Full Azimuth Multi-Rays Pre-Stack Depth Migration in the B Block

Abstract

Abstract Usually, the signal-to-noise ratio is low and velocity spatial change is severe in areas where fault traps develop. Seismic data processing brings challenges to geophysicists. It is extremely difficult to improve imaging in deep parts were faults harm wave propagation. Traditional pre-stack data migration imaging methods based on common middle points or common shot points are generated by the geophysical theory hypothesis. To overcome such kind of challenge and improve imaging, full azimuth multi-rays pre-stack depth migration was applied in the B block. Full azimuth multi-rays pre-stack depth migration brings a new concept. Rays scan is generated from imaging point toward the surface, leading to a simultaneous emphasis on both continuous structure and discontinuous objects such as small faults and small-scale fractures. In this paper, a comparison was conducted between conventional Kirchhoff pre-stack depth migration and full azimuth multi-rays pre-stack depth migration. Sufficient tests have been carried out in the fault-developed areas. For geological attributes analysis, subsequent processing can be conducted on multi-domain gathers from full azimuth multi-rays pre-stack depth migration according to the request of geologists. Application of this method in B block in the Middle East shows that full azimuth multi-rays pre-stack depth migration can improve the imaging quality of medium and deep layers and improve the imaging of small faults and small-scale fractures. Full azimuth multi-rays pre-stack depth migration can use isotropic and anisotropic velocity models to perform reflection and directional imaging in the local angle domain. Migration radius is defined by both aperture and angle. Information from all azimuths and angles is fully involved in the imaging process, which is beneficial to imaging small faults and fractures. Structural attributes such as dip, azimuth and continuity of the target zone can be obtained directly from gathers after migration. High-quality structural imaging results can be obtained by effective reflection enhancement processing on gathers from full azimuth multi-rays pre-stack depth migration. Diffraction wave enhancement processing can be used for geological fracture prediction. This paper studies the principle of full azimuth multi-rays pre-stack depth migration, compares it with the conventional Kirchhoff prestack depth migration, analyses the advantages of this method in imaging principle and subsequent gathers processing, and applies it to seismic data of the Middle East B Block heterogeneous carbonate reservoir. The result shows that imaging accuracy of full azimuth multi-rays pre-stack depth migration technology is higher, especially in complex structural areas.