What is critical water saturation?

Answer 1

critical water saturation (sometimes called Irreducible water saturation) defines the maximum water saturation that a formation with a given permeability and porosity can retain without producing water. This water, although present, is held in place by capillary forces and will not flow. Critical water saturations are usually determined through special core analysis.

The critical water value should be compared to the reservoir's in-place water saturation calculated from downhole electric logs. If the in-place water saturation does not exceed the critical value, then the well will produce only hydrocarbons. These saturation comparisons are particularly important in low permeability reservoirs, where critical water saturation can exceed 60% while still producing only hydrocarbons.