3-D Migration of seismic data using rapid ray tracing (UGE.4124)

Reflection seismic methods represent the most powerful technique to 'look' inside the earth, and are used as such widely by the industry for both exploration and exploitation of oil and gas reservoirs. A crucial step in the processing of seismic data is the transformation of the recorded 'echoes' to a properly located image of the reflectors within the earth. This process is called 'migration'. It is crucial for this imaging procedure that the recorded signals are traced back to their correct origins in the earth's interior. If this is not the case, there is a two-fold problem; not only are the reflectors wrongly positioned, but the image reconstruction is also incomplete which gives rise to an imperfect image. The best quality image is thus also the one most correctly positioned. The errors resulting from interpreting such false images could have severe econonuc consequences, because drilling boreholes is extremely expensive. The importance of an accurate technique for migration of seismic data is thus obvious.
The aim of the research intended to be carried out under the requested funding is to investigate the application of ray perturbation theory - developed for seismology - to three-dimensional (3D) migration of exploration seismic data. The current ray perturbation theory provides a very efficient method of ray-tracing through a 2D or 3D medium with a smoothly varying velocity. The planned work can therefore be divided into three parts:

1. formulation of the migration scheme using the current theory,
2. extension of the theory to more realistic media (anisotropy, velocity discontinuities) and
3. implementation of the scheme in a 3D migration algorithm.

The main advantage vis-a-vis the currently available 3D imaging technology is expected to be an increase in speed while maintaining the accuracy. At both stages 1 and 2 extensive use will be made of real data to evaluate the effectiveness of the method.

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