CGE 674CGE 674CGE 674CGE 674

FORMATION EVALUATIONFORMATION EVALUATIONFORMATION EVALUATIONFORMATION EVALUATION

TENGKU AMRAN TENGKU MOHD

BY:

Introduction1 Introduction1

� Logging History

� Openhole Logging Acquisition

Outline

� Principles of Openhole Logging Tools –GR, SP, Neutron-Density, Resistivity, Sonic

After completing this chapter, you should be able to:

- Understand the basic principle of formation evaluation and well logging

Objectives

- Describe the surface and downholeequipments/ tools to conduct a logging operation

- Describe the principle and log response of each of logging tool.

WHAT ARE FORMATION EVALUATION AND WELL

LOGGING???

Overview

LOGGING???

Formation Evaluation…

Process/method to determine or identify if apotential oil or gas field is commerciallyviable by using all available data (e.g. well

Overview

potential oil or gas field is commerciallyviable by using all available data (e.g. welllog data, core data, mud log, RFT data etc.)for interpretation of reservoir formation

Well Logging…

A method or in situ measurement orrecordings (vs depth) to determine thephysical, chemical and petrophysical

Overview

recordings (vs depth) to determine thephysical, chemical and petrophysicalproperties of the reservoir rocks and fluids.

HOW ABOUT LOGGING WHILE DRILLING (LWD)???

Overview

Logging While Drilling…� Advanced logging operation allowing acquisition of log data

via tools placed in the actual drilling assembly, which transmit the data to the surface on a real-time basis or store the data in a downhole memory from which it may be downloaded when the assembly is brought back to the

Overview

downloaded when the assembly is brought back to the surface.

� Their use may be justified when:

– real time information is required for operational reason, e.g.

steering a well

– acquiring data prior to the hole washing out or invasion

occurring

– safeguarding information if there is a risk of losing the hole

– the trajectory where wireline acquisition is difficult

EVALUATION SEQUENCE

Rock

Overview

Locate the

Reservoir

Reservoir

Non Reservoir

Detect

Hydrocarbons

Hydrocarbons

Water

Gas

Oil

Evaluate

Evaluate

Differentiate

Between gas/oil

What subsurface information is important?

What is value of hydrocarbon in place?

(Potential value)

• Hydrocarbon thickness

• Porosity

• Saturation

• Area

• Hydrocarbon type

How easy is it to drill to the reservoir?

(Cost of drilling, completing…)

How easily can the hydrocarbon flow

out the well?• Permeability

• Pressure

• Lithology

• Depth, pressure, temperature

Formation evaluation is critical to understanding the reservoir

What is value of hydrocarbon in place?

(Potential value)

How easy is it to drill to the reservoir?

(Cost of drilling, completing…)

How easily can the hydrocarbon flow

out the well?

Logging History

Year Description

1927 • First electrical log was recorded in a well in the small oil field of Pechelbronn, in Alsace, a province of north-eastern france.

• Single graph of electrical resistivity of rock formations was recorded by “station” method.• “sonde” was stopped at periodic intervals in borehole, measurements made, and calculated

resistivity was hand-plotted on a graph – this procedures was carried out from station to

Electrical Logging

resistivity was hand-plotted on a graph – this procedures was carried out from station to station until entire log was recorded.

• Resistivity log was used to detect HC present in the formation.

1929 • Electrical resistivity logging was introduced on a commercial basis in Venuzuela, US, Russia and Dutch East Indies.

• Usefulness: for well to well correlation and identification of potential HC-bearing strata.

1931 • Include SP measurement with Resistivity curve on electrical log. • Schlumberger brothers (Marcel & Conrad) perfected a method of continuous recording

1936 • Photographic-film recorder was introduced• Electrical log consisted of SP curve, short normal, long normal & long lateral resistivity

curves, was predominant in logging activity from 1936 to late 1950’s (curves were recorded simultaneously after about 1946).

Logging History

Year Description

1930’s • The development of dipmeter began with the anisotropy dipmeter tool.

1943 • Three-arm dipmeter device, with an associated photoclinometer was introduced – permitted both direction and angle of formation dip to be determined (SP sensor at each arm).

Dipmeter Log

1946 • SP sensors were replaced by short resistivity devices – made dip measurements possible in wells where SP had little correlatable detail.

Mid-1950’s

• First continuously recording electrical dipmeter sonde (used 3 microresistivity arrays and contained a fluxgate compass) was introduced.

Today • A 4-arm dipmeter tool records 10 microresistivity curves simultaneously, and a triaxialaccelerometer and magnetometers provide highly accurate info on tool and deviation azimuth.

• Processing data done exclusively with electronic computers.

