Common Azimuth Migration via Ray Tracing for Seismic Imaging
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Solution Overview
Problem
Current seismic data processing methods, particularly ray-based imaging, are limited in providing azimuth information at reflection points, which is crucial for understanding fracture properties of carbonate reservoirs, as they only produce seismic volumes with constant surface azimuth, failing to account for 3D velocity variations and anisotropy, and are computationally inefficient compared to wave equation methods.
Innovation Solution
A method that uses ray-based imaging to determine direction angles at image points and migrate seismic data into volumes labeled by common azimuthal angles, applicable for any acquisition geometry, allowing for the extraction of azimuthal information valid for any dip of the target reflector, using geometric relationships and ray tracing software to compute azimuthal angles from ray direction angles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If ray-based imaging methods are used, then computational efficiency is improved, but azimuthal information at reflection points cannot be obtained
Solution Approach 1:
The patent segments the imaging process into separate computational steps: first performing standard ray-based migration to obtain image points, then calculating azimuth angles by determining ray directions and their projections onto the reflector surface. This segmentation allows the efficient ray-based method to retain its speed while adding azimuthal information through subsequent geometric calculations.
Solution Approach 2:
The patent adds a new dimension of information (azimuth angle) to the traditional seismic image by calculating the projection of ray directions onto the reflector surface. This transforms the output from simple amplitude images to images that also encode directional information, enabling azimuthal analysis without switching to wave equation methods.
2Loss of information
If wave equation based methods are used, then azimuthal information is obtained, but computational time and cost increase
Solution Approach 1:
The patent introduces ray tracing as an intermediary computational tool to extract azimuthal information from the seismic data. Instead of using the computationally intensive wave equation, ray tracing serves as a mediator that provides the necessary directional information through geometric relationships, achieving the same information goal at much lower computational cost.
3Device complexity
If maps containing only travel times are used, then computational simplicity is maintained, but reflection angle or azimuth information cannot be directed
Solution Approach 1:
The patent performs preliminary calculations of ray directions and azimuth angles during the migration process itself, storing this information alongside the image amplitudes. By preparing this directional information in advance, the method enables subsequent azimuthal filtering and analysis without requiring complex data structures or additional computational steps during interpretation.
Data Source
AI summary
Method for migration of seismic data into datasets having common azimuth angle at the reflection point. A velocity model is selected that prescribes subsurface P and/or S wave velocities including any required anisotropy parameters. (41) For shot locations on a surface grid, rays are traced on to a 3D grid of points in a target region of the subsurface. (42) At least the travel times of the rays and their dip angles at each subsurface point are stored in computer memory as they are computed. (43) Using the stored ray maps, the seismic data are migrated into seismic image volumes, each volume being characterized by at least an azimuthal angle bin, the azimuthal angles being computed from said ray dip angle information (44).