Description

Performs azimuthal anisotropy velocity analysis on 3D seismic data using a CRE-based (Common Reflection Element) search across azimuth sectors. By analysing how seismic velocities vary with azimuth direction, this module detects fracture-related directional velocity variation (azimuthal anisotropy), which indicates the presence and orientation of aligned fracture sets in the subsurface.

Results are stored in a 3D MF database and can be used to guide fracture characterisation, well placement, or anisotropic processing. The search is performed over a configurable range of azimuths and covers the full 3D survey area, optionally limited to a specified inline/crossline sub-volume and time gate.

Input data

GMFPickingItem

Horizon or velocity constraint picks defining the time gate for the anisotropy search. Limits the search to a specific geological interval of interest.

SEG-Y data handle

The primary 3D pre-stack seismic input dataset. This is the data on which the azimuthal CRE search is performed.

Input sorted headers (of seismic data)

Sorted trace header index for efficient data access during the azimuthal search computation.

Input Binning

The input spatial geometry (bin grid) of the seismic data, defining the inline/crossline layout and bin dimensions of the input dataset.

Output Binning

The output grid on which anisotropy results are stored. Can be coarser than the input binning to reduce database size and computation time when a full-resolution output is not required.

MF Tables Parametrization

Quantization precision tables for the internal MultiFocusing search tables. Controls the resolution of the stored MF parameter values.

Parameters

File with picking

Path to an ASCII picking file used to constrain the velocity search range for the anisotropy analysis.

Storage file 3D

Path to the 3D MF database file where the anisotropy search results will be stored. This file is created by the module and used as input for subsequent anisotropy attribute extraction workflows.

Azimuth Geometry

Defines how azimuths are partitioned into sectors for the CRE search. Specifies whether azimuth sectors are defined relative to the survey grid or to geographic north.

Anisotropy

The expected level of azimuthal anisotropy in the data, expressed as a dimensionless fraction (0.0–0.3). This parameter sets the initial search range for the azimuthal velocity variation. A value of 0.1 corresponds to 10% velocity difference between the fast and slow azimuth directions.

Max CRE Anisotropy

Maximum anisotropy allowed in the CRE aperture computation (dimensionless). Acts as an upper bound cap on the anisotropy estimate used for wavefront curvature calculations. Typical values: 0.2–0.3.

Azimuth min

Minimum azimuth angle (degrees) of the search range. Set to 0 for a full-range azimuthal search (0–180°).

Azimuth max

Maximum azimuth angle (degrees) of the search range. Set to 180 for a full-range azimuthal search. Values above 180 are not meaningful for azimuthal anisotropy analysis.

Azimuth increment

Angular step between consecutive azimuth sectors (degrees). A smaller increment provides finer azimuthal resolution but increases computation time. Recommended step: 10–15 degrees for a good balance between resolution and efficiency.

Storage Velocity analize

Path to a secondary storage file for velocity analysis results associated with the anisotropy search output.

Each inLine

Output decimation factor in the inline direction. Results are stored every N inlines. Set to 1 to store results for every inline.

Each xLine

Output decimation factor in the crossline direction. Results are stored every N crosslines. Set to 1 to store results for every crossline.

Calculation area

Spatial subset restriction for the search. Use the First/Last inline and crossline parameters to limit processing to a specific 3D sub-volume.

First inline number(-1 no limit)

First inline to process. Set to -1 for no lower limit.

Last inline number(-1 no limit)

Last inline to process. Set to -1 for no upper limit.

First crossline number(-1 no limit)

First crossline to process. Set to -1 for no lower limit.

Last crossline number(-1 no limit)

Last crossline to process. Set to -1 for no upper limit.

Calculation rule

Selects which bins are processed — every bin, every N-th inline/crossline, or a custom decimation pattern defined by the step parameters.

Step along inLine number

Processing step in the inline direction (used when Calculation rule is set to step-based decimation). A value of 2 processes every second inline.

Step along xLine number

Processing step in the crossline direction. A value of 2 processes every second crossline.

First Time

Start of the two-way time analysis gate (ms). Limits the anisotropy search to the geological interval of interest.

Last Time

End of the two-way time analysis gate (ms).

References

Gelchinsky, B., Berkovitch, A. and Keydar, S., 1999, Multifocusing homeomorphic imaging - Part 1: Basic concepts and formulae: Journal of Applied Geophysics, 42, 229-242.