Target-oriented curved-wave prestack depth migration by controlled illumination

Conventional prestack depth migration (PSDM) based on full prestack data involves many computations for wavefield extrapolation. Areal shot-record technology offers an attractive alternative for efficient PSDM because its synthesis process greatly decreases the amount of prestack data required for migration. Constructing its synthesis operator is key to the image quality of the migrated areal shot record. Curved-wave PSDM technology expands areal shot-record migration. It constructs synthesis operators by defining a complex function as a base kernel of curved wavefields multiplied by a factor of its illumination perturbation related to ray parameter and then synthesizes curved wavefields for migrations. Based on curved-wave-migration theory, we propose an efficient and accurate curved-wave, controlled-illumination method to migrate in a target-oriented way. We construct tar-get-oriented synthesis operators by wave theory, combined with rotation or perturbation of the illuminating direction of a base-kernel synthesis operator. The base-kernel operator is obtained by inverse extrapolation of a predefined source wavefield at the given target level. Different model-constrained synthesis operators are constructed by rotating or perturbing illumination of the kernel operator. Then they are applied to shot records to synthesize curved-wave records. The resulting curved wavefields are entered for depth extrapolation and imaging, combining image results from different curved wavefields to produce the total image. The method controls the illumination of synthesized source wavefields in a target-oriented way directly at the surface and can achieve high-quality images of the target zone with great efficiency. Numerical demonstrations on the standard Marmousi model provide good imaging results of the complicated structure.