Fang Li

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Chapter 4.5-4.6
Quantitative Seismic Interpretation

• Fang Li
• 04-17-2009

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Outline

• Forward seismic modeling
• Future directions in quantitative seismic
  interpretation
• References

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Forward seismic modeling

• What?
• Seismic modeling is essentially the construction
  of geologic computer models and simulating their
  seismic wave propagation response.
• Why ?
• Forward modeling of geophysical data is a tool
  used as a survey design aid and to constrain the
  interpretation of recorded/processed seismic data.

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• When?
• Before and after the acquisition of seismic field
  data.
• Where?
• Laboratory
• Computer
• Solve the equation of motion for seismic waves
• Newtons second law of motion
• Constitutive relation, such as Hookes law

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• How?

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Methods

• Convolution model
• Reflectivity method
• Ray tracing
• Gaussian beams method
• Finite difference method
• Finite element method
• Pseudo spectral method

Ray Theory
Wave Theory
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Convolution model

• 1gt WAVELET NI
• 2gt
• Migrated seismic profile
• 3gt Simplest Useful
• 4gt
• Far more including all
• Multiples, converted
• Waves, and attenuation
• Effects

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From Neil Anderson (2002)
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Reflectivity method

• For the creation of the complete elastic
  body-wave responses from a horizontally layered
  system
• Including all possible multiples,mode
  conversions ,and transmission losses.

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With multiples
Without multiples
PP SS
From CREWES Research Report-Vol16(2004)
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Ray tracing

• Ray tracing can be used to compute seismic wave
  travel times and amplitudes along ray paths in a
  heterogeneous medium when the frequency present
  in the wave are high enough so that the
  geometrical optics approximation can be used.

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From CREWES 2004
Class 2 AVO
Class 1 AVO
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Finite difference method(FD)

• The finite-difference method is powerful and
  flexible in accounting for complex
  non-homogeneities and arbitrary anisotropy of a
  medium
• Produce full wavefield
• Proper for complicated structures
• Involving grid dispersion and edge effects

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From Yongyi Li (2007)
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Summary

• All modeling methods are rooted in the same
  physical theory.
• Each modeling method has specific strengths and
  weaknesses.
• Any particular method has limited ability to
  represent this underlying physical reality.

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Future directions in quantitative seismic
interpretation

• More rigorous modeling and inversion of the wave
  propagation phenomena
• Combing sedimentologic and diagenetic modeling
  with rock physics modeling to obtain more
  realistic predictions of seismic properties

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• Probabilistic Monte Carlo simulations to capture
  uncertainties in both rock physics and inversion
  results
• Incorporation of geostatistical methods to
  account for spatial correlations in reservoir
  properties

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References

• Krebes E.S. , Seismic forward modeling, CSEG
  Recorder, 2004.
• Margrave G.F, Seismic modeling An essential
  interpreters tool, CSEG 2004.
• Anderson N., Forward seismic modeling the key to
  understanding reflection seismic and ground
  penetrating radar(GPR) techniques, 2002.
• Chopra S., Seismic elastic modeling, CSEG 2005
• www.crewes.org

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Thank you !!Have a good day!