Petrophysicist Guide to Log Interpretation

Petrophysicist (Geologist)
For Practical Use and References

PETROPHYSICAL INTERPRETATION:
 Logging Environment & HC EVALUATION
 Logs Show Permeable Zone .
A. Spontaneous Potential (SP)
B. Gamma Ray (GR)
 Logs measure Formation resistivity
A. Log Induction
B. Log Lateral
 Logs measure Formation porosity
A. Log Neutron
B. Log Densities
C. Log Sonic
 Clean Formation Evaluation
 Shaly Formation Evaluation

LOGGING ENVIRONMENT
Logging Environment & HC EVALUATION

Drilling Process:
 Mud Pressure (Pm)
 hydrostatic fluid Pressure in pore
Formation (Pr) Differ to :
 Avoid “Blowout”
 Push Liquid to Formation (invasion proses).
 invasion Proses make solid material (mud cake).
 Liquid in to formation Mud Fitrate
LOGGING ENVIRONMENT

LOGGING ENVIRONMENT
Nomenclature:
Borehole:
Rm = Resistivity of mud.
Rmc = Resistivity of mud cake.
Flushed Zone:
Rmf = Resistivity of mud filtrate.
RXO = Resistivity of flushed zone.
SXO = Water Saturation of flushed zone.
Uninvaded or Virgin Zone:
RT = True resistivity of formation.
RW = Resistivity of formation water.
SW = Formation Water Saturation.
RS = Resistivity of adjacent bed or shoulder
bed resistivity.
di = Diameter of invasion.
dh = Borehole diameter.
h = Bed thickness.

1. “Flushed zone” with diameter (df.)
Contain “Mud Filtrate” (Rm )
Contain “Residual Hydrocarbon”
Has Rock Resistivity Rxo.
Thick~ 6 inches, less or more
2. “Transition zone” with diameter (dj.)
Several feet.
3. Undisturbed zone:
Has Water Formation Resistivity (Rw), Rock Resistivity (Rt), and
Water Saturation (Sw) .

A. Water Formation resistivity, Rw
Archie first measure water Formation resistivity in Tank.
“Measure flow I and voltage V, then water Formation resistivity , Rw”
formulate as follows:
V
Rw = ----- [ ohmm]
I
B. Rock Resistivity, Ro.
Archie analyse the rock. Begin with porosity calculation Ø.
Then the pore filled with water formation which the resistivity
was measured (Sw = 1).
On the experiment is Rw.
therefore :
V
Ro = --------- [ ohmm]
I2
Apparently Ro > Rw
Archie experiment

Archie repeat the experiment with different water salinity formation.
Resulting:
Ro1 = F Rw1
Ro2 = F Rw2
Ro3 = F Rw3
It seen that rock Resistivity (Ro) equal linearly with
Water Formation Resistivity (Rw).
Ro = F Rw (1)
whereF = Formation Resistivity Factor.
The experiment uses F & Ø data for about 300 rock sample.
The Value F & Ø plotted on axis and ordinate mathematically as follows:
1
F = ----------- (2)
Ø m
m = Cementation exponent, m = 1.3 - 2.2
Archie experiment

THE RELATION OF FORMATION RESISTIVITY FACTOR (F) VERSUS
PERMEABILITY (K) AND POROSITY (Ø)

C. Rock Resistivity (Rt).
Due to search oil, then the rock on experiment
begin with filled with oil and water.
Addition oil mean Sw smaller than one:
Sw < 1
The measurement resulting Rock Resistivity ( Rt )
Where:
Rt bigger thanRo,
Rt equal linearly with Ro.
Rt = I Ro (3)
Were I = Resistivity index
“ Smaller Sw mean more oil in the pore & bigger Rt bigger resistivity index (I).”
So I andSw relation as follows:
1
I = ----------- (4)
Sw n
where n = Saturation exponent, about = 2

From above, can be formulated as follows :
F. Rw
Sw n = ------------------- (5)
Rt
The formula known as Archie Formula.
Principal Logging Measurement:
Measure Reservoir Resistivity (R1).
Measure Water Resistivity (R2).
if (R1) > (R2), then there is HC in the reservoir (R1) .

