An Introduction to Well Logging
Pardeep Kumar
DGM(Geophy-Wells)
Prog. No.:GT-Batch,ONGC,Academy
Dec. 17th, 2014
INTEG, GEOPIC
ONGC, DEHRADUN
SOURCES OF INFORMATION IN SUBSURFACE
Field Geological Survey: Exposures of Sedimentary rocks.
Surface Geophysical Survey:
Seismic(2D,3D,4D) @ Non-Seismic(Gravity, Magnetic, sea bed logging )
Mud Logging - Hydrocarbon shows during drilling, ROP , Gas Counts
Cores & Cuttings - SWC/CC
Geological :
Megascopic Study, Thin Sections, XRD, SEM, XRF, EDX
Reservoir :
Porosity, Permeability, wettability, Bulk/Grain density,
Swirr, Electrical Petrophysical parameters.
Borehole Geophysical Survey : Well Logs, Well seismic (VSP)
Well tests : RFT/MDT, DST, Conventional Test
WELL LOGGING TECHNOLOGY
Logging - “ Eye ” of E&P
Industry.
Well Log - Record of
Physical
properties
measured with respect to
depth.
Well Logging involves• Data Acquisition
• Data Processing
• Interpretation of Results
WELL Logging set up at drill site
FEATURES OF WELL LOGGING
INDUSTRY
 High Tech Industry
 Capital Intensive
 Rapid Technological
Obsolescence.
 Globally dominated by
only 2 or 3 MNC players
 India among the select
few countries with inhouse
logging
5 capabilities
LOGGING EQUIPMENT
• SURFACE EQUIPMENT
(LOGGING UNIT)
Truck/Offshore Skid
• DOWN HOLE TOOLS –
SOPHISTICATED
SENSORS &
ELECTRONICS
• ELECTRO-MECHANICAL
CABLE
Tool Conveyance
Open - Cased Hole
Measurements :
• The Traditional Wire-line Logging.
• LWD (Logging While Drilling)
• Logging on Drill Pipe (TLC)
• TRACTOR
Real time Monitoring
Importance of well logging
Usefulness of Well Logging
Well
Birth of Logging
September
5th,
1927
when
H.
Doll
and
Schlumberger brothers,
Conard & Marcel made
semi
continuous
resistivity measurement
in 1600 ft deep France`s
Pechelbronn field
First Log Recorded in Petroleum Industry
Semi-continuous resistivity measurement
at discrete depth points by H.D. Doll, in
in 1600 ft deep well in Pechelbronn field of
France
Logging was thought to be replacement for
Coring and therefore was known as
Electrical Coring.
Later on well Logging became a popular
and most Useful technique for formation
evaluation
History of Well Logging Technology
Cont…
History of Well Logging Technology
WELL LOGGING SERVICES IN ONGC
 Departmental
services cater to
95% of the data acquisition in onshore areas.
 Conform to International Quality
Standards.
 In
house
Processing
&
Interpretation
 Cost effective vis-à-vis Contract
14
services
ECONOMICS OF
DEPT. LOGGING SERVICES
 Cost of Logging Equipment
•
•
•
•
15
OHU & Tools
CH/PLU & tools
Expected Life
Pay Back Period
:Rs. 25 – 30 Crores
:Rs. 15 - 16 Crores
:8 - 10 Years
< 3 Yrs.
Well Logging set up in ONGC
Logging Bases
Nazira, Jorhat, Agartala, Rajahmundry,
Karaikal, Ahmedabad, Ankleshwar,
Mehsana, Kolkata, Mumbai
Logging Institute
Centre for Excellence in Well Log
Technology, Vadodara
MAP
Material Planning & Acquisition, Logging
Services
Logging Manpower also available in
Institutes
• Keshva Deva Malviya Institute of Petroleum Exploration,
Dehradun
• Geo Data Processing & Interpretation Centre, Dehradun
• Institute of Reservoir Studies, Ahmedabad
Assets
MH Asset, N&H Asset, B&S Asset, Ahmedabad Asset,
Mehsana Asset, Ankleshwar Asset, Assam Asset, Tripura
Asset, Rajahmundry and Cauvery Asset
Basins
Western Offshore, Western Onshore, A&AA Basin, Cauvery
and KG Basin, Frontier Basin, MBA Basin
Others
E&D Directorate, Dehradun, CEC, ONGCA, D(E) office, Nhava
Material Acquisition & Planning
Centralized procurement for:
Logging Units
Logging Tools
Equipment, Logging cables
Perforation Material
Hiring of Contractual Services
Wireline Services
LWD Services
Mud Logging Services
LWD Contractual Services
Resistivity-GR : ARC resistivity, Geo-vision & GR
Porosity
