BasicPetro_2.ppt

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Basic Logging Measurement

IntroductionCaliper

SP

GR

NGT

Neutron

Density

Sonic

Resistivity

Induction



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Types of log measurements

• SP & GR (record naturally occurring physical phenomena in in-siturocks)

• Porosity Logs

• Sonic logs

• Density logs• Neutron logs

• Resistivity Logs

• Conventional Electrical Logs

• Induction logs



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Invasion Model

Transition

Zone

Uninvaded

zone

Rt

Rw

Sw

Rxo

Rmf

Sxo

Mud

Rm

Mudcake

Flushed

zone

h

Rmc



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CALIPER LOGS

CALIPER LOGS

- Applications:

• Measure borehole diameter

(borehole geometry if multi-arm

caliper tools with 2 or 3 hole

diameters measurements 90° or 60°

relative to each other).

• Important measurement for drillers:

hole geometry, hole/cement volume.• Hole diameters are an import input

parameter for the environmental

correction of petrophysical logs.

• Oriented multi-arm caliper logs are

used to identify principle stress

directions - “breakout log”

- Basic Quality Control:

Perform casing check - should read

nominal casing ID.

CALI, C1, C2 Washout: Shale zone?

Mudcake: Permeable zone?



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SP (Spontaneous Potential Logging)



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Spontaneous Potential (SP)

• Opposite shales the SP curve

usually defines a more or lessstraight line on the log called the

Shale Baseline

• Opposite permeable formations,

the curves shows excursions from

the shale baseline; in thick beds,these excursions tend to reach an

essentially constant deflection

defining a Sand Line.

• The deflections may be negative or

positive depending primarily on therelative salinities of the formation

water and of the mud filtrate.



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• SP Curve cannot be recorded in holes filled with non

conductive mud, because such mud does not provide theelectrical continuity between the SP electrode and the formation.

• If Rw ~ Rmf => SP deflection will be very small (the curve will

be rather featureless).

•The Position of the shale baseline on the log has no useful

meaning for interpretation purposes. The SP sensitivity scale is

chosen and the shale baseline position is set by the engineer

running the log so that the curve deflections remain the SP track.



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Origin of SP

SP deflections result from electric current flowing in the mud in the

borehole. These SP currents are developed by two types of

interactions :

1. Electrochemical

2. Electrokinetic

Electrochemical

The electrochemical interaction is caused by the difference in

salinity between mud filtrate and water formation.

There two types of Electrochemical components, MembranePotential (Em) and Liquid Junction Potential (Ej)



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SP – Membrane Potential Consider a permeable formation with thick shale beds above and below; assume, too, that the two

electrolytes present, mud filtrate and the formation waters contain NaCl only. Only Na+ cations are

able to move through shales from more concentrated to less concentrated NaCl solution. Shales

are impervious to the Cl- anions. This movement of charged ions is an electric current, and theforce causing them to move constitutes a potential across the shale. Since shales pass only the

cations, shales resemble ion-selective membrane, and the potential across the shale is therefore

called the membrane potential.




SP – Liquid Junction Potential Another component of the electrochemical potential is produced at the edge of the

invaded zone, where the mud filtrate and formation water are in direct contact. Herethe Na+ and Cl- can diffuse (move) from either solution to the other. Since Cl- hasgreater mobility than Na+, the net result of this ion diffusion is a flow of negativecharges from more concentrated to less concentrated solution. The current flowingacross the junction between solutions of different salinity is produced by anelectromagnetic force (emf) called liquid junction potential.




SP




SP

Membrane potential is about 5 x Liquid Junction potential

Electrokinetic potential SP is negligible




Electrokinetic component of SP

This is generated by the electrolyte flow (of the mud filtrate)through a permeable, non metallic, porous medium (mudcake).

The magnitude depends on the differential pressure producing the

flow and the resistivity of the electrolyte.

In practice, little or no electrokinetic is actually generated. It willonly become important if there are high differential pressures

across the formations




SP as a permeability or shale indicator

Since invasion can only occur in

permeable formations, deflections

of SP can be used to identifypermeable formations.

The vertical resolution of SP is

poor, and often the permeable bed

must be 30 ft or more to achieve astatic (flat baseline) SP




Rw from SSP

Under certain circumstances Rw

can be estimated from SP.

•The SP value remains constant for

at least 30 feet.

•The area where the SP is constant

must correspond to a very clean

sandstone.•The value of Rmf must remain

constant across this same interval.

These conditions are rare, and

large errors in the Rw estimatemay occur.

Use this technique with care!

2. _:,

24.065

133.061

10

log

SP Chart R R

C T c K

F T c K

k

SSP

mfeq

weq

weq

mfeqc

mfeqweq

c

R

R

R R K SSP




Rmfeq from Rmf or Rw from Rweq

If Rmf @ 75degF > 0.1 Ohmm

then Rmfeq=0.85 Rmf @ BHT

If Rmf @ 75 degF < 0.1 Ohmm

then Rmfeq from chart sp2

Same with Rw

Chart SP-2




SP as Rw indicator

Rw > Rmf

“Saline mud”

Rmf > Rw

“Fresh mud” Rmf = Rw

SP is more often used“qualitatively” to predict

whether Rw > Rmf or not.




SP for correlation

-ve SP

deflection

+ve SP

deflection




SP for correlation

Keep in mind that SP deflection is Rmf dependent and

never an absolute value




SP log

Rmf > Rw?

Where is Sand?Where is Shale?

What is Vsh?




Static SP (SSP)

SSP is the SP deflection opposite a thick,

clean formation. The deflection is

measured from the shale baseline and itsmagnitude:

we

mfe

R

Rk SSP log

The value of SSP can be determined

directly from the SP curve, if, in a given

horizon, there are thick, clean, water

bearing beds.

