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Converting Russian neutron log unit to conventional units. 
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Joined: Mon Nov 18, 2013 10:05 am
Posts: 4
Post Converting Russian neutron log unit to conventional units.
Hi
I am working on Russian well data. I have difficulty with recognizing neutron log units. I know that the unit is usually in counts per second but the range of the neutron log readings in the well I'm working on does not fit with this unit. I am extracting log data from the Company's database and I am not sure if the data managers have put the units correctly or not. in any case, the units are either "1/s" , "STDU" or "impulses/min" . I think STDU stands for "Standard Units" but what is that? how do I convert it to conventional units? for example in one case the range of values for a neutron log is 1.2 to 6.1 (the assigned unit is "1/s" for this log). or another wells has neutron values between 0.636 to 2.49 (with unit STDU).
could you please advice on how I can convert these units to conventional neutron unit (fraction or %)?
Thanks in advance.


Mon Nov 18, 2013 10:23 am

Joined: Tue Apr 05, 2011 8:38 am
Posts: 80
Post Re: Converting Russian neutron log unit to conventional unit
It is not a straight forward procedure to convert Russian neutron logs, which are usually in count rates, into standard porosity units. You need to know the type of neutron tool which has been used. The Russians have several types of neutron logging tools. Consequently, there are different transforms to convert the count rates in porosity. Furthermore, the neutron count rate is also affected by hole size. Therefore, you will also need to know the hole size.
There is a good reference book called "Russian-Style Formation Evaluation" by Bob Harrison. You will find it very helpful in interpreting Russian type of logs.


Thu Nov 28, 2013 7:42 am

Joined: Mon Nov 18, 2013 10:05 am
Posts: 4
Post Re: Converting Russian neutron log unit to conventional unit
Thanks kokokyi, unfortunately I don't have any information about hole size or tool types. I guess that makes any conversion very uncertain.
Do you know how I can calculate a neutron porosity from near and far count rates? I have seen a formula in "Russian Logging Technology " by S. Rodgers, 1995. but I don't get a reasonable range when I apply that transform.
do you happen to know a general equation that I could use. I know that in the end the result would be uncertain but I will try to handle that . I am lucky in this case to have a sonic and density log to assisst in porosity calculation.
thanks again
Mehr


Mon Dec 30, 2013 2:52 pm

Joined: Tue Apr 05, 2011 8:38 am
Posts: 80
Post Re: Converting Russian neutron log unit to conventional unit
What I can suggest is to compute the neutron count ratio (near counts divided by far counts) and calibrate it with the porosity derived from the density log, using the appropriate matrix density. This should work in water bearing and oil bearing intervals. It would probably not work in gas bearing formations, as density log will be affected by the gas. Once you have established the relationship betwen neutron count ratio to porosity in one or two key wells, you can use the correlation to compute porosity from neutron count ratio in other wells.

An approximate equation that I found from my old course notes on Russian log is as follows:
Porosity = 0.0235(X^2) + 0.0499X - 0.0508
where, X = ratio of near to far neutron count rates

This equation may or may not work in your case.


Tue Dec 31, 2013 8:55 am

Joined: Fri Feb 27, 2015 7:23 am
Posts: 1
Post Re: Converting Russian neutron log unit to conventional unit
I am working on Russian well data. I have difficulty with recognizing neutron log units. I know that the unit is usually in counts per second but the range of the neutron log readings in the well I'm working on does not fit with this unit. I am extracting log data from the Company's database and I am not sure if the data managers have put the units correctly or not. in any case, the units are either "1/s" , "STDU" or "impulses/min" . I think STDU stands for "Standard Units" but what is that? how do I convert it to conventional units? for example in one case the range of values for a neutron log is 1.2 to 6.1 (the assigned unit is "1/s" for this log). or another wells has neutron values between 0.636 to 2.49 (with unit STDU).

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Fri Feb 27, 2015 7:24 am

Joined: Tue Apr 05, 2011 8:38 am
Posts: 80
Post Re: Converting Russian neutron log unit to conventional unit
I believe you must be the same person who posted the same question on 18 November 2013.
Generally, neutron count rates are indirectly proportional to porosity. The lower the count rate, the higher the porosity and vice versa.
However, to convert the count rates into porosity, you need a reference or some form of calibration.
It will be helpful if you have some other logs like sonic to calibrate your neutron porosity.
Some further information on Russian type neutron logs can be found at the following website:

https://www.spec2000.net/17-russian.htm

It is the link to Crain's Petrophysical Handbook, which is an extremely useful reference book on petrophysics.


Fri Feb 27, 2015 8:03 am
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