4. According to
4th Edition of J.A.Jackson’s Glossary of Geology:
Log : A continuous record as a function of depth,
usually graphic and plotted to scale on a narrow
paper strip, of observations made on the rocks
and fluids of the geologic section exposed in
the well-bore.
DefinitionDefinition
16. Resistivity is the key to hydrocarbon saturation determination
Resistivity ApplicationResistivity Application
Water Saturation Estimation
Archie’s Equation
Sw =
F * Rw
Rt
SW - Water saturation
Rw - Formation water resistivity
Rt - True Formation resistivity
( )
1/n
where F =
1.0
Por
m
Sh = 1 - Sw
Resistivity is also used for well to well correlation, and to pick fluid contacts
F - Formation factor
n - Saturation exponent
m - Cementation factor
19. Spontaneous Potential (SP)Spontaneous Potential (SP)
20
40 mV
7470
7430
Given:
Rmf = 0.51 at 135 F
Rm = 0.91 at 135 F
TD = 8007 ft
Bottom hole temp.= 135 F
Surface temp. = 60 F
Determine Rw ?
SP
Limitation
SP is not reliable when you have no or very small contrast
Between Formation water salinity and mud filtrate salinity resulting in no
to small SP deflection
20. Rw calculation from SP logRw calculation from SP log
SSP = -K log
Rmfe
Rwe
Steps of Calculation;
- Determine Temperature at Depth of interval
- Correct Rm and Rmf to this temperature (gen-9)
- Determine SP (log) from shale baseline
- Correct SP to SSP using SP thickness corr. chart
- Determine Rmf/Rwe ratio using SP-1 chart
- Determine Rwe from above equation or SP-1 chart
- Correct Rwe to Rw using SP-2 chart
26. Natural Gamma Ray Log (NGT)Natural Gamma Ray Log (NGT)
• NGT tool measures the spectrum of
Potasium,Uranium, and Thorium
• NGT log is used for;
- Study of Depositional Environments
- Geochemical logging
- Shale typing
- Source Rocks
- Diagenetic History
- Vclay content correction
• With combination of Photoelectric curve can be
used for clay and mica type identification
30. Density LogDensity Log
Main categories in the process of GR energy loss due to
collisions with other atomic particles:
Compton Scattering is selected to be the energy level to
generate GR of the Cesium 137 radioactive source at 662 keV
43. Special ToolsSpecial Tools
• Resistivity Based Imaging Tool
- Pad device on 4 to 6 arm caliper, few mm resolution
- Application: Thin bed Evaluation, Dip meter,
Paleostream direction, fracture evaluation, stratigraphy.
• Nuclear Magnetic Resonance
- Using Permanent magnet to realign hydrogen protons to new
magnetic field, a Lithology dependance porosity, saturartion
and permeability estimation
• Dipole Shear Sonic
- Shear measurement, AVO and Rock mechanics applications
• Borehole sonic imaging
- Acustic based bore hole imaging for 360 deg coverage, lower
resolution than resistivity based imaging tools.
44. Special ToolsSpecial Tools continued
• Modular Formation Test
- Very robust formation tester with the capability to take
unlimited pressure tests, pump the fluid into the borehole,
identify the fluid type before sampling
• Wellbore Seismic
- VSP: Vertical seismic profile surface guns, wellbore detectors
- SAT: Seismic acquisition tool
- WST: Well seismic tool
- DSA: Downhole seismic array tool (3 axis geophones)
46. Log and Seismic Tie EffortLog and Seismic Tie Effort
• Log Data Validation
‐ Check the log quality
‐ See if there is any missing log data
‐ Determine whether sonic peaks/anomalies representing formation
• Log editing
• Velocity Correction Sonic over VSP (using 4‐2 msec resolution)
• Synthetic Seismic Generation
‐ Acoustic Impedance
‐ Convolution Wavelet to tie seismic and log peaks
* Extracted Wavelet ‐ to utilize wavelet as seen in the seismic
it is highly recommended (similar apperance)
* Rickr Wavelet ‐ commonly used to have zero phase
57. • Porosity
• Water Saturation
• Permeability
Fluid types
• Fluid contacts
• Lithology
• Dip angle
• Velocity
Basic Log InterpretationBasic Log Interpretation Continued
Typical properties implied or estimated from
the log Measurements:
58. Porosity =
Volume of pores
Total Volume of Rock
Porosity is estimated using one or combination of
the followings; - Density
- Neutron
- Sonic
Combination of three inputs will get better estimate
Porosity = “Storage Capacity”
POR = (DENmatrix – DENlog)/(DENmatrix – DENfluid)
Density Porosity:
Petrophysical PropertiesPetrophysical Properties
59. SW =
Formation Water in the pores
Total pore space in the rock
Water Saturation is estimated using combination of
the followings; - Porosity
- Resistivity
It requires formation factor and saturation index
derived from core analysis, and formation water resistivity
Petrophysical PropertiesPetrophysical Properties
Archie’s Equation
Sw =
1/Por * Rw
Rt
SW - Water saturation
Rw - Formation water resistivity
Rt - True Formation resistivity
( )
1/n
n - Saturation exponent
m - Cementation factor
m
60. Permeability Estimation from Logs
K=
93 * Por
Swi
Permeability (K) is a measure of rock property to get the fluid passes through the rock.
