consortium alumni association presents a one-day course...
TRANSCRIPT
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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
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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)
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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
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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
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Wireline Logging Logging while Drilling
Cable
Tools
LWD Tools
Mud inMud out
Drill Bit
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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
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The “First” Log recorded in 1927
Well in Pechelbronn - France Surface Recording Instrument
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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
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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
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Basic Theory of MeasurementsBasic Theory of Measurements
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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
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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
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Typical Formation
Rt
WaterSand grain
Grain surface water
Oil
Measured by the tool
Current path
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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
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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
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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
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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.
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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
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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
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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
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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
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Gamma Ray Log (GR)Gamma Ray Log (GR)
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Gamma Ray Log (GR)Gamma Ray Log (GR)
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
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Gamma Ray Log (GR)Gamma Ray Log (GR)
Well-1 Well-2Well-7
GR ResGR Res
GR Res
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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
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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
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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
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Density LogDensity Log
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
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Density LogDensity Log
• 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.
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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.
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Neutron LogNeutron Log
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Neutron LogNeutron Log
• 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.
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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
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Acoustic LogAcoustic Log
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Acoustic LogAcoustic Log
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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.
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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)
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Wellbore SeismicWellbore Seismic
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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
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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
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VSP&VSP&Seismic SectionSeismic Section
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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
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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
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Basic Concept of VSPBasic Concept of VSP
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Basic Concept of VSPBasic Concept of VSP
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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
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Offset VSPOffset VSP
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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
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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
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• 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:
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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
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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
Petrophysical PropertiesPetrophysical Properties
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
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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
Petrophysical PropertiesPetrophysical Properties
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ObjectivesObjectives
♦♦ 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
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Fluid and Lithology Identification From the LogsFluid and Lithology Identification From the Logs
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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
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RES0.1 100
Fluid and Lithology Identification From the LogsFluid and Lithology Identification From the Logs
Oil-Water Contact
Gas-Oil Contact
Water filled Sand
Water filled Sand
Water filled Sand
Oil Sand
Gas Sand
CoalCarbonate/Limestone
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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
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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
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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
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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.
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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
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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
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OFA Gas Detector Optics
Gas Detector SystemGas Detector System
Light Emitting DiodeCylindrical LensPolarizer
Fluid Flow GasLiquid
Gas
SapphirePrism
PhotodetectorArray
Sapphire window
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OFA Spectrometer
How OFA Divice OperatesHow OFA Divice Operates
Fluid flowSapphire
Lamp
LightDistributor
SourceLight path
Solenoids
MeasureLight Path
Filter lensPhotodiode
Chopper motor
Filter LensCatridge
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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)
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ExampleExample--1 : Gas OFA1 : Gas OFA
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ExampleExample--2 : Water OFA2 : Water OFA
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ExampleExample--3 : Oil OFA3 : Oil OFA
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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:
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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 =
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Lateral Continuity ?Lateral Continuity ?
Well-1 Well-2Well-7
GR ResGR Res
GR Res
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Compaction Trend ?Compaction Trend ?
GRRes
DT
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ObjectivesObjectives
♦♦ Get to know various log measurementsGet to know various log measurements
♦♦ 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
♦♦ 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
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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
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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
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Tool SpecificationTool Specification
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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
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Ri
Effects of Borehole EnvironmentEffects of Borehole Environment
RmRxoRmfSxo
RiRzSi
RoRtRwSw
UndisturbedFormation
InvadedZone
FlushedZone
Mud CakeRmc
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Invasion ProfileInvasion Profile
Fresh Mud Rmf > RW
Salt Mud Rmf < Rw
Rxo
Rxo
Rt
Rt
Rm
Rm
DMS
D M S
Low High
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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.
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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
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ObjectivesObjectives
♦♦ Get to know various log measurementsGet to know various log measurements
♦♦ 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
♦♦ Familiarize with factors affecting the log responseFamiliarize with factors affecting the log response
♦♦ 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
♦♦ Exercise with well log designExercise with well log design
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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
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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
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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
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Logging while Drilling
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Why LWD?Why LWD?
• Reduce Rig Time
• Real Time Decisions
• Minimized Borehole Problems
• High Angle/Horizontal Wells
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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
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LWD and Wireline ComparisonLWD and Wireline Comparison
X800
X900
InvasionX800
X900
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Wireline Log ExampleWireline Log Example
X400
X450
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LWD Real time and Recorded LogsLWD Real time and Recorded Logs
GR GRD. RES
D. RESDEN DENNEUNEU
X500
X600
X700
X500
X600
X700
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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?
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Ability to Define Your NeedAbility to Define Your Need
• Geological
• Geophysical
• Reservoir
• Petrophysical
• Mechanical
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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
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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
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Understand the Scales Of ObservationUnderstand the Scales Of Observation
Seismic Section
Wireline Logs
Out-Crops/Core
Thin Sections
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Scales Of ObservationScales Of Observation
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ObjectivesObjectives
♦♦ Get to know various log measurementsGet to know various log measurements
♦♦ 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
♦♦ 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 well logging designsGet to know various well logging designs♦♦ Exercise with well log designExercise with well log design
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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.
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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.
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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
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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.
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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
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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
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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
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Important Aspects To ConsiderImportant Aspects To Consider
• Risk
• Cost
• Environment
• Hole Size
• Well Design
• Tool Speed
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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.
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Important Aspects To ConsiderImportant Aspects To ConsiderSome examplesSome examples
• 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
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Important Aspects To ConsiderImportant Aspects To ConsiderSome examplesSome examples
• 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.
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Important Aspects To ConsiderImportant Aspects To ConsiderSome examplesSome examples
• 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.
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Important Aspects To ConsiderImportant Aspects To ConsiderSome examplesSome examples
• 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.
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Important Aspects To ConsiderImportant Aspects To ConsiderSome examplesSome examples
• 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.
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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
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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
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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
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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
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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
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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
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ObjectivesObjectives
♦♦ Get to know various log measurementsGet to know various log measurements
♦♦ 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
♦♦ 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 well logging designsGet to know various well logging designs
♦♦ Exercise with well log designExercise with well log design
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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?
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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?
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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.
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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?