PVT STB vs bbl: 2005 #41 (similar)

Stock Tank Barrels STB represent fluid at standard conditions with vapor released. The oil "shrinks" when gas leaves. Hence the term "shrinkage factor". Shrinkage factors are often used when the fluid is not fully at STB. Like at a separator. Units are typically STB/bbl.

So if given "oil shrinkage at the separator", 0.9 STB/sep bbl could be a typical number. Considering "total" oil shrinkage (reservoir to surface) 0.7 STB/res bbl is more likely. Note this latter number is just the formation volume factor inverted; a typical value would be 1.4 res bbl/STB.

GOR (gas/oil) can be measured at any location, and thus use any units. For example, separator GOR could be sep SCF / sep bbl, while sales GOR could use SCF/STB.

Given a separator GOR of 700 sep SCF/STB (a typical value where I'm from) and also a separator shrinkage factor of 0.9 STB/sep bbl (typical), dimensional analysis gives 630 sep SCF/sep bbl. Again, these are common numbers/units I've seen.

Use your units to get whatever answer you need; just know what your units mean.