Logging History

Year Description

1941 • Neutron log was first described by Pontecovo.• In combination with GR log, neutron log enhanced lithological interpretations and well-to-well

stratigraphic correlations.

1949 • Attention to neutron log as a porosity indicator.

GR and Neutron Tools (first use of radioactive properties in well logging)

1949 • Attention to neutron log as a porosity indicator.

1962 • SNP sidewall neutron porosity tool was introduced.

1936 • CNL* compensated neutron tool was introduced.• Dual Porosity neutron tool combines those 2 neutron measurements into a single tool.

Logging History

Year Description

1950’s • Microlog tool was introduced – used a miniature linear array of 3 electrodes imbedded in the face of an insulating pad, which is applied to the borehole wall.

• Microlog recording is also useful to delineate permeable beds, and other microresistivitydevices help establish resistivity profile from the invaded zone near the borehole to the non-invaded virgin formation.

Early Porosity Determination & Microresistivity Measurement

invaded virgin formation.

1951 • Laterolog tool was introduced (the first focused deep-investigating resistivity device) –focused resistivity logs are well adapted for investigating of thin beds drilled with low-resistivity muds (eg. Salt muds & highly resistive formations)

1953 • Microlaterolog tool was developed for salt muds. • The MicroProximity log and MicroSFL* log have followed.

Today • DLL* dual lateral log tool (deep laterolog and shallow laterolog measurements) is the standard.

• Usually run with a MicroSFL device as well

Logging History

Year Description

1949 • Induction log was developed, as an outgrowth of wartime work with mine detectors, for use in oil-based mud.

• However, its superiority over electrical log in freshwater muds was soon recognized.

1956 • Combine a five-coil induction device with SP curve and a 16-in normal to make induction

Induction Log (replace original electrical log in freshwater muds)

1956 • Combine a five-coil induction device with SP curve and a 16-in normal to make induction electrical tool.

1959 • Five-coil device was replaced by one with a six-coil array with deeper investigation.

1963 • DIL* dual induction log was introduced, now is the standard – deep induction, medium induction, and shallow resistivity-measurements.

• The shallow resistivity-measuring device is now a focused resistivity device – a Laterolog 8 on the 1963 tool and an SFL device on current tools

• A new dual induction log, the Phasor* induction, provides improved thin-bed response, deeper depth of investigation, and greater dynamic resistivity range.

Logging History

Year Description

Since 1930

• Logging cables have been used to lower geophones into wells to measure long-interval acoustic travel times from sound sources at the surface.

Late1950’s

• Sonic log was accepted as a reliable porosity logs – its measurement responds primarily to porosity and is essentially independent of saturation.

Sonic Log

1950’s porosity and is essentially independent of saturation.• Sonic log, coupled with focused resistivity logs (laterolog and induction) – made possible

modern formation evaluation from well logs.• Sonic log – measure porosity; focused resistivity logs – measure true resistivity of non-

invaded virgin formation.• Subsequent improvements in sonic logging – BHC borehole compensated sonic, LLS*

long-space sonic, and the Array-sonic* tools.

Logging History

Year Description

Early1960’s

• Logging of formation bulk density (measurement of formation porosity), was commercially introduced.

1964 • An FDC* compensated formation density log (compensated for the mudcake), was

Density Log

1964 • An FDC* compensated formation density log (compensated for the mudcake), was quickly followed.

1981 • Litho-Density* log provided an improved bulk density measurement and a lithology-sensitivephotoelectric absorption cross section measurement.

Logging History

Year Description

1937 • Sidewall coring, using a hollow, cylindrical “bullet” shot into formation and retrieved by pulling it out, has existed since 1937.

Recovery of Physical Rock Samples & Formation Fluid Samples with Wireline Tools

1957 • A formation tester was introduced – recovered a sample of formation fluids and pore presurewas measured during the sampling process.

• FIT formation interval tester and RFT* repeat formation tester have followed (RFT tool can make unlimited number of pressure measurements and recover two fluid samples per trip.

1978&

1985

• Dielectric measurements have been developed to handle formation with freshwater formation, or varies in salinity, or in which salinity is unknown.

• EPT* electromagnetic propagation log was introduced in 1978• DPT* deep propagation log was followed in 1985.

Introduction

Well logs or wireline logs are continuous recordings of well depth versus

different petrophysical characteristics of the rocks through which the well is

drilled. There are many types of well logs, depending upon the characteristics

of the rock being measured.

Logging Objectives

The main purpose of well logging is:

- to provide data for evaluating petroleum reservoirs.

Wireline Logging

- to provide data for evaluating petroleum reservoirs.

- to aid in testing, completion and repairing of the well.

To calculate the oil reserve in an oil pool we need to know the following.

• Thickness of the oil bearing formation.