F t Aff ti SP M t



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Factors Affecting SP Measurement

The current flow and hence the SP deflection depends on the

difference between the resistivity of the virgin formation water,Rw, and that of the mud filtrate Rmf

In normal cases Rw<<Rmf, the SP deflection from the shale

baseline is negative (left)

In the opposite condition, Rw>Rmf, found in fresh formationwaters, the deflection is positive (right)

SP Deflection

Negative

SP Deflection

Negative Rw>Rmf

Rw<Rmf



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Rmf > Rw

Shale Little deflection

Clean Ss Negative deflection

Rmf < Rw

Shale Little deflectionClean Ss Positive deflection



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SP Example

The Maximum SP deflection in this

example occurs at the same depths

as the resistivity curves show a separation

The Minimum point on the SP corresponds

to where all the resistivity curves overlay,

no invasion, a shale.

Rw<Rmf?

Where is Sand?

Where is Shale?

SP reading on Sand?



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ESSP

SPONTANEOUS POTENTIAL – SP

APPLICATIONS

• Shaliness Indicator - The example

log is for the case where Rmf > Rw. Baselines

for 100% sandstone and 100% shale can be

established at the maximum and minimum SP

excursions.The percentage of shale can be

directly obtained for any depth on the log by

linearly scaling between the shale and sand

base lines. For example:

• SPshale = -10 mV

• SPsand = -40 mV

• SPlog = SP reading from the log = -25 mV

• The percentage of shale will be (SPlog -

SPsand) / (SPshale - SPsand) = -15/-30 = .5 or 50% shale.



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Code/Name

SP, units = mV



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SPONTANEOUS POTENTIAL – SP

APPLICATIONS

•Correlation - Correlation permits logs made on one trip into the borehole to be

tied-in (depth matched) with those made on another trip. Correlating is done for

two primary reasons:

Depth matching between separate trips in the well.

Positioning of open hole sampling tools.

•Estimation of Rw under the following circumstances:

The SP value remains constant for at least 30 feet.

The area where the SP is constant must correspond to a clean sandstone.

The value of Rmf must remain constant across this same interval.



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SP deflections vs. SalinitySSP = -K log

Rmfe

Rwe

Rmf =Rw Rmf <RwSALINE MUD

Rmf >RwFRESH MUD

K = 61 + .133*F

K = 65 + .24*C



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Rw From SSP (use this technique with care!)



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Resistivity changes with Temperature.

As temperature of the solution increases the activity of the

ions in the solution increases and the solution resistivity

decreases.

Since we measure all resistivities at formation temperature

(FT) we must convert the Rmf at surface measured

temperature to Rmf at formation temperature to compute theratio of Rmf to Rw (ie SSP).

We assume salinity of the formation does not change with

temperature and use chart Gen. 9.



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Rw=0.35 @ 75 degF

What is Rw at 190 degF?? (assuming the salinity does not

change with temperature)



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eg. Rw = .35 @ 75F gives a salinity of 17,000ppm. 17,000ppm @ 190 F yields a resistivity of .135 ohmm.



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Exercises:

1. Rw = 0.21 ohm-m @ 75 degF.

What is the salinity?

What is the Rw @ 200 degF?

30000 ppm

0.08 ohm-m

2. Salinity = 13000 ppm

What is the Rw @ 75 degF?

If FT= 180 degF, what is Rw?

0.44 ohm-m

0.19 ohm-m

Calculation of Rw



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Calculation of Rw

from SP

Get Rmf @ meas. Temp from log heading along with BHT.

Compute FT from BHT.

Calculate SSP from log at maximum deflection (in a clean,

thick, (water-wet) zone). --- Just read SP from logs for this

training Enter Chart SP-1 with SSP, FT., & Rmfe and compute

Rmfe/Rwe.

Compute Rmf @ FT (Gen-9).

Convert Rmf to Rmfe @ FT. from Chart SP-2 Rwe From Chart SP-2 convert Rwe to Rw at formation

temperature.

SP Example for Rw



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SP Example for Rw

SP Example for Rw



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SP Example for Rw

SP Example for Rw



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SP Example for RwSP-1 Chart

SP Example for Rw



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SP Example for Rw

SP Example for Rw



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SP Example for RwSP-2 Chart



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Exercise Essp = -100 mV @250 degF

Rmf = 0.7 ohm-m at 75 degF

What is Rw?

Rmf @ 250 F = 0.2 ohm-m, Salinity = 8000 ppm

From SP-1 chart; Rmfe/Rwe = 11.5

Rmfe = 0.85 * Rmf (in condition if Rmf @ 75 degF > 0.1 ohm-m)

Rmfe = 0.85 * 0.2

= 0.17 ohm-m

Hence, Rwe = 0.015 ohm-m

From SP-2 chart ; Rw ~ 0.023 ohm-m



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GR (Gamma Ray) Logging



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Principle

The Gamma Ray log is a measurement of the formation’s natural

radioactivity

Gamma Ray emission is produced by three radioactive series found in

the Earth’s crust

Potassium (K40) series

Uranium series

Thorium series

Gamma Ray passing through rocks are slowed and absorbed at a rate

which depends on the formation density

Less dense formation exhibit more radioactivity than dense formations

even though there may be the same quantities of radioactive material per unit volume



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It is the conversion of a gamma ray into an

electron and positron when the gamma ray

enters the strong electric field near an atom's

nucleus. It predominates at gamma rayenergy levels above 10 MeV. Because the

electron and positron have a combined mass

equivalent of 1.02 MeV, a gamma ray must

have at least this much energy to cause pair

production.

