Baku and SU supply grid

[Balou]

Is it necessary that Baku is linked to the rest of the SU thru intact rail lines? Or is the SU oil & fuel pool feeded no matter whether Baku is isolated or not ?
In fact, there is a single rail line running close to Grozny and along the coast of the Caspian Sea, which seems to be the only way out of Baku. Because if there is something like a “transportation issue”, the only other way – namely by ship - obviously is not an option (“Caspian Sea Zone: shipping available 0”)

[Balou]

Help still needed: Has Baku (and all its oil/fuel) to be linked to the supply grid ? Because the Axis could cut its only rail line far up northwest.