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Marine seismic data acquisition
Posted: Thu Jun 11, 2020 5:38 am
What is the difference between conventional marine seismic data acquisition and High Resolution marine seismic data acquisition?
I realized that there is a P-cable acquisition which is categorized as HR acquisition, but, in this kind of acquisition the streamer length is only up to tens of meters. Do we have any other type of survey design with streamer length of for example 2-3 kilometres and still be HR?
What is the difference in their P190 navigation files? For conventional we have source and receiver locations in P190 file, how about in HR ones?
Re: Marine seismic data acquisition
Posted: Thu Jun 11, 2020 1:16 pm
High resolution tends to be first and foremost about the frequencies used. You get higher vertical resolution of course, but higher frequencies maker for smaller fresnel zones and so better horizontal resolution as well. For that to be effective you also need smaller CDP bin sizes, so you end up with a shorter group interval in the cable.
The two other things you have to take care of are (a) making sure that the source puts out those frequencies and (b) making sure that they are not suppressed by the "ghost" (caused by the energy reflecting off the sea surface) on the downward leg (source ghost) and upward leg (receiver ghost)
You can do all of that with a longer cable - and people do typically for site surveys ahead of engineering installations; that used to be all about oil rigs, but increasingly its used for offshore windfarms. Companies like Fugro have specialised in this niche (after they sold off Fugro Seismic Imaging back in 2012/13, which did the exploration work)
P-cable is for 3D work; they have to calculate the positions of the receivers and so on as they do not usually have all of the navigation gear in the water that you get on large scale surveys (acoustic pods, buoys with GPS on etc) although technology is getting better all the time. You'd usually get a P1/90 although I have come across people having to calculate them using the nominal positions and so on for gas hydrates work.
TGS were doing some clever stuff with P-Cable by having a P-cable 3D (low cost) then shooting a 2D grid with longrer offset (3-4km) high resolution so they could build a velocity cube and migrate and so on.