Lecture Lecture # 09# 09Introduction to Well Logging andIntroduction to Well Logging andIntroduction to Well Logging and Introduction to Well Logging and Formation Evaluation Formation Evaluation

By: Dr. Mohammad Ebrahim Shafiee

Well Logging and Development of Well Logging and Development of H d b R iH d b R iHydrocarbon ReservoirsHydrocarbon Reservoirs

Th l i t d i ’ l i t d t dThe geologist and engineer’s goal is to understand the processes of hydrocarbon accumulation and recovery factor.y

Well-logging plays a particularly important role in geophysic.

Well logs provide an objective continuous recordWell-logs provide an objective, continuous record of a number of properties of the rocks which have been drilled through.g

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Well Logging and Development of Well Logging and Development of Hydrocarbon ReservoirsHydrocarbon Reservoirs

The link between geophysical measurements on the surface, and well logging subsurfacedatadata.

Well logging provide numerical data, introducing the possibility of fairly rigorousintroducing the possibility of fairly rigorous quantification in the description of sedimentological processes.g p

Logs tell us about the fluids in the pores of the reservoir rocks.

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What is Well LoggingWhat is Well LoggingWell log is a continuous record of measurement made inWell log is a continuous record of measurement made in

bore hole respond to variation in some physical properties

of rocks through which the bore hole is drilled.

Traditionally Logs are displayTraditionally Logs are display

on girded papers

shown in figure.

Now a days the log may be

taken as films, images, g

and in digital format.

Oilfield Glossary DefinitionOilfield Glossary DefinitionOilfield Glossary DefinitionOilfield Glossary Definition

Log: The measurement versus depth or time, or both, of one or more

physical quantities in or around a well. The term comes from the word

"log" used in the sense of a record or a note.

Wireline logs are taken downhole, transmitted through a wireline to

surface and recorded there. LWD "Logging While Drilling" and MWD

“Measurement While Drilling" logs are also taken downhole.

They are either transmitted to surface by mud pulses, or else recorded

downhole and retrieved later when the instrument is brought to surface.

Mud logs that describe samples of drilled cuttings are taken and recorded

on surface.

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LWD and MWD versus Wireline ToolsLWD and MWD versus Wireline ToolsLWD and MWD versus Wireline ToolsLWD and MWD versus Wireline ToolsLWD and MWD are acronyms for "Logging While Drilling" and

"Measurement While Drilling" and refer to the technique of placing the

logging tool somewhere behind the drill bit so that it can record data

during the actual drilling.

Depending on far the tool sits behind the bit, the data can be measured,

more or less, in real time to create Realtime Logs at the surface. After the

tool is pulled from the hole, data can then be downloaded from the toolp

itself to create what are called Memory Logs, which are higher resolution

and more reliable than the Realitme logsand more reliable than the Realitme logs.

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History of Well loggingHistory of Well logging1912 Conrad Schlumberger give the idea of using electrical measurements

to map subsurface rock bodies.

In 1919 Conrad Schlumberger and his brother Marcel begin work on well

logs.

The first electrical resistivity well log was taken in France, in 1927.

The instrument which was used for this purpose is called SONDE, the

d d i di i l i b h l d h i i isonde was stopped at periodic intervals in bore hole and the resistivity was

plotted on graph paper.

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History Cont.History Cont.In 1929 the electrical resistivity logs are introduce on commercial

scale in Venezuela, USA and Russia and the dip meter log were

developed in 1930 and he Gamma Ray and Neutron Log were begin

in 1941

For correlation and identification of Hydrocarbon bearing strata.

The photographic – film recorder was developed in 1936

Dr. Shafiee 8

Logging Units Logging Units

L i iLogging service

companies utilize a

variety of logging units,

depending on the

location (onshore or

offshore) and )

requirements of the

logging runlogging run.

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Logging Work Flow ChartLogging Work Flow Chart

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Logging Units ComponentLogging Units ComponentLogging cable

Winch to raise and lower the cable in the well

Self-contained 120-volt AC generator

Set of surface control panelsSet of surface control panels

Set of downhole tools (sondes and cartridges)

Digital recording systemDigital recording system

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Depth Of Investigation Of Logging ToolsDepth Of Investigation Of Logging Tools

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Log Interpretation ObjectivesLog Interpretation Objectives

Learn the basic concepts and terminology associated

with log interpretationwith log interpretation

Learn basic tool theory so that this knowledge can be

applied to actual log readings from qualitative analysis

Do quantitative log analysis through in class examplesq g y g p

Learn how to correct log reading for environmental

ff t f l i i b h l ditieffects for example invasion, borehole conditions,

shaliness and gas effect

Be able to locate potential hydrocarbon-bearing zones

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Results from Log Interpretation Results from Log Interpretation g pg p

