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Dear All,
in some Petrophysics books, there are equations thus are just written as it, without telling where does the equation come from or the mathematical approach to get it.

any body here know where the equations like porosity, shale volume, water saturation, etc. are obtained? or maybe do you mind to share with me any books (soft file) that explain about this?

i really need your help, because a couple weeks later i will do a thesis trial session for my undergraduate thesis.

you can answer it here or via PM to me.
thank you all.

If you have access to the search site One Petro which can be accessed from the SPE or SPWLA websites you can find what you are looking for. In particular search for papers by G.E. Archie and you can find the Archie Water Saturation Equation. There are also public access downloads available from Schlumberger's website that will give you a lot of information such as " Log Interpretations Principles and Applications". When I was in openhole engineering training we were taken through the steps to derive the equations but I don't think that is taught any longer as most field engineers are instructed to stay away from interpretation due to liability these days.
Good Luck.