Passive Low Frequency Seismic System for Subsurface Imaging
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Solution Overview
Problem
Passive low frequency seismic data acquisition is challenging due to contamination by man-made noise, which can mimic direct hydrocarbon indicators, and the difficulty in retrieving compressional body waves from surface wave noise, leading to misinterpretation and poor resolution in subsurface imaging.
Innovation Solution
A system and method that involves positioning sensors to record microseismic signals with both vertical and horizontal components, filtering noise, and using inversion techniques to extract vertically propagating compressional body waves from ambient background waves, while modeling seismic responses in a multiphase medium to predict subsurface structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If passive low frequency seismic data acquisition is performed, then subsurface imaging capability is improved, but surface wave noise contamination increases
Solution Approach 1:
The patent extracts and removes surface wave noise components from the seismic signal using frequency-wavenumber filtering and adaptive noise subtraction techniques, separating the harmful surface wave energy from the useful body wave signals for improved subsurface imaging
Solution Approach 2:
The patent introduces intermediate processing steps including frequency-wavenumber filtering and adaptive signal processing as mediators between the raw noisy seismic data and the final subsurface image, using these intermediate transformations to suppress surface wave noise while preserving body wave information
2Measurement precision
If compressional body waves are retrieved from ambient noise, then subsurface structure resolution is improved, but signal retrieval difficulty increases
Solution Approach 1:
The patent utilizes the vibrational characteristics and frequency content of compressional body waves to distinguish them from ambient noise and surface waves, using frequency-domain analysis and wavefield separation techniques based on the distinct vibrational signatures of different wave types
Solution Approach 2:
The patent changes the parameter representation of the seismic signal by transforming from the time-domain to the frequency-wavenumber domain, enabling parameter-based separation of body waves from noise through spectral analysis and adaptive filtering in the transformed domain
3Measurement precision
If narrowband harmonic components are filtered, then signal-to-noise ratio is improved, but loss of potentially useful signal occurs
Solution Approach 1:
The patent applies partial filtering by selectively removing only the dominant narrowband harmonic components that represent noise, while preserving other frequency content that may contain useful signal information, using adaptive thresholding and spectral analysis to determine what to filter
Solution Approach 2:
The patent employs adaptive signal processing with feedback mechanisms that continuously analyze the spectral content and adjust the filtering strength based on the detected signal characteristics, reducing the filtered components when they represent noise while preserving them when they contain useful information
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 effectively filters out noise and retrieves vertically propagating compressional waves, enabling accurate imaging and property estimation of subsurface objects, such as underground reservoirs, by improving signal-to-noise ratios and reducing interference from surface waves.
Implementation Method 1
Microseismic signals are recorded in the predetermined area comprising waves with a vertical component and a horizontal component
Implementation Method 2
filtering noise in the recorded microseismic signals associated with a correlated horizontal wave component from the vertical wave component
Implementation Method 3
accumulation of the tensor of cross-correlation functions
Implementation Method 4
Vertically propagating compressional body-waves are extracted from a microseismic ambient background wave field
Implementation Method 5
suppressing the scattered component of the Rayleigh surface wave using the tensor of the cross-correlation functions
Implementation Method 6
a seismic simulation that enables the propagation of seismic waves in a multiphase medium
Implementation Method 7
performing filtering on the collection of cross-correlation functions to exclude an inclined component in the gathering of cross-correlation functions
Implementation Method 8
excluding broadband interference from the microseismic ambient background wave field
Data Source
AI summary
Systems and methods for applying passive low frequency seismic (LFS) techniques to estimate the presence of a search object, its properties, and properties of the exterior environment for onshore or offshore surveys. The process includes the acquisition of LFS data, multi-phase data simulation and data processing using advanced processing graphs that includes seismic interferometry approaches and adapted inversion techniques.