: Neutron & Density with Imaging
EcoScope
: Resistivity-GR & Neutron-Density
StethoScope
: Formation Pressure while Drilling
PeriScope
: Bed Boundary Detection
Wireline Open Hole Services
Service
Departmental
Contractual
Resistivity
DLL, HDIL, HRI, DFL, MSFL, DLL, AIT, HRI, HRLA,
MSFL
MLL
Porosity
SDLT, DSNT, BCDT, DAL
LDL, CNL, BCS, DSI,DAL
Dipmeter
FED, SED, STAR
FMI, SED, STAR, XRMI
Formation
Tester
SFT, SFTT, RCI
MDT, XPT, SFTT, RCI
Coring
SWC
CST, MSCT
Other Tools
GR, NGRT,FIAC
GR, NGS, CALI,CMR, ECS
Cased Hole Services
Service
Departmental
Contractual
Cement Evaluation
CBL-VDL, CAST
CBL-VDL, CAST, USIT,
SCMT
Depth Correlation
N-GR-CCL
N-GR-CCL
Perforation
Gun Perforation, TTP
Gun Perforation, TTP, TCP
Back-Off Services
FPIT- String Shot
FPIT- String Shot
Cutters
Tubing/ Casing/ Split
Cutters
Tubing/ Casing Cutters,
Colloidal
Bridge Plug Setting
BP/ CR
BP/ CR/ MPBT
Analysis Behind
Casing
CHFR/ CHFD/ CHFP/ RST
LOG OF WELL – CAMBAY-1 Date 01.11.1958
Unit -Russian OKC-56
TYPES OF LOGGING
Depending upon the condition of bore hole, logging
operations are classified as;
Open Hole Logging : Reservoir Identification
& Evaluation ( Reservoir Characterisation
/Formation Evaluation)
Cased Hole Logging : Well Completion, Well
Integrity.
Production Logging : Production Problems
& Reservoir Monitoring
ROLE OF OPEN HOLE LOGGING
• Among the whole set of geo scientific data the
log data is most precise, depth controlled,
well resolved and most representative of the
in-situ reservoir condition.
• Well log data plays an important role in
decision making for casing lowering, initial
testing of prospective zones, hydrocarbon
reserve estimation and future reservoir
monitoring.
Contd.
ROLE OF OPEN HOLE LOGGING
Helps Assest and Basin managers for regular prospect
evaluation for making investment decisions and
regularly updating the remaining reserves and accretion
 Helps geologists to correlate different sedimentary
sequences across the field, deduce the depositional
environment, stratigraphic and structural features of
the subsurface formation to firm up a geological model.
ROLE OF OPEN HOLE LOGGING
Helps drillers to identify the zones of lost
circulation, know the free point of a stuck pipe and
to calculate the amount of cement required for
efficient primary cementation job.
Knowledge of fracture pressure gradient, stress
anisotropy for break out analysis, mud weight
optimisation.
WELL LOG IS HOROSCOPE OF WELL
IT IS USED SINCE DRILLING TO
ABANDONMENT OF THE WELL.
Wireline Open Hole Services
SERVICE
RESISTIVITY
FORMATION
DENSITY
LOGGING TOOLS
DLL, HRLA, MSFL, MCFL, MLL, DFL,
DIL, AIT, HDIL, HRI, HRAI, RTEx, RTScanner, 3DEx
LDL, SDLT,
NEUTRON
POROSITY
CNL DSNT
SONIC
BCS, BCDT, DAL
FORMATION
TESTER
MDT, XPT, SFT , SFTT, RDT,RCI
SIDE WALL
CORING
SWC CST, MSCT
GEOMETRICAL RESPONSE PARAMETERS OF LOGGING TOOLS
Subsurface Lithology & Bore hole Environment
Different Saturation States of Formation around Bore hole
Role of Cased Hole Services
• CEMENT EVALUATION : TO ASSESS SEALING BEHIND
CASING AND ISOLATION OF ZONES.
• PERFORATION : MEANS TO ESTABLISH COMMUNICATION
BETWEEN FORMATION AND BOREHOLE
 CRITICAL FOR IMPROVING PRODUCTIVITY, RECOVERY
FACTOR, SAND CONTROL AND REDUCE TIME FOR
ACTIVATION.
• PLUG SETTING : ISOLATION OF ZONES.
• CUTTER : HELPS RETRIEVE TUBINGS / CASING/ DRILL
PIPE ETC. SALVAGE OPERATION SAVES WASTEFUL
EXPENDITURE.
• BACK OFF SERVICES : HELPFUL IN LIQUIDATING STUCK
UPS.
Cased Hole Services
SERVICE
LOGGING TOOLS
CEMENT EVALUATION
CBL-VDL, CAST, USIT, SCMT
DEPTH CORRELATION
N-GR-CCL
PERFORATION
GUN PERFORATION, TTP, TCP
BACK-OFF SERVICES
FPIT- STRING SHOT
CUTTERS
TUBING/ CASING CUTTERS,
COLLOIDAL
BRIDGE PLUG SETTING
BP/ CR/ MPBT
Role of Production Logging
HOW MUCH OF WHAT IS COMING FROM WHERE ???
