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Basic well logging design


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Basic well logging design

  1. 1. 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
  2. 2. 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)
  3. 3. 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
  4. 4. 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 narrow paper strip, of observations made on the rocks and fluids of the geologic section exposed in the well-bore. DefinitionDefinition
  5. 5. Wireline Logging Logging while Drilling Cable Tools LWD Tools Mud in Mud out Drill Bit
  6. 6. 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
  7. 7. The “First” Log recorded in 1927 Well in Pechelbronn - France Surface Recording Instrument
  8. 8. 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
  9. 9. 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
  10. 10. Basic Theory of MeasurementsBasic Theory of Measurements
  11. 11. 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
  12. 12. 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
  13. 13. Typical Formation Rt Water Sand grain Grain surface water Oil Measured by the tool Current path
  14. 14. Resistivity and Measurement ConceptResistivity and Measurement Concept Resistivity is the ability of a substance to impade the flow of electrical current Rw - Formation Water resistivity E - Voltage difference across the formation A - Cross sectional Area L - Length of brine containerr I - Current Rw = E * A I * L L I E A Rw
  15. 15. 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 field Created by the ground loop Secondary magnetic field Induces a current to flow in the receiver Transmitter Receiver
  16. 16. Resistivity is the key to hydrocarbon saturation determination Resistivity ApplicationResistivity Application Water Saturation Estimation Archie’s Equation Sw = F * Rw Rt SW - Water saturation Rw - Formation water resistivity Rt - True Formation resistivity ( ) 1/n where F = 1.0 Por m Sh = 1 - Sw Resistivity is also used for well to well correlation, and to pick fluid contacts F - Formation factor n - Saturation exponent m - Cementation factor
  17. 17. 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.
  18. 18. Spontaneous Potential (SP)Spontaneous Potential (SP) SP Shale Sand Thick clean wet sand (-) (+) - - - - - - - - - - - - - - Thick shaly wet sand Thick clean Gas sand Thick shaly Gas sand Rmf >> Rw in all sands Hydrocarbon effect
  19. 19. Spontaneous Potential (SP)Spontaneous Potential (SP) 20 40 mV 7470 7430 Given: Rmf = 0.51 at 135 F Rm = 0.91 at 135 F TD = 8007 ft Bottom hole temp.= 135 F Surface temp. = 60 F Determine Rw ? SP Limitation SP is not reliable when you have no or very small contrast Between Formation water salinity and mud filtrate salinity resulting in no to small SP deflection
  20. 20. 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
  21. 21. 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 - GRmin GRsh - GRmin IGR - Gamma ray index GRmin - GR clean GRsh - GR shale baseline
  22. 22. Gamma Ray Log (GR)Gamma Ray Log (GR)
  23. 23. Gamma Ray Log (GR)Gamma Ray Log (GR) Mineral Density DT GR Quartz 2.64 56 0-15 Calcite 2.71 49 0-15 Dolomite 2.85 44 0-15 Orthoclase 2.52 69 220 Micas 2.82 49 275 Kaolinite 2.41 - 80-130 Chlorite 2.76 - 180-250 Illite 2.52 - 250-300 Montmorillonite 2.12 - 150-200 Anhydrite 2.98 50 low Pyrite 4.99 39 low Coal 1.47 high low
  24. 24. Gamma Ray Log (GR)Gamma Ray Log (GR) Well-1 Well-2Well-7 GR Res GR Res GR Res
  25. 25. 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
  26. 26. 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
  27. 27. 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
  28. 28. 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 to generate GR of the Cesium 137 radioactive source at 662 keV
  29. 29. Density LogDensity Log • Porosity determination from density log: POR = RHOBma - RHOBlog RHOBma - RHOBfluid RHOBma - Matrix density RHOBfluid - Formation fluid density RHOBlog - Log density PORd - Density derived porosity Exercise: Determine porosity of limestone with field log density inicated 2.5 gr/cc.
  30. 30. 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.
  31. 31. Neutron LogNeutron Log
  32. 32. 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 correction Given: Uncorrected neutron porosity of 34%, 14” borehole size, 0.25” mud cake, 200 kppm borehole salinity, 12 ppg mud at 170 F, 5000 psi pressure, using water based mud with formation salinity of 50 kppm.
  33. 33. 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 sonic Long spacing sonic Array sonic tool Ultrasonic borehole image Dipole shear sonic image 
  34. 34. Acoustic LogAcoustic Log
  35. 35. Acoustic LogAcoustic Log
  36. 36. 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 new magnetic 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.