Calculate Volume HC in Reservoir
HC occurrence in pore can be measure with electrical Formation
resistivity.
Assumes:
Rock Matrix cannot flow the electrical current.
it mean electrical current fully done throgh water on pore
Due to the water contain NaCl.
So the rock contain water with High Conductivity (orlow resistivity).
1
Note : Conductivity = -----------------
Resistivity

Archie formula as follows:
F x Rw Ro
Swn = ---------- = -----
Rt Rt
If n = 2,
Ro
Sw =  --------
Rt
This formula can be use if we have zone with containing water
(water bearing), with no porosity data

For Porosity value that usually seen on logging, Formation
Factor (F) calculated as follows:
1
on limestone: F = ---------
 2
0.81 0.62
on sandstone: F = ------ or F = ------
 2  2.15
wherea = cementation factor

Water Formation Resistivity (Rw) :
Water Formation Resistivity measurement, Rw, can be done using Archie
formula in zone containing water (seefig 2-2) :
Zone D is water zone due to low Resistivity value
, that is Rt = 0.3 ohmm (assumes Sw = 1)
and the Porosity is about 0.35
F Rw
Sw2 = 1 = ---------
0.3
Rw calculated about 0.045 ohmm.

Formation Evaluation conducted with use 3 log type:
 Log show Permeable Zone.
Spontaneous Potential
Gamma Ray
 Log measure Formation Resistivity
Deep Induction
Deep Laterolog
 Log measure Porosity.
Density
Neutron
Sonic

Finding Production zone?
Permeable Zone use Log SP or GR :
“Shale base line” on the right show shale
(impermeable and cannot be produced).
Deflection SP to left shows “Clean Zones”
(sand or limestone) may be productive.
Log-log Resistivity :
High resistivity shows HC or “tight zones” or
zones low porosity.
Low resistivity shows containing water.
Log-log Porosity
Shows zone with pore or
“ tight ”.

SP Log
(Spontaneous Potential)

Log SP APPLICATION :
 To differentiate permeable and non-permeable of rock.
 To “well to well” Correlation.
 As reference of depth for all logs.
 To define layer limit.
 To calculate Rw value.
 As clay indicator.
Work Principal :
 An electrode insert to bore hole then record the electrical potential at
any point with reference on surface electrical potential
 So the SP log is different of potential record between an moveable
electrode in borehole and another electrode on surface
 The Mud must conductive.
 Logging speed may 1500 m/hr.

Figure 1.
Origin Log SP Measurement

Figure 9.
Figure 10.Figure 8.
Figure 7.
Origin Log SP Measurement

SP Deflection.
 The SP curve constant but deflect to another level if pass the limit of the
different formation that differ.
 Rock surface that permeable containing water, then
 If Rmf > Rw SP deflect to left (SP negatif).
 If Rmf < Rw SP deflect right (SP positif).
 There is no SP deflection on rock surface that non-permeabel or shale
surface.

Figure 1. Figure 2.
LOG SP MEASUREMENT

SP Log Presentation:
SP curve presented in I with millivolt unit.
There is no Absolut scale, but use 10 mV per small division.
Usually use scale –80 to 20 mV

Application Log GR.
 Standard Gamma Ray Application:
 As main Reference to all run logging.
 To “well to well” correlation.
 Differentiate permeable and nonpermeable zone .
 Calculate volume clay.
 Natural Gamma Ray Tool (NGT) Application:
 To detect, recognize and evaluate radioactive minerals .
 Recognize the clay type and calculate volume clay.
 Permeable zone that may contain Uranium much more than less permeable
zone.
 Uranium reading on NGT log sometime useful as clue the existing fluid
movement.

Principal work of GR Log.
 Gamma Rays that naturally come:
This Gamma Ray comes naturally in rocks and has relatively low
energy.
Device to measure gamma ray natural are:
1. Standard Gamma ray Tool (SGT)
2. Natural Gamma Spectrometry Tool (NGT)
 SGT measure all natural GR.
 NGT beside measure all GR, also measure GR energy and define
the concentration of 3 type radioactive element that usually in
nature :
Uranium (Ur235/238)
Potassium (isotope 19K40) and
Thorium (Th232)

