tag:blogger.com,1999:blog-7105728614611010325.post4968998287883232680..comments2023-08-01T06:54:03.086-07:00Comments on Seismic Reflections: Marine Processing - Part 1 | Resample & Minimum Phase ConversionGLOBE Claritashttp://www.blogger.com/profile/00646197047930265069noreply@blogger.comBlogger10125tag:blogger.com,1999:blog-7105728614611010325.post-1144691146095236552017-03-01T14:20:16.218-08:002017-03-01T14:20:16.218-08:00the "gun delay" is the difference betwee...the "gun delay" is the difference between the recording system starting and the shot being fired. With some systems that could be the "tigger time" - I think the steam-based vaporchoc tended to be a bit un-predictable (and so the signature was recorded shot-by-shot) but for the most part it was related to the recording system technology, not the source.<br /><br />You often get the "far field signature" supplied without taking the receiver ghost into consideration; historically that was related to how the far field signatures were recorded, but more recently its become about the use of varying tow depths and so on.<br /><br />The general advice I'd give is to *check* what has and has not been done to your signature; you might find that the company also modeled the tow depths and so on. Of course, broadband type deghosting is a whole other issue that I haven't addressed here...GLOBE Claritashttps://www.blogger.com/profile/00646197047930265069noreply@blogger.comtag:blogger.com,1999:blog-7105728614611010325.post-20133382173914285352017-03-01T07:11:15.347-08:002017-03-01T07:11:15.347-08:00Hi Guy,
Thanks for knowledge that you offer whiti...Hi Guy,<br /><br />Thanks for knowledge that you offer whiting this blog. It is very helpful and objective.<br />Well, I follow your step and some questions pop up in my mind and I would like to discuss with you.<br />1- The gun delay that you mention is related to the trigger time to shot? Are there more reasons?<br /><br />2- I am wondering what the physical meaning of the source signature data convoluted with modeled spikes. Is it the signature without the ghost effect? Why that happen?<br /><br />Really thanks for commentsAnonymoushttps://www.blogger.com/profile/09802526313534966919noreply@blogger.comtag:blogger.com,1999:blog-7105728614611010325.post-9743854052984239712016-07-24T15:34:53.035-07:002016-07-24T15:34:53.035-07:00Ah - Vibroseis and phase is a complicated animal; ...Ah - Vibroseis and phase is a complicated animal; one group that has done a lot of work on this is the CREWES consortia from the University of Calgary; as I recall they suggested that the correlated Vibroseis wavelet was actually a reasonable approximation to minimum phase (as opposed to zero or mixed) It's certainly close enough for deconlvoltuion and so on. <br /><br />So - I would suggest press on with the data you have and then worry about phase-matching after you have cleaned up the shots with the appropriate well control (or known-phase seismic); without well control of some sort you can only approximate phase control, not ground truth it. GLOBE Claritashttps://www.blogger.com/profile/00646197047930265069noreply@blogger.comtag:blogger.com,1999:blog-7105728614611010325.post-52561621117482544062016-07-22T14:21:52.849-07:002016-07-22T14:21:52.849-07:00Hi Guy,
Thanks a lot for writing this blog! It...Hi Guy,<br /><br />Thanks a lot for writing this blog! It's a really useful guide.<br /><br />I have an old vibroseis dataset that has been coss correlated to produce raw gathers that are mixed phase. I would like to convert to minimum phase before proceeding with the processing but I have no additional information for creating a source wavelet. <br />I thought I could estimate the source wavelet by taking the first arrival from the first few traces, flatten and stack, then create a minimum phase matching filter. However, the near trace is at an offset of 200 m.... Do you have any advice for this situation? Anonymoushttps://www.blogger.com/profile/09284230579136600067noreply@blogger.comtag:blogger.com,1999:blog-7105728614611010325.post-5381163122593693352016-03-28T18:56:26.075-07:002016-03-28T18:56:26.075-07:00You can estimate the signature from the direct arr...You can estimate the signature from the direct arrival - if the water is deep enough so this is not confused by the seafloor or refracted arrivals - by applying a linear moveout correction and stacking; this in general will exclude source and receiver ghosts, which you will need to.