Common Reflection Angle Migration (CRAM)

CRAM is a cluster-based imaging system that generates conventional reflection angle gathers without azimuth dependency. These gathers can be used in standard interpretation systems for accurate velocity model building and amplitude inversion (AVA). This migration is an anisotropic multi-arrival solution that uses the entire wavefield, making it ideal for solving complex imaging objectives.

CRAM performs imaging in the local angle domain to achieve uniform illumination from all angles and all azimuths, producing amplitude-preserved, angle-dependent reflectivity gathers. These outputs are ideally suited for velocity model determination and amplitude analysis. CRAM can also be customized to optimally solve specific challenges, such as velocity determination and amplitude inversion, or it can be run globally for an entire region.

Unlike conventional ray-based imaging methods (e.g., Kirchhoff or beam migrations), the ray tracing in a Common Reflection Angle Migration (CRAM) is performed from the subsurface grid points up to the surface, forming an accurate system for mapping the recorded surface seismic data into the subsurface Local Angle Domain (LAD) at the image points. The procedure is based on a specially designed point diffractor operator that ensures maximum illumination of the image points from both all subsurface directions and all surface source-receiver locations, where all arrivals are taken into account and amplitudes and phases are preserved.

CRAM can be considered a special beam migration, as the imaging process is applied to local beams (local tapered slant stack events) generated on the fly from the input data traces using optimal computed parameters (surface slowness vectors and estimated Fresnel zones). The beams are then extrapolated from the central (traced) rays to neighbor subsurface points with the right computed weights.