Sonic Petrophysics(11)

7/27/2019 Sonic Petrophysics(11)

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Lecture Presentation

Fundamentals of Well Logging

Petrophysics and Sonic Logging

Carlos Torres-Verdn, Ph.D.Professor

Department of Petroleum and Geosystems Engineering

The University of Texas at Austin

Objectives:1. To understand the physical principles behind the

operation of borehole borehole sonic logging tools,

2. To learn how to interpret sonic logs in terms oflithology, types of fluids, and porosity,

3. To learn how to combine gamma-ray, resistivity,

neutron, bulk density, and sonic logs to estimatelithology, types of fluids, and porosity

4. To understand and learn how to diagnose thelimitations of sonic logs, and

5. To get acquainted with the basic steps of sonic logprocessing


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Mechanical Property Analysis

Formation Evaluation: Lithology,Gas Detection, and Porosity

Geophysical Prospecting (SeismicExploration)

APPLICATIONS OF SONIC LOGS:

Stress and Strain


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Stress and Strain

P and S WAVES


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Static and Dynamic Deformation

The Fastest Borehole Wave Mode(the shortest arrival time)

The Simplest

Sonic Tool


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What do P- and S-wave velocity logsrespond to?

Photograph courtesy of Prof. Jon Olson

Example of Microfracturing

SONIC RESPONSE OF POROUS MEDIA:

Parameters that have a primary influenceon the fastest arrival time


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SONIC RESPONSE OF POROUS MEDIA:Parameters that have a primary influenceon the fastest arrival time

Example of Vuggy Carbonate

Intuitive Model


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Mechanical Properties and Petrophysics

Units and Conversions


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Typical Ranges of Velocit ies

P-WAVE VELOCITIES OF GASES


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P- and S-WAVE VELOCITIES OF SEDIMENTARY ROCKS

Typical Ranges of Velocit ies


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Relationship with Depth

Relationship with Pressure


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Formation Over-Pressure

Compaction and Over Pressure


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Influence of Saturating Fluids

Example of Gas Effect on a P-wave Sonic Log

(high porosity formation negligible invasion)


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Example:Deep Water Gulf of Mexico

Water SaturationPorosity

P-Velocity

S-Velocity

Density

HC Sands

Water Sands

& Shales

Water Sands

& Shales

HC Sands

HC Sands

Water Sands

Shales

Sands

Shales

Sands

Shales

Sands

Shales

Example: CrossPlot Analysis

Siliciclasts

(P-Member)

Carbonates

(O-Member)

P-Impedance (m/s*g/cc)

S-Impeda

nce(m/s*g/cc)

O

P1

P2

P-Impedance vs. S-Impedance


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BASIC PRINCIPLES

STANDARD BAKER ATLAS SONIC TOOL (FOCUS)


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STANDARD BAKER ATLAS SONIC TOOL (FOCUS)

DIPOLE SONIC

ARRAY TOOL


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Traditional Monopole Tool

Monopole in a Fast Formation


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MONOPOLE WAVEFORM

250 cm 200 150 100 50 0 cm

80 cm

80 cm

40 cm

30 cm20 cm

60 cm

5 cm2 cm0 cm

INDUCTION LOG

LATEROLOG

NEUTRON

GAMMA RAYDENSITY

SONIC

MICRO RESISTIVITYMICROLOG

DIPMETER

DEPTH OF INVESTIGATION

RES

OLUTION

RESISTIVITY

RADIOACTIVITY

RESISTIVITY

ACOUSTIC

Logging Tools


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Slow Formations

DIPOLE FLEXURAL WAVE


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Dipole Tool

BOREHOLE DIPOLE SOURCE


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Sonic Porosity

1. The porosity from the sonic slowness is different from that of

the density or neutron tools.

2. Sonic porosity reacts to primary porosity only, i.e. it does not

see the fractures or vugs.

3. The difference between the sonic porosity and the neutron-

density porosity gives a Secondary Porosity Index (SPI) which

is an indication of how much of th is type of porosity there is in

the rock.



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Photograph courtesy of Prof. Jon Olson

Example of Microfracturing

SONIC RESPONSE OF POROUS MEDIA:

Parameters that have a primary influenceon the fastest arrival time


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Intuitive Model

Theory and Measurements


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Compaction Effects

Lithology

Identification:

Bulk Density-SonicCross-Plot


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Lithology

Identification:

Sonic-Neutron

Cross-Plot

Baker Atlas

Schlumberger

Acknowledgements:


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Some Review Questions (Part I):1. What is the difference between P and S waves, which

one is faster? What is the relationship between thevelocity of P- and S-waves, their frequency ofpropagation and their wavelength?

2. Why do standard sonic logging tools only consist of P-wave sources? Is the wavelength of sonic waves longeror shorter than the diameter of the borehole?

3. Which types of waves can a modern sonic tool detect?

4. How is the velocity of P- or S-waves in rock formationsmeasured by a sonic tool? Why are sonic tools said tobe compensated instruments? What do theycompensate for? Give a ball-park figure for the time ittakes for a P-wave to arrive at the detector i f the wavehas traveled through a sandstone.

5. What is the relationship between P- and S-wavevelocities of a rock, the rocks bulk density, and therocks shear and compressional moduli?

Some Review Questions (Part II):6. Why do P-wave velocities in general monotonicallyincrease with depth? Define the so-called compactioneffect on sonic logs.

7. How are P-wave sonic logs used to detect and assessoverpressure zones?

8. What is a Stoneley wave? How are Stoneley waves usedin formation evaluation?

9. How are P-wave and S-wave velocity logs used incombination to assess lithology and types of fluids?

10.What is the length of investigation of a P-wave soniclog? Is the length of investigation of a P-wave sonic logthe same as that of a S-wave sonic log?

11.When will Wyll ies P-wave sonic porosity formula breakdown?

12.How would you modify Wyllies simple porosity formulato account for the presence of shale?

13.Explain the effect of gas-water substitution in P- and S-wave sonic logs? How do variations of porosity andshale content affect P- and S-wave sonic logs?


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Some Review Questions (Part III):14.What is a dipole sonic tool? Why is this sometimes used

instead of standard monopole tools?

15.What are the environmental corrections normally appliedapplied to sonic logs?

16.List three independent petrophysical/geologicalsituations in which the sonic porosity log would bepreferred over the bulk density porosity log to estimatethe porosity of rock formations.

17.Why is it said that sonic porosi ty logs are sensitive toprimary and not to secondary porosity? Whatassumptions are implicitly made behind such astatement?

18.How do modern sonic tools measure in-situ anisotropyof the rocks elastic properties?

19.How do modern sonic tools are used to estimate in-situstress?

20.Are P-wave sonic logs sensitive to the solid or fluidcomponents of the rock, or to both?

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Sonic Petrophysics(11)