basic well logging design

Basic Well Logging DesignBasic Well Logging Design

Coordinated ByCoordinated By

Sigit SutiyonoSigit Sutiyono

Unocal Indonesia CompanyUnocal Indonesia Company

A One-day Course on

Consortium Alumni Association Presents

AgendaAgenda

• Introduction (8:15)

• Lecture‐I Basic Theory/Interpretation

• Break (10 – 10:15)

• Lecture‐II Logging Program/Design

• Break (12:00)

• Workshop (1:30 – 4:00)

• Wrap‐up (4:00 – 5:00)

ObjectivesObjectives

♦ Get to know various log measurements

♦ Recognize fluid type and lithology of major reservoirs, and some practical application of log data

♦ Familiarize with factors affecting the log response

♦ Understand the strategy in well evaluation

♦ Get to know various approaches to well logging design

♦ Exercise with well log design

According to 4th Edition of J.A.Jackson’s Glossary of Geology:

Log : A continuous record as a function of depth,usually graphic and plotted to scale on a narrowpaper strip, of observations made on the rocksand fluids of the geologic section exposed inthe well-bore.

DefinitionDefinition

Wireline Logging Logging while Drilling

Cable

Tools

LWD Tools

Mud inMud out

Drill Bit

Well Logging HistoryWell Logging History

• The first electrical log was introduced in 1927 in France using stationed resistivity method.

• The first commercial electrical resistivity tool in 1929 was used in Venezuela, USA and Indonesia.

• SP was run along with resistivity first time in 1931

• Schlumberger developed the first continuous recording in 1931

• GR and Neutron logs was started in 1941

• Microresistivity array dipmeter and lateralog were first time introduced in 1950’s

• The first induction tool was used in 1956 followed by Formation tester in 1957, Fomation Density in 1960’s, Electromagnetic tool in 1978 and most of Imaging logs were developed in 1980’s

• Advanced formation tester was commercialized in early 1990’s

The “First” Log recorded in 1927

Well in Pechelbronn - France Surface Recording Instrument

Log MeasurementsLog Measurements

Log is an indirect measurement of formation properties exposed by the well‐bore acquired by lowering a device or

a combination of devices in the well bore.

Practical definition of a log

A Formation Evaluation Specialist is essential to understand

The theory of measurements, quality control, interpretation principles, geophysics and petroleum geology as well as

petroleum reservoirs

Advantages and Limitations of Well LoggingAdvantages and Limitations of Well Logging

Advantages:- Continuous measurements- Easy and quick to work with- Short time acquisition- Better resolution than seismic data- Economical

Limitations:- Indirect measurements- Limited by tool specification- Affected by environment- Varying resolution

Basic Theory of MeasurementsBasic Theory of Measurements

Logs are Implied MeasurementsLogs are Implied Measurements

• Log is not a direct measurement of formation properties, it is an implied measurement based on one or combination of the following devices

• Electrical (Resistivity and Induction)

• Acoustic• Nuclear• Electromagnetic• Magnetic

Basic Theory on ResistivityBasic Theory on Resistivity

Current path

Unit volume filled with only water

Current path

Unit volume with water and matrix

Rw

Ro

Typical Formation

Rt

WaterSand grain

Grain surface water

Oil

Measured by the tool

Current path

Resistivity and Measurement ConceptResistivity and Measurement Concept

Resistivity is the ability of a substance to impade the flow of electrical current

Rw - Formation Water resistivityE - Voltage difference across the formationA - Cross sectional AreaL - Length of brine containerrI - Current

Rw = E * A

I * LL

I E

ARw

Resistivity and Measurement ConceptResistivity and Measurement Concept

Schematic diagram of how an induction tool works

Primary magnetic field created by transmitter

Magnetic field induces a current in the ground loop

Secondary magnetic fieldCreated by the ground loop

Secondary magnetic fieldInduces a current to flow in the receiver

Transmitter

Receiver

Resistivity is the key to hydrocarbon saturation determination

Resistivity ApplicationResistivity Application

Water Saturation EstimationArchie’s Equation

Sw = F * Rw

Rt

SW - Water saturationRw - Formation water resistivityRt - True Formation resistivity

( )1/nwhere F =

1.0

Por m

Sh = 1 - Sw

Resistivity is also used for well to well correlation, and to pick fluid contacts

F - Formation factorn - Saturation exponentm - Cementation factor

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

• SP measurement is based on Electrical currents flowing in the mud from electrochemical and electrokinetic

• Salinity difference between mud flitrate and formation waters, ions movement creates currents measured in mVolt

• Negative or Positive SP curve deflection represents which fluid, formation or mud filtrate, has more ionic charge.

• It only works in water based mud !

• The use of SP log; bed boundary, distinguishing permeable from impermeable rock, shalyness indicator, Rw determination and well correlation.