Figure 2.
Figure 3.
Type radioactive element

Gamma Ray (GR)
Specifications
Measurement Range :
Gamma API Units : 0 to 400 API
Measurement Accuracy :
Gamma API Units : ± 1 API
Maxium Ratings :
Pressure : 20,000 psi (138,000 kPa)
Temperature : 350 o F (177 o C)
Dimensions :
Tool Length : 4.4 ft (2.30 m)
Tool Weight 80 lb (36 kg)
Maximum Diameter : 3.5 in (89 mm)
The Gamma Ray measures natural formation radioactivity, making it an excellent tool for correlation
purposes over the life of a well

Induced Gamma Ray Tools:
The devices putted radioactive sources that transmit gamma ray with
high energy.
Example density log tools:
FDC - Formation Density Compensated
LDT – Litho Density Tool
Depth of Investigation and
Vertical Resolution.
Depth of Investigation SGT about 10 inci.
Depth of Investigation NGT about 15 inci.
Vertical Resolution SGT about 10 inci
Vertical Resolution NGT about 15 inci.

Presentation kurva GR
The gamma ray curve presented in
Track I.
Common scale use 0-200 API.
Can reduce to 0-150 API or 0-
120 API if gamma ray activity
low.
The NGT curve presented:
○ SGR: Total Gamma
Ray.
○ CGR: total GR less by
Uranium
○ Ratio Th/K
○ Ratio Th/U

LQC dan Corrections
In free shale Rock, log GR recording low value about 20-30 API.
In “Shaly Formation” log GR has value 80 to 300 API.
Environmental corrections
Large borehole and much weight mud can reduce the value of GR rock
measurement.
“centered” tools in borehole will receive gamma ray less than the GR tools that
“eccentered”.
GR devices that survey in well contain KCl mud will accept GR much more
due to high Potassium content.
Therefore the correction as parameter:
Hole size & mud weight.
Correction KCl content
Casing size & Casing weight
cement.

Example of correction GR
As bore hole
 Find GR value after conduct correction
if value log GR = 32 API,
 hole size (dhole) =12 inci,
 mud weight (Wmud) = 9.2 lb/gal,
 tool diameter (dsonde) = 3 3/8”, as
survey “centered”.
 Calculate:
t = Wmud x [2.54(dhole) –
2.54(dsonde)]/[8.345 x 2]
= 12 g/cm2
 Then follow redline (chart) with input t
= 12 g/cm2 for gain correction factor
1.2
 GRcorrected = 1.2 x GRlog = 38.4 API

Interpretation
 Percentage shale in rocks
calculated by formula:
(GRlog – GRclean)
Vshale = ---------------------------------
(GRshale – GRclean)
 Survey by NGT tool give curve
Uranium, Potassium and
Thorium curve .
Figure Mineral Identification from
Spectral Gamma Ray

Logs that measure
Formation Resistivity

 The Main Basic Formula Interpretation is:
F. Rw
Sw2 = ----------
Rt
 The most important Input is Rt, uninvaded zone resistivity .
 With invasion then logging has create 3 type Resistivity tools:
Deep investigation.
Medium investigation.
Shallow investigation.
 Resistivity a liquid always presented with Temperatur.
Example:
Rmf = 0.30 ohm-m @ 80 degF
Rw = 0.10 ohm-m @ 120 degF
 from resistivity data and temperature, can be found liquid salinity with Chart
Gen-9.
Resistivity Logs

Resistivity of NaCl solution
(Schlumberger chart GEN-9)

Classification and Application.

Table 4-1 above is Resistivity tools classification until 1987
classification based on radius of investigation :
Deep : 3 + feet
Medium : 1.5 - 3 feet
Shallow : 1- 6 inches.
all curve deep, medium and shallow recorded use electrodes or
coils putted on mandrel silindris, and placed more less centralized
in borehole.
Microresistivity devices use sensor that putted on pad that
forced close in wall of borehole wall as survey conducted.

 Log Induction worked in:
Fresh mud
Resistivity formation < 200 ohm-m
Rmf/Rw > 2.0
 Log Lateral will better work in:
Salt Mud
Resistivity formation > 200 ohm-m
Rmf/Rw < 2.0
Large borehole >12 in. also deep invasion (>40in.)

Log Induction & Lateral
Figure 1.

