Wireline Logging

1
Wireline Logging

• Nuclear Tools

2
Overview

• Formation Reservoir quality
• Fluid Oil, Gas or Water?
• Borehole Environmental factors

3
Formation Properties

• Radioactivity
• Porosity
• Grain density
• Pore Size
• Stratigraphy
• Bedding, Dip
• Sonic Velocity
• Seismic Velocity

4
Fluid Properties

• Salinity (Resistivity)
• Density
• Saturation
• Pressure
• Temperature
• Viscosity
• Mobility
• Bubble Point

5
Borehole Properties

• Depth
• Caliper
• Spontaneous Potential
• Temperature
• Cable Tension
• Deviation, Azimuth

6
Nuclear Logging

• Subatomic interactions allow remote sensing.
• Either natural or generated sub atomic particles.
• Major Health and Safety issues.
• Very dependant on external calibrations and
  wellsite QC.

7
Formation Radioactivity Natural Gamma Ray

• 3 naturally occurring radioactive isotopes
• Thorium
• Potassium
• Uranium
• Uranium only one soluble in water
• Mobile
• Not a useful formation identifier

8
Gamma Ray Response

• Data calibrated in API units (GAPI)
• Clean sandstone or limestone contains no
  radioactive elements.
• GR is primarily a shale indicator.
• Can be fooled by other minerals and coal.

9
Gamma Ray Interpretation
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Scintillation Detector Diagram
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Gamma Ray Detection Physics

1. GR enters detector crystal
2. Crystal absorbs GR and emits a photon (flash of
   light)
3. Photon enters photomultiplier tube at the
   PhotoCathode
4. Photon is amplified into an avalanche of
   electrons
5. Electron pulse is detected at the detector Anode
6. Energy of GR correlates to pulse voltage

12
Gamma Ray Calibration

• Normal GR tool is calibrated against a mildly
  radioactive blanket (once per job).
• Natural GR tools normally calibrated to find the
  Thorium activation peak in a GR spectrum.
• Operational check confirms peak stabilisation.

13
Gamma Ray Applications

• Lithology indicator
• Shale Volume
• Formation fingerprint correlation curve
• Clay type input requires Potassium, Thorium and
  Uranium curves

14
Formation Porosity Neutron Porosity Logging

• Atoms consist of three sub atomic particles
• Protons ( charged, mass)
• Neutrons (no charge, mass)
• Electrons (- charged, no mass)
• Hydrogen has an atomic no. of 1
• 1 Proton
• 0 Neutrons
• 1 electron

15
Neutron Scattering and Capture

• At high energies Neutrons will bounce off each
  other, like billiard balls.
• At lower (thermal) energies they may be captured
  by large atoms.
• When they are captured a capture GR is emitted.

16
Neutron Measurement Physics

• AmBe chemical source emitting neutrons at 16 MeV
• Detectors only sensitive to thermal neutrons.
• By taking ratio of two detectors, sensitivity to
  salinity (Chlorine) largely eliminated.

17
Neutron Calibration

1. Primary Reference is block in Houston.
2. Field calibration reference is fresh water
   filled tank (every 2 months).
3. Operational check is radioactive test jig.
4. Calibration corrected for tool diameter and
   water temperature.

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Neutron Response

• The more Hydrogen in the formation the faster
  Neutrons will slow to thermal energy.
• Hydrogen is present in water and oil but not much
  in gas.
• Clay bound water will contribute to effect.
• Chlorine has a high capture rate and affects the
  result.
• Slightly different response in sand vs limestone.

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Neutron Interpretation

• Sensitive gas indicator typically big crossover
  vs density porosity.
• Several significant environmental corrections
• Hole Size
• Salinity
• Standoff
• Temperature, Pressure

20
Formation Density Physics

1. GRs slowed by electron interactions (Compton
   Scattering).
2. When slow enough they are absorbed.
3. Absorption rate related to electron density.
4. Electron density directly related to bulk density.

21
Photoelectric Effect

• The PEF of a formation is related to its ability
  to capture Gamma Rays.
• It can be a valuable lithology identifier.
• It is strongly masked by the presence of Barite
  in the mud system (a strong absorber).
• Only measured on long spaced detector.

22
Density Tool Design

• Cesium137 GR source.
• Detectors are similar to GR tool (but smaller).
• Density mostly derived from LS count rate.
• Short spacing used to correct mudcake / borehole
  effects.

23
Detector Energy Windows
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Density Calibration

1. Primary reference is block in Houston.
2. Field reference is aluminium block with steel
   sheet (monthly).
3. Operational check is stabilisation source only.

25
Neutron/Density Comparison

• Complementary scales
• Overlay in clean wet limestone.
• NPHI 6pu low in wet sand
• NPHI -gt 0 in gas
• NPHI high in shale
• Normally shade Density -gtPorosity
• Both sensitive to bad hole

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Density Interpretation

• Density from density tool is bulk density
  (formation plus fluid content).
• Grain Density is computed by removing estimated
  total porosity and fluid density.
• PEF together with Natural Gamma Ray can
  theoretically be used to accurately calculate
  mineralogy and type shales.

27
Test Part 1

1. List the naturally occurring radioactive
   isotopes.
2. Which isotope is soluble in water and why is this
   important.
3. In a clean sand GR typically reads (HIGH/LOW).
4. In a shale GR typically reads (HIGH/LOW)
5. Describe a standard GR detector design.

28
Test Part 2

1. A GR tool has a monthly master calibration
   (TRUE/FALSE)
2. Name the three main subatomic particles.
3. Name the subatomic particles in a Hydrogen atom.
4. Name the atoms in a water molecule.
5. Describe Hydrogen index

29
Test Part 3

1. Describe the life of a Neutron particle.
2. Explain why the Neutron porosity tool uses 2
   detectors.
3. A Neutron tool has a monthly master calibration
   (TRUE/FALSE)
4. List some of the factors that will affect the
   Neutron porosity output.
5. List some of the environmental corrections
   normally applied to the Neutron log.

30
Test Part 4

1. Explain the GR interaction that allows us to
   measure density.
2. The detectors in a density tool are similar to
   the ones in a GR tool (TRUE/FALSE)
3. Explain why the density tool uses 2 detectors.
4. The density tool has a monthly master calibration
   (TRUE/FALSE)
5. Describe the Density/Porosity response in the
   presence of gas.