In addition to the dominant reflection events, seismic data contain many useful diffraction events: point diffractions, due to small objects like boulders; line diffractions, associated with truncated reflectors due to faults; and continuous features with distinct edges such as channels and steam chambers. The detection and imaging of these subtle features is of high importance for reservoir characterization.
Diffraction Imaging is an imaging method which provides enhanced images of the subtle faults and localised heterogeneities, which are obscured by the much stronger reflection energy.
We use a method based on the focus-defocus algorithm of Khaidukov, Landa and Moser (2004, Geophysics 69, 1478-1490), modified to produce a time-migration result. This approach is based on identification and removal of specular reflections in order to reveal diffraction (non-specular) energy. The suppression of specular energy is achieved by mapping the data to a "reflection focus" domain in which the reflections are very concentrated and can be removed using a sparsity criterion. This focussing for the method is based on migration velocities, and does not require an interpretation of the data or any form of dip field information. The method is amplitude preserving and produces results which are directly comparable with our conventional time migration. It is also applicable to data which has been 5D interpolated.
The results of diffraction imaging can be interpreted side-by-side with the conventional image to map faults and other localized features with greater confidence and in more detail.