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Porosity and Sw equations in IP
http://www.epgeology.com/petrophysics-f23/porosity-and-equations-t3113.html
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Author:  roambold [ Sun Nov 04, 2012 4:29 pm ]
Post subject:  Porosity and Sw equations in IP

hi petrophysicists
i just need to ask some phisw equations that used in IP because i need it for my paper:
1. can you show me some references of calculating hydrocarbon hydrogen index (used in neutron porosity model) and apparent hydrocarbon density (used in density porosity model) that used in phisw algorithm? why should we use apparent hydrocarbon density instead of original hydrocarbon density?
2. in wbm environment, why we limit sxo < sw^sxo limit? reference?

Author:  kokokyi [ Tue Nov 06, 2012 6:49 am ]
Post subject:  Re: Porosity and Sw equations in IP

Hi Roambold,

I will try to answer your questions.

1)The reference for calculating Hydrogen Index of Hydrocarbon (used in neutron porosity model of IP software) can be found in the following book:
Chapter 5 Porosity Logs, Page 5-21, Equation 15-5, Log Interpretation Principles/Applications published by Schlumberger, Seventh Edition 1998. Copyright Schlumberger 1991.
There are a whole bunch of references at the end of Chapter 5, but I could not find out from which reference this equation was taken.

2)IP is using the apparent hydrocarbon density, instead of the actual hydrocarbon density, to calculate porosity from the density log, because the actual hydrocarbon density at downhole reservoir conditions is not known and has to be estimated using the density log reading in the invaded zone. Hydrocarbon density at downhole conditions will probably be different from the actual hydrocarbon density measured at surface. The density log is responding to the fluids inside the invaded zone, under downhole reservoir conditions.

3)In WBM environment, the hydrocarbon in the invaded zone is flushed by the mud filtrate (essentially water). Therefore, the Sxo will be higher than the Sw (for a hydrocarbon bearing interval). However, there will still be some residual hydrocarbon left in the invaded zone, meaning Sxo cannot be 100%. This needs to impose a limit on the Sxo computed by the software. Most log analysis softwares have ways to limit the Sxo to a certain value. Some allow the analyst to choose his own Sxo limit. I could not find any reference on why IP software uses Sxo < Sw^Sxo limit.

Author:  roambold [ Wed Nov 07, 2012 4:09 pm ]
Post subject:  Re: Porosity and Sw equations in IP

ok thanks a bunch kokokyi, it's quite a help :)
if i may, i want to ask one more favor
do yo know where to get table of resistivity log response of various mineral such as kaolinite, smectite, etc?

Author:  kokokyi [ Thu Nov 08, 2012 7:16 am ]
Post subject:  Re: Porosity and Sw equations in IP

I don't think there is a table of resistivity log response to various minerals. The resistivity log responds to the formation porosity and conductive fluid (formation water) inside it. Therefore, the usual reservoir rocks like sandstone (predominantly quatrz), limestaone (predominantly calcite) and dolomite will have varying resistivity values depending on its porosity and saturation of formation water inside it. Other minernals like kaolinite and smectite, which are clay minerals will have lower resistivity due to the conductive clay bound water. Some other conductive minerals or rocks are those which contain conductive minerals like iron inside them. There are log response charts from companies like Baker Atlas (Baker Hughes) and Crocker Data Processing (Petrolog software), showing typical log responses for various formations and rocks. However, they do not give you actual values or ranges of values for the resistivity log. You can Google and download them from the web.

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