Seismic Prestack-Depth Migration GRT

The project on »Generalized Radon Transform« (GRT) depth migration excellently demonstrates how the unified competence in the fields of geophysics, mathematics, and informatics of the department HPC could be used for the successful development of a tailor-made product according to client's particular needs.

Among all other methods for seismic prestack depth migration, GRT is unique by performing a rigorous amplitude-preserving migration that produces results that are directly proportional to the subsurface reflection cofficients measuered in dependence on angle of incidence. Consequently, the interpretation of the results with respect to, e.g., fluid fill of the pores of the potential reservoir formation can be done with considerably higher reliability. This property of GRT is enabled by performing the migration in the domain of local angle of the rays that connect subsurface migration point with surface source and receiver trace loaction.

Seismische Prestack-Tiefenmigration GRT
© Photo ITWM

Ground Layers as a Result of Seismic Migration

Essentially, GRT-migration can be considered as data mapping from the 5-dimensional space of seismic input (5 dimensions according to source-x/y, receiver-x/y, and recording time) to the 5-dimensional output space (x/y/z of the subsurface volume and two angles). The particular aspect here is that there exist no direct relationship by any two dimensions of the input and the output domain. Practically, such a problem can only be solved by keeping the seismic input data (whose typical size is of the order of several TeraBytes) in the memory of a massively parallel compute cluster. The permanent exchange of these data is efficiently managed by our parallelisation library GPI. This allowed us to develop a worldwide unique implementation of GRT that is free of any severe approximations and simplifications of the underlying theory. 

The software is in use at the client's site for various applications. At ITWM, we are offering specialized GRT-processing of oil companies' data that show particular benefit whenever true-amplitude processing is required and the image quality should be exceptionally high.

 

Data Processing with GRT

GRT is a very flexible migration method. It migrates marine surface data, marine OBC data (including the converted PS component), and data from land acquisition. The velocity model can be isotropic, but we also support anisotropic models with VTI, TTI, and tilted orthorhombic symmetry. For all these variants of velocity model we solve kinematic and dynamic ray tracing systems in a bottom-up ray fan shooting mode for generating traveltimes and all quantities needed for the true-amplitude weighting kernel. Special properties like signal-noise enhancement, diffraction imaging, and simulated migration make GRT a software that delivers products far beyond classical migration results.

In the course of several years we have gained siginificant experience in applying GRT to clients' data sets. Main project area so far has been the North-Sea. However, the variety of geological settings we met in these applications has been quite large. For new clients, we offer target-oriented 3D migrations to e,g., an inline or crossline of particular interest for the clients. Costs for such initialisation projects are credited to the complete costs of subsequent full-volume migration projects.