Phase-Only Full Waveform Inversion for Seismic Velocity Models
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Solution Overview
Problem
Traditional methods for computing velocity models from seismic data, especially in complex subsurface areas with faulting and salt bodies, are expensive and computationally intensive, often failing due to the lack of low frequencies in seismic data, which are essential for accurate inversion.
Innovation Solution
A computer-implemented method involving phase-only full waveform inversion, which includes obtaining seismic data, performing forward modeling, transforming data into the temporal Fourier frequency domain, measuring misfit, performing phase unwrapping, and inverting the residual phase to determine subsurface properties, minimizing an objective function defined by misfit, and optionally using phase extrapolation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional full waveform inversion is performed in the time domain or transform domain, then velocity models can be computed from seismic data, but the method fails due to lack of low frequencies in seismic data
Solution Approach 1:
The patent transforms the inversion problem from the time domain to the frequency domain, specifically utilizing the phase information in the frequency domain. This dimensional change allows the method to work effectively with the available frequency content in seismic data, as phase information contains the necessary low-frequency velocity model information even when amplitude information lacks low frequencies.
Solution Approach 2:
The patent extracts and utilizes only the phase portion of the frequency domain seismic data for inversion, separating it from the amplitude portion. This extraction of the phase component allows the method to compute velocity models without being constrained by the lack of low-frequency amplitude information in conventional full waveform inversion.
2Reliability
If traditional migration methods are used to produce subsurface images, then images can be generated, but the methods require a reasonably accurate velocity model which is expensive to determine
Solution Approach 1:
The patent uses phase information as an intermediary that bridges the gap between seismic data and velocity model computation. By utilizing phase information from frequency domain transformed seismic data, the method provides a cost-effective pathway to obtain velocity models without requiring the expensive conventional velocity analysis processes.
Solution Approach 2:
The patent creates a simplified version of the full waveform inversion process that operates solely on phase information rather than the complete seismic waveform. This phase-only inversion acts as a copy or alternative approach that achieves velocity model computation at lower cost and computational expense while maintaining effectiveness for subsurface imaging.
3Measurement precision
If phase unwrapping is performed on frequency domain residual seismic data, then accurate phase information is obtained, but the process requires sophisticated signal processing
Solution Approach 1:
The patent performs phase unwrapping as a preliminary step before the inversion process. By preprocessing the phase information through unwrapping to remove discontinuities and ensure continuity, the method prepares the data in advance for more effective inversion, reducing the complexity of the subsequent inversion process.
Data Source
AI summary
A system and computer-implemented method for determining properties of a subsurface region of interest from seismic data include obtaining seismic data and an initial earth property model, forward modeling using the initial earth property model to create modeled seismic data, transforming the modeled and actual seismic data to create frequency domain modeled and actual seismic data including amplitude portion and phase portions, measuring the misfit between the frequency domain modeled and actual seismic data to produce frequency domain residual seismic data, performing phase unwrapping of certain observed frequency components of the frequency domain residual seismic data to create an unwrapped residual phase portion, and inverting the unwrapped residual phase portion to determine desired properties of the subsurface region of interest.