  37. 37. 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)
  38. 38. Wellbore SeismicWellbore Seismic
  39. 39. 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 seismic it is highly recommended (similar apperance) * Rickr Wavelet ‐ commonly used to have zero phase
  40. 40. 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
  41. 41. VSP&VSP& Seismic SectionSeismic Section
  42. 42. 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
  43. 43. 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
  44. 44. Basic Concept of VSPBasic Concept of VSP
  45. 45. Basic Concept of VSPBasic Concept of VSP
  46. 46. Offset VSPOffset VSP • Offset VSP are used to detect faults and pincouts developed 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
  47. 47. Offset VSPOffset VSP
  48. 48. 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
  49. 49. 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
  50. 50. • 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:
  51. 51. Porosity = Volume of pores Total Volume of Rock Porosity is estimated using one or combination of the 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
  52. 52. SW = Formation Water in the pores Total pore space in the rock Water Saturation is estimated using combination of the followings; - Porosity - Resistivity It 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 saturation Rw - Formation water resistivity Rt - True Formation resistivity ( ) 1/n n - Saturation exponent m - Cementation factor m
  53. 53. 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
  54. 54. 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
  55. 55. Fluid and Lithology Identification From the LogsFluid and Lithology Identification From the Logs
  56. 56. 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 Coal Carbonate/Limestone
  57. 57. RES 0.1 100 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 Coal Carbonate/Limestone
  58. 58. 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
  59. 59. 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
  60. 60. 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
  61. 61. How Is Log Analysis Calibrated?How Is Log Analysis Calibrated? • Core Data Routie Core Analysis - For Porosity and Permeability Calibration Special 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 Test Fluid 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.
  62. 62. 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
  63. 63. Basic components of the toolBasic components of the tool Probe Multi-sample Chambers Resist. sensor Pump Out Module Pre-Test Strain Gauge Quartz Gauge Isolation Valve Optical Fluid Analyzer Flow line Probe HP Gauge Valve Pre-Test Two Sample Chambers OLDOLD NEWNEW
  64. 64. OFA Gas Detector Optics Gas Detector SystemGas Detector System Light Emitting Diode Cylindrical Lens Polarizer Fluid Flow Gas Liquid Gas Sapphire Prism Photodetector Array Sapphire window
  65. 65. OFA Spectrometer How OFA Divice OperatesHow OFA Divice Operates Fluid flowSapphire Lamp Light Distributor Source Light path Solenoids Measure Light Path Filter lens Photodiode Chopper motor Filter Lens Catridge
  66. 66. OFA Spectrometer How Can We Differenciate Fluid Types ?How Can We Differenciate Fluid Types ? Diesel Fuel Oil Mud Filtrate Crude Oil A Crude Oil B Water Visible Near infra-red 0.0 4.0 OpticalDensity 500 1000 1500 2000 Wave Length - (NM)
  67. 67. ExampleExample--1 : Gas OFA1 : Gas OFA
  68. 68. ExampleExample--2 : Water OFA2 : Water OFA
  69. 69. ExampleExample--3 : Oil OFA3 : Oil OFA
  70. 70. 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 Location Well Completion Subsurface Geological Mapping Reservoir Characterization All are useful for The Logs Can Help Us to Determine:
  71. 71. Hydrocarbon Reserves EstimateHydrocarbon 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 Factor h - Thickness, A - Area BoI - Oil Vol. factor BoI = 1.05 + 0.5 * (Gas Oil Ratio/100) Gas rec =
  72. 72. Lateral Continuity ?Lateral Continuity ? Well-1 Well-2Well-7 GR Res GR Res GR Res
  73. 73. Compaction Trend ?Compaction Trend ? GR Res DT
  74. 74. 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
  75. 75. Depth of Investigation and ResolutionDepth of Investigation and Resolution of Logging Toolsof Logging Tools 0 cm50 cm100 cm150 cm200 cm250 cm 2 cm 5 cm 60 cm 20 cm 30 cm 40 cm 80 cm 80 cm Dipmeter Micro resistivity Micro log Sonic Density Gamma-ray Neutron Laterolog Induction log Resistivity Radioactivity Acoustic Resistivity Depth of Investigation Resolution
  76. 76. 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 TypicalTools Size and Measuring point for Typical Oil Based Mud EnvironmentOil Based Mud EnvironmentInduction Sonic Density Neutron GR Measuring point from the bottom of the tool Tool Length This slide helps you to configure the tool string that is appropriate for your well
  77. 77. Tool SpecificationTool Specification
  78. 78. Resistivity Measurement Problems and LimitationsResistivity Measurement Problems and Limitations Resistivity measurements are not reliable when you have: Severe invasion due to overbalanced mud Large washed-out borehole Shoulder bed affects High content of conductive minerals Some older tool generations have limited vertical resolution
  79. 79. Ri Effects of Borehole EnvironmentEffects of Borehole Environment Rm Rxo Rmf Sxo Ri Rz Si Ro Rt Rw Sw Undisturbed Formation Invaded Zone Flushed Zone Mud Cake Rmc
  80. 80. Invasion ProfileInvasion Profile Fresh Mud Rmf > RW Salt Mud Rmf < Rw Rxo Rxo Rt Rt Rm Rm DMS D M S Low High
  81. 81. SP Log LimitationsSP Log Limitations The tool is only for water based borehole environment SP is not reliable when you have no or very small contrast between Formation water salinity and mud filtrate salinity resulting in no to small SP deflection GR Log LimitationsGR Log Limitations Standard GR tool is not reliable when you log an interval with radioactive mineral 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 normalized due to casing, and cement attenuation Density Log LimitationsDensity Log Limitations Density log is a pad device, it is very sensitive to the pad contact with The borehole wall, make sure to consult with your petrophysicist prior to using the data for any other applications.