Gamma Ray Interactions

As they pass through matter, gamma rays experience a loss of energy due to

collisions with other atomic particles. These collisions can be divided into three

basic categories :

Compton Scattering

It is the scattering of a gamma ray by an orbital

electron. As a result of this interaction, the

gamma ray loses energy and an electron isejected from its orbit. Compton scattering

predominates in the 75 keV to 10 MeV energy

range.




GR Log and Uses

Bed definition: The tool reacts if the shale is radioactive

(usually the case), hence show the sands and

shales, the permeable zones and non-

permeable zones

Computation of the amount of shale: The minimum value gives the clean (100%)

shale free zone, the maximum 100% shale

zone. All other points can then be calibrated in

the amount of shale

Vsh=(GRlog-GRsand)/(GRshale-GRsand)

Shale

Reservoir






Application

Correlation

This is the most widely used application of the GR log. It permits logsmade on one trip into the borehole (openhole, cased hole or both) to betied in (depth matched) with those made on another trip.

Correlation is done for three primary reasons:

Depth matching between separate trips in the well.

Positioning of open hole sampling tools. Providing the depth control needed for cased hole perforation.

General lithology indicator

In areas where certain lithology aspects are already known, the GR logcan be used as a lithology indicator.

Quantitative shaliness evaluation The GR log reflects the proportion of shale and, in many regions, can beused quantitatively as a shale indicator.




Operating Environment

One of the biggest features of the GR log is its wide range of operating environments. It can be run in almost any logging

situation including cased wells, or in openholes drilled with

air, salt mud, oil-based mud or fresh mud.




The Natural Gamma Ray Spectrometry

(NGS)

•Unlike the GR log, which measures only the total

radioactivity, this log measures both the number of gamma

rays and the energy level of each and permits the

determination of the concentrations of radioactive

potassium, thorium and uranium in the formation rocks.




Principles

Natural Gamma Rays

Gamma ray emission is produced by three radioactive series found in the

Earth's crust.

•Potassium (K40) series, Uranium (U238) series and Thorium (Th 232)

series.

NGT Example




NGT Example




NGT Applications

Lithology identificationStudy of depositional environments

Investigation of shale types

Correlation of the GR for clay content evaluation

Identification of organic material and source rocksFracture identification

Geochemical logging

Study of s rock’s diagenetic history

A major application was to solve North Sea log interpretation problems inmicaceous sands

NGT El t




NGT Elements

The three radioactive elements measured by the NGT occur in different parts of the reservoir. If we know the lithology, we can deduce further information

In Carbonates:

U - indicates phosphates, organic matter and stylolites

Th – indicates clay content

K – indicates clay content, radioactive evaporites

In sandstone:

Th – indicates clay content, heavy minerals

K – indicates micas, micaceous clays and feldspars

NGT Elements (continued)




NGT Elements (continued)

In shales:

U – in shale, suggest a source rock

Th – indicates the amount of detrital material or degree of

shaliness

K – indicates clay type and mica

NGT/GR P t




NGT/GR Parameters

No formation is perfectly clean, hencethe GR readings will vary. Limestone is

usually cleaner than the other two

reservoir rocks and normally has a

lower GR

Anhydrite and salt are normally very

clean, and have very low values

Vertical resolution 18”

Depth of investigation 6”-8”

Readings in: API units

Limestone <20

Dolomite <30

Sandstone <30

Shale 80-300

Salt <10

Anhydrite <10




Code/Name

GR

CGR

SCGR

POTA

THOR

URAN

*GR




Exercise

What is the VSH from GR @ 10235

ft?

VSH = (GR log – GR sand) /

(GR shale – GR sand)

Approximately 43%

Shale



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GR log example

Which has better

vertical resolution,

SP or GR?



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Porosity Logs

The major porosity logs are:

Neutron Logs, n

Density Logs, b

Sonic Logs, t

The tool response is

affected by the formation

porosity, fluid and matrix.

If the fluid and matrix effects are known or can be determined, the

tool response can be related to porosity, therefore these devices

are referred to as porosity logs.



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Sonic Logging



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Principles :

In its simplest form, a sonic tool consists of :

A transmitter that generates a sound pulse

A receiver that picks up and records the pulse

as it passes the receiver.

It is simply a recording versus depth of the time, t , required for a

sound wave to traverse 1 ft of formation. Known as the interval

transit time, transit time, t, or slowness, t is the reciprocal of thevelocity of the sound wave.

Sonic Logs



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Sonic borehole waves



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Sonic Tool The sonic tools create an acoustic signal and measure how long it takes to pass

through a rock.

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.

Borehole Compensated Sonic (BHC)



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Borehole Compensated Sonic (BHC)

A simple tool that uses a pair of transmitters and four receivers tocompensate for caves and sonde tilt

The normal spacing between the transmitters and receivers is 3’ – 5’

It produces a compressional slowness by measuring the first arrival

transit times

Used for:

Correlation

Porosity

Lithology

Seismic tie in / time-to-depth conversion



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Long Spacing Sonic (LSS)

The BHC tool is affected by near borehole altered zones hence alonger spacing is needed with a larger depth of investigation

The tool spacing are 8’-10’, 10’-12’

The tool cannot be built with transmitters at each end like a BHC

sonde, hence there are two transmitters at the bottom A system called DDBHC – depth derived borehole compensation,

is used to compute the transmit time

Same as the BHC tool for applications

A S i Di i l S i T l



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Array Sonic: Digital Sonic Tool

Multi-spacing digital tool First use STC processing

Able to measure shear waves and Stoneley waves in hard

formations

Used for: Porosity, lithology

Seismic tie/ time-to depth conversion

Mechanical properties (from shear and compressional)

Fracture identification (from shear and Stoneley)

Permeability (from Stoneley)

Array Sonic: Digital Sonic Tool (cont )



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Array Sonic: Digital Sonic Tool (cont.)

