Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Earth science
Reexamination Certificate
1999-10-12
2001-05-29
McElheny, Jr., Donald E. (Department: 2862)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Earth science
Reexamination Certificate
active
06240370
ABSTRACT:
BACKGROUND OF INVENTION
The present invention relates to a method of processing seismic data signals. Seismic data are collected in order to analyse the subsurface of the Earth, in particular for hydrocarbon exploration. The data for analysing sub sea structures may be collected on land or, over water, using sea-going vessels. In order to obtain the data a seismic source which may comprise explosives (on land) or an impulse of compressed air (at sea) is provided. The signals reflected by the various layers beneath the surface of the Earth are known as traces and are sensed by a large number, typically hundreds, of sensors such as geophones on land and hydrophones at sea. The reflected signals are recorded and the results are analysed to derive an indication of the layer formations beneath the subsurface. Such indications may then be used to assess the likelihood of hydrocarbon deposits.
However, the physical formation of layers beneath the surface do not always characterise the subsurface geology sufficiently well and the likelihood of hydrocarbon deposits are not assessed as accurately as is desired.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved method of processing and analysing seismic data signals.
According to the present invention there is provided a method of processing seismic data signals reflected by a particular subsurface feature, the method comprising analysis of the spectrum of the seismic data signals by decomposing the reflected signals with respect to a series of orthogonal polynomials and deriving a series of polynomial coefficients which characterise the reflectivity of the subsurface feature.
The invention provides a spectral decomposition of the reflected signals from a particular subsurface feature, for example a layer or a horizon. In the case of a layer this provides a quantification of the volume reflectivity (Volume Reflectivity Spectrum or VRS). The spectral decomposition is performed to an orthogonal base since spectral decomposition by Fourier transformations is not sufficiently accurate in the spectral analysis of seismic signals. The reason for this is that the signals to be analysed exist in short time windows and the infinite nature of the sinusoidal waveforms used in Fourier analysis result in undesirable window effects and side lobes.
A particular set of orthogonal polynomials which are a special set of Chebyshev polynomials are described but a variety of other orthogonal polynomials (in other words a different polynomial base) may be used.
Orthogonal polynomial functions have been used, in other contexts, for creating mathematical representations of received data. European Patent Application No. EP 0216609 A2, Seislith Development, for instance, discloses a method of using orthogonal polynomial functions to express reflection coefficients as functions of offset distances as part of a method for quantitatively relating reflection wave amplitude to corrected source-detector offset data.
Prior to the spectral decomposition, the seismic data may be resampled to ensure an equal number of (time or distance) samples at each point of a layer under investigation irrespective of its relative thickness at each position.
This spectral decomposition to an orthogonal base may also be applied to a priori or synthetic seismic data, for example well logs and data derived from elastic models. This synthetic data (or a priori knowledge) may then be compared with observed data to further characterise the observed data. This provides model-based compensation for transmission effects, spherical spreading and inelastic attenuation. To more accurately characterise the measured data, the synthetic data which provides the best match may be perturbated to provide a still better match.
Further preferred features of the present invention are set out in the dependent claims.
REFERENCES:
patent: 4729101 (1988-03-01), Hanson et al.
Berge Gunnar
Boge Knut Steen
Gehrmann Thomas
Sonneland Lars
Tennebo Per-Ola
Bouchard John H
McElheny Jr. Donald E.
Schlumberger Technology Corporation
LandOfFree
Method of processing seismic data signals 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 of processing seismic data signals, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of processing seismic data signals will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2462696