SVM: Illumination Analysis Toolbox

Imaging in areas of complex, near-surface velocity variations

WesternGeco utilizes an illumination algorithm based on wavefront construction techniques where ray attributes (e.g. travel times, amplitudes, etc) are computed along various ray paths synchronized by an isotime surface (the wavefront). At each time increment, the wavefront is propagated through the model using ray-tracing techniques and the energy of the wavefront is assessed. Where the energy dissipates, new rays are added in order to ensure illumination even in areas where large geometrical spreading of the rays would otherwise result in shadow zones.

The latest edition of the SVM illumination analysis toolbox now includes the ability to perform studies that incorporate the effects of velocity anisotropy. Using Thomsen's parameters (delta, epsilon, alpha and beta), VTI and TTI earth models can be defined in forward-modeling studies producing synthetic datasets to help answer difficult survey design and imaging questions.

Unlike some other ray-tracing methods, our approach aims to maximize preservation of the wavefront energy. New ray paths are shot from the source location and computed to pass through the new sites using a minimum traveltime ray-bending algorithm. This allows us to calculate true amplitude information at target and receiver locations rather than approximating with an interpolation technique.

The WesternGeco implementation takes advantage of our ray-tracing model format that allows for velocity discontinuity across discrete and complex structural elements. This ensures greater accuracy of ray reflection and transmission results. In addition, our velocity modeling capabilities allow for structurally complex and spatially variable property fields and are optimized for analytical ray tracing.

Illumination analysis and other forward modeling capabilities are now fully integrated within SVM. This enables immediate transfer and application to velocity models built in a depth imaging workflow and allows direct QC of results within the context of seismic interpretation, velocity model building, tomographic inversion or migration. Illumination studies can be performed across a range of acquisition configurations.

Related information

• Chang T., Chih-Wen Kue, Caneles L., Shih, C. L, Forward modeling attribute Analysis for AVO and Prestack Depth Migration: 72nd Ann. Internat Mtg., Soc. Expl. Geophys. 2002, Expanded Abstracts, 48-51