Sonic Logs



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Sonic Logs

Compr. Shear Stoneley

Rec1

Rec8

Example waveforms from the eight-receiver Array-Sonic tool

Sonic Logs




Sonic velocities In Formations In sedimentary formations the speed of sound depends on

many parameters; principally, it depends on the rock matrix

material (sandstone, limestone, dolomite…) and on the

distributed porosity.

Porosity decreases the velocity of sound through the rock

material and correspondingly, increases the interval transit

time ( t)

Sonic Logs

POROSITY LOGS SONIC TOOL





STANDARD DISPLAY OF

BOREHOLE COMPENSATED

SONIC LOG (BHC)

- Primary Logging Curves:

DT … Delta Time or Slowness

[μsec/ft; μsec/m]

TT1 - 4 … Transit Times [μsec] for LogQuality Control

- Optional Logging Curves:

SPHI … Sonic Porosity [vol/vol]

SVEL … Sonic Velocity [ft/sec; m/sec]

- Sonic Specific Output:

Integrated Transit Time for comparison

with Seismic One Way Time


Check for Cycle Skips and TT1 - TT4.

These curves should run in parallel.

Integrated Transit Time

Cycle Skip






Dipole Shear Imager (DSI)- Primary Logging Curves:

DT4P… DTcomp, Compressional Slowness

[μsec/ft; μsec/m]

DT4S … DTshear, Shear Slowness [μsec/ft;

μsec/m]

- Optional Logging Curves:

VpVs…. Dtshear /Dtcomp PR…….. Poisson’s Ratio

- Sonic Specific Output:

Integrated Transit Time for comparison with

Seismic One Way Time


See display left: Coherency Plot projectedonto Slowness Axis

Reprocessing in the field or Computing

Centre possible.

Application of Sonic Logs




In common oilfield formations, 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:

Porosity (estimated from the

compressional slowness measured by

the sonic log.

Lithology

Presence of natural gas

Determination of Lithology with Cross

Plot






Detection of the presence of natural gas






Cement Bond Logs -> used to evaluate

the cement that was put during the well

completion process.

The Cement Bond Log shows how theamplitude of the waveform increases

when there is poor cement and

decreases in the intervals when there is

good cement.


Vertical Resol tion




Sonic

Parameters

Vertical Resolution:

Standard STC (BHC,LSS,MSTC) 24”

36”

6” DT 6”

Depth of investigation BHC(5”) LSS-SDT(12”)

Readings in zero porosity: (With 12 feet spacing)

Limestone (0pu) 47.5 us/ftSandstone (0pu) 51-55 us/ft

Dolomite (0pu) 43.5 us/ft

Anhydrite 50 us/ft

Salt / Coal 67 / >120 us/ft

Shale

Steel (casing)

>90 us/ft

57 us/ft

Code/Name




Code/Name

DT AC

DT*

Sonic Porosity




Sonic Porosity

The porosity from the sonic slowness is different than that from the density or neutron tools

It reacts to primary porosity only, I.e. it doesn’t “see” the fracture or vugs

The difference between the sonic porosity and the neutron-density porosity gives a Secondary

Porosity Index (SPI) which is an indication of how much of this type of porosity there is in the

formation

The basic equation for sonic porosity is the Wyllie Time Avearge:

maf ttt 1log

maf

ma

tt

tt

log

Sonic Porosity (continued)




Sonic Porosity (continued)

The Wyllie Time Average equation is very simple with the inputs of a matrix slowness and a

fluid slowness There is another possibility for transforming slowness to porosity, called Raymer Gardner

Hunt, this formula tries to take into account some irregularities seen in the field. The basic

equation is:

A simplified version used on the Maxis is: (C is a constant, usually taken as 0.67 )

f macttt

211

log

log

t

ttC

ma

Sonic Porosity Chart




Sonic Porosity Chart

This Chart shows the relationshipbetween the sonic compressional

slowness and the porosity. Both the

lithology and the equation must be

known prior to using this chart

This chart is entered with the interval

transit time, move up to the lithologyline and read the porosity

E i




Exercise

Calculate SonicPorosity @10200 ft

assuming the matrix

delta is 65 msec/ft and

the fluid delta t is 189

msec/ft.

Density - Lithology




The density logging tool measures the formation density and

formation lithology.

Density Lithology

Density Tool History



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Density



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Principles :

Gamma Ray Interactions

y

Gamma Ray Interactions depend on the current Gamma Ray’s energy level

G R S



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Gamma Ray Source

•Use of chemical source.

•Gamma Ray energy level is generated in Campton Scatteringrange (77 keV – 100 MeV).

Gamma Ray Detection

•Using Scintillation Detector

Formation Density Measurement



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Formation Density Measurement

•Gamma rays lose their energy when they collide with electrons (Campton Scattering)

•The number of Compton-scattering collision is related directly to the number of electrons in the formation. Consequently, the response of the density tool is

determined essentially by the electron density. Understanding the relationship

between electron density and bulk density is an essential part of the density

measurement.

Relationship between Electron Density to Bulk Density

Atomic weight (A) - the mass of an atom.

Atomic number (Z) - the number of electrons in a neutral atom.

Rhoe = Rhob * ( 2Z / A ) Rhoe = RhobMost cases, 2Z/A = 1



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Some conditions that must exist in order to measure the

density of the formation:

•The source must emit gamma rays at an energy level where Compton

scattering predominates.

