Ukraine is shutting off transshipment of Russian oil and gas products through their huge pipeline network. The end of this year is scheduled to be a big shutoff of Russian pipeline natural gas to Austria and Hungary. But some more oil flow was just shut off in recent weeks.
In the event of peace and security, Ukraine could refill those pipelines with Ukrainian oil and gas - especially natural gas, as they sit on about 2 Trillion cubic meters of proven reserve - approaching the size or Norway’s. That energy supply to Europe should be preserved Strategically, in any peace agreement - and that means retaking Crimea.
OilPrice.com reports:
Russian Oil Supply to Hungary Halted Due to Ukraine Sanctions on Lukoil (By Charles Kennedy - Jul 17, 2024)
“Despite the fact that EU pipeline crude imports from Russia are not banned by the embargo, Russia is not delivering crude oil to Hungary at present after Ukraine imposed stricter sanctions on Russian oil giant Lukoil, effectively banning it from using Ukraine as a transit for oil exports.
Lukoil was supplying Hungary with crude via the southern leg of the Druzhba oil pipeline which crosses Ukraine. With the toughened sanctions Kyiv imposed on Lukoil in June, Russian oil does not reach Hungary now.”
IMHO, this is the "real" reason that putin invaded Ukraine.
I believe a lot of the natural gas is located in eastern Ukraine.