  82. 82. Neutron Log LimitationsNeutron Log Limitations Neutron 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 Limitations Sonic log is likely affected by strong attenuation when we log unconsolidated formation, fractured formation, gas saturated reservoirs, aerated muds, rugose and enlarged borehole sections. Typically shows some curve skippings. Formation Test Log LimitationsFormation Test Log Limitations Formation test problems normally occur when you don not have a good Rubber pad seal, causing a communication with the mud giving you much Higher pressure reading. Depleted and highly invaded zone would cause long fluid pumping before you get clean sample or fluid identification
  83. 83. 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
  84. 84. Why Wireline Well loggingWhy Wireline Well logging 1. Better Resolution 2. More advanced tools 3. Better depth control 4. Only choice available (certain tools) 5. More certain on data quality
  85. 85. Disadvantages of Wireline Disadvantages of Wireline  logginglogging 1. Invasion effect 2. Hole condition dependant 3. Unable to log in high angle wells (>60 deg) 4. Acquired after drilling, more rig time 5. More uncertainty in getting data or good data in problem prone wells
  86. 86. Important Issues with Important Issues with  Running Wireline logsRunning Wireline logs 1. Borehole fluid type 2. Borehole size 3. Well deviation 4. Tool combination 5. High Mud Weight resulting in over balanced
  87. 87. Logging while Drilling
  88. 88. Why LWD?Why LWD? • Reduce Rig Time • Real Time Decisions • Minimized Borehole Problems • High Angle/Horizontal Wells
  89. 89. 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
  90. 90. LWD and Wireline ComparisonLWD and Wireline Comparison X800 X900 Invasion X800 X900
  91. 91. Wireline Log ExampleWireline Log Example X400 X450
  92. 92. LWD Real time and Recorded LogsLWD Real time and Recorded Logs GR GR D. RES D. RES DEN DENNEUNEU X500 X600 X700 X500 X600 X700
  93. 93. 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?
  94. 94. Ability to Define Your NeedAbility to Define Your Need • Geological • Geophysical • Reservoir • Petrophysical • Mechanical
  95. 95. 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
  96. 96. 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
  97. 97. Understand the Scales Of ObservationUnderstand the Scales Of Observation Seismic Section Wireline Logs Out-Crops/Core Thin Sections
  98. 98. Scales Of ObservationScales Of Observation
  99. 99. 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
  100. 100. 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 drilling Objectives.
  101. 101. 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.   
  102. 102. 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
  103. 103. 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. 
  104. 104. 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 contigency in case LWD data is not reliable ‐ Wireline formation test for pressure correlation ‐ Wireline OBMI for stratigraphic information to help well to well correlation
  105. 105. ExampleExample‐‐1 1 ‐‐ Logging ProgramLogging Program • 26 “ Conductor ‐ 3500’ to 3700’MD None • 20” Casing ‐ 3700’ to 4100’ MD None • 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 required Borehole image as required Nuclear Magnetic tool as required
  106. 106. ExampleExample‐‐2  Logging Program2  Logging Program Continued • 8‐1/2” Hole Section 9000’ to 12000’ MD LWD: 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 reliable Formation tests for pressures and water samples H.C. Case: Triple combo as a contingency when LWD data is not reliable Formation tests for pressures and fluid samples Borehole image log for dip and stratigraphic information Nuclear Magnetic tool when considerable thick‐shaly sand reservoirs are  penetrated Borehole seismic for velocity survey
  107. 107. Important Aspects To ConsiderImportant Aspects To Consider • Risk • Cost • Environment • Hole Size • Well Design • Tool Speed
  108. 108. Important Aspects To ConsiderImportant Aspects To Consider Some 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.
  109. 109. Important Aspects To ConsiderImportant Aspects To Consider Some 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 
  110. 110. Important Aspects To ConsiderImportant Aspects To Consider Some 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. 
  111. 111. Important Aspects To ConsiderImportant Aspects To Consider Some 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. 
  112. 112. Important Aspects To ConsiderImportant Aspects To Consider Some 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. 
  113. 113. Important Aspects To ConsiderImportant Aspects To Consider Some 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. 
  114. 114. What do you have in mind?What do you have in mind? On Shore Development Well Off Shore Deep water development-well In respect to Risk, Cost, Environment, Hole Size, Well Design, Tool Speed
  115. 115. 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
  116. 116. 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
  117. 117. An Example of rather complex Logging Program An Example of rather complex Logging Program  Decision TreeDecision Tree West Seno Data Gathering Strategy Standard well PAY Fully Loaded Wireline Full Cores SAMPLING 12 1/4 “ PAY LWD SAMPLES LWD WIRELINE PRESSURE P.O PEX MDT CST Cores Special Logging Velocity Uncertainty 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 N N N N N N LWD MDT Objective Deepest Well VSP STOP N
  119. 119. 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
  120. 120. 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
  121. 121. 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? 
  122. 122. 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?
  123. 123. 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.
  124. 124. 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?