•The source-to-detector spacing must be as such that the gamma rays

travel farther into the formation without losing their energy when they

reach the detector.



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Porosity from Density

For a clean formation of known matrix density and fluid

density, the porosity density is:

den = (Rhoma – Rhob)/(Rhoma-Rhof)



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Photoelectric Effect Measurement

• The spectrum represents the energy lost by gamma rays (emitted from thesource) as they interact with the formation.

• Plot 1 shows the different regions of the energy spectrum.

The basic principle of lithology

measurement is having the counts of

gamma rays drop in the energy region

where photoelectric interactionspredominates.




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•Number of electron = atomic number,

Z.

• If you know Z in the given formation,

you can predict the lithology of theformation.




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PEF (photoelectric absorption index)A parameter that links the number of gamma rays that are absorbed by

photoelectric absorption to lithology.

LDT Uses



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The density tool is extremely useful as it has high accuracy and

exhibits small borehole effects

Major uses include:

Porosity

Lithology (in combination with the neutron tool)

Mechanical properties (in combination with the sonic tool)

Acoustic properties (in combination with the sonic tool)

Gas identification (in combination with the neutron tool)

Borehole diameter - A single axis diameter of the borehole is measured from the

face of the skid pad to the end of the caliper arm that holds the skid against the

formation.

Typical Density Response



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POROSITY LOGS- DENSITY & PHOTOLECTRIC EFFECT



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LDT Parameters



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Vertical Resolution:Standard 18”

Enhanced 6”

Depth of Inverstigation 6”-9”

Readings in zero porosity:

Limestone(0 pu) 2.71

Sandstone(0 pu) 2.65

Dolomite(0 pu) 2.85

Anhydrite 2.98

Salt 2.03

Shale 2.2-2.7

Coal 1.5

P P t



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Pe Parameters


Standard 4”


Limestone 5.08

Sandstone 1.81

Dolomite 3.14

Anhydrite 5.05

Salt 4.65

Shale 1.8-6

Code/Name



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Code/ a e

RHOB

RHOZ

DEN

RHO*

PEF

PE

Density Porosity



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y y

There are two inputs into the porosity equation: the matrix density and thefluid density

The fluid density is that of the mud filtrate

1maf b

f ma

bma

Por-5: Density Porosity



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12 p.u

2.46 g/cc

Clean Sand Formation Porosity:



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Density

ρb = (1-Φd) * ρma + Φd * ρf

For ρma:

Sandstone: 2.65 g/cc

Limestone : 2.71 g/ccDolomite : 2.87 g/cc

f ma

bma D

Scaling/Porosity



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g y

The density tool is usually run with the neutron

To aid quicklook interpretation they are run on

“compatible scales”

This means that the scales are set such that for a given

lithology the curve overlay

Scaling/Porosity (continued)



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The standard scale is the “limestone compatible” where the neutron porosity

scale is:

To fit this, the density log has to have its zero limestone point (2.7 g/cc) on the

same position as the neutron porosity zero and the range of the scale has to fit

the neutrons 60 porosity units hence the scale is:

Changing to a sandstone compatible scale would put the zero sandstonedensity, 2.65, over the neutron porosity zero to give:

Exercise



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Exercise

Calculate Density Porosity@ 10200 with fluid density

= 1.0 g/cc. Assuming that

the lithology is sandstone

Density Por ~33%

Neutron



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Neutron tools emit high energy neutronsfrom either a chemical source or a neutrongenerator device (minitron) and measurethe response of these neutrons as theyinteract with the formation, or in many

cases, the fluids within the formation. Thismeasured response is affected by thequantity of neutrons at different energylevels and by the decay rate of the neutronpopulation from one given energy level toanother. A neutron interacts with the

formation in a variety of ways after leavingthe source, it is the aftermath of theseinteractions that is detected by the tool.



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Neutron logs are used principally for delineation of porous

formations and determination of their porosity. Neutron logs respond primarily to the amount of hydrogen in

the formation. Thus, in clean formations whose pores are filled

with water or oil, neutron log reflects the amount of liquid-

filled porosity. Gas zones can often be identified by comparing the neutron

log with another porosity log or a core analysis.

N t l t i ll t l ti l h h i l t



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Neutrons are electrically neutral particles, each having a mass almost

identical to the mass of a hydrogen atom.

When emitted from the radioactive source, the neutrons will collide with

nuclei of the formation materials (billiard-ball collisions). This causes the

neutron to lose some energy.

The loss of energy per collision depends on the relative mass of nucleus

with which the neutron collides. The greater energy loss occurs when

neutron strikes hydrogen nucleus (having equal mass).

The slowing of neutrons depend largely on the amount of hydrogen in the

formation.

When hydrogen concentration in the formation is large, most of neutrons

are slowed and captured within short distance of the tool. On the contrary,

if the hydrogen concentration is small, the neutrons travel farther from the

course before being captured.



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The response of neutron tools primarily reflects the amount of hydrogen in

the formation. Since oil and water contain practically the same quantity of

hydrogen per unit volume (HI), the responses reflect the liquid-filled

porosity in clean formations.

Liquid hydrocarbons have HI close to that of water. Gas, however, has

lower hydrogen concentration, hence neutron log reads too low a porosity.

This characteristic allows the neutron log to be used with other porosity

logs to detect gas zones and identify gas/liquid contacts.

A neutron and density log combination provides a more accurate porosity.

Neutron – Principles of Operation




The Figure shows that the neutron slows down to a thermal energy level at a

fairly quick rate. The slowing down rate is determined by the hydrogen index (HI)

of all components of the formation and formation fluids that contain a significant

fraction of hydrogen.