Principal Work.
 Induction devices to define
resistivity with measure rocks
conductivity. In transmitter
flowed by high frequency current
with constant amplitude that will
attain magnet field in rocks.
 The magnet fields attain Eddy
current or Foucault current in
other name called ground loop.
 The value of the current equal to
rocks conductivity

Simultaneous triple induction (STI)
SPHERICALLY FOCUSSED RESISTIVITY SECTION
• Electrode System : Integrated into mandrel
• Measurements Range : 0,2 to 2000 ohm-in
• Outputs : V0 and I0
• Accuracy : 5 % of reading
• Inputs : Cal, Zero, Return select
• Full Vertical Resolution : 25 in (64 cm)
Accurate resistivity measurement with high vertical
resolution is vital for the determination of true
formation resistivity and flushed zone resistivity, two
essential parameters of formation evaluation
Open Hole Services

Depth of Investigation & Vertical Resolution.

LATEROLOG – INDUCTION LOGS
Better use Induction than
Laterolog if
1. Rmf/Rw > 2.5
2. Rt < 200 ohmm
3. Thickness > 10ft
If porosity bellow Rw but
Rmf/Rw still > 2.5 then
Laterolog should be used

Presentation Log Induction.
 The deep Induction log
presented on track 3-4 with
logarithmic scale, as dashed
curve with mnemonic ILD.
 The medium induction log
also on track 3-4 with
logarithmic scale, as dashed
curve with mnemonic ILM.
 The shallow focused log
also on track 3-4 with
logarithmic scale, as
continue curve with
mnemonic SFLU (spherically
focused log).
 logarithmic Scale usually 4
cycles, from 0.2 s/d 2000
with unit [ohmm].

LQC / Interpretation
 Due to mud filtrate, therefore ILM
between ILD and SFLU.
 ILD<ILM<SFLU Profile must shown on
log Induction,
because of this condition Rmf/Rw > 2.5
fulfilled.
Figure 4.

Correction Log Induction.
 Induction log need to be
corrected with:
 Borehole corrections: mud
resistivity and borehole size
(figure 11)
 Tool standoff corrections
(figure 11)
 Bed thickness and shoulder
bed corrections (fig.12)
 Invasion corrections (figure
13)
 SFLU log also need to be
corrected as mud resistivity
and borehole size. (figure 10)

Application Log Lateral.
Laterolog device designed for measure rock resistivity that drilled with salty
mud or very conductive mud also used for detect zones that contain HC.
Prinsipal work Log Lateral.
Sonde on resistivity tools has bucking electrode to focus survey current and
insist to flow in vertical to sonde.
The focused current make possible to measure done on rocks with presize
direction.
This is the fixing tools that use unfocused current such ES (Electrical Survey)
the previous, where the current survey more likely flow in mud due to mud
resistivity is lesser than rock resistivity

The Dual Laterolog measures
formation resistivity over a wide
dynamic range. It provides accurate
readings up to 40,000 ohm-m.
The DLL is generally the resistivity
tool of choice in wells drilled with salt
mud's, Especially if formation resistivity
are high.
DUAL LATEROLOG (DLL)
Measurenment Range
Deep Resistivity, LLd : 0,2 to 40,000 ohm-m
Medium Resistivity, LLm : 0,2 to 40,000 ohm-m
Measurement Precision
Deep Resistivity, LLd : ± 2 %
Medium Resistivity, LLm : ± 2 %
Open Hole Services

Micro Spherically Focused Log (MSFL)
SPECIFICATIONS
MEASUREMENT RANGE :
MSFL Conductivity : 0 to 5,000 ms/m
Caliper : 4 to 21 in (100 to 530 mm)
MEASUREMENT PRECISION:
MSFL Conductivity : +/-2 mS/m
Caliper : +/-0,1 in (+/-2.5 mm)
MAXIMUM RATINGS :
Pressure: 20,000Psi (138,000 kPa)
Temperature : 350 o F (177 o C)
DIMENSIONS
• Tool Length : 10,6 ft (3,23m)
• Tool Weight : 200 lb (91 kg)
• Maximum Diameter : 4,0 (102 mm)
The MSFL can be used in fresh or saline muds. The pad
mounted device incorporates a caliper measurement and the
tool is typically run in combination with another resistivity
device, most often the Dual Laterolog.
The MSFL is a pad-Type microresistivity device employing a
concentric arrangement of five electrodes to force the measurement current into a hemispherical pattern
Open Hole Services