Spontaneous Potential (SP)Spontaneous Potential (SP)

SP

ShaleSand Thick clean wet sand

(-) (+)

- - - - - - -

- - - - - - -

Thick shaly wet sand

Thick clean Gas sand

Thick shaly Gas sand

Rmf >> Rw in all sands

Hydrocarbon effect

Spontaneous Potential (SP)Spontaneous Potential (SP)

20

40 mV

7470

7430

Given:Rmf = 0.51 at 135 FRm = 0.91 at 135 FTD = 8007 ftBottom hole temp.= 135 FSurface temp. = 60 F

Determine Rw ?

SP

Limitation

SP is not reliable when you have no or very small contrastBetween Formation water salinity and mud filtrate salinity resulting in no to small SP deflection

Rw calculation from SP logRw calculation from SP log

SSP = -K log Rmfe

Rwe

Steps of Calculation;- Determine Temperature at Depth of interval- Correct Rm and Rmf to this temperature (gen-9)- Determine SP (log) from shale baseline- Correct SP to SSP using SP thickness corr. chart- Determine Rmf/Rwe ratio using SP-1 chart- Determine Rwe from above equation or SP-1 chart- Correct Rwe to Rw using SP-2 chart

Gamma Ray Log (GR)Gamma Ray Log (GR)

• GR tool measures natural radioactivity of the formation from the emmision of all these; (Total GR)

Potasium, Uranium and Thorium• GR log is used for;

‐Well to well geological correlation‐ Bed definition, more accurate than SP log‐ Shale Volume Indicator (most reliable)‐ Lithology and mineralogy indicator (NGT)

IGR = GRlog - GRminGRsh - GRmin

IGR - Gamma ray indexGRmin - GR cleanGRsh - GR shale baseline


Mineral Density DT GRQuartz 2.64 56 0-15Calcite 2.71 49 0-15Dolomite 2.85 44 0-15Orthoclase 2.52 69 220Micas 2.82 49 275Kaolinite 2.41 - 80-130Chlorite 2.76 - 180-250Illite 2.52 - 250-300Montmorillonite 2.12 - 150-200Anhydrite 2.98 50 lowPyrite 4.99 39 lowCoal 1.47 high low


Well-1 Well-2Well-7

GR ResGR Res

GR Res

Natural Gamma Ray Log (NGT)Natural Gamma Ray Log (NGT)

• NGT tool measures the spectrum of Potasium,Uranium, and Thorium

• NGT log is used for;- Study of Depositional Environments- Geochemical logging- Shale typing- Source Rocks- Diagenetic History- Vclay content correction

• With combination of Photoelectric curve can be used for clay and mica type identification

Natural Gamma Ray Log (NGT)Natural Gamma Ray Log (NGT)

0 2 4 6 8 10

2

4

6

8

10

0

K, Potasium (%)

Pe

Kaolinite

Montmorillonite

Illite

Glauconite

Muscovite

Biotite

Density LogDensity Log

• Density tool is one of the most important instruments used to evaluate formations which measures formation density and directly ties to formation porosity

• The density tool measures the electron density, by emitting gamma ray from radioactive source and returning to two detectors

• The amount of Gamma rays that return depend on the number of electrons present, electron density is related to bulk density of mineral or rock

• In most cases environmental correction for Density log is not significant, field log density can be readily used for interpretation


Main categories in the process of GR energy loss due to collisions with other atomic particles:

Compton Scattering is selected to be the energy level togenerate GR of the Cesium 137 radioactive source at 662 keV


• Porosity determination from density log:

POR = RHOBma - RHOBlog

RHOBma - RHOBfluid

RHOBma - Matrix densityRHOBfluid - Formation fluid densityRHOBlog - Log densityPORd - Density derived porosity

Exercise: Determine porosity of limestone with field logdensity inicated 2.5 gr/cc.

Neutron LogNeutron Log

• The tool measures the Hydrogen Index which is the quantity of Hydrogen per unit volume

• The tools emit high energy neutrons either from radioactive source or minitron. They are slowed down by collisions with formation nuclei, collision will result energy loss, and the element mostly slowed down is H

• Water has high neutron counts, Oil has a little less counts than Water, Gas will have very low neutron counts

• Neutron log is very sensitive to environment change; bore hole size, mud cake, mud weight, temperature, stand‐off, pressure and formation salinity, measurement is compensation of far and near count rates.


• Neutron tool has a wide range of applications‐ Porosity Determination‐ Gas Detection‐ Borehole and formation salinity‐ Reservoir Saturation‐ Reservoir Monitoring‐ Borehole Fluid dynamics

• Neutron radioactive source in normally uses Am 241

Exercise Neutron Log environmental correctionGiven: Uncorrected neutron porosity of 34%, 14” borehole size,0.25” mud cake, 200 kppm borehole salinity, 12 ppg mud at170 F, 5000 psi pressure, using water based mud with formationsalinity of 50 kppm.