HOW MUCH IS GOING WHERE ???
• Analyse problems of sick wells &
suggest remedial measures in aged &
depleted fields.
• Can be done under dynamic conditions
without loss of production Deployment
of rigs not essential
• Monitor profile of flowing wells &
injection wells for better reservoir
management.
• Should be done at the start of
production life of a well , which will act
as a base log for future analysis.
Production Logging Services
1
TEMPERATURE
2
FLUID DENSITY
3
FLOW METER: SPINNERS
4
PRESSURE: STRAIN GAUGE/ QUARTZ
GAUGE
5
HOLD UP: GAS / WATER
6
CASING INSPECTION: MULTI ARM
CALIPER
Schematic Diagram of Completed Well
Casing
Tubing
Packer
Tubing Shoe
Perforations
Gas Zone
Gas Zone
Oil Zone-1
Oil Zone-1
Shale
Shale
Oil Zone-2
Oil Zone-2
Water Zone
Water Zone
PLUG
Grease Injection Schematic
Pack Off
Assembly
Grease Seal
Flow Line
Grease Line
Riser Pipe
Grease Drum
Wire Line BOP
ROLE OF CASED HOLE / PRODUCTION LOGGING
Helps surface and subsurface managers to diagnose
well/reservoir problems such as movement of oil water
contacts, gas water contacts, development of secondary gas
cap, water coning, gas cusping, water fingering, preferential
break through of injected water, water /polymer injection
profiling, casing leakage, channeling behind casing, cement
quality for optimal recovery and efficient reservoir
management.
TYPICAL LOG PRESENTATION
TYPICAL LOG PRESENTATION
TYPICAL LOG PRESENTATION
Detection and location of reservoirs from well logs
Hydrocarbon
Reservoir-rock
Seal-rock
and/or
source-rock
Hydrocarbon
Hydrocarbon
Hydrocarbon
Detection and location of reservoirs from well logs
ELAN Processed Results along with Log Data
IDENTIFICATION OF OWC & GOC
Shale
Shaly/sand G.B.
Shale
GOC
OWC
Shale
Tools Nomenclature
DLL
Dual Latero Log
HRI
High Resolution Induction Log
HDIL
High Resolution Dual Induction log
AIT
Array Induction Tool
HRLA
High resolution Lateral Array Resistivity
MSFL
Micro Spherical Focused Resistivity Log
MLL
Micro Latero Log
LDL
Litho Density Log
SDLT
Spectral Density Litho Tool
CNL
Compensated Neutron Log
DSNT
Dual Spaced Neutron Tool
BCS
Borehole Compensated Sonic
BCDT
Borehole Compensated Sonic Tool (DITS)
DAL
Digital Acoustic Log
Tools Nomenclature
DSI
Dipole Shear Sonic Imager
FED
Four Arm Electrode Dipmeter
SED
Six Arm Electrode Dipmeter
FMI
Formation Micro Imager
STAR
Simultaneous Acoustic & Resistivity Imager
XRMI
Extended Reach Micro Imager
XMAC
Cross Multi Pole Acoustic Tool
SFT
Selective Formation Tester
MDT
Modular Dynamic Tester
MDT-LFA
Modular Dynamic Tester-Live Fluid Analyzer
MDT-CFA
Modular Dynamic Tester-Chromatographic Fluid Analyzer
XPT
Extreme Pressure Express
RCI
Reservoir Characterization Tool
RDT
Reservoir Description Tool
Tools Nomenclature
SWC
Side Wall Coring
CST
Sequential Core Sampler Tool
MSCT
Motorized Sidewall Coring Tool
GR
Gamma Ray
NGS
Natural Gamma Ray Spectral
CMR
Combinable Magnetic Resonance
MRIL
Magnetic Resonance Imaging Log
ECS
Elemental Capture Spectroscopy
CALI
Caliper
PEX
Platform Express
CBL-VDL
Cement Bond Log – Variable Density Log
USIT
Ultra Sonic Imaging Tool
SCMT
Slim hole Cement Mapping Tool
CAST
Circumferential Acoustic Scanning Tool
RST
Reservoir Saturation Tool
Tools Nomenclature
CHFR
Cased Hole Formation Resistivity
CHFD
Cased Hole Formation Density
CHFP
Cased Hole Formation Porosity
FPIT
Free Pint Indicator Tool
BP / CR
Bridge Plug / Cement Retainer
TCP
Tubing Conveyed Perforation
TTP
Through Tubing Perforation
TLC
Tough Logging Conditions
LWD
Logging While Drilling
MPBT
Mechanical Plug Back Setting Tool
VSP
Vertical Seismic Profiling
CPLT
Compact Product Logging Tool
Max Track
Tractor Conveyance
FSI
Flow Scan Imager
Tools Nomenclature
3DRI
3D Resistivity Imager / RT Scanner
TWSS
Multi level Tri-axial Well Seismic Service
PSP
Production Service Platform
WSTPL
Well Shuttle Services
FPWD
Formation Pressure While Drilling (StethoScope)
DBBI
Directional Bed Boundary Imaging Tool (PeriScope)
ELAN PROCESSING RESULTS ALONGWITH
OPEN HOLE LOGS & OVERLAYS
ESTIMATION OF RESERVES
For oil, the number of barrels in Place is given by
N=7758 × ø (1-Sw) × h × A
where ø is the porosity, Sw is water saturation, h is the
pay thickness in feet and A is the areal extent in acres.
