#  > Petroleum Industry Zone >  > Geology & Exploration >  >  >  need help. how to do regional velocity analysis?

## zhuhuan

hello fellows, who has some materials about reginal velocity research? I wanna do some research on reginal velocity in order to eventually get a more accurate depth structural map.I think I should do analysisi from the well log at first.But how to do it step by step?Any suggestion are welcomed.Thanks in advance.

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## GEO2000

Hello
That a very good topic. I did quite the same thing a few years ago. I used GMT software. Where i did implement the gravity data from both ship/satellite and converted inside that GMT program to plotted as velocity. The gravity is based on density conversion to velocity in regional scale. 
Hope this help lit.
Good luck

GEO

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## GEO2000

Hello
That a very good topic. I did quite the same thing a few years ago. I used GMT software. Where i did implement the gravity data from both ship/satellite and converted inside that GMT program to plotted as velocity. The gravity is based on density conversion to velocity in regional scale. 
Hope this help lit.
Good luck

GEO

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## zhuhuan

Thanks,GEO.But I don't have magnetic data at present.Is there any other way to find the velocity anomaly?You know there were two wells drilled in a structure .And they are very close.And in the time map the lower well are actually drilled higher.almost flat layer above and no faults.

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## GEO2000

Dear, have never said magnetic data, you can download the gravity data for your location from the internet webside, you need only gravity from satellite.

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## zhuhuan

Oh , thanks .

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## ahmedsisy

i think V=V0+KZ method will be good for you 
but doing any thing (regional) depending on many parameters such as:
1- how big the are of study is ?
2- how many wells you have ? and which data are available which are not ?
3- what is the level of structure and stratigraphy comlexity in the area ?? this is very critical point
4- what is the purpose of study ? just to study ? or to extract emperical relations ? or to help in a bigger project ?
anyway ... read these papers , i think it will help you if  i understood what you mean

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brother geo2000 , it is intereisting to know about your research , using gravity data for velocity model , can you explain to us more please ? and for which purpose was your study ? i guess it was for seismology or engineering , am i right ?
waiting your reply
thanks

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## zhuhuan

thanks,my friend.That's what I want most.I will read the paper first. Thanks again.

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## ahmedsisy

i just noticed what you wrote ... you have only 2 wells in one structure ? no faults and the problem is only diiference in average velocity between the 2 wells ??? is this the case ?
if so .... it's not regional ... and V=V0+KZ will not be useful 
if this is the case you need to apply synthetic , compare sonic logs and checkshots of both , check also the stacking velocity if available (not always works) .... determine the anomalous layer from sonic log , check it on seismic sections , check it's effict on Vav and Vint, generate synthetic seismogram ... try to change the thickness of anomalous layer using the wedge model module (you can find in hampson russel, then check this layer continuity and thickness variation in your area .... then use layer cake method to convert from time to depth any layer below the anomalous layer.
let me know if this is helpful or if you need any more details.

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## GEO2000

Hi Guys
I don't understand when you guys mentions only two wells, and the guy is asking about regional velocity. As I explain before use gravity from ship if your comapny boughted together with your seismic, if not plz If you saying regional velocity use the gravity from Sateliate. Gravity if function of density, that density will be convert to velocity. Use GMT software to get  your plot and files.
Ahmedsisy, I do have Master of Science in Petroleum Geology and Geophysic.
Good luck again

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## ahmedsisy

Mr GEO2000
thank you for answer , ofcourse i respect that you have Master of Science in Petroleum Geology and Geophysic
but i didn't ask you about your degrees 
i asked you about this method to convert gravity into regional velocity ... which is absolutely unknown in Petroleum Geology and Geophysics , i wanted to know more information about it.
i would like to ask in which country you are working ? because in my country we don't know any thing about gravity into regional velocity ... because gravity methods has very low resolution and too low accuracy , what i know (honestly i know very few about gravity) is that we use gravity only qualitatively , while the density values from gravity are inacurate and represent very thick section of the subsurface , so ..... it's  (as i understand) useless in the oil exploration....
i would like to know more about this subject , and it is good chance to know directly from some one how applied this technique  practically , if you can give us a presentation or paper about your work or any other project to understand the technique , it will be very kind of you.
thanks

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## GEO2000

Hi Ahmedsisy
So sorry to understand your question, any way to converation of gravity to velocity is based on Naf& Drake methods, as we know that gravity is function of density. By using Naf&Drake methods you can convert density to velocity or vice versa.
I did used gravity and magnetic in South Atlantic marin for re-construct and light shadow of that margin (West Africa-Brazil).
What you need to do is use one of the software programs like (GMT if you have the data for area of interest or use GeoSoft), point out your coordinate and start plotting. These programs will create for you plot and files.
Sorry again for misunderstanding your question dear.

GEO

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## ahmedsisy

thanks

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## zhuhuan

> i just noticed what you wrote ... you have only 2 wells in one structure ? no faults and the problem is only diiference in average velocity between the 2 wells ??? is this the case ?
> if so .... it's not regional ... and V=V0+KZ will not be useful 
> if this is the case you need to apply synthetic , compare sonic logs and checkshots of both , check also the stacking velocity if available (not always works) .... determine the anomalous layer from sonic log , check it on seismic sections , check it's effict on Vav and Vint, generate synthetic seismogram ... try to change the thickness of anomalous layer using the wedge model module (you can find in hampson russel, then check this layer continuity and thickness variation in your area .... then use layer cake method to convert from time to depth any layer below the anomalous layer.
> let me know if this is helpful or if you need any more details.



Sorry for replying late,my friends. have meeting all these days.After I read the two articles ,I think it can't be called regional velocity reseach. In my study area it have merely 20 wells drilled at present. And in the article it commonly have hundreds of wells.
In my study area  we often encounter with the depth conversion question.In a structure, we usually use the velocity of wildcat well to convert time to depth.But on appraisal well ,the actual depth are higher or lower.  sometimes  the depth in appraisal well  were higher than the wildcat.You know we commonly drill wildcat well in the top of the structure.
Your suggestion are very good. I will have a try.Thanks my friend.
And sorry for my poor english expression about "regional velocity".

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## gustavohd

If you have sufficient wells with sonic logs you could try to tabulate the DT reading at reservoir marked depth. Do this for all wells. You must know x,y coordinates for all wells involved. The inverse of the DT reading is a measure of seismic velocity. Now you have seismic velocity data distributed at all well locations. For the map you can use any contour software like SURFER.

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## SLB

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