Example of NEUTRON LOGS




STANDARD DISPLAY OF

COMPENSATED NEUTRONLOG (CNL)


TNPH … Neutron Porosity [vol/vol]

(NPHI*… Neutron Porosity [vol/vol])

* obsolete replaced by TNPH

- Optional Logging Curves:NPOR … Alpha Processed (hi-res)

Neutron Porosity [vol/vol]

TALP … Alpha Processing Quality


Neutron Porosity values should be

taken with care in front of bad hole -washout - values might read too high.

CNL is usually run in combination with

LDT(DNL). Zones of poor density

readings are usually identical with poor

neutron porosity readings.

Typical Density Response




CNT (Compensated NT) Parameters





Standard (TNPH) 24”

Enhanced 12”

Depth of Investigation 9”-12”


Limestone(0%) 0

Sandstone(0%) -2

Dolomite(0%) 1

Anhydrite -2

Salt -3

Shale 30-45

Coal 50+

Code/Name




NPHI

TNPH

CN

CNL

CNT Uses




The tool measures hydrogen index

Its prime use is to measure porosity

Can be used to detect gas

Combined with the bulk density, it gives the best possible answer

for lithology and porosity interpretation

It can be used in cased hole

CNT in Cased Hole

C f




The CNT can be run in cased hole for the porosity

In addition to the standard corrections some others are needed to take into

account the extra elements of casing and cement The standard conditions are:

8 ¾” borehole diameter

Casing thickness 0.304”

Cement thickness 1.62”

Fresh water in the borehole and formation

No stand-off

75F

Atmosphere pressure

Tool centred in the hole





y

Neutron Matrix Correction (Chart)

NPHI = (1-Φn) * NPHIma + Φn * NPHIf

(NPHI – NPHIma)Φn = ---------------- (Chart Por-13b)

(NPHIf – NPHIma)

If NPHI is in LIMESTONE Matrix

Por-13b: Neutron Porosity




33.5 p.u in LS

38 p.u in Ss

Archie’s Equation



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t

m

w

w

R

Ra

S

Water

saturation,

fraction

w S

Resistivity of

formation water,

-mw R

Resistivity of

uninvaded

formation, -m

t R Porosity,

fraction

Empirical constant

(usually near unity)

a

Saturation

exponent(also usually

near 2)

n Cementation

exponent

(usually near 2)

m

Archie Parameters




Rw = resistivity of connate water

m = “cementation factor”, set to 2 in the simple case

n = “saturation exponent”, set to 2 in the simple case

a = constant, set to 1 in the simple case

All the constants have to be set

Two common sets of numbers for these constants are:

In a simple carbonate, the parameters are simplified to:

m=2, n=2, a =1

In a sandstone they become:

m=2.15, n=2, a =0.62

Saturation EquationsTh l b f t ti ti h




There are large number of saturation equations, such as:

Indonesia Equation

Nigeria Equation

Waxman-Smiths Equation

Dual-Water Equation

All reduce to Archie’s equation when there is no shale

1

Rt

S w2

F * Rw

BQvS w

F *

C t t mS wt n

aC w

S wb

S wt C wb C w

S w

1

V cl 1

V cl 2

Rcl

e Rw

*1

Rt

1

Rt

V cl 1.4

Rcl

e

m2

aRw

2

S wn

Rw Determination




• Rw from SP

• Rw from porosity and resistivity (wet zone)

Rw=(Φ^m)*Rt

• Rw from resistivity only (wet zone)

Rt*Rmf

Rw = --------------

Rxo• Rw from client (water chemical analysis)

All the Rw from different sources should be in consistent.

Rmf and Rw



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•Rmf and Rw should be corrected by temperature (BHT).

•Chart Gen-9

Exercise



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Exercise

Rt = 20 ohm-m

Rw = 0.6 ohm-m @ 75 degF

= 0.2 ; Vcl = 0

BHT = 150 degF

M=n=2 ; a = 1

What is water salinity?

What is Rw @ 150 degF?

What is Sw?

10Kppm

0.3 ohm-m

0.61

Exercise



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Rt = 100 ohm-mSalinity (Cl-) = 45 Kppm

= 0.22 ; Vcl = 0

BHT = 180 degF

M=n=2 ; a = 1

What is salinity (NaCl)?

What is Rw @ 180 degF?

What is Sw?

74 Kppm

0.04 ohm-m

0.09

Clean Sand Formation Workflow



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(Density-Neutron)

Φd Φn

Φ1

RwRw from SP or

Sw

Crossplot porosity 2

22

nphidphi

x

t m

wa R R

Rw Ro F

Sw Ro Rt I

R

RaS

m

m

n

t m

w

w

/ / 1

/ 1/

/ 1

f ma

bma D

Electric Resistivity Logging



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Electric Resistivity Logging

Resistivity Logs



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Resistivity is one of the primary inputs required to evaluate the producingpotential of an oil or natural gas well. This measurement is needed to

determine Sw, which is needed to estimate the amount of oil or natural gaspresent in the well.

Principles

(Conventional electrical logs)

Currents were passed through the formation from the currentelectrodes and voltages were measured between measuring

electrodes.

Resistivity of a formation depends on :Resistivity of the formation water

The amount of water Pore structure geometry

Focusing



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g

It is forcing the electrical currents to flow in the formation in the situation where the

formation resistivity gets high.

Laterolog devices are focused devices. The term laterolog came about because the

current is forced to flow "laterally" away from the tool.