Acoustic LogAcoustic Log

• Sonic tool generates acoustic signals to measure the time travel to pass through a formation, log measurement in time required to travel in one foot formation (microsec/foot)

• Rock properties can be implied from sonic measurements;Porosity, Lithology, Gas shows, Compaction and Rock strength

• Main current use : ‐ Seismic Tie‐Mechanical properties‐ Fracture identification

• Tool types; Borehole compensated sonicLong spacing sonicArray sonic toolUltrasonic borehole imageDipole shear sonic image

Acoustic LogAcoustic Log

Special ToolsSpecial Tools

• Resistivity Based Imaging Tool- Pad device on 4 to 6 arm caliper, few mm resolution- Application: Thin bed Evaluation, Dip meter,Paleostream direction, fracture evaluation, stratigraphy.

• Nuclear Magnetic Resonance- Using Permanent magnet to realign hydrogen protons to newmagnetic field, a Lithology dependance porosity, saturartion and permeability estimation

• Dipole Shear Sonic- Shear measurement, AVO and Rock mechanics applications

• Borehole sonic imaging- Acustic based bore hole imaging for 360 deg coverage, lower resolution than resistivity based imaging tools.

Special ToolsSpecial Tools continued

• Modular Formation Test- Very robust formation tester with the capability to take unlimited pressure tests, pump the fluid into the borehole, identify the fluid type before sampling

• Wellbore Seismic- VSP: Vertical seismic profile surface guns, wellbore detectors- SAT: Seismic acquisition tool- WST: Well seismic tool- DSA: Downhole seismic array tool (3 axis geophones)

Wellbore SeismicWellbore Seismic

Log and Seismic Tie EffortLog and Seismic Tie Effort

• Log Data Validation‐ Check the log quality‐ See if there is any missing log data‐ Determine whether sonic peaks/anomalies representing formation

• Log editing

• Velocity Correction Sonic over VSP (using 4‐2 msec resolution)

• Synthetic Seismic Generation‐ Acoustic Impedance‐ Convolution Wavelet to tie seismic and log peaks

* Extracted Wavelet ‐ to utilize wavelet as seen in the seismicit is highly recommended (similar apperance)

* Rickr Wavelet ‐ commonly used to have zero phase

Synthetic SeismogramsSynthetic Seismograms

• Synthetic Seismograms are used to correlate seismic sections

• Theoretically this method uses many simplification and assumptions put into the model

• It provides important link to understand the tie between seismic data and well log responses

VSP&VSP&Seismic SectionSeismic Section

Velocity SurveyVelocity Survey

• Velocity or check shot surveys are performed in the wellbore to obtain vertical travel paths through the formations by locating sources and detectors/receivers at certain configuration, normally the receivers are placed near the gelogical horizons

• The survey only utilize first arrival to use in the recorded seismic trace

• First arrivals are then converted into vertical travel times on time‐depth graphs which can be used to calculate average velocities

• Sonic log calibration needs to be done prior to generation of synthetic logs, normally borehole effects are found very often causing drift which is to be removed to prevent shifting in time of seismic reflections or pesudoevents

Vertical Seismic ProfileVertical Seismic Profile

• Vertical Seismic Profiling (VSP) uses both entire recorded seismic trace and first break. Receivers are spaced at very closed intervals in the wellbore in order to get a seismic section in the wellbore

• The seismic wave and all effects are measured as a function of depth as it propagates through the formations

• Thr receivers are close to reflectors where up‐going and down‐going waves are recorded as a function of depth

• The down‐going wavelets are used to design deconvolution filters

• In general VSP provide much better spatial and temporal resolution, the signal changes interm of bandwidth and energy loss are measured

• Applicatios of VSP are to correlate the actual seismic events with more confidence, and with much better resolution due to shorter travel paths it can provide a tool to generate high resolution maps, and better estimate of rock properties

Basic Concept of VSPBasic Concept of VSP

Offset VSPOffset VSP

• Offset VSP are used to detect faults and pincoutsdeveloped to illuminate structure away from the wellbore

Multiple offset and walkaway VSP

• Multiple offset VSP were developed to provide high-resolution seismic structural details in the area where interference from the shallow layers

• The disadvantages is very time consuming, it requires few days for the acquisition by putting multiple source positioned in different locations

Offset VSPOffset VSP

Basic Log InterpretationBasic Log Interpretation

Logs Data Applications

• Determine depth and thickness• Identify productive zones• Distinguish fluid types, gas, oil and water• Estimate hydrocarbon reserve• Help geological correlation and subsurface mapping• Determine facies and drilling locations

Basic Log InterpretationBasic Log Interpretation Continued

• Gamma Rays• Self Potential• Resistivity• Induction• Density• Neutron• Sonic• Magnetic Resonance• Formation Test

Common Tools in the Logging Industry

• Porosity• Water Saturation• Permeability

Fluid types• Fluid contacts• Lithology

• Dip angle• Velocity

Basic Log InterpretationBasic Log Interpretation Continued

Typical properties implied or estimated from the log Measurements:

