Multi-Geophone Node for Broadband Seismic Data Acquisition
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Solution Overview
Problem
Conventional seismic prospecting methods fail to capture a broad frequency spectrum of seismic data, particularly missing data below 8 Hz, which is crucial for detailed analysis of rock densities and substructures in hydrocarbon exploration.
Innovation Solution
An array of receiver locations is created with each node equipped with at least two geophones, one sensitive to frequencies below 10 Hz and another to frequencies up to 120 Hz or higher, allowing for the capture of a broader frequency range by combining their signals, mimicking the concept of component speakers in a hi-fi system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single geophone is used at each node, then the device complexity is reduced, but the frequency spectrum coverage is limited and data below 8 Hz is missing
Solution Approach 1:
The geophone system is segmented into multiple units with different frequency sensitivities. Each node contains multiple geophones (typically 2-5) with varying natural frequencies, allowing the array to capture a broader frequency spectrum than a single geophone could achieve alone.
Solution Approach 2:
Each node serves multiple functions by incorporating geophones with different frequency responses. The same node structure and data acquisition system handle both low-frequency and high-frequency signals simultaneously, making the system universal across different frequency ranges without requiring separate recording systems.
2Loss of information
If multiple geophones are used at each node, then the frequency spectrum coverage is improved, but the device complexity increases
Solution Approach 1:
Multiple geophone signals are merged at each node through the data acquisition system. The electrical outputs from multiple geophones are combined and digitized together, creating a composite signal that represents the broader frequency spectrum while maintaining individual geophone characteristics for later processing.
Solution Approach 2:
The system changes the parameter of geophone natural frequency across multiple units at each node. By selecting geophones with different natural frequencies (e.g., 4 Hz, 10 Hz, 25 Hz, 50 Hz), the system captures different portions of the seismic frequency spectrum, with lower frequency geophones capturing more low-frequency energy and higher frequency geophones capturing more high-frequency energy.
3Measurement precision
If geophones with tight tolerance magnets and precisely engineered springs are used, then the frequency sensitivity range is improved, but the manufacturing precision requirements increase
Solution Approach 1:
Different nodes or different positions within the array use geophones with locally optimized qualities for specific frequency ranges. Rather than requiring all geophones to meet the same high precision standards across all frequencies, each geophone is optimized for its specific frequency band, allowing relaxed tolerances overall while maintaining high measurement precision in each targeted range.
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 configuration enables the recording of a much broader bandwidth of seismic data, including frequencies below 8 Hz, providing more comprehensive insights into subsurface structures and hydrocarbon prospecting.
Implementation Method 1
An individual geophone typically includes a magnet and an electrically conductive coil where one or both are arranged to move vertically or horizontally in the case of a three component geophone along an axis, one relative to the other. As the magnet and coil move relative to one another, the magnet induces a small electrical current in the coil that can be measured and recorded.
Implementation Method 2
Typically, springs having very minimal resistance to movement are used to bias the moving elements into a central location or neutral position where vibrations from the earth cause the magnet to deflect from the neutral position.
Data Source
AI summary
The invention relates to acquiring seismic data from the earth using geophones that are tuned to have differing frequency sensitivity ranges. The differing frequency sensitivity ranges cover a broader effective frequency range so that low frequency energy and high frequency energy are less attenuated in the raw data record. Two separate geophones would be used at the same node and three or more geophones may be used in combination at each node. When three or more geophones are used in combination, each may have a separate but overlapping frequency sensitivity range or two or more of the geophones may have the same frequency range sensitivity.