Marine and Land data multiple attenuation

Oil and natural gas exploration -- geology and geophysics
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jefry123
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Marine and Land data multiple attenuation

Post by jefry123 »

Hey guys,

I would like to know what methods and approaches can be used to attenuate multiple reflections in marine and land seismic data respectively?
Thank you in advance.

GuyM
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Re: Marine and Land data multiple attenuation

Post by GuyM »

Well that's kind of a big topic....

Broadly your main approaches are:

- treat a (short period) multiple as a reverberating, ringy wavelet; this is where deconvolution in the XT or Linear Tau-P domains works
- model the multiple are remove it with adaptive subtraction; these are methods like "free surface" demultiple
- remove the multiple on gathers based on its apparent velocity, using things like the FK or Parabolic radon domain
- flatten the multiple (on a stacked section or offset planes) and remove the flat energy

These all work well on marine mutliples, and tend to be more complex on land ones.

Typically on a marine dataset you would use SRME (free surface) demultiple to hit longer periods (>200ms), then tau-P domain deconvolution for shorter periods, followed by a residual parabolic radon multiple for any pesky multiple tails the SRME had missed.

Of course, a lot depends on your specific problem; diffracted multiples tend to be hard, and the issue is often that there is not very much signal under the multiple once you have removed it.

There's also a lot of theme-and-variation, so for example you can do Radon demulitple by applying a 90% of primary NMO correction to gathers (primaries are up dip, multiples downdip) but in some situations you might want to apply a water-velocity NMO or even pick a mulltiple trend and remove things that way.

There's a description of Radon here : http://seismicreflections.globeclaritas ... iples.html

If you can post some data I can make some suggestions...

jefry123
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Re: Marine and Land data multiple attenuation

Post by jefry123 »

Thank you for your complete answer as always Guy.
The reason for my general question is that you can see a lot of new methods or categorizations for multiple attenuation in literature. I wanted a general categorization in which marine and land data applications be possible. for example, I know that these methods can be categorized as data-driven or model-driven, but I don't know the methods in each group or their usage on land or marine data.

GuyM
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Re: Marine and Land data multiple attenuation

Post by GuyM »

Ah - understood.

The devil tends to be in the details, so for example if you look at SRME then "Company A" might have a better 2D SRME modelling package that addresses the critical near-offset multiples better where "Company B" might have a more sophisticated adaptive subtraction and so on.

You can get into all sorts of clever things like splitting the data into frequency bands for the adaptive subtraction and running it in a cascaded sense and so on, which can all help to gain a little bit of an "edge."

I had a brainstorm one day and decided that since deconvolution "worked", then the actual data could be used as a multiple model if the water depth was shallow (<100ms); all you would have to do is to copy the input trace, and shift it down based on the non-zero time lag peak in the auto-correlation function.

So - I spat out a whole dataset of pre-stack auto-correlation functions, dropped them into the "first break" picking tool, auto picked the lot and then gave it a go. Now ideally I would have run a water-velocity wavefield downward continuation based on those pick times but I figured the seafloor was flat enough and I'd just use a static shift and a cascaded adaptive subtraction with different frequency bands first. Worked very well...

And - stack is still the most effective demultiple....

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