The equations are based on empirical study, accurate K estimation can be obtained from
formation test, drillstem test (DST) or from core analysis
( )2.2 2
K=
250 * Por
Swi
( )3 2
Timur’s
Tixier’s
where Swi = Irreducible water saturation
Petrophysical PropertiesPetrophysical Properties
64. RES
0.1 100
Fluid and Lithology Identification From the LogsFluid and Lithology Identification From the Logs
Oil-Water Contact
Gas-Oil Contact
Water filled Sand
Water filled Sand
Water filled Sand
Oil Sand
Gas Sand
Coal
Carbonate/Limestone
65. How Can We Remember These Easily?How Can We Remember These Easily?
About Lithology Interpretation
• Claystone ‐ has large amount of water, and radioactive materials, is denser when it has
less water, is not harder than limestone and is very conductive.
• Sandstone‐ is less dense than limestone, has less water than clay, contain more water
than limestone except when it is saturated with dry gas, its conductivity is depending on
fluid type it contains, has small to none radioactive fragments.
• Limestone ‐ is harder than both clay and sand, contains least water of the three, very
resistive, it has low radioactivity materials, fast velocity, high density.
• Coal ‐ Normaly low radioactive, rarely radioactive, lowest density and very resistive
66. How Can We Remember These Easily?How Can We Remember These Easily?
About Fluid Interpretation
• High Radioactivity ‐ High GR
• Very Conductive ‐ Low Resistivity
• High Water ‐ High Neutron and Low Resistivity
• High Gas ‐ Low Neutron and High Resistivity
• High Oil ‐ Higher Neutron than Gas, denser
than gas Less Neutron than water,
less dense than water, more
resistive than water, less‐
resistive than gas when other
properties are the same
• Dry Gas ‐ Very resistive, largest density
neutron crossover
• High GOR ‐ Larger density‐neutron crossover
than oil with low GOR
• Fresh Water ‐ Reservoir filled with high resistive water
68. How Is Log Analysis Calibrated?How Is Log Analysis Calibrated?
• Core Data
Routie Core Analysis - For Porosity and Permeability Calibration
Special Core Analysis - For detailed rock and fluid properties such as
X Ray Diffraction, Scanning Electron Microscopy, Petrophysical
parameters (a,m and n determination), PVT, Gas Analysis and finger
prints of fluid samples, and etc.
• Formation Test
Fluid Identification from the logs is not direct, when the parameters are
not well established, formation test fluid samples can be used to
calibrate fluid identification using the logs. Formation test is also used
when possible log response anomalies encountered to get conclusive
fluid identification.
69. Modern Formation For Fluid IdentificationModern Formation For Fluid Identification
Single Probe Module
Hydraulic Power ModuleHydraulic Power Module
Electric Power Module
Fluid Description ModuleFluid Description Module
MDT String Configuration
Multi sample ChambersMulti sample Chambers
Test ProbeTest Probe
Large sample ChamberLarge sample Chamber
73. OFA Spectrometer
How Can We Differenciate Fluid Types ?How Can We Differenciate Fluid Types ?
Diesel
Fuel
Oil
Mud
Filtrate
Crude Oil A
Crude Oil B
Water
Visible Near infra-red
0.0
4.0
OpticalDensity
500 1000 1500 2000
Wave Length - (NM)
82. Depth of Investigation and ResolutionDepth of Investigation and Resolution
of Logging Toolsof Logging Tools
0 cm50 cm100 cm150 cm200 cm250 cm
2 cm
5 cm
60 cm
20 cm
30 cm
40 cm
80 cm
80 cm
Dipmeter
Micro resistivity
Micro log
Sonic
Density
Gamma-ray
Neutron
Laterolog
Induction
log
Resistivity
Radioactivity
Acoustic
Resistivity
Depth of Investigation
Resolution
83. AIT SDT LDT CNT SGT LEH TCC AMS
Additional combinable tools:
- Dipmeter
- Magnetic Resonance
- Borehole Imager
- Dipole Sonic
- Formation Tester
- Others
Tools Size and Measuring point for TypicalTools Size and Measuring point for Typical
Oil Based Mud EnvironmentOil Based Mud EnvironmentInduction
Sonic
Density
Neutron
GR
Measuring point from
the bottom of the tool
Tool Length
This slide helps you to configure the tool string that is appropriate for your well
88. SP Log LimitationsSP Log Limitations
The tool is only for water based borehole environment
SP is not reliable when you have no or very small contrast
between Formation water salinity and mud filtrate salinity resulting in no
to small SP deflection
GR Log LimitationsGR Log Limitations
Standard GR tool is not reliable when you log an interval with radioactive
mineral rich rocks. NGT is recommended to use for this type of
Formation to get reliable GR derived clay volume calculation.
GR measurements in cased hole environment need to be normalized
due to casing, and cement attenuation
Density Log LimitationsDensity Log Limitations
Density log is a pad device, it is very sensitive to the pad contact with
The borehole wall, make sure to consult with your petrophysicist prior to
using the data for any other applications.
89. Neutron Log LimitationsNeutron Log Limitations
Neutron log is very sensitive to environment change; bore hole size,
mud cake, mud weight, temperature, stand-off, invasion, pressure and
formation salinity, measurement is compensation of far and near count
rates.
Sonic Log LimitationsSonic Log Limitations
Sonic log is likely affected by strong attenuation when we log
unconsolidated formation, fractured formation, gas saturated reservoirs,
aerated muds, rugose and enlarged borehole sections. Typically shows
some curve skippings.
Formation Test Log LimitationsFormation Test Log Limitations
Formation test problems normally occur when you don not have a good
Rubber pad seal, causing a communication with the mud giving you much
Higher pressure reading. Depleted and highly invaded zone would cause
long fluid pumping before you get clean sample or fluid identification