Porosity = Volume of pores

Total Volume of Rock

Porosity is estimated using one or combination ofthe followings; - Density

- Neutron- Sonic

Combination of three inputs will get better estimate

Porosity = “Storage Capacity”

POR = (DENmatrix – DENlog)/(DENmatrix – DENfluid)

Density Porosity:

Petrophysical PropertiesPetrophysical Properties

SW = Formation Water in the pores

Total pore space in the rock

Water Saturation is estimated using combination ofthe followings; - Porosity

- ResistivityIt requires formation factor and saturation index derived from core analysis, and formation water resistivity


Archie’s Equation

Sw = 1/Por * Rw

Rt

SW - Water saturationRw - Formation water resistivityRt - True Formation resistivity

( )1/n

n - Saturation exponentm - Cementation factor

m

Permeability Estimation from Logs

K= 93 * Por

Swi

Permeability (K) is a measure of rock property to get the fluid passes through the rock.

The equations are based on empirical study, accurate K estimation can be obtained from formation test, drillstem test (DST) or from core analysis

( )2.2 2

K= 250 * Por

Swi( )3 2

Timur’s

Tixier’s

where Swi = Irreducible water saturation



♦♦ Get to know various log measurementsGet to know various log measurements

♦♦ Recognize fluid type and lithology of major Recognize fluid type and lithology of major reservoirs, and some practical applications of log reservoirs, and some practical applications of log datadata

♦♦ Familiarize with factors affecting the log responseFamiliarize with factors affecting the log response

♦♦ Understand the strategy in well evaluationUnderstand the strategy in well evaluation

♦♦ Get to know various approaches to well logging designGet to know various approaches to well logging design

♦♦ Exercise with well log designExercise with well log design

Fluid and Lithology Identification From the LogsFluid and Lithology Identification From the Logs


Gas

Oil

Water

Oil-Water Contact

Gas-Oil Contact

Water filled Sand

Water filled Sand

Water filled Sand

Oil Sand

Gas Sand

CoalCarbonate/Limestone

RES0.1 100


Oil-Water Contact

Gas-Oil Contact

Water filled Sand

Water filled Sand

Water filled Sand

Oil Sand

Gas Sand

CoalCarbonate/Limestone

How Can We Remember These Easily?How Can We Remember These Easily?About Lithology Interpretation

• Claystone ‐ has large amount of water, and radioactive materials, is denser when it has less water, is not harder than limestone and is very conductive.

• Sandstone‐ is less dense than limestone, has less water than clay, contain more water than limestone except when it is saturated with dry gas, its conductivity is depending on fluid type it contains, has small to none radioactive fragments.

• Limestone ‐ is harder than both clay and sand, contains least water of the three, very resistive, it has low radioactivity materials, fast velocity, high density.

• Coal ‐ Normaly low radioactive, rarely radioactive, lowest density and very resistive

How Can We Remember These Easily?How Can We Remember These Easily?About Fluid Interpretation

• High Radioactivity ‐ High GR

• Very Conductive ‐ Low Resistivity

• High Water ‐ High Neutron and Low Resistivity

• High Gas ‐ Low Neutron and High Resistivity

• High Oil ‐ Higher Neutron than Gas, denser than gas Less Neutron than water, less dense than water, more resistive than water, less‐resistive than gas when other properties are the same

• Dry Gas ‐ Very resistive, largest density neutron crossover

• High GOR ‐ Larger density‐neutron crossover than oil with low GOR

• Fresh Water ‐ Reservoir filled with high resistive water

Are There Any Anomalies?Are There Any Anomalies?About Fluid Interpretation

• In a gas zone‐Mud filtrate invasion will cause the neutron‐density crossover looks like that of oil zone, the shallow investigation resistivity will be less resistive than that of deeper depth of investigation, resistivity difference is larger when conductive mud is used

‐ High Irreducible water (water bounds in clays and grains’ surface) will demonstrate little density‐neutron crossover similar to that of oil or water zones but less resistive than gas or oil zones with less irreducible water

• In an oil zone ‐ similar to above

How Is Log Analysis Calibrated?How Is Log Analysis Calibrated?

• Core DataRoutie Core Analysis - For Porosity and Permeability CalibrationSpecial Core Analysis - For detailed rock and fluid properties such as X Ray Diffraction, Scanning Electron Microscopy, Petrophysical parameters (a,m and n determination), PVT, Gas Analysis and finger prints of fluid samples, and etc.

• Formation TestFluid Identification from the logs is not direct, when the parameters are not well established, formation test fluid samples can be used to calibrate fluid identification using the logs. Formation test is also used when possible log response anomalies encountered to get conclusive fluid identification.

