Chapter Fang Li 《 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? Dimensions 1D2D3D DomainsTimeFrequency Frequency- wavenumber Mappings Cartesian coordinates Cylindrical coordinates Spherical coordinate Properties of medium IsotropyAnisotropy AcousticElasticViscoelasticMulti-phase Applications Complex structural (fracture, crack, pore space etc) Stratigraphic MethodsNext 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 * NI 2> Migrated seismic profile 3> Simplest & Useful 4> Far more including all Multiples, converted Waves, and attenuation Effects;

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,  Margrave G.F, Seismic modeling: An essential interpreter’s tool, CSEG  Anderson N., Forward seismic modeling: the key to understanding reflection seismic and ground penetrating radar(GPR) techniques,  Chopra S., Seismic elastic modeling, CSEG 2005 

Thank you !! Have a good day!