Oil & Natural Gas Projects
Exploration and Production Technologies
Realistic Velocity Anisotropy Estimation in Complex 3-D Environments
The objective of this research is to develop forward modeling, velocity analysis,
and migration methods in anisotropic media. The methodology and algorithms developed
by this project will improve the quality and resolution of seismic images that
are critical to the economic exploration for hydrocarbons. In addition, this
project provides critical understanding of the fundamental physics of wave propagation
in anisotropic media, which is necessary for the design of optimal seismic surveys
used in hydrocarbons exploration.
Lawrence Berkeley National Laboratory
Based on the new forward-modeling codes, researchers have developed reverse-time
migration codes for both isotropic and anisotropic media. In addition, a two-step
velocity analysis procedure has been developed to estimate anistropic parameters
using common midpoint gathers.
This project has resulted in the development of:
- A new Eikonal solver in isotropic and tilted transverse isotropic (TTI)
- New anisotropic finite-difference codes.
- A new reverse-time migration code.
- New 3-D Fourier finite-difference depth migration in vertical transverse
isotropy (VTI) media.
- A new 3-D Fourier finite-difference common-azimuth migration code.
- A new velocity-analysis code using non-hyperbolic moveout.
The model results show that the anisotropy tilt angle has significant effects
on amplitude and travel time. Therefore, using a VTI assumption for real TTI
media will introduce significant errors in migration and inversion. Acoustic
anistropic media might exist in the real world, and the "artifacts"
in acoustic anistropic wave equations actually are true shear waves. Numerical
and real data examples demonstrate that 3-D Fourier finite-difference depth
migration methods developed by this project are better than the generalized
screen propagator methods currently in use by industry. Synthetic data have
been used to test velocity analysis methods. Tests have demonstrated that using
the near-offset traces to estimate the normal moveout velocity (Vnmo) first-followed
by estimating the effective anisotropy (n) using large offset traces by fixing
(Vnmo)-is faster and more accurate than that seen by estimating Vnmo and n simultaneously.
The effects of velocity anisotropy on reflection seismic imaging have been discussed
in the literature for more than a decade. As the petroleum industry has moved
into 3-D processing and migration in complex geologies, the adverse effects
of unknown velocity anisotropy on depth estimates and image quality have become
A significant component of this project has been the development of finite-difference
forward-modeling algorithms. The project has developed new celerity-domain Eikonal
equation algorithms that are faster and more accurate than any previously developed.
The new Eikonal solver models diffractions and head waves with an adaptive,
fast-sweeping method, resulting in a more robust and accurate algorithm when
compared with existing methods.
A second significant development has been a new finite-difference anisotropic-elastic
seismic algorithm using optimal coefficients and a variable-grid finite-difference
method to solve the wave equation. The optimal finite-difference coefficients
are obtained by a least-squared method in the wavenumber domain. The grid spacing
is adapted to the velocity structure using spatial differential operators in
a non-uniform grid.
Current Status (June 2006)
The project is in its final year. Algorithms are being documented, and codes are being set up for licensing.
The project ended at the end of 2005. It was not funded in FY 2006.
Project Start: March 27, 2002
Project End: March 26, 2006
Anticipated DOE Contribution: $911,000
Performer Contribution: $850,000 (48% of total)
NETL - Purna Halder (Purna.Halder@netl.doe.gov or 918-699-2083)
LBL - Michael Hoversten (firstname.lastname@example.org or 510-486-5085)
Zhang , L., Hua, B., and Calandra, H., 2005, 3-D Fourier Finite-Difference Anisotropic
Depth Migration , SEG 2005, accepted.
Zhang, L., Hua,B., Calandra, H., Rector, J.W., and Hoversten, G.M., 2005, 3-D
FFD commom-azimuth depth migration, submitted to Journal of Seismic Exploration.
Zhang, L., Rector, J.W and Hoversten, G. M., 2004, Eikonal Solver in the Celerity
Domain, Geophysical Journal International, accepted for publication.
Zhang, L., Rector, J.W., Hoversten, G.M, and Fomel, S., 2004, Split-step complex
Pade-Fourier depth migration, Geophysics, in revision.
Zhang, L., Rector, J.W., and Hoversten, G.M., 2004, An Eikonal Solver in Tilted
TI media, Geophysics, submitted for publication.
Zhang, L., Rector, J.W., and Hoversten, G.M., 2004, An acoustic wave equation
for tilted transversely isotropic media, Geophysical Prospecting, accepted for
Zhang, L., Rector, J.W., and Hoversten, G.M., 2004, Reverse time migration in
tilted transversely isotropic media, J. of Seismic Exploration, 13, 173-187.
Grechka, V., Zhang, L., and Rector, J.W, 2004, Shear waves in acoustic anisotropic
media, Geophysics, 69, 576-582.
Zhang, L., Rector, J.W., and Hoversten, G.M., 2003, Split-step complex Pade
migration, J. of Seismic Exploration, 12, 229-236.
Zhang, L., Rector, J.W., Hoversten, G.M., and Fomel, S., 2004, Split-step complex
Pade-Fourier depth migration, 74th Ann. Internat. Mtg., SEG.
Grechka,V., Zhang, L., and Rector, J. W., 2004, Shear waves in acoustic transversely
isotropic media, 74th Ann. Internat. Mtg., SEG.
Zhang, L., Rector, J.W., and Hoversten, G.M., 2003, An acoustic wave equation
for modeling in tilted TI media, 73rd Ann. Internat. Mtg., SEG (153-156).
Zhang, L., Rector, J.W., and Hoversten, G.M., 2002, Eikonal Solver in the Celerity
Domain, 72nd Ann. Internat. Mtg., SEG (2023-2026).
Zhang, L., Rector, J.W., and Hoversten, G.M., 2002, An Eikonal Solver in Tilted
TI Media, 72nd Ann. Internat. Mtg., SEG (1955-1958).
Rector, J.W, Zhang, L., and Hoversten, G.M., 2002, Optimized coefficient finite-difference
method for wave equation, SEG workshop, 72nd Ann. Internat. Mtg., SEG.
Determinations of vertical anisotropy are used to measure amplitude and travel