Atlantic Richfield Company

Mobil Oil Corporation

Dennis Corrigan

John James Sallas

Kenneth Paul Allen

Vaughn L Ball

A method and system for correcting seismic survey signals for separating and correcting for the effects of azimuthal anisotropy caused by the overburden, rather than the subsurface reflectivity, is disclosed. Following an initial estimate and normal moveout correction of the traces in a common midpoint gather, analytical traces are generated for coefficient series corresponding to zero-offset travel time response and to the azimuthal anisotropy, over the corrected gather. The quadrature-phase component of the azimuthal anisotropy coefficient series relative to the zero-offset travel time coefficient series indicates the effects of overburden azimuthal anisotropy, while the in-phase component indicates the effects of azimuthal anisotropy from subsurface reflective interfaces. Additional normal moveout correction to correct for the overburden azimuthal anisotropy may then be performed.

Filtering of overburden azimuthal anisotropy effects from 3D seismic

A method and computer system for applying corrections to dual sensor ocean bottom cable marine seismic signals, for purposes of eliminating ghosts and reverberations, are disclosed. According to the disclosed method and system, both phase and amplitude corrections are derived in common receiver gathers, and applied to each geophone trace in the gather; preferably, the derivation of the corrections is performed on a limited offset common receiver gather. The phase correction is determined by minimizing a folded cross-correlation of the hydrophone and geophone signals over varying phase angles, with the appropriate phase correction corresponding to the angle at which the minimum is obtained; preferably, stacked cross-correlations are used in the phase correction determination to reduce the effects of random noise. The phase correction is then applied to the geophone traces in the gather, and an amplitude correction is derived by minimizing a cross-ghosting relationship. Preferably, the cross-ghosting minimization is based upon stacked cross-correlations of the geophone and hydrophone signals and a stacked hydrophone autocorrelation, to eliminate the effects of coherent noise on the geophone trace and the effects of random noise on both the geophone and hydrophone traces. The amplitude correction is then applied to each of the geophone traces in the gather, and the summation scalar is then derived and used to sum the geophone and hydrophone traces for each source-receiver path. The summation scalar may be selected to compensate not only for ghosts, but also for receiver-side reverberations. The summation scalar may also be derived using an estimate for the seafloor reflectivity that takes into account source-side reverberations.

Amplitude and phase compensation in dual-sensor ocean bottom cable

A method of separating the effects of the earth response on vibratory energy from individual ones of multiple vibrators to geophones, in generating a seismic survey, is disclosed. According to the disclosed method, measurements of the actual vibrations generated at the source are made, in addition to the geophone measurements of the refracted and reflected vibrations, both over a number of frequency sweeps. The source and geophone vibrations are first transformed into frequency domain representations, by way of Discrete Fourier Transforms. An inverse matrix of the recorded frequency-domain source vibrations is then generated for each frequency. When the number of sweeps equals the number of vibrators, the inverse matrix is merely the multiplicative inverse of the source measurements; if the number of sweeps exceeds the number of vibrators, the inverse matrix is the generalized inverse of the original matrix. The inverse matrix for the frequency is applied to the recorded geophone vibrations at that frequency, to derive the transfer function, corresponding to the earth response, for each vibrator-geophone path in the survey. A weighting factor may be used to discount the effects of poorly behaved sweeps, and may be based on the ratio of the maximum and minimum eigenvalues for the inverse matrix. Using these derived transfer functions, an earth reflectivity function may be derived for each vibrator-geophone path by applying a minimum phase filter to the separated vibrator-geophone transfer function over frequency; this filter removes the effects of a ##EQU1## term, and yields the earth reflectivity function for the path.

High fidelity vibratory source seismic method with source separation

A method of separating the effects of the earth response on vibratory energy from individual ones of multiple vibrators to geophones, in generating a seismic survey, is disclosed. According to the disclosed method, measurements of the actual vibrations generated at the source are made, in addition to the geophone measurements of the refracted and reflected vibrations, both over a number of frequency sweeps. The source and geophone vibrations are first transformed into frequency domain representations, by way of Discrete Fourier Transforms. An inverse matrix of the recorded frequency-domain source vibrations is then generated for each frequency. When the number of sweeps equals the number of vibrators, the inverse matrix is merely the multiplicative inverse of the source measurements; if the number of sweeps exceeds the number of vibrators, the inverse matrix is the generalized inverse of the original matrix. The inverse matrix for the frequency is applied to the recorded geophone vibrations at that frequency, to derive the transfer function, corresponding to the earth response, for each vibrator-geophone path in the survey. A weighting factor may be used to discount the effects of poorly behaved sweeps, and may be based on the ratio of the maximum and minimum eigenvalues for the inverse matrix.

Method and apparatus for source separation of seismic vibratory signals

A computer system and method for eliminating the effects of ghost reflections from marine seismic survey traces obtained via ocean bottom cables are disclosed. Dual sensors are used in the ocean bottom cables, to obtain both pressure and velocity traces. The disclosed method combines, in a common receiver gather, the corresponding pressure and velocity traces for each source-receiver path using several values of a scalar value that serves as a weighting factor. Conventional corrections and filtering, including spiking deconvolution, are applied to the combined traces, and the combined traces for each value of the scalar are stacked over a limited offset range. Autocorrelation and other spectral techniques may be applied to identify the residuals of the ghost reflections using each of the multiple scalar values; the optimal value may then be selected, for each common receiver gather, as that which has the minimum ghost reflection residuals. The combined traces for each common receiver gather are then used in conventional survey generation.

Method and system for eliminating ghost reflections from ocean bottom

A method for correction of seismic data for taking into account azimuthal anisotropy in the subsurface is described. The data is corrected using an azimuthally anisotropic normal moveout equation, thereby yielding better signal to noise ratio as well as providing valuable information as to the degree and direction of azimuthal anisotropy in the subsurface.

Method of correction of seismic data for the effects of azimuthal

An improvement in a method of treating seismic data in which predictive noise, as measured along one of the axes is discriminated and subtracted from the total signal along another of the axes recorded by geophone recording the reflection from subterranean strata of energy input from a source at the surface.

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Plano, TX, United States of America

Dennis Corrigan