Depth of Investigation and Vertical Resolution

LIMITATION & PRESENTATION
 Laterolog tools used to survey on well filled with mud with low
resistivity also in rocks high resistivity
 Laterolog tools can accurately measure rocks resistivity about 0.2 –
40000 ohmm.
Laterolog tools recomed to use if:
 Ratio Rmf/Rw < 2.5
 Rocks resistivity > 200 ohmm.
 Thickness < 10 feet.
 Deep laterolog presented in track 3-4, logarithmic scale as thin line
dashed with mnemonic LLD
 Shallow laterolog presented in track 3-4, logarithmic scale as dotted
line with mnemonic LLS
 Microresistivity presented in track 3-4, logarithmic scale as solid line
with mnemonic MSFL.
 logarithmic scale usually in 4 cycle : 0.2 – 2000 ohmm.

Resistivity Curve can be use as
indicator percentage
clay in rocks, VRT:
(Rsand – Rt)
VRT = ------------------------- x 4 Rclay/Rt
(Rsand – Rclay)
VRT usually relatively too high,
except the rocks with high
Resistivity.
Due to clay is conductive, with
minimal value Rsand will get value
VRT 100%
LATEROLOG PRESENTATION

Correction Lateral Log
MSFL borehole corrections (fig.14)
Borehole corrections – to mud resistivity and borehole size (fig.15)
Bed thickness corrections (fig.16)
Invasion corrections – to invasion mud filtrate (fig. 17)

Fig.15 Laterolog Borehole Correction Chart

Fig. 17: Laterolog Invasion Correction Chart

Log Density Application
 Density tool measure density of rocks then use to define rock porosity.
 Together with another logs such log neutron, rocks lithology and fluids
type containing in the rocks can be defined.
 Log density can differentiate Oil to gas in pore due to the fluids has
different density.
 Density tool in modern age also measure PEF (photoelectric effect) that
useful for defining rocks lithology, identify heavy minerals and evaluate
clay.
 Log density also use to define Vclay also to calculate “reflection
coefficients” along with log sonic to make synthetics seismogram.

Principal work Density tool
 A radioactive sources Cs137 has 1.5 Curie transmit GR
energy 662 kev to the rocks.
 Gamma rays interact with rocks electrons with
Compton scattering mechanism, where gamma rays
lose its energy also spread to many direction.
 Compton scattering Proses result “clouds” gamma
ray around source with radius vary according Rocks
electron.
 The more rocks electron the shorter clouds radius and
therefore lesser gamma ray reach to the detector
(count rates).
 So e reverse equal to count rates or cps that accepted
by detector
 Gamma ray detected that less amount shows the
existing larger electron density.
 Bulk density b for many element has value near equal
with electron density e as empirical equation bellow:
b = 1.0704 e – 0.1883

 The Litho density tools not only measure density, but also photoelectric
absorption index PEF.
 Photoelectric absorption happen if gamma ray that come has low energy.
 There gamma ray catch by core atom and an electron throw by the atom.
PEF = (Z/10)3.6
where:
Z = number atom (= amount electron inatom).
 Each element has Z particular value therefore PEF can be use as clue for
rocks type.
 PEF value very little depends on rocks porosity as seen on figure bellow
 PEF also only little influenced by fluid in pores, but log PEF influenced by
barite content on mud, because number atom Barium is high (Z=56).

tools

Figure 2.
Figure 1.

Calculation of Density Porosity PHID
(its porosity from RHOB) :
Due to bulk density b is amount of matrix density ma and fluid density f in pores
then the porosity value of rocks can be define if the value ma (Recognize first the
lithology).
b = ma (1-PHID) + f (PHID)
the equation will be:
PHID = (b - ma ) / (f - ma )
where:
ma = matrix density
f = fluid density in pores

QC/Interpretations.
 Shales Density usually smaller than rocks density that free of clay (clean
formation). Therefore shales porosity higher than rocks porosity.
 The term “limestone compatible scales”, then:
 In clean limestone RHOB & NPHI will overlay in shales RHOB will be in
right side of NPHI,
 In limestone that contain gas, NPHI will be in the right side of RHOB.
 In clean sand that contain water, NPHI will be in right side of RHOB
about 6-7 p.u.
 In dolomite RHOB will be in right side of NPHI, similar with shale but
gamma ray usually has higher value in dolomite.
 The term “Sandstone compatible scales”, then :
 In sandstone rocks the curve RHOB and NPHI will overlay.
 Due to PEF water, hydrogen and oxygen is near zero, then porosity effect
to PEF vey small and basic lithology usually can be define direct to PEF
curve (see6.2 Typical log reading).

