Sonic Logging

Wireline LoggingWireline Logging

Sonic ToolsSonic Tools

OverviewOverview

• Formation: Reservoir qualityFormation: Reservoir quality

• Fluid: Oil, Gas or Water? Fluid: Oil, Gas or Water?

• Borehole: Environmental factorsBorehole: Environmental factors

Formation PropertiesFormation Properties

• RadioactivityRadioactivity

• PorosityPorosity

• Grain densityGrain density

• Pore SizePore Size

• StratigraphyStratigraphy

• Bedding, DipBedding, Dip

• Sonic VelocitySonic Velocity

• Seismic VelocitySeismic Velocity

Fluid PropertiesFluid Properties

• Salinity (Resistivity)Salinity (Resistivity)

• DensityDensity

• SaturationSaturation

• PressurePressure

• TemperatureTemperature

• ViscosityViscosity

• MobilityMobility

• Bubble PointBubble Point

Borehole PropertiesBorehole Properties

• DepthDepth

• CaliperCaliper

• Spontaneous PotentialSpontaneous Potential

• TemperatureTemperature

• Cable TensionCable Tension

• Deviation, AzimuthDeviation, Azimuth

Sonic UnitsSonic Units

• Sonic tools measure formation slowness or Sonic tools measure formation slowness or delta time (dt).delta time (dt).

• Slowness is measured in us/ftSlowness is measured in us/ft• uS/ft = 1000000 / ft/suS/ft = 1000000 / ft/s• Slowness of steel: 57 us/ft (5400 m/s)Slowness of steel: 57 us/ft (5400 m/s)• Slowness of water: Approx 220 us/ftSlowness of water: Approx 220 us/ft• Different waves have different speeds.Different waves have different speeds.• Shear wave is approx twice as slow as Shear wave is approx twice as slow as

compressional wave.compressional wave.

Sonic MeasurementSonic Measurement

• The compressional slowness is normally The compressional slowness is normally measured using a monopole measured using a monopole (omnidirectional) source around 15kHz.(omnidirectional) source around 15kHz.

• The slowness is computed by taking the The slowness is computed by taking the difference in transit (arrival) times difference in transit (arrival) times between two different receivers.between two different receivers.

• In this way mud velocity and borehole size In this way mud velocity and borehole size are eliminated from the equation.are eliminated from the equation.

• Washouts and other borehole effects are Washouts and other borehole effects are reduced by averaging two measurements reduced by averaging two measurements from different transmitters.from different transmitters.

Simple Tool DesignSimple Tool Design

Borehole CompensationBorehole Compensation

Sonic WaveformsSonic Waveforms

• Different types of sonic waveforms are of interest Different types of sonic waveforms are of interest for different applications.for different applications.

• Compressional slowness gives a useful porosity Compressional slowness gives a useful porosity indication.indication.

• Compressional slowness is also used to calibrate Compressional slowness is also used to calibrate surface seismic velocities.surface seismic velocities.

• Shear slowness (together with compressional) is Shear slowness (together with compressional) is used to calculate rock properties.used to calculate rock properties.

• Shear slowness is also used in certain types of Shear slowness is also used in certain types of seismic processing.seismic processing.

• Stoneley waves are often used to look for fractures.Stoneley waves are often used to look for fractures.

Waveform DetectionWaveform Detection

• First (compressional) arrival is easily First (compressional) arrival is easily detected using simple circuits.detected using simple circuits.

• Shear and Stoneley waves must be Shear and Stoneley waves must be detected using coherence processing detected using coherence processing on an array of waveforms.on an array of waveforms.

• The coherence matches similar The coherence matches similar events at different parts of each events at different parts of each waveform using a velocity filter.waveform using a velocity filter.

Coherence ProcessingCoherence Processing

Array Waveform ToolsArray Waveform Tools

Limitations of Monopole Limitations of Monopole SourcesSources• The monopole source is omni directional.The monopole source is omni directional.• Frequency is between 12kHz and 20KhzFrequency is between 12kHz and 20Khz• The compressional wave in the mud will be The compressional wave in the mud will be

faster than the formation shear wave for faster than the formation shear wave for slow formations.slow formations.

• This large arrival will mask the shear we This large arrival will mask the shear we want to measure.want to measure.

• Mud does not directly support shear waves Mud does not directly support shear waves – we only detect them due to mode – we only detect them due to mode conversion.conversion.

Dipole Source TheoryDipole Source Theory

• We use a pair of dipole sources perpendicular to We use a pair of dipole sources perpendicular to the borehole wall.the borehole wall.

• The pressure wave they produce creates a The pressure wave they produce creates a flexural wave along the borehole.flexural wave along the borehole.

• At low frequencies this wave has a speed close to At low frequencies this wave has a speed close to the shear speed.the shear speed.

• Because the source is directional and Because the source is directional and perpendicular to the tool axis, mud arrival is perpendicular to the tool axis, mud arrival is small.small.

• Mud arrival also reduced by subtracting signal Mud arrival also reduced by subtracting signal from pairs of receivers.from pairs of receivers.

Dipole SourcesDipole Sources

Shear vs Flexural SpeedShear vs Flexural SpeedWellbore

Head wave

Flexural waveDirectional source

FormationCompressional

wave

Shearwave

Compressionalwave

Flexuralwave

Shearwave

Sonic Test 1Sonic Test 1

1.1. What is the normal unit of sonic slowness?What is the normal unit of sonic slowness?

2.2. What is expected slowness of steel such What is expected slowness of steel such as casing?as casing?

3.3. What is approximate ratio of shear to What is approximate ratio of shear to compressional slowness?compressional slowness?

4.4. Which one is slower?Which one is slower?

5.5. What type of source is generally used to What type of source is generally used to measure compressional slowness?measure compressional slowness?


6.6. How are mud velocity and borehole size How are mud velocity and borehole size effects eliminated from our effects eliminated from our measurements of compressional measurements of compressional slowness?slowness?

7.7. How do we compensate for washouts and How do we compensate for washouts and borehole geometry?borehole geometry?

8.8. Name two applications of compressional Name two applications of compressional slowness.slowness.

9.9. Name two applications of shear slowness.Name two applications of shear slowness.10.10.Name one other waveform type with Name one other waveform type with

practical applications.practical applications.


11.11.Explain how shear slowness is computed Explain how shear slowness is computed from an array of sonic waveforms.from an array of sonic waveforms.

12.12.Monopole sources are (HIGH/LOW) Monopole sources are (HIGH/LOW) frequency?frequency?

13.13.Dipole sources are (HIGH/LOW) frequency?Dipole sources are (HIGH/LOW) frequency?

14.14.We have difficulty measuring shear We have difficulty measuring shear slowness with a monopole source in slowness with a monopole source in (FAST/SLOW) formations?(FAST/SLOW) formations?

15.15.Explain why this is so.Explain why this is so.


16.16.A Dipole source is omni-directional A Dipole source is omni-directional (TRUE/FALSE)?(TRUE/FALSE)?

17.17.The type of wave it generates in the formation The type of wave it generates in the formation is (STONELEY /FLEXURAL /SHEAR is (STONELEY /FLEXURAL /SHEAR /COMPRESSIONAL) ?/COMPRESSIONAL) ?

18.18.Mud can carry (true) shear waves (TRUE Mud can carry (true) shear waves (TRUE /FALSE)?/FALSE)?

19.19.What is difference in receiver arrangement for What is difference in receiver arrangement for dipole vs monopole sources?dipole vs monopole sources?

20.20.Name two factors that reduce or eliminate mud Name two factors that reduce or eliminate mud arrivals for Dipole modes.arrivals for Dipole modes.

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