<br /><br />Of course, if you have an acquisition report you may be able to find a signature (that can be digitised) or even contact the acquisition company who may have the signature on record; there's also software that can simulate an array (Gandelf, Nucleus)if you know the air gun sizes, pressure and their arrangement.<br /><br />It is also probably worth thinking about whether you need a signature or not - for example whether you can run through with just a deconvolution and then address the phase post-processing via well ties and so on. <br /><br />GuyGLOBE Claritashttps://www.blogger.com/profile/00646197047930265069noreply@blogger.comtag:blogger.com,1999:blog-7105728614611010325.post-51832852690732537662016-03-24T10:28:23.824-07:002016-03-24T10:28:23.824-07:00I have some older data for which I do not have a s...I have some older data for which I do not have a source signature. What is the best way to create one?<br />Anonymoushttps://www.blogger.com/profile/14980711090396337200noreply@blogger.comtag:blogger.com,1999:blog-7105728614611010325.post-17134289184215437372014-04-28T17:26:35.576-07:002014-04-28T17:26:35.576-07:00You are correct Ayaz, thank you for pointing it ou...You are correct Ayaz, thank you for pointing it out.GLOBE Claritashttps://www.blogger.com/profile/00646197047930265069noreply@blogger.comtag:blogger.com,1999:blog-7105728614611010325.post-83843270196925687192014-04-06T04:23:41.655-07:002014-04-06T04:23:41.655-07:00I think there is a mistype. Related to receiver gh...I think there is a mistype. Related to receiver ghost, if you tow the receiver on 7 m you will need to divide 14/1500?Ayaz Gasimovhttps://www.blogger.com/profile/10104989073689194609noreply@blogger.comtag:blogger.com,1999:blog-7105728614611010325.post-39199798973203708032014-02-22T19:37:01.790-08:002014-02-22T19:37:01.790-08:00Hi Fabio -
Any frequencies that you have above 12...Hi Fabio -<br /><br />Any frequencies that you have above 125Hz in the dataset will "wrap back" into the data - so if you had some data at 130Hz-140Hz, this would appear after the resampling to be data in the 100-120Hz range and so on.<br /><br />Once it is aliased that's it - you can't then remove the aliased information from the signal. This is what its important to address this upfront. <br /><br />It is very unlikely on this type of survey that you will have any real reflection data over 125Hz, which is even worse as now you have some aliased noise to deal with that is wrapped into the "signal band"...<br /><br />Removing the "ghost" is a different matter; broad-band seismic techniques use a combination of acquisition methods (different tow depths and so on) coupled with processing to address the ghost issues, mainly at the low end. There are processing methods to address the ghost too, but these are still estimating completing the spectrum in various ways.<br /><br />You don't have to resample the data from 2ms to 4ms, however unless your seismic experiment has been designed to capture higher frequencies its a good idea. A key factor in the design is the spacing of the receivers - the higher the frequency you want to record, the close the spacing (to avoid spatial aliasing). Plus of course all the processing takes twice as long at a 4ms sample interval.<br /><br />There's a long discussion on the pros and cons of 2ms and 4ms sampling (mainly for land data) on LinkedIn in the Seismic Processing group.<br /><br />GuyGLOBE Claritashttps://www.blogger.com/profile/00646197047930265069noreply@blogger.comtag:blogger.com,1999:blog-7105728614611010325.post-9010141570241463542014-02-22T08:43:44.891-08:002014-02-22T08:43:44.891-08:00What happen if you before sample from 2 to 4 these...What happen if you before sample from 2 to 4 these filter were not applied? Would I have the aliasing effect and removed it later? What about the ghost? Can I remove later as well? Should I use these filters even if I not resample the data?<br />Anonymoushttps://www.blogger.com/profile/16435194915209121838noreply@blogger.com