Marine Seismic Multiple Attenuation via Wavefield Segmentation
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Solution Overview
Problem
Marine seismic data is contaminated by multiples and ghosts, which obscure the interpretation of desired reflections from the earth's interior, and existing methods for removing these are inefficient.
Innovation Solution
A method involving obtaining two sets of seismic signals with different travel times through the water, separating them into up- and down-going wavefields, and subtracting or combining them to remove multiples, while accounting for non-flat sea surfaces and tidal changes, using filters and mathematical operators to correct for amplitude mismatches and position variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional single-set seismic data acquisition is used, then the acquisition process is simple and quick, but multiples and ghosts contaminate the data and obscure subsurface reflections
Solution Approach 1:
The acquired seismic data is segmented into two separate wavefields (up-going and down-going) based on propagation direction. This segmentation allows selective processing where multiples in one wavefield can be identified and removed without affecting the primary reflections in the other wavefield, thereby improving data quality while maintaining processing efficiency
Solution Approach 2:
The harmful multiple reflections are extracted and isolated from the total seismic signal by analyzing the relationship between up-going and down-going wavefields. Once identified through the mathematical relationship D=G×U, multiples are separated and removed, leaving only the desired primary reflections for subsurface imaging
2Reliability
If deghosting and demultiple methods are applied to remove ghost reflections and multiples, then data purity improves, but processing complexity increases
Solution Approach 1:
The deghosting and demultiple operations are merged into a single integrated processing workflow. By simultaneously analyzing up-going and down-going wavefields and applying the mathematical relationship between them, both ghost removal and multiple attenuation are achieved in one process rather than as separate sequential steps, reducing overall processing complexity
Solution Approach 2:
The down-going wavefield (containing multiples) is treated as a copy or transformation of the up-going wavefield through the ghost operator G. This copying relationship allows the use of the cleaner up-going wavefield to predict and remove multiples from the down-going wavefield, simplifying the processing by leveraging the existing wavefield structure rather than requiring independent multiple removal algorithms
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
Effectively removes multiples and ghosts from seismic data, improving the accuracy of subsurface imaging by isolating primary events and reducing contamination, applicable to various marine seismic acquisition techniques.
Implementation Method 1
The source imparts an acoustic wave to the water, creating a wavefield which travels coherently into the underlying earth. As the wavefield strikes interfaces between earth formations, or strata, it is reflected back through the earth and water to the detectors
Implementation Method 2
The wave that travels only once upwards, termed the 'primary', travels through the water and past the seismic detector which records its presence. The wavefield then continues to travel upward to the water's surface (which can be regarded as a free surface), where it is reflected back downwards
Implementation Method 3
Knowledge of G or an approximation thereof, allows an operator to remove ghost from the recorded data using subtraction and/or an inverse operation
Data Source
AI summary
A method is described for reducing multiples in marine seismic data using at least two sets of signals representing seismic energy reflected and/or refracted from an earth structure using a plurality of seismic receivers located in a body of water with the two sets differing in the traveltime of signals through the body of water, separating said signals into up- and down-going wavefields and combining the two sets to remove multiples.