For gas, the number of cubic feet in situ is given byG=43560 × ø (1-Sw) × h × A
SPONTANEOUS POTENTIAL
(SP LOG)
SPONTANEOUS POTENTIAL LOG
Simplest Log from Recording Point of View But Very Useful from
application point of view.
SP is naturally occurring electrical potentials opposite each lithological
unit penetrated in a well bore with respect to local potential of earth surface.
Measured potential between a movable electrode & a fixed surface electrode
SP is generally recorded along with resistivity by including a ring type electrode
in the resistivity tool body or a cylindrical electrode in the cable armour and
presented in first track
SP is generated due to electrochemical and electro kinetic phenomenon
Membrane potential, Liquid junction potential and Electro-kinetic potential
REQUIREMENTS FOR OCCURRENCE OF SP
•ELECTRICALLY CONDUCTIVE BOREHOLE FLUID
(BRINE, WATER BASED MUD)
•A SANDWICH OF A POROUS AND PERMEABLE BED
BETWEEN LOW POROSITY AND IMPERMEABLE FORMATIONS.
(SAND SHALE SEQUENCE)
•SALINITY CONTRAST BETWEEN THE BOREHOLE FLUID AND
THE FORMATION WATE
•PRESSURE DIFFERENTIAL BETWEEN BOREHOLE AND
FORMATION ( NOT ESSENTIAL IF SALINITY CONTRAST EXISTS)
SPONTANEOUS POTENTIAL
STATIC SP (SSP)
Electro-kinetic Potential
The electro-kinetic potential also known as streaming or filtration potential
is caused by filtration of mud through the mud cake, shale and sometimes
low permeability reservoir sections. This potential is generally regarded as
very small and is neglected in practice. Potential developed across shale and
mud cake is considered to cancel each other.
EK =  D ΔP Rmf,
4
Where, , D, P, Rmf &  are Zeta potential of rock surface in relation to
saturating brine, dielectric constant of mud filtrate, pressure differential,
resistivity and viscosity of the mud filtrate respectively.
This potential is denoted by EH also as the relation was given by Helmholtz.
As , D, Rmf and  depends upon the salinity of the mud filtrate and nature
of ions , EK strongly depends upon the chemistry of invading solution.
IDEALISED AND REAL SP LOG EXAMPLES
FIELD EXAMPLES
NaCl Mud, Rmf>Rw
KCl Mud, Rmf<Rw
PSEUDO STATIC SP (PSP)
SP DEFLECTION (AMPLITUDE)
AGAINST SHALY SANDS MEASURED
FROM SHALE BASELINE .
PRESENCE OF SHALES REDUCE SP
AMPLITUDE.
THIS FACT IS USED TO COMPUTE
VOLUME OF SHALE IN A SHALY
SAND
VSH = 1- PSP/SSP
OR
VSH= (SPSh – SPZone)/ (SPSh-SP Sd)
Applications of SP Log
Identification porous permeable reservoir zones
Define bed boundaries
Well to well correlation
Information about depositional environment
Determination of formation water resistivity
Estimation of shale content in a shaly reservoir.
Identification of hydrocarbon zones
Computation of realistic water saturation in LRLC reservoirs
NATURAL GAMMA RAY LOG
NATURAL GAMMA RAY LOG
GR IS MEASUREMENT OF NATURAL RADIOACTIVITY
OF THE FORMATION
RADIOACTIVE ELEMENTS TEND TO CONCENTRATE IN
SHALES.
