Improvement of RTM image with a de-primary algorithm and impedance-matching technique

Abstract

When implementing reverse-time migration (RTM), reflected waves that are generated during migration may produce false reflectors. One effective method to remove these artefacts is to apply a de-primary RTM algorithm. This de-primary RTM algorithm uses the Hilbert transform to remove RTM artefacts without explicitly separating wavefields. However, multiply reflected down-going waves, such as surface-related multiples and internal multiples that are generated when simulating source and receiver wavefields, are not excluded during cross-correlation even if we adopt the de-primary RTM technique. Therefore, these down-going multiples may produce troublesome RTM artefacts. In this paper, we attempt to reduce these RTM artefacts by combining the de-primary RTM and impedance-matching techniques. Impedance-matching is only effective for normal incidence, so we also apply an absorbing boundary condition to the free surface to remove surface-related multiples. We evaluate the proposed method through the SEG/EAGE salt model. These numerical examples show that the proposed method effectively reduces RTM artefacts and provides clear migration images.