Modern Formation For Fluid IdentificationModern Formation For Fluid Identification

Single Probe Module

Hydraulic Power ModuleHydraulic Power Module

Electric Power Module

Fluid Description ModuleFluid Description Module

MDT String Configuration

Multi sample ChambersMulti sample Chambers

Test ProbeTest Probe

Large sample ChamberLarge sample Chamber

Basic components of the toolBasic components of the tool

Probe

Multi-sampleChambers

Resist.sensor

Pump OutModule

Pre-Test

Strain Gauge

Quartz Gauge

IsolationValve

Optical FluidAnalyzer

Flow line

Probe

HP GaugeValve

Pre-Test

Two Sample Chambers

OLDOLD NEWNEW

OFA Gas Detector Optics

Gas Detector SystemGas Detector System

Light Emitting DiodeCylindrical LensPolarizer

Fluid Flow GasLiquid

Gas

SapphirePrism

PhotodetectorArray

Sapphire window

OFA Spectrometer

How OFA Divice OperatesHow OFA Divice Operates

Fluid flowSapphire

Lamp

LightDistributor

SourceLight path

Solenoids

MeasureLight Path

Filter lensPhotodiode

Chopper motor

Filter LensCatridge

OFA Spectrometer

How Can We Differenciate Fluid Types ?How Can We Differenciate Fluid Types ?

Diesel

FuelOil

MudFiltrate

Crude Oil A

Crude Oil B

Water

Visible Near infra-red

0.0

4.0

Opt

ical

Den

sity

500 1000 1500 2000Wave Length - (NM)

ExampleExample--1 : Gas OFA1 : Gas OFA

ExampleExample--2 : Water OFA2 : Water OFA

ExampleExample--3 : Oil OFA3 : Oil OFA

Are There Any Other Logs Applications?Are There Any Other Logs Applications?

• Volume of Hydrocarbon

• Fluid continuity

• Reservoir Extent

• Reservoir Rock Properties

• Depositional Environtment

• Diagenesis and Compaction

• Trapping

• Heterogeneity

Selecting Drilling LocationWell CompletionSubsurface Geological MappingReservoir Characterization

All are useful for

The Logs Can Help Us to Determine:

Hydrocarbon Reserves Estimate Hydrocarbon Reserves Estimate

Oil rec = 7758 * (1-Sw) * h * Por * RF * A

BoI

(43560 * DEPTH*0.43)* (1-Sw)* h* Por*RF*A

15

Where : RF - Recovery Factorh - Thickness, A - AreaBoI - Oil Vol. factorBoI = 1.05 + 0.5 * (Gas Oil Ratio/100)

Gas rec =

Lateral Continuity ?Lateral Continuity ?

Well-1 Well-2Well-7

GR ResGR Res

GR Res

Compaction Trend ?Compaction Trend ?

GRRes

DT



♦♦ Recognize fluid type and lithology of major reservoirs, and Recognize fluid type and lithology of major reservoirs, and some practical applications of log datasome practical applications of log data



♦♦ Get to know various approaches to well logging designGet to know various approaches to well logging design


Depth of Investigation and Resolution Depth of Investigation and Resolution of Logging Toolsof Logging Tools

0 cm50 cm100 cm150 cm200 cm250 cm2 cm

5 cm

60 cm

20 cm

30 cm

40 cm

80 cm

80 cm

Dipmeter

Micro resistivityMicro log

Sonic

Density

Gamma-ray

Neutron

Laterolog

Inductionlog

Resistivity

Radioactivity

Acoustic

Resistivity

Depth of Investigation

Res

olut

ion

AIT SDT LDT CNT SGT LEH TCC AMS

Additional combinable tools:- Dipmeter- Magnetic Resonance- Borehole Imager- Dipole Sonic- Formation Tester- Others

Tools Size and Measuring point for Typical Tools Size and Measuring point for Typical Oil Based Mud Environment Oil Based Mud Environment In

duct

ion

Son

ic

Den

sity

Neu

tron

GR

Measuring point fromthe bottom of the tool

Tool Length

This slide helps you to configure the tool string that is appropriate for your well

Tool SpecificationTool Specification

Resistivity Measurement Problems and LimitationsResistivity Measurement Problems and Limitations

Resistivity measurements are not reliable when you have:Severe invasion due to overbalanced mudLarge washed-out boreholeShoulder bed affectsHigh content of conductive mineralsSome older tool generations have limited vertical resolution

Ri

Effects of Borehole EnvironmentEffects of Borehole Environment

RmRxoRmfSxo

RiRzSi

RoRtRwSw

UndisturbedFormation

InvadedZone

FlushedZone

Mud CakeRmc

Invasion ProfileInvasion Profile

Fresh Mud Rmf > RW

Salt Mud Rmf < Rw

Rxo

Rxo

Rt

Rt

Rm

Rm

DMS

D M S

Low High

SP Log LimitationsSP Log Limitations

The tool is only for water based borehole environmentSP is not reliable when you have no or very small contrastbetween Formation water salinity and mud filtrate salinity resulting in no to small SP deflection

GR Log LimitationsGR Log LimitationsStandard GR tool is not reliable when you log an interval with radioactivemineral rich rocks. NGT is recommended to use for this type of Formation to get reliable GR derived clay volume calculation.GR measurements in cased hole environment need to be normalizeddue to casing, and cement attenuation

Density Log LimitationsDensity Log LimitationsDensity log is a pad device, it is very sensitive to the pad contact withThe borehole wall, make sure to consult with your petrophysicist prior tousing the data for any other applications.

