Elastic RTM Velocity Model Updating for Geo-Body Boundaries
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Solution Overview
Problem
Traditional seismic imaging methods, particularly reverse-time migration (RTM), fail to accurately account for elastic waves in complex geology, leading to incorrect determination of high-contrast geo-body boundaries and noise in imaged sections due to the ignorance of shear waves and elastic scattering information.
Innovation Solution
The method employs elastic reverse-time migration (eRTM) to build seismic imaging velocity models by utilizing elastic reflection/scattering information, including PP, PS, SP, and SS wave modes, and prism waves to correctly handle phase and amplitude characteristics, providing more accurate illumination and positioning of geo-body boundaries.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If traditional acoustic RTM is used for seismic imaging, then the imaging process is simpler and faster, but the accuracy of geo-body boundary determination deteriorates due to ignoring elastic waves
Solution Approach 1:
The patent changes the fundamental parameter of wave propagation modeling from acoustic (pressure-only) to elastic (including shear waves and mode conversions). This is achieved by implementing elastic wave equation-based RTM that tracks P-waves, S-waves, and their mode conversions (PP, PS, SP, SS) through the subsurface, thereby capturing the true elastic behavior of seismic waves in complex geology without sacrificing computational feasibility
Solution Approach 2:
The patent introduces elastic wave mode conversion coefficients as intermediaries to bridge the gap between acoustic and elastic imaging. By calculating PP, PS, SP, and SS conversion coefficients at interfaces, the method accurately represents how elastic waves transform when encountering geo-body boundaries, enabling precise boundary determination while maintaining a systematic imaging workflow
2Device complexity
If acoustic algorithms are used to image elastic waves, then the processing is simpler, but noise increases and valuable elastic scattering information is lost
Solution Approach 1:
The patent segments the seismic wavefield into distinct wave modes (P-waves, S-waves, PP reflections, PS conversions, SP conversions, SS reflections) and processes each mode separately through elastic RTM. This segmentation allows the algorithm to selectively preserve and image elastic scattering information while maintaining computational efficiency by treating different wave types with appropriate physical models
Solution Approach 2:
The patent converts what would traditionally be considered noise (elastic converted waves and scattering) into valuable imaging information. By implementing elastic RTM that explicitly models PS and SP conversions, the method transforms previously ignored elastic effects into useful signals that improve boundary detection and provide additional illumination of subsurface structures
3Measurement precision
If elastic RTM is implemented to utilize elastic scattering information, then boundary determination accuracy improves, but computational complexity increases
Solution Approach 1:
The patent performs preliminary calculation of elastic reflection and transmission coefficients before the main RTM imaging process. By pre-computing PP, PS, SP, and SS conversion coefficients based on impedance contrasts at interfaces, the method reduces the computational burden during the actual wavefield propagation and imaging stages, enabling accurate elastic imaging without excessive computational cost
Solution Approach 2:
The patent implements a dynamic elastic RTM framework that adaptively handles different wave modes and their interactions. The algorithm dynamically tracks the propagation of P-waves and S-waves, their mode conversions at interfaces, and their interactions with complex geological structures, allowing accurate boundary determination while optimizing computational resources through efficient wavefield management
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 accuracy of seismic imaging by maximizing the use of elastic energy and correctly imaging geo-body boundaries, reducing noise and misplacement errors, and improving the velocity model updating process.
Implementation Method 1
Elastic waves propagating in a rock medium cause local stretching ('strain') of the rock, but the rock goes back to zero strain when the elastic wave passes. Shear waves must be present to demonstrate the elastic properties of the rock medium
Implementation Method 2
scattering and/or reflection, even of (P) waves, from high-contrast boundaries show different amplitudes and sometimes different phases when the medium is treated as acoustic versus elastic
Implementation Method 3
These high-contrast media produce large-amplitude elastic conversions and scattering at their boundaries
Data Source
AI summary
Method for building a seismic imaging velocity model, particularly at the boundary of a geo-body, and to perform imaging, by taking into account the elastic reflection and scattering information in the seismic data. More illumination of the base and flanks (or in general, the boundary) of the geo-body is provided from (a) inside of the geo-body (502), with elastically converted waves at the geo-body boundary used (via elastic RTM flooding); and (b) from outside the geo-body (503), by utilizing prism waves with elastic RTM to handle the phase correctly in the model building step. The increased illumination and correct elastic phase are used for geo-body boundary determination. Elastic RTM is then applied (505), along with the elastically derived imaging velocity model, to maximize the use of elastic energy in the imaging step, and to obtain the correct image with the correct phase.