• Porosity of the formation.

• Oil saturation.

• Lateral extent of the pool.

Logs should always be calibrated with core data to improve

interpretations.

Wireline Logging

• In situ meas. (vs. depth) of

– Rock properties

– Fluid properties

• When

– Openhole (before casing)

• While drilling (LWD / MWD).

Casing

• While drilling (LWD / MWD).

• After drilling (wireline).

– Cased hole (C/O, sigma)

• Interpretation for:

– Geological properties.

– Petrophysical properties.

– Production properties.

Open hole

Types of Well Logging

Well logging is classified into three broad

categories:

� Open Hole Logging

� Cased Hole Logging

� Production Logging

Logging surveys taken before the hole is cased are called open

hole logs. The logs included in this group are:

� Electrical surveys (induction, laterolog and microlog logs).

Open Hole Logging

� Sonic logs.

� Caliper Logs.

� Dipmeter Logs.

� SP logs

� Radioactive surveys (density, neutron and gamma ray logs).

Electrical Logs

Electrical logs (Induction, laterolog, and microlog)

measure the electrical properties of the formation

alongwith the formation fluids.

Sonic/ Acoustic Logs

Sonic logs measure the elastic or (sound) wave Sonic logs measure the elastic or (sound) wave

properties of the formation.

Caliper Logs

Caliper logs measure the size or geometry of the hole.

Dipmeter Logs

Dipmeter logs measure dip of the formations.

SP Logs

SP logs measure potential different between a shale-sand or

shale-carbonate due to difference salinity of formation water shale-carbonate due to difference salinity of formation water

and mud filtrate.

Radioactive Logs

Gamma ray & neutron logs measure radioactive and neutron

absorption properties. Density logs measure electron density of

the formation which is related to formation density.

OPEN HOLE LOGGING MEASUREMENTS

27

LO

GG

ING

TO

OL

Cased Hole Logging

Logging surveys taken after the casing is lowered are usually categorized as cased hole logs. The surveys included in this group are:

� Gamma Ray

� Neutron

� Temperature

� Pulsed Neutron

� Cement Bond Log

� C/O and sigma Log

Some of these surveys like the gamma ray, neutron and temperature

logs can be run in both open and cased hole wells.

CASED HOLE LOGGING MEASUREMENTS

Production Logging

Well logging surveys taken to improve production or repair the well are

termed as production logs. Surveys included in this category are:

� Flowmeter

� Pressure� Pressure

� Temperature

� Fluid Density

VALUE AND LIMITATIONS OF WELL LOG DATA

Strengths

• Provides remotely sensed values of reservoir properties and fluids.

• Among the most abundant reservoir data.

• Presentation results fairly well standardized.

• Allows evaluation of lateral (map) and vertical (cross section) • Allows evaluation of lateral (map) and vertical (cross section)

changes in reservoir properties and fluids.

Limitations

• Indirect measurements.

• Vertical resolution.

• Depth of investigation.

Petrophysical Logging Tools - Primary

Log Type Tool Type Physical

Measurement

Derived

Parameter

Interpreted

Parameter

Resistivity

-Induction

-Laterolog

-Micro laterolog

Array

Array

Pad

Voltage (V)

V and Current (I)

Current

Rt

Rt

Rxo

Sw

Sw

Sxo

Acoustic

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Acoustic

- Sonic Array Transit Time PHIs Lithology

Nuclear

-GR (Density)

- Neutron

Pad

Mandrel

Gamma Ray

Neutron

RHOB, PHID

RHON

Lithology

Lithology

Auxiliary

-Natural GR

-SP

-Caliper

Mandrel

Electrode

Gamma Ray

mV

(*various)

None

None

Dh, Volume

Vsh

Vsh

SOME QUESTIONS ADDRESSED BYLOG INTERPRETATION

• Geophysicist / Geologist

– Are the tops as predicted?

– Are potential zones porous?

– Formation intervals?

– Lithology?

• Reservoir Engineer

– How thick is the pay zone?

– How homogeneous is the zone?

– Porosity?

– Permeability?– Lithology?

– Hydrocarbons?

– What type of hydrocarbons?

– Commercial quantities?

• Production Engineer

– Which zone(s) to complete?

– What production rates?

– Any water production?

– Is zone hydraulically isolated?

– Will well need stimulation?

– What stimulation would be best?

Fig. 3.1: A Logging Truck

WIRELINELOGGING

EQUIPMENT

Computer-based units offer the following features:

� Computer control of the data allows logs to be recorded

either logging up or down with all curves on depth.

Computerized Logging Units

� Calibration are performed under programme control and can

be performed more quickly, consistently and accurately.

� Logs can be played back from the data tapes on many

different formats.