Neutron Log LimitationsNeutron Log LimitationsNeutron log is very sensitive to environment change; bore hole size, mud cake, mud weight, temperature, stand-off, invasion, pressure and formation salinity, measurement is compensation of far and near count rates.

Sonic Log LimitationsSonic Log LimitationsSonic log is likely affected by strong attenuation when we logunconsolidated formation, fractured formation, gas saturated reservoirs,aerated muds, rugose and enlarged borehole sections. Typically showssome curve skippings.

Formation Test Log LimitationsFormation Test Log LimitationsFormation test problems normally occur when you don not have a goodRubber pad seal, causing a communication with the mud giving you muchHigher pressure reading. Depleted and highly invaded zone would causelong fluid pumping before you get clean sample or fluid identification



♦♦ Recognize fluid type and the lithology of major reservoirs, Recognize fluid type and the lithology of major reservoirs, and practical uses of log dataand practical uses of log data


♦♦ Understand the strategy of a well evaluationUnderstand the strategy of a well evaluation♦♦ Get to know various approaches to well logging designGet to know various approaches to well logging design


Why Wireline Well loggingWhy Wireline Well logging

1. Better Resolution2. More advanced tools3. Better depth control4. Only choice available (certain tools)5. More certain on data quality

Disadvantages of Wireline Disadvantages of Wireline logginglogging

1. Invasion effect2. Hole condition dependant3. Unable to log in high angle wells (>60 deg)4. Acquired after drilling, more rig time5. More uncertainty in getting data or good

data in problem prone wells

Important Issues with Important Issues with Running Wireline logsRunning Wireline logs

1. Borehole fluid type2. Borehole size3. Well deviation4. Tool combination5. High Mud Weight resulting in over balanced

Logging while Drilling

Why LWD?Why LWD?

• Reduce Rig Time

• Real Time Decisions

• Minimized Borehole Problems

• High Angle/Horizontal Wells

Disadvantages of LWDDisadvantages of LWD

• Borehole size and rugosity are not known• Good data collected only when the tool is rotating• Data quality is rate dependant• Log resolution is generally poorer than that of wireline• Ability to configure the tools is limited• Not a good application for a slow drilling rate for cost

consideration especially for expensive rig.• Depth control is poorer than wireline data

LWD and Wireline ComparisonLWD and Wireline Comparison

X800

X900

InvasionX800

X900

Wireline Log ExampleWireline Log Example

X400

X450

LWD Real time and Recorded LogsLWD Real time and Recorded Logs

GR GRD. RES

D. RESDEN DENNEUNEU

X500

X600

X700

X500

X600

X700

Selecting the Tools to runSelecting the Tools to run

It depends on what type of information you are about to get and the cost you are willing to spend.

Need Want

What is the value of information you are getting?

What tools do you run in the hole?

Ability to Define Your NeedAbility to Define Your Need

• Geological

• Geophysical

• Reservoir

• Petrophysical

• Mechanical

Type of Information to AcquireType of Information to Acquire

•• GeologyGeology‐ Sand development and sand thickness‐ Stratigraphic information‐ Lateral continuity‐ Hydrocarbon source

•• GeophysicsGeophysics‐ Velocity uncertainty‐Well to seismic tie‐ Seismic and fluids/lithology correlation

Type of Information… Type of Information… continued

•• PetrophysicsPetrophysics‐ Porosity‐Water saturation‐ Permeability‐Mineralogy

•• ReservoirReservoir‐ Compartment‐ Fluid properties‐ Reservoir pressure‐ Reservoir monitoring

•• Rock MechanicsRock Mechanics‐ Stress direction‐ Pressure profile‐ Fracture orientation

Understand the Scales Of ObservationUnderstand the Scales Of Observation

Seismic Section

Wireline Logs

Out-Crops/Core

Thin Sections

Scales Of ObservationScales Of Observation






♦♦ Get to know various well logging designsGet to know various well logging designs♦♦ Exercise with well log designExercise with well log design

Well Logging Design ObjectiveWell Logging Design Objective

The objectives of a well logging design should follow your drilling objectives, if drilling objective is not met, the objectives of logging program should be adjusted accordingly.

A logging program would vary depending on drillingObjectives.

Well Logging DesignWell Logging Design‐‐11

•• Onshore wellOnshore well

A development well, A‐5, is to drill updip structure of A‐Sand to accelerate oil production, the A‐4 well has produced this Reservoir for a year, and currently produces 80% water. The reservoir has a strong aquiver drive mechanism.

