Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Earth science
Patent
1997-08-11
1999-06-01
McElheny, Jr., Donald E.
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Earth science
G06F 1900
Patent
active
059096551
DESCRIPTION:
BRIEF SUMMARY
The present invention concerns a method for processing reflection seismic traces recorded for variable offsets. It refers more particularly to a method of processing energy concentration areas obtained in the transforms resulting from the application of a parabolic type transform to common midpoint (CMP) seismic trace gathers.
In petroleum exploration, one standard method of obtaining a seismic subsurface image is the reflection seismic method. In a method of this kind, acoustic waves are emitted by appropriate energy sources, referred to as emitters, propagate in the subsurface to be explored and are reflected at the various reflectors that it contains. The reflected waves are recorded as a function of time by appropriate receivers disposed on the surface of the ground or in the water. Each record provided by a receiver and known as a seismic trace is then subjected to projection of the point at the middle of the straight line segment joining the emitter and the receiver. This corresponds to common midpoint sorting.
In the well known seismic prospecting technique known as multiple coverage the emitters and the receivers are disposed on the surface of the ground in such a way that several recordings have the same midpoint. The series of records, or seismic traces, associated with the same midpoint forms what is known as a common midpoint gather of records or traces. This common midpoint gather of traces is a diagram in which the seismic traces corresponding to the same midpoint, which are recorded as a function of time t for variable offsets x of the receivers from said midpoint, are represented parallel to a time axis t from respective abscissa points x on an abscissa axis perpendicular to the time axis at the time origin. The set of common midpoint trace gathers is associated with a series of different midpoints preferably situated along a common line on the surface. Seismic processing produces from these trace gathers a seismic image in the vertical plane passing through all these midpoints. The arrival time of a recorded wave varies with the angle of incidence .theta., which is the angle between the normal to the reflector at the point of reflection, known as the mirror point, and the direction of the (downgoing) incident wave. For the same gather and the same mirror point, this angle varies for each record as a function of the offset x of the receiver relative to the midpoint. Under the standard hypothesis of a homogeneous and isotropic subsurface, with plane and parallel strata, the reflections associated with each of the subsurface reflectors, as observed on a common midpoint seismic trace gather, are theoretically aligned along hyperbolas centred on a vertical line through the midpoint and referred to as indicators. These common midpoint trace gathers are generally subjected to a time-dependent correction, known as normal moveout dynamic correction (NMO correction), the aim of which is to straighten the hyperbolic indicators so that they become theoretically horizontal. The dynamic correction conventionally applied is a correction based on the following equation: ##EQU1## in which: x is the offset as previously defined, emitter and receiver, the waves, and emitter/receiver pair for an offset x.
Applying a parabolic transformation, and in particular the Radon generalised transformation, to common midpoint seismic trace gathers after dynamic (NMO) correction, designated hereinafter d(t,x) gathers, where t and x have the meanings given above in relation to NMO corrections, leads to a decomposition of the d(t,x) gathers along parabolas having the equation t=.tau.+qx.sup.2, where .tau. is the propagation time of the waves for a null offset x and x.sup.2 is the square of the offset.
The Radon parabolic transform of the d(t,x) gather is a diagram representing the function .mu.(.tau.,q) defined by the equation: ##EQU2## in which t, x, .tau., q have the meanings indicated above and 0 everywhere else. An event represented on the d(t,x) gather with an amplitude varying slowly along the parabola having equatio
REFERENCES:
patent: 5258960 (1993-11-01), Swan
Thorson, et al., "Velocity-Stack and Slant-Stack Stochastic Inversion", Geophysics, vol. 50, No. 12, Dec. 1985, pp. 2727-2741.
E.C. Reiter, et al., "2-D Velocity Inversion/Imaging of Large Offset Seismic Data Via The Tau-P Domain", Geophysics, vol. 58, No. 7, Jul. 1, 1993, pp. 1002-1016.
E. Bazelaire, "Normal moveout revisited: Inhomogeneous media and curved interfaces", Geophysics, vol. 53, No. 2, Feb. 1988, pp. 143-157.
Canadas Guy
Dunand Jean-Pierre
Elf Aquitaine Production
McElheny Jr. Donald E.
LandOfFree
Method for processing reflection seismic traces recorded for var does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for processing reflection seismic traces recorded for var, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for processing reflection seismic traces recorded for var will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-962343