Wavefield Separation via Direct Arrival Prediction and Subtraction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In seismic exploration, accurately separating up-going and down-going wavefields is hindered by the challenge of properly correcting direct arrivals when estimating fluid particle velocities from pressure measurements, leading to errors in wavefield separation.
Innovation Solution
The direct arrivals are predicted using calculations based on the notional source signature, reflectivity of the sea surface, and acoustic velocity, and then subtracted from measured pressure and fluid particle motion data to correct the wavefield separation, allowing for accurate separation of up-going and down-going wavefields.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If direct arrivals are not corrected when estimating fluid particle velocities from pressure measurements, then wavefield separation can be performed, but errors in wavefield separation occur due to the presence of direct arrivals
Solution Approach 1:
The patent applies preliminary action by predicting and removing direct arrivals from the pressure data before performing wavefield separation. The direct arrival prediction uses the source signature, propagation velocity model, and sensor positions to calculate and subtract the direct wavefield component, ensuring that subsequent wavefield separation is performed on corrected data free from direct arrival contamination
Solution Approach 2:
The patent extracts the direct arrival component from the total pressure signal by predicting it separately using the known source characteristics and propagation physics, then removing this extracted component from the measured pressure data. This isolation and removal of the harmful direct arrival component enables accurate fluid particle velocity estimation and wavefield separation
2Measurement precision
If direct arrivals are corrected by muting them, then fluid particle velocity can be estimated, but the direct wave energy is lost and wavefield separation accuracy is reduced
Solution Approach 1:
Instead of muting (completely removing) the direct arrivals, the patent extracts and separates the direct arrival component from the total signal, allowing it to be removed from the pressure data for accurate particle velocity estimation while preserving the ability to add it back to the down-going wavefield later, thus preventing energy loss
Solution Approach 2:
The patent temporarily discards the direct arrival component during the wavefield separation process by removing it from the pressure data, performs the separation operations, and then recovers the direct arrivals by adding them back to the down-going wavefield portion, ensuring no energy is permanently lost while still achieving accurate separation
3Measurement precision
If direct arrivals are predicted and removed from pressure data, then wavefield separation accuracy is improved, but additional processing steps are required
Solution Approach 1:
The patent performs preliminary prediction of direct arrivals using efficiently computable methods based on the known source signature, propagation velocity model, and sensor geometry, completing this correction step before the main wavefield separation processing to streamline the overall workflow and improve accuracy
Solution Approach 2:
The patent creates a predicted copy of the direct arrival wavefield based on the known source characteristics and propagation physics, using this synthetic copy to subtract from the measured pressure data, avoiding the need for complex direct measurement and simplifying the processing
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 method enables precise separation of wavefields, reducing errors and improving the accuracy of fluid particle velocity estimates, thereby enhancing the quality of geophysical data products.
Implementation Method 1
The acoustic source is suspended in the water at a known depth and the acoustic source is activated at known times. The acoustic wavefield, comprising pressure wavefield and fluid particle velocity wavefield components, propagates through the water
Implementation Method 2
a portion of the acoustic energy therein is reflected and propagates back for detection by sensors deployed in the water body or on the sea floor beneath the water body
Data Source
Figure 1
Figure 2
Figure 2A
AI summary
At least some embodiments are directed to a system. The system includes a processor and a memory coupled to the processor. The memory stores a program that, when executed by the processor, causes the processor to calculate a pressure response of a first sensor, and correct pressure wavefield data obtained from the first sensor responsive to a first acoustic wavefield. The correction is based on the calculated pressure response of the first sensor. The pressure response of the first sensor is responsive to a second acoustic wavefield having a propagation path between a source of the second acoustic wavefield and the first sensor, in which the propagation path includes no reflection from a subsurface formation.