Well Logging DesignWell Logging Design‐‐1 1 continued

• Drilling objective is to drill and complete the A‐Sand Level• Logging program objective for this well is then to locate the

top of the A‐Sand and make sure that the interval is still in the oil column.

• Other information: Strong water drive means it has good pressure maintenance, therefore, no need to take pressure data.

• Rig type: Onshore Rig (inexpensive), a vertical well.• Logging Design : Wireline GR‐Resistivity‐Neutron‐Density

Well Logging DesignWell Logging Design‐‐22

•• Offshore wellOffshore well

A third appraisal well is proposed on the west flank of the structure. First two‐wells suggest that well to well log correlation is not easy, however pressure data has helped the well to well correlation. This well is to reveal the lateral continuity and the compartment issue of the reservoirs.

Well Logging DesignWell Logging Design‐‐1 1 continued

• Drilling objective is to drill and to find out the lateral continuity of some reservoirs.

• Logging program objective is to collect as much data to confirm lateral continuity and well to well correlation.

• Other information: The well is still in the appraisal phase.

• Rig type: Offhore Rig (expensive), directional well?

• Logging Design : ‐ LWD GR‐Resistivity‐Density‐Neutron‐Wireline GR‐Resistivity‐Density‐Neutron as contigencyin case LWD data is not reliable‐Wireline formation test for pressure correlation‐Wireline OBMI for stratigraphic informationto help well to well correlation

ExampleExample‐‐1 1 ‐‐ Logging ProgramLogging Program

• 26 “ Conductor ‐ 3500’ to 3700’MDNone

• 20” Casing ‐ 3700’ to 4100’ MDNone

• 17‐1/2” Hole section 4100’ to 6000’ MD‐ LWD: GR‐Resistivity

• 12‐1/4” Hole Section 6000’ to 9000’ MD‐ LWD: GR‐Resistivity‐Density‐Neutron‐Wireline: Triple combo only when LWD fail

Formation test as required

• 8‐1/2” Hole section 9000’ to 12000’ MD‐ LWD: GR‐Resistivity‐Density‐Neutron‐Wireline: Triple combo only when LWD fail

Formation test as requiredBorehole image as requiredNuclear Magnetic tool as required

ExampleExample‐‐2 Logging Program2 Logging Program Continued

• 8‐1/2” Hole Section 9000’ to 12000’ MDLWD:GR‐Resistivity‐Density‐Neutron

Wireline:Triple combo as a contingency when LWD fail

Wet Case:Triple combo as a contingency when LWD data is not reliableFormation tests for pressures and water samples

H.C. Case:Triple combo as a contingency when LWD data is not reliableFormation tests for pressures and fluid samplesBorehole image log for dip and stratigraphic informationNuclear Magnetic tool when considerable thick‐shaly sand reservoirs are penetratedBorehole seismic for velocity survey

Important Aspects To ConsiderImportant Aspects To Consider

• Risk

• Cost

• Environment

• Hole Size

• Well Design

• Tool Speed

Important Aspects To ConsiderImportant Aspects To ConsiderSome examplesSome examples

• Risk

‐While we are running in hole with wireline tools, the tools could not go down at certain depth. The company representative has decided to pull out of hole to run different tool configuration.

‐ In case of a risk that we are not able to go down passing the same depth with new tool configuration, the petrophysicist has asked the log engineer to log up while pulling out of hole to get data assurance.


• Cost‐ After the well reached TD at 6000 ft, the team found out that they do not have room to get all log data to the base of the reservoir near TD if they use typical triple combination wireline tools, to drill additional 50 ft would take 24 hour rig time including RIH and POOH.

‐ The petrophysicist has then decided to split the tools into two runs, which only require additional 6 hour rig time for second wireline run. By doing that it would have saved 18 hour rig time if they drill additional 50 ft to have only one logging run


• Environment‐ The well is to drill complex lithology interval in Jurasic section. Where coal, shale, sand, limestone can be penetrated in the same hole section.

‐ The geologist and petrophysicist have suggested their drilling team to drill the well with oil based mud to help possible swelling clay problem, formation of limestone ledges and washed‐out sand section, therefore it would promote a smooth and successful logging operation after they reach TD.


• Hole Size‐ The Drilling engineer has suggested to run only LWD in the 12‐1/4” hole section to reduce well cost.

‐ The petrophysicist has argued and suggested to run wireline because based on previous wells in this field where they have drilled at average rate of 300 ft/hr resulting in not reliable data. The team has supported their petrophysicist to run wireline because it would help to support field certification.


• Well Design‐ After the G&G team provide the targets to the drilling engineer, the team has to end up with a well design that it requires a highly deviated well exceeding 60 deg.

‐ LWD log data acquisition is then put in their logging program because based on their experience in this field 50 deg well was the highest deviated well that they could log with wireline.


