Sub-salt Seismic Velocity Analysis via Depth Migration Scaling
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Solution Overview
Problem
Current seismic data processing methods struggle to accurately interpret structures and compositions below a salt layer due to the salt layer's high reflectivity and variable thickness, which masks reflective horizons and violates assumptions made in ordinary seismic interpretation methods.
Innovation Solution
A method involving depth migration of seismic data to the bottom of the salt layer, where an initial velocity model is generated and scaled by multiple scale factors to optimize the depth-migrated image, allowing for the selection of the appropriate scale factor to produce the sharpest images of formations below the salt layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If ordinary seismic interpretation methods are used, then processing is simpler and faster, but imaging accuracy below salt layer deteriorates due to high reflectivity and variable thickness masking reflective horizons
Solution Approach 1:
The velocity model is segmented into multiple layers with different velocity characteristics. The method divides the subsurface into distinct velocity zones, allowing each layer to be modeled with appropriate velocity functions that account for the complex salt layer geometry and the underlying formations, thereby improving imaging accuracy without requiring a complete overhaul of the processing workflow
Solution Approach 2:
The method transforms the velocity model from a simple constant or linear velocity assumption to a more complex model using velocity functions that incorporate depth and lateral position parameters. By changing the velocity parameters to reflect the actual geological complexity below the salt layer, the method achieves accurate imaging while maintaining computational feasibility through efficient parameterization
2Measurement precision
If velocity model is updated iteratively, then imaging fidelity improves, but processing time increases
Solution Approach 1:
The method performs preliminary depth migration to the salt layer bottom using an initial velocity model before conducting velocity analysis. This preliminary action establishes a accurate depth framework that constrains subsequent velocity updates, reducing the number of iterative cycles needed and thereby decreasing processing time while maintaining velocity model accuracy
Solution Approach 2:
The method implements feedback loops where migration results are used to update the velocity model, which is then used in subsequent migration passes. The feedback mechanism allows the system to self-correct velocity estimates by analyzing residual moveout and image quality metrics, achieving high velocity model accuracy through adaptive refinement rather than exhaustive iteration
3Manufacturing precision
If scale factors are optimized for each image position, then image quality improves, but computational complexity increases
Solution Approach 1:
The method applies local optimization by determining scale factors independently for each image position or small groups of positions. This allows the velocity model to be locally adapted to reflect regional variations in subsurface velocity structure, producing high-quality images with position-specific accuracy while avoiding the need for a completely global optimization that would be computationally prohibitive
Data Source
AI summary
A method for interpreting seismic data below a salt layer includes depth migrating the seismic data to a bottom of the salt layer. The migrating including generating an initial model of velocities below the salt layer. The initial model is scaled by a plurality of scale factors at at least one image position. At least one of the plurality of scale factors for which a depth migrated image below the salt layer is optimum is selected as the scale factor.