Seismic Source Array Ghost Response Compensation
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Solution Overview
Problem
Current seismic source arrays fail to behave as monopole sources when sea surface reflection is considered, as reducing array size to minimize directivity results in a dipole source instead, and existing methods do not effectively minimize angular variation of the far field spectrum.
Innovation Solution
A method for selecting parameters of a seismic source array that calculates the ghost response and directivity effects to compensate for angular variation, adjusting parameters such as source element depths and positions to minimize angular variation of the far field response, and determining the phase center that minimizes angular phase variation by calculating the far field spectrum and adjusting the vertical reference position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the array size is reduced to minimize directivity, then the source behaves more like a monopole, but the sea surface reflection causes the source to behave as a dipole instead
Solution Approach 1:
The patent converts the harmful effect of sea surface reflection (which causes dipole behavior) into a beneficial effect by deliberately designing the array to exploit the ghost response. The method calculates the ghost response function and adjusts array parameters so that the ghost response compensates for directivity effects, transforming the reflection from a problem into a solution that achieves monopole-like behavior.
Solution Approach 2:
The patent changes physical parameters of the seismic source array, specifically the depths of source elements and the length to depth ratio (optimized at 1.5 to 3). By adjusting these parameters, the array achieves optimal compensation between directivity effects and ghost response, minimizing angular variation and achieving improved monopole source configuration.
2Stability of the object's composition
If the array size is reduced to minimize directivity effects, then angular variation is reduced, but the frequency response becomes limited and the source spectrum is degraded
Solution Approach 1:
The patent optimizes specific parameters including the length to depth ratio (1.5 to 3) and the relationship between minimum wavelength and maximum source element depth (λmin > 4/3 dmax). These parameter changes enable the array to maintain both minimal angular variation and high frequency response quality simultaneously.
3Stability of the object's composition
If source elements are positioned to compensate directivity effects, then monopole behavior is improved, but the phase variation with angle increases
Solution Approach 1:
The patent performs preliminary calculation of the far field spectrum at multiple spherical angles and determines the phase center by minimizing phase difference across angles. This preliminary optimization of the vertical reference position ensures that the array achieves monopole behavior while maintaining stable phase characteristics.
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
The method achieves an improved monopole source configuration with minimized angular variation of the far field spectrum, optimizing the source array to behave as closely to a monopole source as possible, even with sea surface reflection considered, by offsetting ghost response and aperture smoothing function variations.
Implementation Method 1
seismic source arrays exhibit directivity. This directivity may produce directivity patterns that are determined by the notional source signatures, the positions and the activation times of the source elements in the array. The reflected signal from the sea surface may strongly affect the directivity pattern
Implementation Method 2
The reflected signal from the sea surface may strongly affect the directivity pattern
Implementation Method 3
adjusting the parameters of the array such that the directivity effects of the array are compensated by the ghost response to minimize angular variation of a far field response in a predetermined frequency range
Data Source
AI summary
A method for selecting parameters of a seismic source array comprising a plurality of source elements each having a notional source spectrum is described, the method comprising calculating a ghost response function of the array; calculating directivity effects of the array; and adjusting the parameters of the array such that the directivity effects of the array are compensated by the ghost response to minimize angular variation of a far field response in a predetermined frequency range. A method for determining a phase center of a seismic source array is also related, the method comprising calculating a far field spectrum of the array at predetermined spherical angles, and minimizing the phase difference between the farfield spectra within a predetermined frequency range by adjusting a vertical reference position from which the spherical angles are defined.