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AVO Modeling for the Effects of Attenuation and Random Scattering Using Thin-Slab Propagator

AVO Modeling for the Effects of Attenuation and Random Scattering Using Thin-Slab Propagator. *. Xian-Yun Wu & Ru-Shan Wu. Modeling and Imaging Lab. University of California, Santa Cruz. * Presently at URC, ExxonMobil. Outline. Introduction. Dual-domain one-way thin-slab propagator.

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AVO Modeling for the Effects of Attenuation and Random Scattering Using Thin-Slab Propagator

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  1. AVO Modeling for the Effects of Attenuation and Random Scattering Using Thin-Slab Propagator * Xian-Yun Wu & Ru-Shan Wu Modeling and Imaging Lab. University of California, Santa Cruz * Presently at URC, ExxonMobil

  2. Outline • Introduction • Dual-domain one-way thin-slab propagator • Numerical examples • Effects of scattering • Effect of attenuation • AVO in heterogeneous visco-elastic media • Frequency-Dependent AVOs • Conclusions

  3. Introduction • AVO analysis (elastic parameters and fluid contents) • Significant effects of wave propagation on local true-amplitude (scattering, anelasticity, frequency-dependent, etc.) • Developing efficient AVO forward modeling tools (high efficiency, complicated models) • Dual-domain one-way thin-slab propagator and its applications

  4. -domain 0 0 0 p + U s + U p U updated field s U X-domain Dual-domain one-way propagator (thin-slab) elastic Incident field

  5. Elastic thin-slab propagator Scattered field (P wave):

  6. Elastic thin-slab propagator Scattered field :

  7. Complex velocities : Elastic parameters : Perturbations : Incorporate Q factors into the propagator

  8. Numerical examples • Effects of scattering (heterogeneities) • Effect of attenuation (intrinsicity) • AVO in heterogeneous visco-elastic media • Frequency-dependent AVO

  9. Effects of scattering due to heterogeneities in elastic parameters Type: exponential function Corrl. lengths: 100m in x and 40m in z. The rms: 2%

  10. Plane P-wave Homogeneous Random Transmitted wavefront

  11. FD Reflection amplitudes in random media Thin-slab

  12. White-noise Reflection amplitudes in random media Exponential

  13. Effects of attenuation Qp=Qs=500 Qp=Qs=50

  14. Reflection amplitude in elastic random media Reflection amplitudes in anelastic random media

  15. Reflection amplitudes in random mediawith Q

  16. AVO in anelastic and random media

  17. 1/Q ~ frequency * S R shale oil sand • Frequency-dependent AVO

  18. Spatially correlated heterogeneities (even as weak as rms=1%) may produce significant effects on AVO. In visco-elastic heterogeneous media, local reflections may be the result of interaction between Q and elastic parameters. Properties of target zones control the AVO trends; Qs mainly affect the absolute amplitudes of reflections; scatterings mainly increases local variations in reflected amplitudes. Conclusions

  19. shale 3170 1668 2.36 0.31 gas 3350 2231 2.02 0.10 Oil 3527 2131 2.22 0.21 brine 3551 2109 2.27 0.23 Table 1. Reservoir model Note: Parameters are taken from Simmons and Backus (1994).

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