Beam Tomography Velocity Model Correction
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Solution Overview
Problem
Current seismic imaging methods, such as traveltime reflection tomography, are sensitive to minor details of the velocity model and require an assumed reflector structure, which can lead to misalignments and inaccuracies, especially in faulted and difficult-to-map reflection surfaces.
Innovation Solution
A beam tomography method that combines aspects of rays and wavefields to improve seismic velocity models and images without dependence on reflector structure, using Gaussian beam migration and cross-correlation to iteratively refine the velocity model and align seismic data beams, thereby reducing sensitivity to minor velocity model details.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If ray-based traveltime tomography is used to correct velocity models, then velocity corrections can be calculated to align seismic images, but the method becomes highly sensitive to minor details of the velocity model and assumed reflector structure
Solution Approach 1:
The patent combines ray-based traveltime information with wave-equation-based imaging to create a hybrid approach. Rays provide geometric information for velocity correction, while the wave equation provides robust imaging that is less sensitive to velocity errors. This merging allows the system to maintain velocity model accuracy while reducing sensitivity to minor velocity details through the wave equation's natural smoothing effect.
Solution Approach 2:
The patent changes the fundamental parameter from pure ray-based traveltime analysis to a hybrid ray-wave approach. By incorporating the wave equation, which solves the full wave propagation problem rather than just ray paths, the system transforms the sensitivity characteristics of the velocity correction process, making it more robust to minor velocity model errors while maintaining correction accuracy.
2Measurement precision
If raypaths are traced densely from many reflection points to calculate velocity corrections, then alignment between images can be improved, but the method requires assumed reflector structure that is uncertain where images are degraded
Solution Approach 1:
The patent extracts the velocity correction problem from the reflector structure assumption. Instead of requiring detailed reflector geometry to define raypaths, the system uses wave-equation-based imaging to identify reflection events and their positions, then uses rays only for the velocity correction calculation itself. This separation removes the dependency on assumed reflector structure while maintaining the ability to calculate precise velocity corrections.
Solution Approach 2:
The patent introduces wave-equation-based imaging as an intermediary between the seismic data and the velocity correction process. This intermediary step identifies reflection events and provides initial velocity estimates without requiring reflector structure assumptions, then passes this information to the ray-based correction process, which uses it to calculate velocity updates without needing to assume reflector geometry.
3Productivity
If conventional traveltime tomography is used, then velocity corrections can be calculated on a grid, but small changes in reflector dip cause rays to go in greatly different directions and alter the inversion
Solution Approach 1:
The patent merges the efficiency of ray-based grid calculations with the stability of wave-equation-based imaging. Rays provide computationally efficient velocity correction calculations on a grid, while the wave equation provides stable identification of reflection events that is insensitive to small velocity changes. This combination maintains computational productivity while achieving inversion stability, as the wave equation's natural robustness prevents small reflector dip changes from causing large ray direction variations.
Data Source
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AI summary
A beam tomography computer implemented method and system for generating improved seismic images and earth models without dependence on reflector structure is disclosed. Recorded seismic data is transformed into data beams which are compared to forward modeled beams using an earth model having a velocity model to compute raypaths and a seismic image to specify the reflectors. The tomographic updates to the earth model and velocity model are based on misalignments between the data beams and the same beams forward modeled from the velocity model and the seismic image. The updated earth model and seismic image better describe the true propagation of the beams through the earth.