Wave-equation diffraction imaging using pseudo dip-angle gather

Abstract

Diffraction images can directly indicate local heterogeneities, such as faults, fracture zones, and erosional surfaces, that are of high interest in seismic interpretation and unconventional reservoir development. We have adopted a new tool called pseudo dip-angle gather (PDAG) for imaging diffractors using the wave equation. PDAG has significantly lower computational cost compared to the classic dip-angle gather (DAG) due to the use of plane-wave gathers, a fast local Radon transform algorithm, and a one-side decomposition assumption. Pseudo dip angle is measured from the vertical axis to the bisector of the plane-wave surface incident angle and scattered wave-propagation angle. PDAG is generated by choosing the zero lag of the correlation of the plane-wave source wavefields and the decomposed receiver wavefields. It reveals diffraction and reflection patterns similar to DAG, that is, diffractions spreading as a flat event and reflections focused on a specular angle, whereas they may have dissimilar coverage for diffraction and different focused locations for reflection compared to that of DAG. A windowed median filter is then applied to each PDAG for extracting the diffraction energy and suppressing the focused reflection energy. In addition, the stacked PDAG can be used to evaluate the migration accuracy by measuring the flatness of the image gathers. Numerical tests on synthetic and field data sets demonstrate that our method can efficiently produce accurate results for diffraction images.