The Rw we Get and the Rw we Want
The Rw we want is in the hydrocarbon zone. We are primarily concerned with evaluating the hydrocarbon zone, not the aquifer, but pore water is immovable above the transition zone, and cannot be bought to surface without bringing the rock with it. Recovery of the Rw we want is a further advantage of coring oil zones with oil base mud (Sec 10.1.3.2) and when Rw is determined from within the hydrocarbon zone it is often found to differ from the aquifer value, and vary. The assumption of using an aquifer Rw for a hydrocarbon zone is usually ignored. Well tests taken from transition zones may flow older waters than aquifer tests because transitional water is less likely to have been replaced than aquifer water. The aquifer may have been flushed since hydrocarbon emplacement and have salinities unrelated to the immovable water in the hydrocarbon zone.
The Rw we want is six out of the 12 possible Rw sources in the slide below and have been marked as @Swi.