Chapter 4.5-4.6

Fang Li

04-17-2009

《 Quantitative Seismic Interpretation 》

Outline

Forward seismic modeling Future directions in quantitative seismic

interpretation References

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.

When? Before and after the acquisition of seismic field

data. Where?

Laboratory Computer

Solve the equation of motion for seismic waves;

Newton’s second law of motion;

Constitutive relation, such as Hooke’s law;

How?

Dimensions1D 2D 3D

Domains Time FrequencyFrequency-

wavenumber

MappingsCartesian

coordinatesCylindrical

coordinates Spherical coordinate

Properties of medium

Isotropy Anisotropy

Acoustic Elastic Viscoelastic Multi-phase

ApplicationsComplex structural

(fracture, crack, pore space etc)Stratigraphic

Methods Next slide

Methods

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

Ray Theory

Wave Theory

Convolution model

1> WAVELET * NI2> Migrated seismic profile3> Simplest & Useful4> Far more including allMultiples, converted Waves, and attenuationEffects;

From Neil Anderson (2002)

For the creation of the complete elastic body-wave responses from a horizontally layered system;

Including all possible multiples,mode conversions ,and transmission losses.

Reflectivity method

Without multiples With multiples

From CREWES Research Report-Vol16(2004)

PP

SS

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.

Class 1 AVO

Class 2 AVO

From CREWES 2004

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;

From Yongyi Li (2007)

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.

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;

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;

References

Krebes E.S. , Seismic forward modeling, CSEG Recorder, 2004.

Margrave G.F, Seismic modeling: An essential interpreter’s 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

Thank you !!

Have a good day!