– POTASSIUM SERIES , K 40(1.46 MEV
– URANIUM SERIES , TH232 (2.61 MEV )
– THORIUM SERIES, U 238(1.76 MEV)
DOLOMITES MAY HAVE SOME URANIUM CONTENT
NATURAL GR SPECTRUM
Radioactive potassium
Isotope (K40) with half life
1.3x109 years
Argon 40
Uranium238 (U238) with
half-life of 4.4 x 109 years
Thalium 208
Thorium232 (Th232) with
half-life of 1.4 x1010 years
Bismuth 214
GAMMA RAY LOG
CLEAN SANDS AND CARBONATES EXHIBIT LOW GR
SHALES AND SHALY SANDS ARE HIGHER IN
RADIOACTIVITY
FELDSPARS AND MICAS RICH IN RADIOACTIVITY
AMONG CLAY MINERALS ILLITE HAS MAXIMUM GR
SOMETIMES SILTS ARE MORE RADIOACTIVE THAN
SHALES
HOT SHALES EXHIBIT TREMENDOUSLY HIGH GR (
THOUSANDS API)
SOURCES OF RADIOACTIVITY IN SHALES
SHALES ARE FINE GRAINED CLAY RICH ROCKS
CONTAINING MICA, FELDSPAR, CALCITE, DOLOMITE ,
QUARTZ & ORGANIC MATTER.
1.
RADIOACTIVE ELEMENT (K-40) IS FOUND ONLY IN
CRYSTAL LATTICE ILLITE CLAY. EVEN MORE
CONCENTRATION IS FOUND IN MICA & FELDSPAR.
2. THORIUM IS ABSORBED ON CLAY PARTICLE
SURFACES. THORIUM IS PRESENT IN MICAS &
FELDSPARS.
3. URANIUM ASSOCIATED WITH ORGANIC SHALES
PROVIDES HIGH GR
GR LEVELS AGAINST SEDIMENTARY ROCKS
GAMMA RAY TOOL
• GR ENTERING TOOL BODY AFTER PASSING
THROUGH FORMATION & BOREHOLE ARE
COUNTED WITH SCINTILLATION /G.M. COUNTER
• GAMMA RAYS PASSING THROUGH ROCKS ARE
SLOWED AND ABSORBED AT A RATE WHICH
DEPENDS ON THE FORMATION DENSITY.
• COUNT RATE (CPS) IS CONVERTED INTO API UNITS
AND PRESENTED ON LOG GENERALLY IN FIRST
TRACK.
Estimation of Clay Volume from GR
O il
Examples of GR variation across Formation
P y rit e
B io t it e
Q u a rt z
ILD ILD @ M IN C O M
1
MD
1 : 200
150
m
G R C O . W E _ D S _ f in
0
6
( gAPI )
C A LI C A LI@ M IN C
-1 0
( mV )
100
( ohm .m )
M SF L.D F M SF L@ D
0.45
1
100
( ohm .m )
R T @ A S C IILoad;1
1.95
70
T EN S
0 0)
(4 5m0V
1
( ohm .m )
100
( m 3 / m 3 ) -0 . 1 5
R H O B . W E _ D S _ F in
2.95
( g/c m 3 )
D T . W E _ D S _ F in a l
140
( us /ft )
B M S _ to p
3450
3250
3475
3500
0.5
( m 3/m 3 )
Sw
0
1
( m 3/m 3 )
0
N P H I . W E _ D S _ F in
1
T VDS S
16
( in )
S P S P @ M IN C O M 2;
100
( ohm .m )
ILM ILM @ M IN C O M
PH IE
40
B ound W ater
R F _ c ly s t n
SW
C la y
E LA N _V O LU M E S E
PH IE
1
( V/V )
0
APPLICATIONS OF GR LOG
• Determination of lithology (sand , shale, coal, limestone etc.)
for identification reservoir layers, seals.
• Estimatation of shale or clay volume in shaly reservoirs
• Stratigraphic correlation of depositional sequences and
formations
• Determination of depositional environment
• Determination of source rock potential
Depositional Environment from GR Log
CALIPER LOG
CALIPER LOG
EXAMPLE OF HEAVING/SWELLING CLAY
APPLICATIONS OF CALIPER LOG
Identification of porous and permeable zones.
Used for applying environmental corrections to various log
measurements
Helps in decision making for formation testers and side wall
Coring.
It provides volume of cement slurry required for efficient
cementation job with knowledge of casing outer diameter
Annular Volume={Cali2 -(Casing OD) 2 }* Casing Length
RESISTIVITY LOGS
RESISTIVITY LOGS
Resistivity of formation rock is the key parameter in
determining hydrocarbon saturation.
Resistivity
resistivity.
devices
record
values
of
apparent
Interpretation depends upon assumption that the
logging sonde is surrounded by an Infinite,
homogeneous and isotropic medium.
The capability of measuring true formation resistivity
as close as possible is an ultimate objective
Determination of Resistivity
Ohms law:
V = I*R
where:
V
= Voltage, Volts,
R
= Resistance, Ohms,
I
= Current, Amps.
R

r
A
l
=  *l/A
= Resistivity, Ohm.m,
= Resistance, Ohms,
= Area, m2,
= Length, m.
