Passive Seismic Imaging via Signal Cross-Correlation
Solution Overview
Problem
Existing passive seismic imaging techniques face challenges in providing unambiguous results and requiring long signal recording times to generate three-dimensional images of the Earth's subsurface, and they often present environmental hazards due to the need for controlled seismic energy sources.
Innovation Solution
A method using an array of seismic sensors to detect and cross-correlate seismic signals from subsurface events, processing these signals to determine hypocenters and reflectivity series, which constrains the model of seismic property distribution, allowing for the generation of three-dimensional subsurface images without controlled seismic energy sources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If passive seismic transmission tomography is used to produce three-dimensional images of the subsurface, then subsurface imaging capability is improved, but signal recording time becomes excessively long and results may be ambiguous
Solution Approach 1:
The patent combines multiple data sources including passive seismic signals, active seismic signals, and well logs into a unified integrated imaging system. This merging of data types allows the system to leverage the temporal advantage of passive seismic data while using active seismic data to provide immediate structural information, thereby reducing the overall recording time required while maintaining imaging precision.
Solution Approach 2:
The system employs a multi-functional approach where the same seismic sensor network serves multiple purposes: detecting passive seismic events, recording active seismic signals, and providing data for both velocity model construction and direct imaging. This universal use of the sensor array eliminates the need for separate dedicated systems, reducing total operational time while improving imaging capability.
2Measurement precision
If conventional controlled source seismic techniques are used for subsurface evaluation, then imaging quality is improved, but environmental hazards increase due to seismic source actuation
Solution Approach 1:
The patent segments the imaging process into multiple data acquisition phases using different signal types. Passive seismic data is collected during natural events without human intervention, avoiding environmental hazards. Active seismic data is collected during dedicated operational phases when safety can be controlled. This segmentation allows high-quality imaging to be achieved through composite data while minimizing environmental impact during any single phase.
Solution Approach 2:
The system utilizes naturally-occurring seismic events to provide imaging data without requiring external controlled sources. The Earth's own seismic activity serves the imaging function, eliminating the need for human-generated seismic sources and their associated environmental hazards. This self-service approach maintains imaging quality while removing the harmful factor of controlled source actuation.
3Ease of operation
If passive seismic sensing is used in environmentally sensitive areas, then access safety is improved, but imaging reliability deteriorates due to ambiguous results
Solution Approach 1:
By merging passive and active seismic data along with well log information, the system achieves reliable imaging in environmentally sensitive areas. The passive data provides safe access without controlled sources, while the active data and well logs provide the structural constraints needed to resolve ambiguities and ensure imaging reliability, thereby combining safety with reliability.
Solution Approach 2:
The system incorporates well log data and seismic velocity models as feedback constraints to guide and validate the passive seismic imaging process. This feedback mechanism allows the system to continuously adjust and refine its interpretations, ensuring reliability while maintaining the safety advantages of passive sensing in environmentally sensitive areas.
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 need for controlled seismic energy sources, minimizing environmental hazards and enabling subsurface imaging with reduced signal recording time, providing clear and efficient three-dimensional images of the Earth's subsurface.
Implementation Method 1
detecting seismic signals from within the Earth's subsurface
Implementation Method 2
The three-component seismic sensors may be placed 10 to 30 or more meters below the Earth's surface
Implementation Method 3
Seismic signals detected at selected ones of the seismic sensors are cross-correlated to signals detected at other selected ones of the seismic sensors
Implementation Method 4
Travel time inversion is used to estimate the compressional and/or shear wave velocity distribution in the target volume from the recorded signals
Implementation Method 5
PSTT can produce such images of the Earth's subsurface using observed travel time of seismic signals
Data Source
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AI summary
A method of imaging the Earth's subsurface using passive seismic emissions includes detecting seismic signals originating from within the Earth's subsurface over a selected time period using an array of seismic sensors deployed proximate the Earth's surface. Hypocenters of seismic events in the subsurface are determined from the detected signals. Seismic signals detected at selected ones of the seismic sensors are cross-correlated to signals detected at other selected ones of the seismic sensors. The cross-correlated signals are processed to obtain a reflectivity series at a geodetic position of the selected one of the seismic sensors. A spatial distribution of at least one seismic property in the subsurface is determined using the determined hypocenters and the reflectivity series.