Surface multiple attenuation success for deepwater ocean bottom seismic
Posted: 13 June 2006
Convolutional SRME methods cannot usually be applied to ocean bottom seismic.
However, CGG has developed an innovative wavefield modelling approach that provides the ideal solution for all ocean bottom surveys.
Seismic data recorded for deepwater exploration and development often suffers from high-amplitude surface-related multiple energy which can easily obscure the reservoir zones.
Attenuating this multiple energy is a critical issue, especially when the data is acquired for reservoir characterisation or time-lapse studies.
Recent advances in the industry have seen 3D Surface-Related Multiple Elimination (SRME) methods set new standards for the attenuation of these problematic multiples. The convolutional approach for 3D SRME based on the work of Berkhout,Verschuur and Biersteker, is now widely adopted.
It proves relatively effective at removing the high-amplitude surface-related multiples from streamer data, especially when the streamer geometry allows a fine sampling of the recorded wavefield.
This convolutional method cannot be applied on OBS data (cables or nodes) as its two main assumptions are not fulfilled. Firstly there is no co-location of sources and receivers for the surface-consistent convolutions, and secondly, with typically a few, sparse receivers, the wavefield is not well sampled.
At the 68th Annual EAGE conference in Vienna, CGG will be presenting a unique solution to OBS surface multiple attenuation, using its proprietary 3D wavefield multiple modelling approach.
This method generates the surface multiple model using wavefield extrapolation of shot or receiver gathers within a reflectivity model.
With no limiting assumptions on source-receiver co-location and a model-based approach, the method is as equally valid for sparse ocean bottom data as it is for marine streamer data.
The suitability of the wavefield modelling SRME algorithm is only part of the OBS solution. This method still requires a reflectivity model, a shallow migrated section which includes the water-bottom, to perform the wavefield modelling.
With a sparse distribution of receivers sitting at the water bottom, conventional migration of the upgoing wavefield is unable to provide a clear image of the water bottom.
However, by using the hydrophone and geophone components we can derive the downgoing wavefield recorded at the node which includes water-bottom multiples and the direct arrival.
Using a "mirror" migration scheme the information contained within the multiples can be used to generate the shallow reflectivity section required for our wavefield modelling.
This is comparable and, in this case, superior to the water-bottom image from streamer data.
This unique combination of techniques which allows effective surface multiple attenuation for OBS data, using only the OBS data, has successfully been applied to a deepwater dataset with excellent results.
The comparison shows a stack section of data from five OBS nodes in which the multiple energy is clearly visible, before and after the application of SRME.
Whilst this example is for an area with a flat (but dipping) seafloor, the model-based method naturally handles structured seafloors and any kind of receiver geometry and bathymetry.
Antonio Pica will be presenting these results in his paper Using and Removing 3D Surface-Related Multiples from OBS data during Monday’s workshop on “Removing or using multiples” at 13:30 pm.
Posted by Richard Price, Editor EnergyME.com
Information supplied by companies or PR agencies who are responsible for content. Send press releases to richard@energyme.com |
