Pseudo-acoustic Wave Equations for VSP Full-waveform Inversion
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Solution Overview
Problem
Conventional seismic processing methods, such as semblance and ray-based tomography, fail to exploit full-data information in vertical seismic profile (VSP) data, resulting in sub-optimal velocity models for anisotropic subsurface formations, which affects reservoir characterization and production.
Innovation Solution
The implementation of full-waveform inversion using pseudo-acoustic formulations that eliminate shear wave contributions, allowing for the generation of high-fidelity velocity models by iteratively matching simulated data with raw field data through a nonlinear gradient-based optimization approach, specifically for vertically transverse isotropic media.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional VSP processing methods (semblance or ray-based tomography) are used, then processing simplicity is maintained, but measurement precision and reliability of velocity models deteriorate due to failure to exploit full-data information
Solution Approach 1:
The patent replaces conventional mechanical/geometric processing methods (semblance analysis, ray-based tomography) with a physics-based full-waveform inversion approach using pseudo-acoustic wave equations. This substitution enables exploitation of both kinematic and dynamic information in VSP data, significantly improving velocity model accuracy for anisotropic formations while maintaining computational feasibility through the simplified pseudo-acoustic formulation.
2Measurement precision
If full-waveform inversion is implemented, then measurement precision and reliability of velocity models improve by exploiting full-data information, but computational complexity and processing time increase
Solution Approach 1:
The patent transforms the complex elastic wave equation into a simplified pseudo-acoustic wave equation by changing the physical parameters and assumptions (neglecting shear wave contributions, assuming acoustic behavior). This parameter transformation maintains the essential physics needed for full-waveform inversion while dramatically reducing computational complexity and processing time, enabling practical application to real VSP data.
Solution Approach 2:
The patent extracts and eliminates the computationally burdensome shear wave components from the full elastic wave equation, retaining only the essential acoustic P-wave behavior. This extraction allows full-waveform inversion to exploit complete VSP data information while avoiding the excessive computational cost of modeling all elastic wave modes, thus reducing processing time.
3Productivity
If pseudo-acoustic formulations are used, then processing time and computational complexity are reduced, but manufacturing precision of velocity models for elastic media may deteriorate due to simplified physics
Solution Approach 1:
The patent applies local quality by using pseudo-acoustic formulations specifically targeted at VSP data characteristics where P-wave dominant behavior is sufficient for velocity model construction. The simplification is locally optimized for this specific application context, maintaining adequate accuracy for the intended purpose (velocity modeling from VSP data) while achieving significant computational efficiency gains compared to full elastic wave modeling.
Data Source
AI summary
High fidelity velocity models are generated for acoustic vertically transverse isotropic media by taking advantage of full-waveform based modeling using VSP data. The present disclosure determines VTI parameters in acoustic media using pseudo-acoustic equations which can eliminate the contribution from shear waves, and thus significantly reduce the time needed to perform inversion. The methods disclosed herein provide workflows for performing full waveform inversion to provide velocity models used to generate seismic images with high quality and resolution.