Calculating water saturation -- Ratio method
Sometimes all you have are resistivity logs and you don't have a good source for formation porosity. This program uses an empirical equation to derive Sw from resistivity data:
Sw = ((Rxo/Rt)/(Rmf/Rw))^(5/8)
where:
Rxo=flushed zone resistivity, from a microresistivity tool
Rt=deep resistivity, from an induction or laterolog
Rmf=mud filtrate resistivity, measured or est from Rm
Rw=formation water resistivity
You have the option of entering a measured Rmf value, or of letting
the program estimate Rmf for you. Try it both ways, if you have the data,
but keep in mind that field-measured Rmf values are often inaccurate.
Porosities are back-calculated from water saturation using the Archie, Humble, and an optional formation factor if you specify both 'a' and 'm.'
This relationship ties the water saturation in the formation to that in the flushed zone, assuming moderate invasion and average residual oil saturation. It can indicate oil mobility:
Flushed zone saturation, Sxo=Sw^(1/5)
--If the ratio Sw/Sxo = 1, then no hydrocarbons were
moved by invasion, whether or not the formation contains
hydrocarbons.
--If the ratio Sw/Sxo <= 0.7, then the drilling process has apparently moved hydrocarbons out of the flushed zone.
DATA LOGGING
Do you want to save your calculations? The input box at the very bottom of the screen records all the inputs and outputs for each calculation run. To save this information, select all the text in the box and copy it, then open a spreadsheet and paste it in as comma-separated values. Each data type will land in its own column, and each calculation run, or depth, will occupy a row. Format the spreadsheet to separate rows into different geologic formations, and you're done. Isn't that easier than writing everything down?
Don't have a spreadsheet handy? If you are working on a phone or a tablet, you can still copy the text and paste it into a note or an email.
The Recording box will reset if you press the "Help" or "Reset" buttons, or if you navigate to a different page.