More importantly, so does supply logistics. When Hitler's army ran across the Southern Plains towards Moscow they captured the oil fields along the way, but that oil could not be used for fuel and the advance had to be stopped for lack of go-juice.
Knock a few refineries off-line, hit a few fuel depots, cripple a few pipe line pumping stations, rpg a few fuel trucks and you've altered the ability of an army to move and supply itself.
Russian oil is making too much money for those who are brokering it for Russia to ever run low on fuel.
For Ukraine to shut down fuel supplies it would have to make war against the ships bringing oil into Crimea.
Ukraine doesn't have a navy which can challenge Russia. NATO does, of course. But that's WWIII.
