In this paper we show that specular imaging in the dip-angle domain significantly reduces 4D imaging noise. Specular imaging limits the migration aperture to rays obeying Snell’s law. Since it is based on improved image formation, specular imaging is superior to signal processing methods applied to a noisy image. In the context of 4D, the improved imaging can prove useful in simplifying, and therefore speeding up, the 4D processing. By better imaging the data, based on a physical principle, we can avoid extraneous signal processing, such as dip-filtering, and thereby avoid signal damage and additional processing time. Separating the seismic energy at the imaging stage into specular and non-specular components in the dip-angle domain additionally provides the opportunity to identify diffraction energy. The particular behaviour of diffracted energy in the dip-angle domain, i.e. creating flat events across the whole dip-angle range, makes them separable from both specular energy and migration artefacts. We present the performance of the proposed specular imaging approach on a 4D dataset from the Caspian Sea. Significant uplift is obtained not only on the 4D image, but also on the 3D pre-stack gathers leading to improved AVO.


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