RTM Ghost Compensation via Modified Boundary Conditions
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Solution Overview
Problem
Current methods struggle to effectively compensate for source and receiver ghosts in marine seismic data, which cause angle-dependent frequency and amplitude distortion, limiting the achievement of wide bandwidth pre-stack depth images essential for high-resolution imaging and seismic inversion.
Innovation Solution
The method modifies the boundary conditions of Reverse Time Migration (RTM) acoustic wave equations to generate a ghost-compensated seismic image by solving modified equations for both source and receiver wavefields, using a processor-based system to output a compensated image.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional RTM methods are used, then processing simplicity is maintained, but ghost effects cause angle-dependent frequency and amplitude distortion
Solution Approach 1:
The patent applies preliminary action by modifying the boundary conditions of the wave equation before performing the RTM process. Specifically, it modifies the pressure boundary condition at the sea surface to include ghost compensation terms, and adjusts the vertical velocity boundary condition accordingly. This preliminary modification allows the standard RTM algorithm to automatically compensate for ghost effects during the migration process, eliminating the need for separate ghost removal steps while improving image quality.
2Manufacturing precision
If source and receiver ghosts are not compensated, then processing complexity is reduced, but wide bandwidth imaging and high resolution are limited
Solution Approach 1:
The patent applies parameter changes by modifying the boundary condition parameters in the wave equation to account for ghost effects. It introduces ghost compensation terms in the pressure boundary condition (Equation 5) and adjusts the vertical velocity boundary condition (Equation 6) to include these corrections. By changing these boundary condition parameters, the method recovers the true subsurface reflectivity and achieves wide bandwidth imaging with improved resolution without requiring complex post-processing steps.
3Adaptability or versatility
If fixed depth source excitation is used, then acquisition simplicity is maintained, but notch diversity is lacking and data aliasing increases
Solution Approach 1:
The patent applies asymmetry by treating the source and receiver boundary conditions differently in the ghost compensation process. It modifies the pressure boundary condition at the sea surface to include source ghost compensation, while separately handling receiver ghost compensation through the vertical velocity boundary condition. This asymmetric treatment of boundary conditions allows the method to compensate for both source and receiver ghosts even when sources are excited at fixed depths, thereby creating effective notch diversity without changing the acquisition geometry.
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 results in a wide bandwidth seismic image with improved frequency balance and sharper wavelets, accurately representing geological features and correcting amplitude versus angle relations, enhancing the reliability of seismic data for resource exploration.
Implementation Method 1
solving a modified first RTM acoustic wave equation associated with a source wavefield and a modified second RTM acoustic wave equation associated with a recorded wavefield
Data Source
AI summary
Methods and systems for compensating for source and receiver ghost effects in a reverse time migration (RTM) equation are described. Boundary conditions associated with the RTM acoustic wave equations for the source and recorded wavefields are modified. The resultant modified RTM acoustic wave equations are solved to generate ghost compensated modeled seismic images. In another aspect an imaging condition is also modified and the resultant RTM acoustic wave equations are solved to generate velocity and impedance perturbation images.