Pgs Americas, Inc.

Pgs America, Inc.

Steve Michael Kelly

Jiaxiang Ren

Ruben D Martinez

Prestack seismic data is imaged by calculating an individual reflectivity for each frequency in the seismic data. Then, a mean reflectivity is calculating over the individual reflectivities. A variance is calculated for the set of reflectivities versus frequency. A second variance is calculated for the upgoing wavefield, using the mean reflectivity. A spatially varying pre-whitening factor is then calculated, using the variance for the reflectivities and the variance for the upgoing wavefield. A reflectivity is calculated at each location, using the spatially varying pre-whitening factor.

Method for imaging of pre-stack seismic data

A set of pre-stack seismic data is downward extrapolated, by first determining a migration interval in the seismic data set. A maximum error criterion is selected for the migration interval. A maximum relative error in phase calculated as a function of frequency, propagation angle, and the relative variation in velocity in the migration interval. The maximum relative error in phase is compared to the maximum error criterion. The type of extrapolation to use in the migration interval is determined from the comparison of the maximum relative error in phase to the maximum error criterion. The type of extrapolation is selected from a set comprising Gazdag phase-shift extrapolation, split-shift Fourier extrapolation, and implicit finite difference extrapolation.

Method for downward extrapolation of pre-stack seismic data

A method of migrating seismic data is provided. The seismic data has associated therewith a wavefield at a first level. The method comprises extrapolating the wavefield from the first level to a second level; correcting the extrapolated wavefield; computing intermediate sample points for an output image between the first and the second levels; computing a contribution to the wavefield at each intermediate sample point; and summing the contributions to the wavefield at each intermediate sample point.

Method and system for migration of seismic data

A method of migrating seismic event data in the presence of a vertically time-varying velocity field defined by a migration velocity function is provided. The method comprises approximating a migration velocity function by constant stepwise stage velocities. The seismic event data is time stretched and is then successively migrated using residual velocities. After the seismic event data is fully migrated, the effect of time stretching is removed by time unstretching the fully migrated seismic event data by a reverse operation to obtain a finally migrated seismic event data.

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Houston, TX, United States of America

Steve Michael Kelly