Zone-Based Directional Seismic Source for Shadow Zone Elimination
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Solution Overview
Problem
Conventional seismic acquisition methods using constant source directivity fail to provide reliable subsurface information in areas with high seismic velocity deposits or intrusions, resulting in noisy 'shadow zones' due to overcritical energy generation, especially in regions like the Nordkapp Basin with varying critical angles near the seafloor.
Innovation Solution
Adapting seismic source directivity angles to match the varying critical angles at and close to the seafloor by using a zone-based directional seismic source with directivity angles equal to or close to the measured critical angle, allowing for optimized energy distribution and reduced noise, achieved through a method involving a vessel towing a source with multiple sub-arrays tuned to different critical angles and steerable streamers maintaining position within defined zones.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a constant source directivity is used for seismic acquisition, then the acquisition process is simple and efficient, but overcritical energy is generated causing noisy shadow zones beneath high velocity layers
Solution Approach 1:
The source directivity is made variable rather than constant, allowing it to be adjusted dynamically to match the critical angle of the underlying geological layer. This enables the source to adapt its radiation pattern to minimize overcritical energy generation while maintaining acquisition efficiency.
Solution Approach 2:
The critical angle parameter is used to control the source directivity angle. By changing the source directivity parameter to match the critical angle of the target layer, the system optimizes energy distribution and eliminates the harmful shadow zones caused by overcritical energy.
2Illumination intensity
If the source directivity is adjusted for younger strata with high critical angles, then illumination is optimized for those layers, but overcritical energy is generated when shooting over older high velocity deposits with low critical angles
Solution Approach 1:
The source directivity is customized for each local geological condition rather than using a uniform setting. By matching the source directivity to the specific critical angle of the underlying layer (whether young or old strata), the system optimizes illumination locally while avoiding overcritical energy generation.
Solution Approach 2:
The source directivity angle is made dynamically adjustable based on the critical angle of the target layer. This allows the system to switch between different directivity settings depending on whether it is shooting over young or old strata, eliminating the trade-off between illumination and overcritical energy.
3Reliability
If processing methods are used to remove source-generated noise, then data quality improvement is attempted, but the noise removal is unsuccessful especially in shadow zones
Solution Approach 1:
Instead of attempting to remove noise during processing, the invention prevents overcritical energy generation at the source through proper directivity alignment. By taking preliminary action to match the source directivity with the critical angle before data acquisition, the harmful noise is avoided entirely rather than requiring unsuccessful post-processing removal.
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 enhances data quality by minimizing overcritical energy and optimizing illumination of subsurface targets, improving seismic imaging and exploration capabilities in areas previously hindered by noisy data, enabling better well planning and potential production in high-velocity regions.
Implementation Method 1
a seismic source with a constant predefined directivity, is applied for shooting direction following a regular pattern at the sea surface
Implementation Method 2
the critical angle is defined as the arcsine of the velocity ratio between two layers with different physical properties (Snell's law)
Data Source
AI summary
A method of conducting a seismic survey of an area including a region of high seismic velocity regimes in a shallow overburden. According to the method, a zone is identified in which the boundary of the high seismic velocity region has a substantially constant critical angle and a course is plotted through the identified zone. A zone based directional seismic source is applied sequentially, with a directivity angle equal to or close to the measured critical angle. The response is detected using receivers.