• Tool Speed‐ Based on the statistics drilling the Pliocene section is very quick, averaging 400 ft/hr, the company is drilling a horizontal gas well at about 3000 ft TVD.

‐ LWD engineer and the petrophyscist have worked together and have given a recommendation to do controlled drilling at about 200 ft/hr to get an acceptable log data quality.

What do you have in mind?What do you have in mind?

On ShoreDevelopment Well

Off ShoreDeep waterdevelopment-well

In respect to Risk, Cost, Environment, Hole Size, Well Design, Tool Speed

Exploratory WellExploratory Well

• Seismic Information

• Regional Geology Information

• Drilling the well using “Learning while doing” concept

• High Risk but must be manageable

• Mostly Vertical well

Development WellDevelopment Well

• In Many cases with little to no need of seismic information

• Local Geology Information

• Drilling with full knowledge

• Low Risk mainly mechanical

• Vertical, highly deviated to horizontal wells

An Example of rather complex Logging Program An Example of rather complex Logging Program Decision TreeDecision Tree

West Seno Data Gathering StrategyStandard

well PAY

FullyLoadedWireline

FullCores

SAMPLING

12 1/4 “PAY

LWD

SAMPLES

LWD

WIRELINE

PRESSUREP.O

PEXMD T

CSTCores

SpecialLogging

VelocityUncertainty

UBI or CBL

SAMPLING

Cased Hole GR

CSAT or VSP

GR to bottom of 13 3/8 “

STOPSTOP

Objective driven-logging

Y

N

Y

Y YY

Y

Y

Y

Y

Y

Y N

N

N

N

N

N

NN

N

N

N

N

LWD

MD T

Objective

DeepestWell VSP

STOPN

Another Way To Save Cost!Another Way To Save Cost!

• ACQUIRE DATA WITHOUT USING COSTLY RIG TIME (PIPE DECISION NOT NECESSARY ‐ NO DRY HOLES)

– GATHER DATA REALTIME WHILE DRILLING

– GATHER DATA THROUGH TUBING AFTER COMPLETION

– COMBINATION OF BOTH

Project Base ApproachProject Base Approach

UOME company has $200 MM program for

exploratory wells for the year 2004.

As a follow up of their exploration campaign,

UOME Company has $ 600 MM program for

developing a new deepwater field for the year

2005 that will have peak production of 100,000

BOPD






♦♦ Get to know various well logging designsGet to know various well logging designs


Exercise‐1

• PT Indooil Co., the sole owner of mineral right on Block A, on‐shore, 2 km in adjacent to a known oil producing area in the Block B. The company is looking at a prospect to drill the first well, Indoco‐1, in the block targeting for the same producing interval in Block B at about 4000 ft depth, and it is estimated 50 ft down dip in this block.

• The costs for various available log data acquisition are as follow:• Wireline GR ‐ $1/ft, Induction ‐ $4/ft, BHC Sonic ‐ $1/ft, Density‐$2/ft, Neutron‐$2/ft• Formation test ‐ $100/pressure, $1000/fluid identification, $2000/fluid sample • Depth charge for each Wireline tool is free.• LWD GR and Induction ‐ $10,000/day, Density and Neutron ‐ $10,000/day• The rig cost is $5000/day • 1) What is your recommended data gathering strategy and well logging design for

the well?• 2) While drilling, the well penetrates 5 thick sand units with high mud log gas from

3,000 to 4,200 ft. How do you recommend the company on the logging design?• 3) After the well reached the proposed TD, there were no encouragement seen from

the mud log signs, what would you do for your logging program?

Exercise‐2

• The exercise‐1 was seismically to test the amplitude anomaly at Orange horizon, equivalent to the Berani Clastic Formation. The Indoco‐1 well encountered 300 ft of Oil column and was completed and produced from this level for over one year with cumulative production of 4 mmbo. The company is looking at similar seismic character 1‐1/2 km away from Indoco‐1 well, which was connected by dim event to the amplitude at the Indoco‐1 well. It has been interpreted as a different channel lobe. The company did low profile and ran only simple wireline GR, resistivity, density, neutron and sonic on the Inoco‐1 well.

• What is your data gathering strategy for this Indoco‐2 well?

Exercise‐3

• A subsurface team is evaluating a four‐way closure structure offshore East Kalimantan, based on their synthesis, if the timing of migration is right, it is a big structure filled with hydrocarbon. The water depth around the prospect is about 4500 ft. To properly evaluate the prospect, the team thinks that they need at least 8 wells drilled at various locations on the structure. Some apparent faults due to regional compressive stress cut the structure into possible many compartments.

• Make assessment on options the company needs to do and make recommendation on well evaluation strategy.

Exercise‐4

• An offshore well is proposed to redrill the A‐5 well with updip direction from this well to get the gas leg of clean and blocky sand found with gas water contact in the A‐5 well. The company is trying to get more gas production. The team is looking at drilling horizontal well with about 500 ft of producing section. What is your recommended logging program for this well and why?

basic well logging design

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