Seismic Velocity Model Inversion Using Iterative Relaxation
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Solution Overview
Problem
Conventional full waveform inversion (FWI) methods face challenges in achieving good velocity resolution for streamer data due to limitations in low-frequency reflections and maximum offset, leading to incomplete recovery of velocity models, especially in complex geological environments.
Innovation Solution
The method involves relaxing the dependency on low-frequency reflections by implementing a non-linear iterative relaxation process, splitting the velocity model into long and short wavelength components, and using true amplitude migration and local optimization schemes to update these components iteratively, thereby generating an improved velocity model.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional full waveform inversion methods are used, then velocity models can be generated, but the velocity resolution is insufficient due to limitations in low-frequency reflections and maximum offset
Solution Approach 1:
The velocity model is segmented into long wavelength and short wavelength components. The long wavelength component is updated using low-frequency data and direct/refracted waves, while the short wavelength component is updated using high-frequency reflection data. This segmentation allows each component to be optimized independently, resolving the contradiction between velocity resolution and loss of low-frequency information.
Solution Approach 2:
The method changes the frequency parameters used for different components of the velocity model. Low-frequency data is utilized for updating the long wavelength component, while high-frequency data is used for the short wavelength component. This parameter change enables effective use of available data across different frequency ranges to improve overall velocity resolution.
2Adaptability or versatility
If conventional FWI relies on low-frequency reflections, then velocity model updates can be performed, but the method fails in complex geological environments where low-frequency reflections are absent or limited
Solution Approach 1:
The method makes the velocity model updating process universal by enabling it to work with different types of seismic waves (direct waves, refracted waves, and reflected waves) and different frequency ranges. By not relying exclusively on low-frequency reflections, the method becomes adaptable to various geological environments including those with complex structures where low-frequency reflections may be absent.
Solution Approach 2:
Direct waves and refracted waves serve as intermediaries to provide low-frequency information when low-frequency reflections are unavailable. These wave types can penetrate complex geological structures more effectively and provide the necessary low-frequency content for updating the long wavelength component of the velocity model, enabling the method to function in complex geological environments.
3Measurement precision
If the velocity model is updated using all available frequency components simultaneously, then computation time increases, but iterative relaxation processes improve resolution
Solution Approach 1:
The velocity model updating is performed through periodic iterative relaxation processes where the long wavelength and short wavelength components are updated alternately in separate steps. This periodic action allows the computation to focus on one wavelength component at a time, reducing the computational burden compared to simultaneous updates, while still achieving improved velocity model resolution through multiple iterations.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances the resolution of velocity models by effectively updating long and short wavelength components, improving the accuracy of velocity models in underwater seismic exploration, even in complex geological settings.
Implementation Method 1
generating seismic waves (i.e., sound waves) directed toward the subsurface area
Implementation Method 2
gathering data on reflections of the generated seismic waves at interfaces between layers of the subsurface
Data Source
AI summary
A system and method are described herein for generating a velocity model of returned seismic signals for under-ocean floor environments. The system and method generate a series of source signals, receive a corresponding set of direct signals, reflected signals, and refracted signals, solve a velocity model equation using a full waveform inversion function with respect to the received set of direct signals, reflected signals and refracted signals to minimize a least square misfit function by relaxing a dependency on low frequency reflections in the full waveform inversion function. The system and method then generate the velocity model based on the solution to the velocity model equation, and display the velocity model.