Calculating Water Saturation

[Yengineer]

There are some wells with wich I am dealing lately and the formation water that they have is very fresh (about 2000 p/million). The net pay is sandstone and so far we are seing very little to no water in production. I want to know what is the actual Sw in that formation but the geologist said that it is impossible to calculate Sw from the logs (at least not accurately) with such a fresh water.
Is he right? Is any way to get an accurate Sw from the logs?

Thanks

[geo81]

you can not calculate the Sw from the log. You need to know the proprieties of your rock. How much is the mineral mix, the clay or the quartz in it. Then after regisetring p and s waves velocity you can get the water saturation and the total porosity of your sandstone from calculation densities and bulk modulus (from formula). I am a geoscientist, but a geologist may not have that knowledge because it is the application of petrophysics

[ARaj]

You actually can calculate Sw from logs. These logs include Gamma Ray* SP and resistivity logs. There is the Silva-Bassiouni method if the SP log is available or the Archie/Simandoux methods.