A simplified schematic diagram of the borehole environment
and the effects produced by the invasion of drilling fluids
Types of Resistivity Logs
DIFFERENCE BETWEEN INDUCTION & LATERO LOG MEASUREMENTS
Effective Resistance, Ra
Ra = Rm + Rxo + Rt
Highest resistantion element
dominates the signal
1/Ra = 1/Rm+ 1/Rxo+ 1/Rt
Lowest resistance element
dominates the signal
CHOICE OF APPROPRIATE RESISTIVITY TOOL
Choice of better tool for Rt determination
depending upon Rmf/Rw ratio and porosity. At
lower right use both logs in area under
appropriate Rw curve.
Choice of better tool for Rt determination based on
Rmf/Rw ratio and Sw for step profile of invasion and
worst case of Annulus. 6FF40 is configuration for
deep induction in DIL tool.
Relationship Between Resistivity
& Hydrocarbon Saturation
Un-invaded Zone
Flushed Zone
RESISTIVITY LOG EXAMPLE
Interpretation of Resistivity Log
Neutron Tool
Neutron Porosity Log
•Neutron logs respond to the fundamental formation
property of hydrogen richness.
•If all of the formation's hydrogen is contained in
the form of liquids, and if these liquids completely
occupy the total pore volume, hydrogen richness is
an index to porosity.
•Hence, a neutron log is used to determine Porosity
through Hydrogen Index.
HYDROGEN INDEX OF FLUIDS
Hydrogen Index is defined as the ratio of amount of
hydrogen present in a given volume of rock or any
substance to the amount of hydrogen present in equal
volume of water
HI of water :
1
HI of light H.C (h <0.25): 0.2h
HI of heavier H.C (h >0.25): h +0.3
NEUTRON RADIATION
• Neutrons are uncharged particles having mass
approx. equal to that of protons They are classified
by the amount of energy they possess. This energy
is directly related to their speed of travel.
1. Fast neutrons > 100 KeV of energy
2. Intermediate neutrons -100 KeV to 100 ev
3. Slow neutrons < 100 ev of energy
• Epithermal neutrons - between .1 and 100 ev
• Thermal neutrons - < 0.025 ev at room temp.
RELATING COUNT RATE TO POROSITY
• In high porosity, liquid-filled formations, the
neutron flux is thermalised close to the source, so
that relatively few neutrons or capture gamma
rays are detected.
– Thus high porosity is indicated by a low neutron
counting rate.
– The reverse reasoning will relate low porosity to a
high count rate.
FIELD EXAMPLES
FORMATION DENSITY TOOL
• Most useful of all
porosity tools.
• Measures formation bulk density
(RHOB) and photoelectric absorption
factor (Pe)
• Based upon principle of Compton
scattering and photo-electric
absorption of gamma ray
• Pe is dependent on Z, the atomic
number, and is used to identify
lithology.
Density Tool utilizes Cesium 137
(Cs137) gamma ray source and
two Sodium Iodide scintillation
detectors mounted on an
articulated pad.
INTERACTIONS OF GAMMA RAYS WITH MATTER
In Compton scattering Gamma photons collide with the orbital electrons
If the energy given to the electron is greater than the binding energy of the
electron, the electron will be ejected from the atom and the photon is
"scattered," at an angle to its original path.
The energy reduction is proportional to the scattering angle θ
hν′
=
hυ / {1+ (1-Cosθ) ε} , Where, ε = hυ/meC2
Photoelectric effect occurs when the incident gamma ray is completely absorbed
by the electron. It is favoured in low photon energy & high Z targets
RELATIVE IMPORTANCE OF INTERACTIONS
FORMATION DENSITY TOOL
Measures formation porosity based upon mixing law;
In fully water bearing formation
ρb =
Φ
Φ *ρf + (1- Φ) *ρma
= (ρma - ρb)/(ρma – ρf )
APPLICATIONS OF DENSITY TOOL
• Measurement of bulk density & hence porosity
• Lithology determination using Pe.
• Lithology determination using density-neutron
Overlay & cross plots.
• Synthetic seismogram and acoustic
impedence logs for calibration of bore hole
gravimetry and well seismic surveys.
RELATING GAMMA INTERACTIONS TO LOG VALUES
Gamma rays lose their energy when they
collide with electrons of formation material
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.
Denser formation gives low count rate
Understanding the relationship between
electron density and bulk density is an
essential part of the density measurement
e = b * (2 Z / A)
Most cases, 2 Z / A = 1
e = b
RELATING GAMMA INTERACTIONS TO LOG VALUES
energy spectrum divided into
four energy windows SOFT,
SFT2, HRD1 and HRD2.
Total counts occurring in
windows HRD1 and HRD2 are
due to Compton Scattering, and
are used in combination with
the SS detector count rate to
determine bulk density.
Pe is derived from the ratio of
the counts in the SOFT window
to HRD2 window.