There are three types of focusing systems in use today:

Passive Focusing Systems – DLL, ARI

Active Focusing Systems - ARI

Computed Focusing - HRLA

Example of Passive Focusing Passive Focusing Systems



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Distortion of equipotential

surfaces

Laterolog measurements began with a

device called the bucking electrode.To

focus the measured current laterally intothe formation, bucking electrodes are

place above and below the measure

electrode. As shown in "Passive

Focusing" graphic, equal current is

emitted from all three electrodes to focusthe current into the formation. With this

arrangement, the equipotential shapes

distort very quickly. This electrode

configuration is called the Laterolog

Three (LL3) and is known as a passive

bucking system

Example of Active FocusingActive Focusing



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To maintain the shape of the equipotential

surfaces and ensure the measured current

is flowing laterally into the formation in

formations of higher resistivities, the active

bucking system was introduced (LL5

device). As shown in the "Active Focusing"

graphic, this system places two voltage

electrodes, M1 and M2, between thecurrent-emitting measure electrode and the

bucking electrode. The measured current is

adjusted until the voltage difference

between M1 and M2 is zero. This ensures

that the area in front of these monitor electrodes is equipotential and the

measure current is flowing laterally away

from the tool. This is known as the laterolog

deep (LLD) measurement.

Computed Focusing



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The Laterolog Tool uses the main monitoring condition of M1 - M2 = 0 as the main control condition.

Limited Dynamic Range. To maintain M1 - M2 conditions in very high resistivities requires infinitegain.

Temperature Variations. Variations in temperature introduce errors in the measurements.

Continued developments in data processing, transmission, and digital conversion capabilities have

made it possible to take advantage of some electromagnetic principles, specifically the principles of

electromagnetic superposition. These capabilities allow us to obtain focused measurements throughcomputations instead of by mechanical means. The principles of computed focusing allow us to

maintain the condition of M1 - M2 = 0 by mathematically combining linear combinations of pairs of

operating modes. These operating modes and the combinations used to obtain the different depths of

investigation are shown in the "Computed Deep Focusing" and the "Computed Shallow Focusing"

diagrams. Array laterolog devices have multiple operating modes that are combined together to obtain

a series of computed focusing modes with increasing depths of investigation. An in-depth discussion

of these modes is beyond the scope of this text.

Example of Computed Focusing



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Example of Computed Focusing

Depth Of Investigation



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Different depths of investigation are obtained by varying lengths of bucking current electrodes.

Shallow Focusing

If the current is returned to the tool body, instead of the surface electrode, the equipotential

surfaces distort very quickly and the resistivity measurement is influenced by events very

close or shallow to the tool. This is known as the laterolog shallow (LLS) measurement.

Deep Focusing

In this system the currents are returned to the surface electrode instead of the tool body.

This maintains the shape of the equipotential surfaces much deeper into the formation

insuring the measure current is flowing deeper into the formation than the shallow

measurement. To measure both the shallow and deep depths of investigation

simultaneously is very desirable to help estimate the invasion profile for more accurate

measurements. The Dual Laterolog (DLT), a device that measures at two depths of investigation was developed for this purpose.

This tool combines the measurement principles of the LLD and LLS into a single device by

having each measurement operate on a different frequency.




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Invaded Zone or Rxo Devices

To complete the borehole description, devices were developed that measured at

very shallow depths of investigation in the invaded zone (Rxo), also referred to

as the flushed zone. These devices use the principles of active and passive

focusing and change the distance between the emitting electrodes and the

return electrode to achieve very shallow depths of investigation. Example of the

tools are MSFL, Microlog and MCFL.

Azimuthal Resistivities

Azimuthal resistivities are resistivity measurements made around the

circumference of the borehole. Azimuthal measurements are very useful in

evaluating highly deviated and horizontal boreholes.




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Array Resistivities - HRLA

Laterolog array resistivities are obtained through multi-frequency operating modes (5curves) employing a shallow-style measurement. By taking an array of measurements we

are able to solve a formation model to determine and correct for environmental effects

(such as shoulder bed effects and invasion) and hence calculate the un-invaded

formation resistivity, Rt, which is the main goal of this type of measurement.

Laterolog Borehole Effects



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Laterologs measure Resistivity in Series

Laterologs see the borehole environment as

RLL=Rm+Rmc+Rxo+Rt

Rm: Mud resistivity

Rmc: Mud cake resistivity, usually neglected as very small

Rxo: Flushed zone resistivity, depends on Rmf, needs to be known

Rt: Parameter to be measured, the higher the better

Best measurement is in salt

saturated, low resistivity mud.

Worst readings obtained in fresh

mud.

Measurement can’t be taken in OBM

Tornado Charts

f



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The simple invasion model is used to solve for the three unknowns: Rt, Rxo, di

Three resistivity measurements are needed

Deep: ILD,ILDH,LLD,AIT90,RLA5

Medium: ILM,IMPH,LLS,SFL,AIT30,RLA2

Shallow: MSFL,AIT10,RLA1

The equation can be solved using Tornado charts

Several charts exist: one for each possible configuration of the resistivities. The correct one must be

chosen for each situation

There are zones on each chart where the solution is impossible, this is where the tool is being run

outside its specifications or the corrections have not been properly applied

Example Tornado Chart



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Code/Name



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Deep: RT,LLD,RLA5,RT*

Medium: LLS,RLA3

Shallow: RXO,MSFL,SFLU,RLA1/RLA2

RESISTIVITY - DUAL LATEROLOG LOG EXAMPLE



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STANDARD DISPLAY OF

(PHASOR) INDUCTION LOG (PI)


LLD … Deep Laterolog Resistivity [Ωm]

LLS… Shallow Laterolog Resist. [Ωm]

SP*…... Spontaneous Potential

* not shown on this display


Dual Laterolog readings for formation

resistivities < 1.0 Ωm become inaccurate -

Induction might have been the better

choice. LLS can be severely affected in

large holes - washouts - and not be in

agreement with LLD (LLD less sensitive to

borehole conditions).