Perhitungan Volume Shale (Vsh)
A shaly formation on the figure if Vsh is shale part in
rocks, then matrix part is (1-Vsh-), then:
b = ma (1-Vsh-) + sh Vsh + f 
and
(ma - b ) – Vsh (ma - sh )
 = -----------------------------------------------
(ma - f )
therfore
(ma - b ) –  (ma - f )
Vsh = ----------------------------------------
(ma - sh )
Shale influence the porosity density and porosity
neutron.
If both corrected with shale effect, it will get effective
porosity as follows:
e = D - Vsh D
e = N - Vsh N

Typical Log Readings:
Recommend Parameter

RHOB correction should be done to:
Mud cake thickness ( in real time)
Mud weight (alsoreal time)
Rugose hole (real time)
Borehole size.

Application Log Neutron
 Neutron tools used for define primary rocks porosity, that is rocks
pore filled by water, oil or gas
 Together with another log lain such log density, can be use to
define rock type /lithology also fuluid type that fill the rocks pores.
 Elastic scattering:
Neutron Particle collide with another atom, therefore neutron
particle change direction, but has still same energy.
 Inelastic scattering:
The collide with another atom, neutron particle has lose half
its energy that given to atom that collided. This Atom
experiencing “excitation”,then transmit energy again in
Gamma Ray form that has specific spektrum.
neutron Particle also change direction in this collide.

Principal work Neutron tools
 Radioaktif source Am241Be transmit Neutron particle to the rocks about
5 MeV energy.
 After collition with the rocks, the neutron energy reduce to level 0.1-10
eV (level epithermal).
 The collisions next reduces energy further to less than 0.025 eV (level
thermal).
 Due to mass Hydrogen near with Neutron, atom Hydrogen has bigger
ability in slowing down neutron particle than another atoms in rocks.
 Two thermal detector put on 1-2 ft upper radioactive sources.
Ratio between amounts pulse : Nn/Nf are porosity function.
 This Ratio has:
Bore hole influence reduced
Penetration depth further than one detector system .

Depth of Investigation and Vertical Resolution.

Presentation Log Neutron.
Neutron porosity presented on
track 5 - 6 with mnemonic NPHI
with scale:
45% sampai - 15% or
.45 sampai -.15 p.u
60% sampai 0% or
.60 sampai 0 p.u

Log Quality Control and Interpretation.
 Shale influence reading log, then NPHI higher than true porosity due to
water bound on shales.
 The washed out well also make reading log higher than true porosity.
 Rocks contain gas has hydrogen concentration lower than contain oil or
water, therefore reading neutron log willl smaller than true porosity.
The term “limestone compatible scale” are:
RHOB : 1.95 - 2.95
NPHI : 45% - -15%
 In limestone without shale content water RHOB curves and NPHI will
overlay.
 In shale rocks RHOB on right side NPHI.
 In limestone contain gas, RHOB on left side NPHI. Separation larger than 6-
7 p.u
 In sand without shale contain water , RHOB on left side NPHI with
separation 6-7 p.u
 In dolomite without shale contain water, RHOB on the right side NPHI.

The term “sandstone compatible scale” are:
RHOB: 1.90 gr/cc - 2.90 gr/cc
NPHI : 45 % - -15 %
 In sandstone without shale contain water RHOB and NPHI curves will
overlay.
 In shale RHOB on the right side NPHI.
 In sandstone contain gas, RHOB on the left side NPHI. Separation larger
than 3 p.u
 In sandstone without shale contain oil , RHOB on the left side NPHI with
separation 1-3 p.u

Log Quality Control and Interpretation

Formation content liquid.
 All points porosity contain water will fall in area line sandstone and
dolomite.
 True Porosity can predict by:
PHI = (PHID + PHIN)/2
 For clean formation contain liquid, porosity above are effective porosity,
and the value can be read as middle Density & Neutron logs.
Formation content gas.
 The exchange liquid with gas in pores reduce bulk density and hydrogen
content.
 Density go down - PHID go up.
 Hydrogen content go down - PHIN go up.
 The result is crossover effect recognize in Neutron and Density logs
shows gas.
 PHIN most bigger than PHID except crossover zone, that shows interval
contain gas.