CURVE
ENERGY WINDOW
DOMINANT INTERACTION
SOFT
60 - 100 keV
Photoelectric Absorption
SFT2
100 - 140 keV
Photo & Comp for low Z
HRD1
140 - 200 keV
Scattering
HRD2
200 - 540 keV
Scattering
LOG EXAMPLE
Figure-34: Sandstone Reservoir from
Western Onshore Basin, Upper Part
(1200-1272 m.) is shale from GR, Cali,
SP(+ve),
Neutron(CNCF),
Density(ZDEN).Interval 1272-1306 m
is reservoir with Gas Oil Contact at
1284 m and Oil Water Contact at 1
296 m. Zone below 1306 is again
Shale. See hydrocarbon effect on
Resistivity and SP. Gas Effect on
Neutron.
SONIC LOG(ACOUSTIC VELOCITY)
• The Sonic Log is a porosity log that measures interval transit
time (Δt) of compressional sound wave travelling through the
formation along the axis of the borehole.
• Acoustic transit time Δt and is usually expressed in
microseconds per foot.
• Velocity, v and transit time Δt are related by:
Δt (μsec/ft) = 106 / v(ft/sec)
• Sonic tools consist of transmitters and receivers arranged
according to the goals of the measurement.
• The tool response is affected by the formation matrix, fluid
and porosity
Acoustic wave Propagation from a Monopole source
ACOUSTIC WAVE PROPAGATION IN FLUID FILLED BOREHOLE
SONIC VELOCITY OF FLUIDS
Formation Fluid
Sonic
velocity(ft./sec)
5,300
Travel
Time(μsec/ft)
189
5,000
200
4,800
208
4,600
218
Oil
4,200
238
Methane
1,600
626
Air
1,100
910
Water with 20%
NaCl
Water with 15%
NaCl
Water with 10%
NaCl
Water (pure)
SONIC VELOCITY OF EARTH FORMATIONS
Formation
Sandstone:
Unconsolidated
Semi-consolidated
Consolidated
Limestone
Dolomite
Shale
Calcite
Anhydrite
Granite
Gypsum
Quartz
Salt
Sonic velocity(ft./sec) Travel Time(μsec/ft)
³17,000
18,000
19,000
21,000
23,000
6,000-16,000
22,000
20,000
20,000
19,000
18,000
15,000
58.8 or more
55.6
52.6
47.6
43.5
167-62.5
45.5
50.0
50.0
52.6
55.6
66.7
BASIC SONIC TOOL PRINCIPAL
ACOUSTIC LOGGING APPLICATIONS
SONIC LOG EXAMPLE
SONIC POROSITY ESTIMATION
Wyllie time-average equation
ROCK SAMPLING(SIDE WALL CORING)
Chronological Sample Taker
Mechanical sidewall coring
These types of tools allow the sampling of rock at a desired depth. These rock
samples allow a better evaluation of the porosity and permeability, as well as their
mineralogical composition, the clay type and distribution, the grain
and pore size.
(Schlumberger’s courtesy)
FORMATION TESTER PRINCIPLE
DOWN HOLE FLUID SAMPLING
Pressure
Invaded Zone
Quartzdyne Gauge (L)
Time
Drawdown
pump
Piston Position
Sensor
Packer
Back-up arm
Sample Isolation
Valve
CASED HOLE SERVICES
CEMENT QUALITY EVALUATION
CEMENT BOD LOG-CBL
CBL/VDL
The CBL measurement is the
amplitude in millivolts of the first
arrival E1 at the 3 –foot receiver.
No
Cement
It is a function of the attenuation
due to the shear coupling of the
cement sheath to the casing.
The attenuation rate depends on
the cement compressive
strength, the casing diameter,
the pipe thickness, and the
percentage of bonded
circumference
Good
Bond
Cement Quality Evaluation –
Cont.
Cement Quality Evaluation –
Cont.
• Basic interpretation
5
– Free pipe
• No cement to casing bond
• No attenuation of the signal
Free Pipe Signal
3
E1
T0
Threshold
2
TT
T
•
Cement Quality Evaluation –
Cont.
Good cement to casing
bond
– If casing is well bonded,
soundwave
will
be
attenuated.
– The received CBL amplitude
will be low.
CBL: Free Pipe
5
3
2
CBL: Good Bond
T
Cement Quality Evaluation –
Cont.
• Variable density log
– 5 ft Receiver for VDL
Analysis
– Allows
easy
differentiation between
casing and formation
arrivals
Tx
R3
R5
5 ft
Cement Quality Evaluation –
Cont.
• Factors affecting CBL
Free Pipe Signal
E1
– Good cement – Stretch
T0
Good Bond
Signal
Threshold
TTTT’
DT
– Good cement – Cycle skipping
Threshold E1
E3
T0
TT
TT’
E2
Cement Quality Evaluation –
Cont.