� Basic wellsite, processing/analysis of data is available.

DETAILS OF WIRELINE LOGGING RIGUP

LOGGING CABLE

39

Log Presentation

• Heading.

• Curves related to some physical property of rock/casing

surrounding the wellbore.

LOG PRESENTATION - THE HEADING

• Well location

• Depth references

• Well depth

• Date of log

• Casing shoe depth

41

• Bit size

• Mud data

– Type

– Properties

– Resistivities

• Max. Temperature

LOG PRESENTATION

LOG PRESENTATION - LINEAR GRID

Track 1Depth

track Track 2 Track 3

43

LOG PRESENTATION - COMMON DEPTH SCALES

44

TYPES OF LOGS TO BE RUN

• Logging suites generally include one resistivity and one

porosity device.

• The logging string will also have other tools like the gamma

ray, SP and caliper tools.

• However, logging suites usually have two porosity devices to

give more information about rock type, hydrocarbon type and give more information about rock type, hydrocarbon type and

porosity.

• Other considerations – to estimate permeability or to take

fluid samples – require other special tools like the formation

testers.

MUD FILTRATE INVASION

Uninvaded Zone(Rt)Invaded

Zone

Wellbore

Mud(Rm)

Mud Cake(Rmc)

Zone (Rxo)

Uninvaded Zone(Rt)

MUD FILTRATE INVASION

Borehole

Rm : Borehole mud resistivity

Rmc : Mudcake resistivity

Invaded zone

Rmf : Mud filtrate resistivity

Rxo : Invaded zone resistivity

Sxo : Invaded zone water saturation

COMMON TERMINOLOGY

Sxo : Invaded zone water saturation

Uninvaded zone

Rw : Interstitial water resistivity

Rt : Uninvaded zone resistivity

Sw : Uninvaded zone water saturation

Radial Fluid and Resistivity

Distribution

Resis

tivity

Resis

tivity

Rx0 Rt Rx0 Rt

Rxo

Rt

RxoRt

Water Based Muds

Qualitative Distribution of Resistivity (Rmf > Rw)

Rt

Fresh mud, salt water zone

Salty mud, Hydrocarbon zone

NOMENCLATURE FOR ZONES INAND AROUND THE BOREHOLE

Sources of subsurface data

Data collected during drilling

Core analysis

Penetration rateDrill cuttings analysisDrill mud analysisMud gains/lossesShows of gas/oil/water

LithologyPresence of showsPorosityPermeabilitySpecial core analysis

Wireline log analysis

Productivity tests

Special core analysis

Electric logsAcoustic logsRadioactivity logsPressure measurementsSpecial logs

Formation testerDrill stem testProduction test

Hydrocarbon thickness

Porosity

Sources of subsurface data

Data needed: Data source:

Porosity

Saturation

Area

Hydrocarbon type

Permeability

Pressure

Lithology

Cuttings, Mud log

Coring

Logging

• LWD – Logging while drilling

• WL – Wireline (usually open hole)

Mud Log

• Immediate interpretation of what the drill bit has penetrated and whether there are any hydrocarbons present (a show).

• Making maps of the subsurface geology.• Making maps of the subsurface geology.

Sources of data – Mud log

Mud log

Hydrocarbon thickness

Porosity

Sources of subsurface data

Data needed: Data source:

Porosity

Saturation

Area

Hydrocarbon type

Permeability

Pressure

Lithology

Cuttings, Mud log

Coring

Logging

• LWD – Logging while drilling

• WL – Wireline (usually open hole)

Coring - Conventional

• Taking a core requires that the regular drill bit be removed from the hole. It is replaced with a "core bit", which is capable of grinding out and retrieving the heavy cylinder of rock.

• The core bit is usually coated with small, sharp diamonds that can grind through the hardest diamonds that can grind through the hardest rock. A core bit cuts very slowly.

• A core is a solid cylinder of rock about 4-5 inches in diameter, and a single core will usually be about 30 feet long.

Coring - Conventional

Whole Core Slab Core

Sources of data – Core

Coring - Sidewall

• This method is cheaper than the conventional coring.

• Cores can be taken in hours, instead of days.

• In sidewall coring, a slim wireline coring tool is run into the hole. The tool may be of two general types; either "rotary sidewall" or "percussion".

• Typically, cores about 1" in diameter and 1" to 2" long can be retrieved with this method.

Coring - Sidewall

Hydrocarbon thickness

Porosity

Sources of subsurface data

Data needed: Data source:

Porosity

Saturation

Area

Hydrocarbon type

Permeability

Pressure

Lithology

Cuttings, Mud log

Coring

Logging

• LWD – Logging while drilling

• WL – Wireline (usually open hole)

Sources of data – Logs