Re: Interpretation Module in Interactive Petrophysics
You can use the NPHI
recorded in limestone units as it is, without converting to sandstone units. IP uses the NPHI log to do neutron/density crossplot as well as compute the crossplot porosity.
However, you have the option to choose which porosity you want to use in your interpretation. In the porosity module, there is an option to choose the method of porosity determination that you wish to use. You even have the option of using an external porosity, like porosity from other sources e.g. thermal decay neutron log, core porosity etc.
You can use the NPHIC, if you have already corrected for borehole and environmental corrections. I believe the IP software has an option to choose the neutron/density crossplot either with or without environmental corrections. I am not sure about this, since I am using an old version of IP software (for quicklook interpretation for operational purposes), as our corporate software is now Geolog.
To avoid overestimating the clay volume, it is usually advisable to choose the minimum clay volume from different methods of computation. I would advise you to use the clay volume from neutron and density logs, unless you are in a gas reservoir. If you have gas, you need to make gas correction on both density and neutron logs before computing the Vclay. The clay volume from Gamma Ray log tends to be more pessimistic, especially if you use the linear equation.
The IP results you sent me are statistical analyses of the different methods of Vclay computation. They are giving the results in terms of Net Sand, Minimum Vclay, Maximum Vclay, Mean Value, Median, etc.
I suggest you read the help file in IP for the explanations of these terms.
Here again, IP gives you an option to choose the Vclay that you wish to use in your interpretation, either Vcl(average) from all methods or from a particular method, like from GR
or Neutron/Density, etc.
Ko Ko Kyi