Marine Seismic Source Array Cavitation Control
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Solution Overview
Problem
Controlled-frequency marine seismic source arrays face challenges with cavitation, which distorts seismic signals and reduces controllability, especially when deployed at shallow depths, leading to broadband noise and potential damage.
Innovation Solution
Deploying swept-frequency sources at varying depths to position them outside the frequency band of interest, using multiple sources with non-overlapping frequency bands to avoid cavitation and optimize source placement, allowing for deeper towing while maintaining control over the seismic signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If controlled-frequency marine seismic sources are deployed at shallow depths to avoid ghost reflection notches, then the source can operate within the frequency band of interest, but cavitation occurs causing signal distortion and broadband noise
Solution Approach 1:
The frequency band of interest is divided into multiple sub-bands, with each source in the array assigned to a specific sub-band. This segmentation allows each source to operate at optimized depths for its frequency range, preventing cavitation while maintaining signal quality across the entire frequency spectrum
Solution Approach 2:
Different sources within the array are assigned different frequency bands and deployed at different depths optimized for their specific frequency ranges. Higher frequency sources are positioned deeper to avoid cavitation, while lower frequency sources remain at shallower depths, creating local optimization throughout the array
2Reliability
If multiple sources are used to cover different frequency bands, then cavitation can be avoided for each source, but the system complexity increases
Solution Approach 1:
The seismic source array is designed as a universal system where multiple sources with different frequency characteristics work together to achieve the overall imaging goal. Each source maintains its specialized frequency band while contributing to the collective function of subsurface imaging, allowing the system to handle diverse frequency requirements through a unified deployment strategy
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 reduces the likelihood of cavitation, maintains signal quality, and allows for deeper deployment of seismic sources, minimizing noise and damage while maintaining effective seismic data acquisition.
Implementation Method 1
The source of the down-going sound energy might come, for example, from explosions or seismic vibrators on land, or air guns in marine environments
Implementation Method 2
A seismic survey represents an attempt to image or map the subsurface of the earth by sending sound energy down into the ground and recording the 'echoes' that return from the rock layers below
Implementation Method 3
This includes swept-frequency sources which emit a sinusoidal signal whose amplitude and frequency can be independently controlled
Implementation Method 4
the lowest non-zero-frequency spectral notch introduced by the surface ghost reflection
Implementation Method 5
If deployed at too shallow a depth in the water (e.g. 7.5m) cavitation can occur at the sources during the collection of a marine survey. The term 'cavitation' refers to the formation of cavities (bubbles of vacuum or low-pressure vapor) in a fluid and the subsequent collapse thereof. The collapse generates a shock wave by implosion
Data Source
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AI summary
There is provided herein a method of seismic acquisition that utilizes an arrangement of marine sources where each source is positioned at a water depth shallow enough for the surface ghost notch to fall at a frequency greater than or equal to the maximum radiated frequency of interest. If the marine seismic source has a ratio of signal bandwidth to maximum frequency that is less than one half, then it is possible to deploy it at a greater depth at which ghost notches fall below and above its frequency band but not in it. Further, by placing two or more sources at different depths for the same frequency, any undesired nulls in the radiation pattern caused by the deeper tow can be filled in.