Seismic Source Signature Determination Using Ghost Separation
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Solution Overview
Problem
Current methods for determining far field seismic energy source signatures from near field measurements face challenges due to the complexity of seismic energy interactions between multiple sources and the geometrical configuration of seismic sensors, which results in substantial computational demands and limited accuracy, especially when dealing with non-linear behavior at the free surface.
Innovation Solution
The method modifies the existing notional source approach by incorporating notional ghosts, which are linear radiated wavefields due to ghost reflections, allowing for more precise determination of seismic energy signatures by using twice as many near field seismic measurements to separate up-going and down-going wave components, and solving the resulting equations using a least squares method.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the existing notional source approach is used to determine far field seismic energy source signatures from near field measurements, then the method can handle multiple source interactions, but the computational complexity increases substantially and accuracy is limited, especially for non-linear free surface behavior
Solution Approach 1:
The patent segments the seismic wavefield into distinct up-going and down-going components by using twice as many near field measurements as sources. This segmentation allows separate determination of notional source signatures and ghost signatures, simplifying the inverse problem and reducing computational complexity while improving accuracy in handling non-linear free surface behavior
Solution Approach 2:
The patent adds a temporal dimension to the measurement system by requiring twice as many near field measurements as sources. This additional dimensional constraint enables the separation of source and ghost components in the time domain, transforming an ill-posed inverse problem into a well-determined system that can be solved more efficiently
2Measurement precision
If twice as many near field measurements are used to separate up-going and down-going wave components, then the accuracy of determining notional source signatures and ghosts improves, but the measurement system complexity increases
Solution Approach 1:
The patent segments the wavefield into up-going and down-going components by strategically placing measurements at different depths. This segmentation enables independent determination of source signatures (from up-going waves) and ghost signatures (from down-going waves), improving measurement precision while organizing the complexity into manageable separate systems
Solution Approach 2:
The patent introduces notional sources and notional ghosts as intermediary constructs that mediate between the physical measurements and the far field source signatures. These intermediaries simplify the relationship between measurements and targets, making the inversion process more tractable despite the increased measurement requirements
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 enables more accurate and efficient calculation of far field source signatures by accounting for ghost effects and non-linear surface behavior, improving the interpretability of seismic data without relying on assumptions about surface reflection functions.
Implementation Method 1
Each of the N notional sources is reflected by the free surface creating N notional ghosts
Data Source
AI summary
A method for estimating a far field seismic energy source signature includes using detected near field seismic signals corresponding to actuation of each one of a plurality of seismic energy sources in an array of seismic energy sources. The near field seismic signals are detected at two spaced apart locations in the near field of each seismic energy source, the at least two spaced apart locations being arranged such that a direction of propagation of the detected near field seismic signals is determinable from the detected near field signals. A notional source signature for each seismic energy source and a notional ghost for each seismic energy source using the detected near field seismic signals. A far field signature is determined for the plurality of seismic energy sources using the determined notional source signature and notional ghost signature from each seismic energy source.