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|Author||Topic: What is a typical 2D marine geometry workflow?||3884 Views|
7 February 2011 at 4:01pm Last edited: 8 February 2011 9:45pm
We generally use the simple 2D marine geometry in conjunction with the MGEOM module for all 2D marine surveys.
This has a number of plus points over the QSORT module, including the ability to create a "receiver location" trace header. This can be useful later in the sequence, if we want to apply Tau-P domain deconvolution or swell noise attenuation on common receiver gathers.
When assigning 2D marine geometry, the easiest way to configure the parameters is to set:
SHOT ID and distance to be the first shotpoint and the maximum offset.
CDP ID and distance to be the first desired live CDP number, and half the maximum offset.
If you have full navigation available for shots, and receivers we'd suggest:
- Assigning offsets via ADDP190.
- Regularising offsets to their nominal values via OFFREG.
- Using MGEOM to assign offsets based on the regularised data.
7 February 2011 at 5:01pm Last edited: 9 February 2011 3:34pm
1) then why bother ADDP190 if you have to specify the geometry anyway - obviously I have missed something here
2) MGEOM has no place for perpendicular offsets, correct???
8 February 2011 at 9:45pm Last edited: 13 February 2011 6:11pm
Hi Ted -
The simple 2D marine geometry set up in MGEOM is direct straight line, with no perpendicular offset.
One approach you can take is to use the geometry tool, which supports a source-streamer file type with perpendicular offset, or can work with P/190 data.
You'd then "bin" this inside the geometry tool, as per land data.
The approach I describe is designed to manage feather (or perpendicular offset) in the case where you have P1/90 information, without using the geometry tool - so as a batch process. In these cases the actual distance to the far channel can be a lot less than the nominal far offset.
ADDP190 just assigns the offsets to the data - it doesn't then bin the data to create CDPs.
In the 3D marine workflow we then use BIN3D to assign CDP, INLINE, CROSSLINE etc.
OFFREG does a full spatial interpolation, so it gives better results than moveout-and-change-offset-value type approaches.
MEGOM is then just effectively assigning the CDP, CDPTRACE values (as well as REC_PEG and so on)
Even on projects without significant feather I've seen improved results using this methodology; Tau-P, FK Radon and NMO all work just a little bit better. Obviously the more severe the feather angle, the greater the "uplift."
If you are planning to use OFFREG anyway (for SRME, or to improve resolution or spatial aliasing issues for Tau-P/FK work) then there's no additional overhead in the processing sequence.
I've attached a slide showing a (severe, but real) example of how this works.
19 June 2011 at 9:40pm Last edited: 20 June 2011 6:43pm
Here's an extended version of the poweroint, showing the different options.
3 August 2016 at 1:02pm
Hi, just a quick technical question on an old topic... Following the proposed simple work flow (addp190, offreg, mgeom) the MGEOM processor will automatically overwrite the offsets when assigning the CDPs and CDP traces (in CDP a OFFSET mode). Is it recommended to save the offsets after the OFFREG processor and re-apply them after MGEOM?
4 August 2016 at 2:29pm
Could you give more details about the data and what you are trying to achieve?
For 2D marine data that follows a reasonably straight line with little feathering (say less then 10 degrees at far offset) the offsets from MGEOM should be sufficient to use throughout processing. The offsets from OFFREG and MGEOM should probably be pretty similar anyway. The real world co-ordinates (i.e. from ADDP190) can always be preserved in user specified/created headers for when the data is shown to clients, transferred to another program, or archived.
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