Phase Encoding for Vibratory Seismic Data
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Solution Overview
Problem
Current methods for selecting phase encoding schemes in high fidelity vibratory seismic surveys are inefficient and lack a clear-cut method to ensure optimal source separation, often requiring extensive time and effort due to the complexity of choosing among infinite combinations of phase angles, especially when noise contaminates seismic records.
Innovation Solution
A method using eigenvalue analysis and singular value decomposition to evaluate and determine optimal phase encoding schemes for seismic data acquisition, which involves examining the condition number and eigenvalue separation of Fourier transformed sweep signals to select schemes that yield superior data quality and are resilient to noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple seismic vibrators are operated simultaneously to create complex source signals, then data coverage and survey efficiency are improved, but source separation becomes difficult and data quality deteriorates
Solution Approach 1:
The patent applies parameter changes by systematically varying the phase angles of multiple vibrators across different sweeps. Each vibrator is assigned a unique phase encoding scheme where the phase angle changes from sweep to sweep, creating distinct phase signatures for each vibrator. This allows the recorded composite signals to be mathematically decomposed into individual vibrator contributions during processing, resolving the source separation problem while maintaining high survey efficiency.
2Measurement precision
If extensive trial and error is used to select phase encoding schemes, then optimal source separation may be achieved, but time consumption and computational resources increase significantly
Solution Approach 1:
The patent implements preliminary action by providing a systematic framework for selecting phase encoding schemes before conducting the actual seismic survey. The methodology includes evaluating different phase encoding configurations using mathematical criteria (such as orthogonality measures and condition numbers) to identify optimal schemes in advance. This preliminary selection process eliminates the need for time-consuming trial and error during field operations, as the best phase encoding scheme is determined through systematic analysis prior to data acquisition.
Solution Approach 2:
The patent employs feedback mechanisms by incorporating mathematical evaluation metrics that assess the quality of phase encoding schemes. These metrics provide quantitative feedback on how well different phase encoding configurations will perform for source separation. The feedback loop allows operators to select phase encoding schemes that maximize orthogonality and minimize mutual coherence, ensuring optimal source separation without requiring extensive trial and error in the field.
3Reliability
If noise is present in seismic records, then signal-to-noise ratio decreases, but the ability to determine optimal phase encoding schemes becomes more challenging
Solution Approach 1:
The patent introduces an intermediary mathematical framework that acts as a mediator between the noisy recorded signals and the phase encoding evaluation process. By using phase encoding schemes with optimized orthogonality properties, the methodology creates a mathematical structure that separates signal from noise more effectively. The systematic phase variations encode information about each vibrator's contribution, allowing the true signal to be recovered even in noisy conditions through appropriate signal processing and decomposition techniques.
Data Source
AI summary
In accordance with the present invention, there is provided a method of determining whether a particular high fidelity vibratory seismic survey phase encoding is likely to be a good one based on an analysis of the eigenvalue structure (i.e., eigenvalues, eigenvalue separation, condition number, and model resolution matrix) of a matrix formed from the Fourier transforms of the sweep signals. Preferably, a singular value decomposition will be used to calculate the eigenvalues. Using this same approach, the condition number and eigenvalues of matrices that are associated with multiple proposed designs can be compared with each other to determine which is likely to be yield the best seismic data. This approach is preferably used either as a component of the advanced planning for a survey or in the field during pre-survey testing. The use of the instant approach to determine an optimal phase encoding scheme is also taught.