• Basic interpretation
5
– Free pipe
• No cement to casing bond
• No attenuation of the signal
Free Pipe Signal
3
E1
T0
Threshold
2
TT
T
Good Cement Example
Weak casing arrival
CBL flat, low
Strong formation arrival
Cement Quality Evaluation
X
X
X
Good casing to cement to formation bond
CASED HOLE SERVICES
CEMENT QUALITY EVALUATION
CEMENT BOD LOG-CBL
CBL/VDL
The CBL measurement is the
amplitude in millivolts of the first
arrival E1 at the 3 –foot receiver.
No
Cement
It is a function of the attenuation
due to the shear coupling of the
cement sheath to the casing.
The attenuation rate depends on
the cement compressive
strength, the casing diameter,
the pipe thickness, and the
percentage of bonded
circumference
Good
Bond
Cement Quality Evaluation –
Cont.
• Variable density log
– 5 ft Receiver for VDL
Analysis
– Allows
easy
differentiation between
casing and formation
arrivals
Tx
R3
R5
5 ft
Good Cement Example
Weak casing arrival
CBL flat, low
Strong formation arrival
Cement Quality Evaluation
X
X
X
Good casing to cement to formation bond
LOG INTERPRETATION OF CLEAN FORMATION
Can you tell where to complete this well?
Gamma
Radiation
Electrical Porosity
Resistivity
good porosity
200’
poor
resistivity,
probably
water
poor
porosity
good porosity
500’
good
resistivity,
may have
oil or gas
Looks
like
good
sand
quality
poor
porosity
good
porosity
poor
porosity
poor
resistivity,
probably
water
3000’
good
porosity
}Right here! This shows a clean sand,
with good porosity and resistivity.
CLEAN
FORMATIONS
Chances of encountering clean limestone are more than sandstone
Ortho-quartzites may be considered as clean formation.
These sands are very porous and permeable
Feldspar, mica are very rare
They have also the characteristics of winnowed sand deposited on submarine
rises or of Aeolian sands
Evaluation of clean formation is basically a question of inserting the right
values of the parameters Rw, Rt & Ø with appropriate a, m, n values in
Archie water saturation equation:
Sw = (a Rw /Øm Rt)1/n
Highly saline formation waters make shaly reservoirs suitable for
evaluation with Archie’s equation as maximum current flows pore spaces
INTERPRETATION OF CLEAN FORMATIONS
Clean Zones:
Shale/Clay free from
GR, SP, Caliper,N-D.
Clastics :
Sandstone, volcaniclastics
Carbonates
Clastics :
Carbonates:
: Limestone, Dolomite
Check ResistivityFirst
Check PorosityFirst
Tight Zones : Low DT, High RHOB, Low PHIN
Water Zones :
Zone of
Low Resistivity, Good SP,
Separation between deep &
shallow Resistivity
Interest : High porosity & Resistivity
Fluid Contact :
Cross over porosity/Resistivity
Drop in resistivity
Drop in porosity
Detailed Analysis : Computation of  ,SW &He
POROSITY COMPUTAION IN CLEAN RESERVOIRS
SONIC POROSITY
DENSITY
POROSITY
BEST ESTIMATE
IN OIL/WATER
ZONES
BEST ESTIMATE
IN GAS ZONES
s 
Dtlog  Dtma
Dt f  Dtma
ma  b
d 
ma   f
7D  2N
 S
9
e 
2
SATURATION DETERMINATION
Archie gave an expression for computation of water saturation
In 1942, which is still being used with some modifications.
Electrical efficiency theory (EET) was given by D.C. Herrick &
David Kennedy in 1994., which has not been well taken by
The industry.
Basic Information Needed
Lithology
Many log analyses require knowledge of lithology for
calculations (e.g., porosity logs require matrix
information, and Sw calculations use formation factor, F,
which depends on lithology)
Formation Temperature
Formation Temperature is important because mud, mud
filtrate and formation water resistivities vary with
temperature.
FORMULATION OF ARCHIE’s EQUATION
Swn xmxCw = Ct
Swn = Ct / mxCw
C= x Cw = Cw
Change from conductivity to resistivity
Swn = Rw / mxRt
Archie used a=1, m=n =2
C= mxCw = C0
C= Sw
Sw2 = Rw / 2xRt
Later on Humble
suggested
A=0.62, m=2.15, n=2
n
xmxCw
= Ct
Final expression in use
today is
ARCHIES’s Equation :
Swn
=
a Rw
m.R
t
ARCHIE’ Parameters
‘a’ , ‘m’ , ‘n’
ARCHIE’ Parameters
For Limestone :
a=1, m=2, n=2
For sandstones
a=0.62, m=2.15, n=2,
a=0.81, m=2, n=2
a=1, m=1.96,n=2
How a, m & n are calculated
1. In laboratory
2. From logs.
What are m* & n*.
Courage to Explore
Knowledge to Exceed
Technology to Excel
Thank You