 Another way measure porosity is use formula:
PHI = (PHID2 + PHIN2)/2
 With above formula will get porosity that close with the chart.
 Therefore in formation contain gas, porosity not middle between
Neutron and Density, but 2/3 distance between log Neutron to log
Density.
 Shale reduce the porosity Density measurement and Neutron. shale
Volume can be calculated as follows:
VDshale = (PHID - PHIeff)/PHIDsh
VNshale = (PHIN - PHIeff)/PHINsh

Environmental Corrections.
 The quality of log guarantee good if been contacted between neutron tools with
borehole wall.
 Environmental corrections should be done to log NPHI are:
 Borehole size
 Borehole salinity
 Borehole temperature and pressure.
 Mud cake
 Mud weight
 Formation salinity
 Toll stand-off from wall of bore hole

Example Neutron Environmental Correction:
 Uncorrected TNPH =34 pu in hole 12” reduce with 2 pu as correction to bore hole size.
 If mud cake ¼ inch, no mud cake effect.
 If salinity borehole 100 kppm, add with 1 pu.
 If used natural mud with density 11 lb/gal then add with 2 pu.
 If temperature borehole 150 degF, add with 4 pu.
 If 5kpsi water based mud, reduce 1 pu
 If 100kppm formation salinity, reduce 2.5 pu
Total borehole correction: -2+1+2+4-1-2.5 = 1.5 pu.
Associated Mnemonics

Example of Neutron Environmental Correction:
 Uncorrected TNPH =34 pu in hole 12” less by 2 pu as correction to bore
hole size.
 If mud cake ¼ inch, no mud cake effect.
 If salinity borehole 100 kppm, add 1 pu.
 If use natural mud with density 11 lb/gal then add 2 pu.
 If tem. borehole 150 degF, add 4 pu.
 If 5kpsi water based mud, remove 1 pu
 If 100kppm formation salinity, remove 2.5 pu
Total borehole correction: -2+1+2+4-1-2.5 = 1.5 pu.

log sonic Application
To define sonic porosity (s)
To define volume of clay (Vs)
Along with another logs to define lithology
Time-depth relationship
To define reflection coefficients
Mechanical properties
To define cement CBL-VDL quality
Theory of measurement
Sonic tool measure: speed of voice/sonic in formation.
The principal on figure below :
Transmitter transmit a “pressure pulse” frequency 25 kHz.
The pulse resulting 6 wave:
Compressional wave and refracts wave
shear waving in formation.
direct two wave as long as sonde and in mud.
two surface wave as long as hole wall of well (pseudo Raleigh dan Stoneley)
The speed of the waves about 4000 to 25 000 ft/sec depend on lithology

 A compressional wave waving from transmitter via mud to formation ,
the waving in formation, then waving in mud again to reach receiver.
 Transmitter transmit one pulse.
 An electronic tool measure time from this pulse until time reach “the
first negative excursion” detected by near receiver.
 Transmitter transmit one pulse again.
 Measured the time from pulse second to time reach “the first negative
excursion” detected by far receiver.
The Differ between those both time then divide by distance between
receiver-receiver (span) as two ft resulting formation
transit times in microseconds/ft (sec/ft).
Compressional transit times vary:
40  sec/ft in hard formation
150  sec/ft in soft formation.
Reverse transit time is velocity [feet/sec].
Shear wave travel time can be measured by logging
Particular along with wave form processing.
Principal log sonic tool

Log sonic presented as DT in track 2
and 3, with sec/ft unit, bigger from
right to left .
The raise of porosity deflect curve to
the left, equal to reading density and
neutron.
Small pips in depth track is
“integrated travel time”.
With small pips: 1 msec; between
large pips: 10 msec
The Caliper dan Gamma Ray curves –
in track 1.
Presentation log sonic

