Wave equation modeling
Wave equation modeling of water layer multiples can be achieved by downward continuation of shot records followed by adaptive matching of the multiple model to the input record.
Multiple estimation is done with F-K extrapolation and removal of the estimated water-related multiples is done by a 3-component method on a trace-by-trace basis. Each multiple trace is analyzed for an optimum overall time shift, amplitude factor and phase angle to convert it into the original shot trace. The factors are then applied to the multiple trace prior to subtraction from the original.
Success is dependent on the degree of seabed dip which is not comprehended.
Radon Filter
TGS Imaging routinely uses Radon Filtering techniques to attenuate multiples. Normally the multiples are modeled and subsequently subtracted from the input seismic trace data. The Radon Analysis tool is used to transform the data to Time-Moveout space (‘p’ space) so that a suitable mute can be picked to eliminate the primary energy. The remaining multiple energy is then subtracted from the input data. Our technique uses a two-pass approach to give better attenuation. In the first pass the CDP gathers are NMO’d using water velocity and the water bottom multiples are removed. Later in the processing sequence, and after initial velocity analyses have been run, a second pass of Radon is applied. Here the gathers are corrected with primary velocity and the radon mute picked as above to enable subtraction of remaining multiple energy. The example shows a CDP gather after 1st and 2nd passes of Radon have been applied.
High Fidelity Radon Demultiple
A development of the Radon filter is available for use in situations where the information to be passed can be represented by a limited range of traces in the transform domain. Commonly this would be applied to accurately NMO corrected primary data. The advantage of this process is in its improved ability to handle aliased input data. As the degree of preservation of amplitude information in the passed events is high, its main use is in the final conditioning of gathers for amplitude analysis.
SRME
Surface Related Multiple Elimination is a method of multiple attenuation, developed by the Delphi Consortium at TUDelft . All surface related multiples are predicted by convolving the traces in the shot domain with the traces in the receiver domain. The predicted multiple energy is adaptively subtracted from the input gathers using a least squares subtraction routine. The method is very flexible, and may be particularly beneficial on marine data from areas with water depths over one hundred metres. Its main advantage is that no picking or knowledge of primary stacking velocities is required.this makes it very attractive in areas where velocities are poorly known or are difficult to pick due to severe multiple contamination.
SRWEMR ( Surface Related Wave Equation Multiple Rejection)
This process is a development of the ProMAX WEMR technique which uses downward continuation of the recorded wave field through a picked earth model to create a model surface multiple wave field. Like SRME this is subtracted from the input data using a least squares adaptation method and is useful in water depths over one hundred metres.
F/K Demultiple
NMO corrected CMP gathers are modelled in frequency/wave number space as combinations of dipping plane waves. Multiple energy is muted in the F/K plane on the basis of its differential dip relative to flat primary energy.
Following NMO correction near offset multiple, like primary energy, has little dip. For this reason this technique is incapable of suppressing near offset multiple without also suppressing near offset primary energy. Thus near trace muting must be used following this technique to remove the residual multiple.