SP……see SP section on log quality

control.

Applications Correlation Water saturation and Invasion analysis



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Correlation, Water saturation, and Invasion analysis

Because laterolog tools have the ability to control the region of investigation inVertical, radial and azimunthal directions, these tools have additional apps :

Evaluate mud cake and mud resistivity for borehole correction using very shallow

measurements.

Enhance the evaluations of horizontal and or highly-deviated wells using azimuthaland array measurements.

Fracture analysis using azimuthal measurements.

Enhance the evaluations of thin and invaded formation using array measurements.

Enhance the accuracy of Rt evaluation in difficult environments such as Groningen

affected areas, high contrasts, thinly bedded formations and high apparent dip byusing array measurements and formation inversion processes.

Open Hole Formation Evaluation



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Section 10:

Induction Logging

Induction Theory



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An induction tool uses ahigh frequencyelectromagnetictransmitter to induce acurrent in a ground loop of formation

This, in turn, induces anelectrical field whosemagnitude is proportionalto the formationconductivity

Induction Logs




Induction Principles :

A high-frequency AC of constant intensity is sent through atransmitter coil -> magnetic field -> create currents in the

formations as ground loops coaxial with the transmitter coil ->

magnetic field that induces a voltage in the receiver coil.

Induction tool works best when the borehole fluid is an insulator,air or gas, even when the mud is conductive.

Induction: Borehole Effects

Induction tools measure Conductivity




Induction tools measure Conductivity.

Induction measures resistivity in Parallel

Thus induction tools see the borehole environment as:

Cm: Best readings occur in high resistivity mud, OBM is better,

fresh mud is good, salt-saturated mud is worst

Cmc: usually neglected as very small

Cxo: depends on Rmf – needs to be known

Ct: Parameter to be measured, the higher the better

Code/Name




Deep: RT,ILD,IDPH,AIT90,RT* Medium: ILM,IMPH,AIT30/AIT60, A*

Shallow: RXO,MSFL,SFLU,AIT10/AIT20, A*

RESISTIVITY - INDUCTION Log Example




STANDARD DISPLAY OF

(PHASOR) INDUCTION LOG (PI)- Primary Logging Curves:

IDPH … Deep Induction Resistivity [Ωm]

IMPH… Medium Induction Resist. [Ωm]

SFL* … Spherical Focused Log [Ωm]

SP*…... Spontaneous Potential

* not shown on this display


Induction readings for formation

resistivities > 50 Ωm are inaccurate - Dual

Laterolog might have been the better

choice. IMPH (medium induction) can be

severely affected in large holes - washouts -

and not be in agreement with IDPH (IDPH

less sensitive to borehole conditions).

SP……see SP section on log quality

control.

Induction vs Laterolog




Laterolog Induction

OBM no yes

Salt Water Mud yes Possible in small holes*

Fresh mud No** yes

High resistivity yes noAir-filled hole no yes

Low resistivity Possible*** yes

Rt<Rxo Induction prefered

Rt>Rxo Laterolog

Prefered

FMI image versus core




AUXILIARY LOGS




• TEMPERATURE MEASUREMENT

Vital Input Log Analysis:

Fluid resistivity changes with temperature - Rw (formation water resistivity)

and Rmf (mud filtrate resistivity) vary with temperature.

Temperature/Mud Resistivity Measurements:

- Maximum Thermometer’s: Thermometers tied to the tool string and read once

the string returns to surface. The time the tool string reaches the bottom of the

well is recorded on the log header together with the temperature reached. Using

the maximum recorded temperature a linear temperature gradient is established

to correct mud sample measurements to down-hole conditions.

- Auxiliary equipment such as the Environmental Measurement Sonde (EMS) or

auxiliary sensors on logging equipment such as the Platform Express perform

continuous recording of temperature and mud sample resistivity.

LOGGING RESULTS DELIVERABLES




GRAPHICS - Films Prints usually in two different depth scales:1/200 as main working copy and 1/500 (1/1000) for

correlation purposes.

Certain measurements are being delivered with Log

Quality Displays verifying the quality of the data

recorded.

DIGITAL DATA - usually recorded on DAT (Digital Audio Tape) in DLIS

(Digital Log Information Standard - API RP 22). The

digital records contain raw data and auxiliary allowing

for subsequent re-computation of log parameters.

Other formats such as LIS, BIT, TIF, XTF, DIPLOG,

LAS (Log ASCII Standard) are also used for small

data sets covering primary log information only.

LOG DISPLAY PRINCIPLE COMPONENTS




LOG HEADER - includes all information about the well logged and information

necessary to describe the environment the measurement has been

informed in (e.g. drilling mud parameters). Tool sketches and

remarks informing about specific events during the logging

operation complete the header.

MAIN LOG - main display of measurement performed.

REPEAT SECTION - short section of log to prove repeatability of log or re-log of sections

with measurement anomalies.

LOG TRAILER - includes tool/computation parameter table and calibration records.

LOG DISPLAY LOG HEADER 1




LOG DISPLAY LOG HEADER 2




LOG DISPLAY LINEAR SCALE




LOG DISPLAY LOGARTIHMIC SCALE




LOG DISPLAY LOG TRAILER 1



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Tool/Computation

Parameter Table

LOG DISPLAY LOG TRAILER 2



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Calibration

and Check

Summary

LOG DISPLAY LOG TRAILERS (3)



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Tool Calibration

Details

Petrophysical Analysis Results



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Documents

BasicPetro_2.ppt