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!
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