Multi-Depth Streamer Wavefield Separation
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Solution Overview
Problem
Geophysical surveys, particularly seismic surveys, face interference from ghost signals that attenuate up-going wavefields and create notches in measured signals, reducing survey resolution and accuracy in locating hydrocarbon-bearing geological structures.
Innovation Solution
Towing streamers at different depths allows for the separation of up-going and down-going wavefields through scaled or weighted summation of measured wavefield components, and combining data from pressure and particle motion sensors to mitigate the effects of ghost signals, thereby improving survey resolution and reducing streamer complexity and cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If streamers are towed at a single depth, then the survey system is simpler and less costly, but ghost signals attenuate the up-going wavefield and create notches in measured signals, reducing survey resolution
Solution Approach 1:
The streamer system is segmented into multiple streamers towed at different depths (e.g., first streamer at depth d1, second streamer at depth d2). Each streamer records wavefield data independently, allowing the system to capture both up-going and down-going wavefields with different ghost signal characteristics. This segmentation enables subsequent separation of wavefield components to improve survey resolution while maintaining manageable complexity through modular deployment
Solution Approach 2:
The solution adds the depth dimension to the streamer configuration by towing streamers at multiple discrete depths rather than a single depth. This dimensional expansion creates diverse sampling of the wavefield at different ghost signal attenuation levels, enabling mathematical separation of up-going and down-going components. The multi-depth arrangement transforms a single-depth limitation into a multi-dimensional data acquisition capability that resolves ghost signal interference
2Measurement precision
If multiple streamers at different depths are used, then ghost signal effects are reduced and survey resolution is improved, but the device complexity and cost increase
Solution Approach 1:
The streamer system is divided into multiple independent streamers that can be deployed and manufactured separately. Each streamer contains standard sensors (hydrophones, particle motion sensors) and can be processed independently during data acquisition. This segmentation allows manufacturers to produce standardized units and simplifies deployment procedures, reducing the overall complexity despite using multiple streamers
Solution Approach 2:
Each streamer in the multi-depth configuration is designed to perform multiple functions: recording up-going wavefields, recording down-going wavefields, and providing depth-specific sampling. The universal design of streamers with standardized sensor packages allows them to be deployed at different depths while maintaining ease of manufacture and deployment. The same streamer design can be replicated at multiple depths without requiring custom manufacturing for each depth position
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 the accuracy of geophysical data by reducing the impact of ghost signals, leading to better prediction of hydrocarbon-bearing structures and more effective determination of oil and natural gas deposits.
Implementation Method 1
Acoustic waves generated by the source may then be transmitted to the earth's crust and then reflected back and captured at the geophysical sensors
Implementation Method 2
up-going wavefields may reflect from the water surface, resulting in down-going ghost signals that may be detected by geophysical sensors along with desired up-going wavefields from the formation
Implementation Method 3
Ghost signals may attenuate the up-going wavefield and cause notches in measured signals at particular frequencies
Data Source
AI summary
Techniques are disclosed relating to geophysical surveying and data processing using streamers at different depths. In one embodiment, a method includes obtaining geophysical data specific to a geophysical formation that includes a first set of data representative of a first particle motion signal and a first pressure signal recorded using sensors at a first depth and a second set of data representative of a second particle motion signal and a second pressure signal recorded using sensors at a second, greater depth. In this embodiment, the method includes generating first and second wave separation equations from the first and second sets of data and determining a cross-line wavenumber value that reconciles the first and second equations. The determined cross-line wavenumber may be used to separate measured up-going and down-going wavefields.