Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Earth science
Reexamination Certificate
1999-05-10
2001-04-03
Oda, Christine (Department: 2862)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Earth science
C367S053000, C367S038000, C702S011000, C702S006000
Reexamination Certificate
active
06212477
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to the art of seismic signal processing. More specifically, the invention relates to migration and velocity analysis of converted wave data.
Current methodologies for velocity analysis or imaging p-s seismic data (a.k.a. “converted wave” data) require knowledge of p-wave velocity to get a converted s-wave velocity. However, one of the reasons for using converted waves is that s-waves can be detected in some areas where there is no p-wave data. Thus, accurate knowledge of the p-wave velocity cannot be derived from the data. Therefore, an estimate of the p-wave going down and the s-wave coming up is made to calculate a Vp/Vs ratio. Events on a gather are viewed, and a velocity is picked for the “move-out” that would best fit the actual event in the data with a curve.
In a specific example, seen in
FIG. 1
, a p-wave section is seen in which a gas cloud
10
is present. No p-wave velocity picking can be done in that area.
FIG. 2
is a p-s image, showing that the s-wave data travels through the gas cloud. The velocity picked is, effectively, a weighed average of the down-going and up-going fields, but it is not known whether the ratio of the s-wave velocity Vs to the p-wave velocity Vp is 40/60, 50/50, or something else.
In some cases, where there is p-wave data available, a Vs/Vp ratio is estimated by determining Vp from the p-p data (e.g. from a hydrophone or vertical geophone in a multicomponent system). In the alternative, Vp data from nearby well logs might be used. When p-p data is used, a time equation that is dependent only on Vp is compared to events in the data. Vp is varied, and the Vp where there is maximal energy is chosen as the correct Vp. Converted wave data is then viewed (for example, from a horizontal component of a multicomponent detector), and a different equation is used. That equation is dependent upon both Vp and Vs. Vp is presumed to be what was found from the vertical geophone or hydrophone. Then, Vs is varied, and the Vs where there is maximum energy is chosen as Vs. If Vp is wrong, Vs will be wrong. NMO, DMO, and migration are then performed. Since these processes are heavily dependent on having a correct Vp, errors can be great.
Thus, there is a need for a method and system of analyzing velocity of converted wave data in which the need for well-log data is reduced or eliminated and in which there is less dependence on accurate Vp analysis.
SUMMARY OF THE INVENTION
It is an object of the present invention to address the above needs. Therefore, according to one aspect of the invention, a process is provided for processing c-wave data, the process comprising: providing zero-offset gather, substantially uncorrected by normal move-out; performing migration on the zero-offset gather; performing velocity analysis on the migrated zero-offset gather; and performing NMO on the migrated data using the velocity from the velocity analysis.
According to another aspect of the invention, a system is provided for processing converted wave seismic data comprising: means for providing zero-offset gather substantially uncorrected by normal move-out; means for performing velocity analysis on the migrated zero-offset gather; and means for performing NMO on the migrated data using the velocity from the velocity analysis.
According to another aspect of the invention, a system is provided for processing converted wave seismic data comprising: a migration module positioned and arranged to receive a zero-offset gather and output a migrated set of data substantially independent of velocity analysis; a velocity analysis module positioned and arranged to receive migrated data from said migration module and perform velocity analysis on the migrated data; and a NMO module positioned and arranged to receive a velocity model from said velocity module and the migrated data from said migration module and perform NMO on the migrated data using the velocity from the velocity analysis.
REFERENCES:
patent: 4797861 (1989-01-01), Beasley
patent: 4839869 (1989-06-01), Corcoran
patent: 5097452 (1992-03-01), Beasley
patent: 5500832 (1996-03-01), Berryhill
patent: 5596547 (1997-01-01), Bancroft et al.
Zhong, Benshan, et al., “A new strategy for CCP stacking,” Geophysics, vol. 60, No. 2 (Mar.-Apr. 1995); pp. 517-521.
Leon Thompson, “Converted-wave reflection seismology over anisotropic, inhomogeneous media,” 68thAnnual Internat Mtg., Soc., Expl. Geophys., 1998, 2048-2051.
M.P. Harrison and R.R. Stewart, “Poststack migration of P-SV seismic data,” Geophysics, 1993, 58, No. 8, 1127-1135.
M.P. Harrison, “Processing of P-S Surface Seismic Data: Anisotropy Analysis, Dip Move-out, and Migration,” 1992, Ph.D. Thesis, University of Calgary.
G. Tessmer and A. Behle, “Common reflection point data-stacking technique for converted waves,” Geophysical Prospecting, 1988, 36, 661-688.
H.F. Gerlad et al., “Dip Movement and Pre-stack Imaging,” 18thAnnual Offshore Technology Conference, Abstracts, 75-84.
P.J. Fowler, “A Comparative Overview of Pre-stack Time Migration Method,” 67thAnnual International Meeting of the SEG, 1999, Excarded Abstracts, 1571-1574.
J.C. Bancroft and H.D. Geiger, “Equivalent offset CRP gathers,” 64thAnnual Internat Mtg., Soc. Expl. Geophys., 1994, 672-675.
M.T. Taner and F. Koehler, “Velocity spectra-digital computer derivation and applications of velocity functions,” Geophysics, 1969, 34, No. 6, 859-881.
P.S. Schultz and J.F. Claerbout, “Velocity estimation and downward-continuation by wavefront synthesis,” Geophysics, 1978, 43, No. 4, 691-714.
J.R. Berryhill, “Wave-equation datuming before stack,” Geophysics, 1984, 49, 2064-2066.
Altan Suat
Brzostowski Matthew A.
Wang Weizhug
Zhu Xianhuai
Arnold & Associates
Jolly Anthony
Oda Christine
PGS Tensor Inc.
LandOfFree
Converted-wave analysis system and method does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Converted-wave analysis system and method, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Converted-wave analysis system and method will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2535319