Rw Calibration (Per Sand Interval)

A different unit of calibration entirely: instead of pooling wells sharing a formation name, or fitting one number per well, Rw is fitted separately for every individual water-bearing sand interval that's thick enough to support it. A single sand interval is one genetically coherent deposit -- assuming uniform water chemistry within one is far more defensible than assuming it across a whole well (which can cross several unrelated sand bodies) or a whole named formation (which pools sand bodies from many wells that may never have been in contact). Every interval's fit still carries its own formation, so a real distribution of Rw builds up per formation from genuine evidence.