Sonic porosity transform:
By using Willie Time Average (WTA):
DTlog – DTma 1
S = -------------------- x -------
DTfl - Dtma Cp
where:
S = porosity sonic
DTma = transit time in 100% matrix.
DTlog = transit time read on log.
DTfl = transit time in 100% fluid
Cp = compaction factor:
Cp = 1 in hard formation
Cp = DTsh/100 in unconsolidated formation
Formula Raymer Hunt Gardner (RHG):
Sonic Porosity calculated with this formula no need Cp and more close to core
porosity value also porosity density-neutron differ by WTA.
Equation RHG as follows:
S = c x (DTlog-DTma)/DTlog
where : c = 0.67
c = 0.60 in gas saturated reservoir rock

Calculate Vsh from log Sonic:
If shale exist in rocks, the formula WTA tobe:
DTlog= DTma (1--Vsh) +DTfl.  + DTsh Vsh.
DTsh value usually found about 80-110 sec/ft.

Quick-look with Delta Log R
 Delta Log R quick-look method to find hydrocarbon by overlay between
deep resistivity curve with curve porosity
 No need to know a,m,n and Rw first
Basic Method Delta log R:
 deep resistivity curve and porosity curve overlay in clean zone content
water.
 In hydrocarbon zone, curve resistivity will raise.
 Resistivity scale: raise for example 0.2 - 2000 ohmm.
 So the raise of resistivity caused curve deflect to right

Delta Log R
Quick-look with Delta Log R

md (k) = (kcoef*PHIE**kexp)/(SWirr**2) (graphic 3)
REGRESION LOGARITMIC
grafik 2 Regresi Logaritmik kcore dan PHIcore sumur TJS-03
grafik 3 Permeabilitas core dan Log

md (k) = (kcoef*PHIE**kexp)/(SWirr**2) (graphic 3)
REGRESION LOGARITMIC
graphic 3 Permeability core and Log

INTERPRETATION METHODE
 Quick Look : D LOG R (DELTA LOG R)
 Interpretation by Cross Plot
a. Lithology Model Approach
- Cross Plot N-D
- Cross Plot N-S
- Cross Plot S-D
- Cross Plot M-N
b. Parameter Petrophysic calculation
- Picket Plot (a, m & Rw)
- Hingle Plot (Rw)
- Cross Plot RWA-GR (Rclay & Water formation salinity)
- Cross Plot PHIE-RHOMAU ( RhoH)
c. Permeability Calculation Approach
K = (kcoef x PHIEkexp)/(SWirr2) , mD

Picket Plot (a, m & Rw)
Hingle Plot (Rw)

Cross Plot RWA-GR
Cross Plot PHIE-OMAU ( RhoH)

CASE: T-42 (T-Field in South Africa)

T-42
(T-Field in South Africa)

T-42
PHI cutoff ~ 0.17
Sw cutoff ~ 0.57
Vcl~0.35
a= 1, m=1.99, n=2
(in South Africa)

Log-Core Data Validation
Core Data:
Dean Stark
Avg. PHIE~21.7
Avg. Density 2.65
Avg. SW~11.16
PRELIMINARY
CLEAN PLUG CORE
ANALYSIS DATA
Avg. Perm~341.98mD
Petrophysic:
Avg. PHIE~19.83
(Mod simandoux,
A=1, m=2, n=2 )
Avg. SW~24.12
Or 16.2 (@ Sand)
(Resistivity Log)
Perm X~330mD
( PHIE & Vcl)
RWA adjustment to
0.1

1.00
10.00
100.00
1000.00
0 10 20 30 40 50
Permeability - Vcl Cross Plot
Perm X
VClay
Permeabili
ty
Permeability - VClay Crossplot of The OBSF-05 well
Properties Parameter cut
off
SW - Perm X Crossplot of The OBSF-05 well
SO-PHIE Crossplot of The OBSF-05 well

Reservoir Rock Type
Perm X - PHIE of The OBSF-05 well
PermX
Reservoir sand formation
divided three Rock type
based on Permeability –
PHIE (fraction) relation with
Vshale of OBSF-05 Core
data.
The Formation sand Rock
types consist of RT 1, RT 2
and RT 3 where each has
particular formula. RT 1 with
Volume Shale (Vsh) less
than 20% has low
permeability and low
porosity, RT 2 with Vsh.
20% to 40% has medium
permeability and medium
porosity, RT 3 with Vsh. Up
to 40% has high
permeability and medium-
high porosity.

 From many Sources
Reference

Petrophysicist Guide to Log Interpretation

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