Depth to lithological Rock strengthp g

Lithological boundaries

g

In-situ stress orientation

F fLithology identification

Minerals grade/quality

Fracture frequency

Porosity

Inter-borehole

correlation

Permeable zones

Fluid salinitycorrelation

Structure mapping Water-bearing zones

Hydrocarbon bearing zonesDip determination

Hydrocarbon -bearing zones

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Well Log and Formation EvaluationWell Log and Formation EvaluationWell Log and Formation EvaluationWell Log and Formation Evaluation

Auxiliary Tools Porosity Toolsy

Callipers

Gamma Ray

Porosity ToolsAcoustic

Formation Density

Spontaneous Potential

SP

y

Neutron

Resistivity Tools

InductionInduction

Laterlog

Micro Resistivityy

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Resistivity LogResistivity Log

Resistivity logs measure the ability

of rocks to conduct electricalof rocks to conduct electrical

current and are scaled in units of

ohm-metersohm meters.

The Usage: Resistivity logs are

electric logs which are used to:

Determine Hydrocarbon

versus Water-bearing zones,

Indicate Permeable zones,

Determine Porosity.Dr. Shafiee 17

Spontaneous Potential Log (SP)Spontaneous Potential Log (SP)Spontaneous Potential Log (SP)Spontaneous Potential Log (SP)

The spontaneous potential

(SP) curve records the

t ll i l t i lnaturally occurring electrical

potential (voltage) produced

by the interaction ofby the interaction of

formation connate water,

conductive drilling fluid, andg ,

shale

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Gamma Ray LogGamma Ray LogGamma Rays are high-energy electromagnetic waves which

are emitted by atomic nuclei as a form of radiationy

Gamma ray log is measurement of natural radioactivity in

f ti d thformation verses depth.

It measures the radiation emitting from naturally occurring

U,Th, and K.

Thorium is a natural radioactive chemical element with the symbol Th and atomic

number 90

Uranium is a silvery-white metallic chemical element in the actinide series of the

periodic table with atomic number 92 It is assigned the chemical symbol Uperiodic table, with atomic number 92. It is assigned the chemical symbol U

Potassium-40 (40K) is a radioactive isotope of potassium which has a very long half-life

of 1.248×109 years, or about 39.38×1015 seconds. Dr. Shafiee 19

Gamma Ray LogGamma Ray Log

It is also known as shale log and reflects shale org

clay content.

A d f h l hAn advantage of the gamma log over some other

types of well logs is that it works through the steel

and cement walls of cased boreholes. Although

concrete and steel absorb some of the gammag

radiation, enough travels through the steel and

cement to allow qualitative determinationscement to allow qualitative determinations.

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Neutron LogNeutron Log

The Neutron Log is primarily

used to evaluate formation

porosity, but the fact that it is

really just a hydrogen detector

should always be kept in mind

It is used to detect gas in

certain situations, exploiting

the lower hydrogen density, or

hydrogen index Dr. Shafiee 21

Density LogDensity LogThe formation density log is a

porosity log that measures electron

density of a formation

It determine porosity by measuring

the density of the rocks. Because

these logs overestimate the porosity

of rocks that contain gas they result in

"crossover" of the log curves when

paired with Neutron logs (described p g (

under CNL logs below).Dr. Shafiee 22

Acoustic LogAcoustic Log

Acoustic tools measure the

speed of sound waves in

subsurface formations. While

the acoustic log can be used to

determine porosity in

consolidated formations, it is,

also valuable in other

applications such as:applications, such as:

Indicating lithology (using the

ratio of compressional

velocity over shear velocity),Dr. Shafiee 23

Acoustic Log cont’d Acoustic Log cont’d D t i i i t t d t lDetermining integrated travel

time (an important tool for

seismic/wellbore correlation),

Detecting fractures and

evaluating secondary porosity,

Evaluating cement bondsg

between casing, and

formationformation,

Determining acoustic

impedance (in combination

with the density log).Dr. Shafiee 24

Major Logging CompaniesMajor Logging CompaniesSchlumberger

Baker Hughes

Halliburton

G iGeoservices

Recon Petrotechnologies

Ltd.

Datalog

Logdigi

T k E S iTucker Energy Services

Weatherford Dr. Shafiee 25

QUESTION?QUESTION?QUESTION?QUESTION?

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