Marine Passive Seismic Detection Using Zero-Frequency Microtremor Analysis
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Solution Overview
Problem
Current passive seismic methods for detecting hydrocarbon reservoirs are limited to land-based and water-bottom surveys, lacking the capability to effectively use towed marine acquisition systems for direct detection beneath a body of water.
Innovation Solution
A method employing a marine seismic data acquisition system with spatially distributed seismic sensors in a body of water, utilizing both pressure and motion responsive sensors, and omitting high pass filters to detect seismic signals down to zero frequency, allowing for the detection of hydrocarbon-bearing formations by analyzing spectral content in the 2 to 6 Hz range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If land-based and water-bottom passive seismic methods are used, then hydrocarbon detection capability is achieved, but the capability to detect beneath water bodies is limited
Solution Approach 1:
The patent introduces an intermediary processing system that separates microtremor signal analysis from conventional seismic analysis. The system uses bandpass filtering (0.5-10 Hz) to isolate microtremor signals from ambient noise, enabling reliable hydrocarbon detection beneath water bodies where conventional methods fail. This intermediary approach allows the system to adapt to marine environments while maintaining detection reliability.
2Measurement precision
If conventional marine seismic surveying is performed, then subsurface imaging is achieved, but direct hydrocarbon detection capability is lacking
Solution Approach 1:
The patent merges conventional marine seismic surveying with passive microtremor analysis into a single integrated system. The same streamers and sensors used for conventional imaging are also used to record passive seismic signals. The system processes both active source data for subsurface imaging and passive microtremor data for direct hydrocarbon detection simultaneously, achieving enhanced measurement precision without proportionally increasing device complexity.
Solution Approach 2:
The patent makes the marine seismic survey system multi-functional by enabling it to perform both conventional subsurface imaging and direct hydrocarbon detection using the same hardware infrastructure. The streamers equipped with sensors serve dual purposes: recording reflected seismic waves for imaging and capturing ambient microtremor signals for hydrocarbon identification, thereby achieving universality.
3Measurement precision
If high pass filters are applied to marine seismic data, then noise reduction is achieved, but low frequency microtremor signals are attenuated
Solution Approach 1:
Instead of applying high pass filters to remove low frequency noise as in conventional processing, the patent inverts the approach by applying bandpass filters that specifically preserve and enhance low frequency microtremor signals (0.5-10 Hz). The system treats low frequency content as the desired signal rather than noise, fundamentally inverting the conventional filtering strategy to achieve precise microtremor detection while managing ambient noise through selective frequency preservation.
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
Enables direct detection of hydrocarbon-bearing formations beneath the water surface, providing a cost-effective method for hydrocarbon exploration that can be performed contemporaneously with conventional seismic surveys, reducing exploration risks and overcoming geological barriers.
Implementation Method 1
recording signals generated by the sensor(s) in response to natural seismic energy emanating from the subsurface
Implementation Method 2
Background acoustic energy within the Earth of oceanic origin (in a frequency range of about 0.1 - 0.35 Hz) is polarized within or around a hydrocarbon-saturated subsurface rock formation into vertically-propagating energy with a frequency range of about 1 - 7 Hz
Implementation Method 3
utilizing both pressure and motion responsive sensors
Implementation Method 4
recording signals generated by the sensor(s) in response to natural seismic energy
Data Source
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AI summary
A method for detection of hydrocarbon bearing formations below the bottom of a body of water from seismic signals includes moving a plurality of spatially distributed seismic sensors in a body of water and detecting seismic signals including response to any seismic energy having frequencies down to proximate zero. The method includes stacking the acquired seismic signals from the plurality of the sensors in both longitudinal and transverse directions with respect to motion of the sensors in the body water. The stacked signals are analyzed for presence of passive seismic energy indicative of hydrocarbon bearing formations below the bottom of the body of water.