”
(shallow), 20”, 30”, 60”, 90”.
 Laterolog Tools
– Run in highly conductive muds (salt based)
– HRLA

Resistivity
 Resistivity of the salt
water is low (highly
conductive)
Resistivity of the Oil is high
(Poor conductor)

Resistivity
 Dry, nonmetallic minerals (rock matrix) have a very
high resistivity

Resistivity
 The resistivity of a rock is a measurement of the
resistivity of the rock matrix as well as the
resistivity of the fluid within the porous volume of
the rock.

Induction

Borehole
Effects
on
Resistivity
Logs

Resistivity Profiles
 Depth of Investigation:
– Logging tools are designed to
measure resistivity at different depths
radially from the wellbore to
determine the resistivity of the
flushed zone and the virgin zone.
– Flushed zone - is closest to the
wellbore and has been invaded by
drilling fluids (original fluids have
been flushed out).
– Virgin zone - is farthest from the
wellbore and has not been invaded
by drilling fluids. Clients will want to
use Virgin zone measurements

Invasion
 Resistivity profile is the radial
distribution of resisitivity
resulting from the invasion of
fluids having different
conductivity than the formation
fluids.
 Resistivity Profiles can tell a
client about permeability on a
qualitative level.

Laterolog
 Laterolog
Principle:
– Measuring the
voltage difference
between two
electrodes is the
fundamental idea
behind laterolog
devices.

Example Log With Resistivity
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/f
150 50
001) BONANZA 1
10700
10800
10900
Resistivity
Log

Porosity
 Porosity Tools
 Density
 Neutron
 Sonic
 Magnetic Resonance

Density a 1 / Porosity
Density
 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

Bulk Density
Matrix Fluids
  






 f
ma
b 1

Porosity From Density Log
 Porosity equation
 The fluid density equation
 
xo
h
xo
mf
f S
1
S 





f
ma
b
ma









Bulk Density 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/f
150 50
001) BONANZA 1
10700
10800
10900
Bulk Density
Log

Example Solution Density 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
DPHISS
dec
0.45 -0.15
DT
us/f
150 50
001) BONANZA 1
10700
10800
10900
DPHI

Neutron
 Neutron tools emit high energy
neutrons from either a
chemical source or a neutron
generator device (minitron)
and measure the response of
these neutrons as they
interact with the formation

Neutron
 Hydrogen is the most
effective element in the
slowing down (elastic
scattering) process of the
Neutron

Density - Neutron
 GAS EFFECT
– In sedimentary rocks the
presence of gas causes low
readings of porosity for the
neutron tool and causes high
values for the density tool
– This Crossover is called Gas
Effect and is colored in red on
the log
– The actual porosity is
determined by crossplotting
the Density porosity vs. the
Neutron porosity in a chart
book
*Sonic  is not significantly affected by
gas
This is why 2 different porosity tools are run at once

Example Compensated Neutron 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/f
150 50
001) BONANZA 1
10700
10800
10900
Neutron
Log

Sonic
 Sonic Tools are based on
the measurement of the
velocity and amplitudes of
the sonic body waves in
the Rocks
 Applications:
– Mechanical properties :
 Rock strength, Earth
stress
 Rock Mechanical
Properties
 Rock failure
mechanisms
– Formation evaluation
– Cement bond logging

Sonic - Formation Evaluation
 The speed of sound depends
principally upon the rock matrix
material and the porosity.
 The measurement of
compressional and shear wave
slowness can help us estimate:
– Primary porosity
– Lithology
– Presence of natural gas
Gas Effect
in Sonic
Log

Sonic Log
 The response can be written as follows:
  



 f
ma
log t
1
t
t
ma
f
ma
t
t
t
t




log

Sonic 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/f
150 50
001) BONANZA 1
10700
10800
10900
Sonic
Log

Example Solution Sonic Log
GRC
0 150
SPC
MV
-160 40
ACAL
6 16
ILDC
0.2 200
SNC
0.2 200
MLLCF
0.2 200
CNLLC
0.45 -0.15
RHOC
1.95 2.95
DT
us/f
150 50
SPHISS
dec
0.45 -0.15
001) BONANZA 1
10700
10800
10900
SPHI











t
m
w
n
w
R
R
a
S
Formation Water Resistivity

Determining Rw
 Directly
– From measured water sample
– This is the most accurate Rw reading
 Indirectly
– From openhole well logs
 SP logs
 Pickett plots
 Rwa technique

Rw Using the Rwa Technique
t
m
wa R
R 


Mechanical Properties from Logs
 From sonic data the mechanical
properties of the rock can be calculated
giving a continuous stress and
mechanical properties profile, but it
needs to be calibrated with external,
data either from core test or DataFRAC
 Dipole Sonic is an Array tool which
gives Mechanical Properties. Geoquest
will process the data and create a
FracHite log and Mechanical Properties.

Sonic - CBL
 Cement Bond
Logging
– Cement bond logs (CBL)
are used to evaluate the
quality of the cement
that was put in place
during the well
completion process
– An Amplitude gives a
quantitative reading and
the VDL (Variable
Density Log) shows the
quality of the bond

CMR - Combinable Magnetic
Resonance
 CMR Gives information on:
– Grain size and distribution
– Permeability
– Free-fluid porosity
– Bound-fluid porosity
 Helps client determine how much water will
actually flow out of the formation, and how much
is irreducible

CMR
T2 Distribution
MDT Perm
plotted on top
of CMR Perm

FMI
 By wrapping the log we
can envision the wellbore
 Faults and fractures can
be
 traced on the log
 Thin laminations can be
seen in the images

Intro_Logging.ppt

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