There's no riddle. Some specific civil infrastructure is protected by LOAC, basic survival stuff like water supply, hospitals.

Economic infrastructure is not inherently protected. It is commonly (especially by the US) not targeted initially, better to go after military assets first and see if that encourages them to negotiate. Next up would be mil industrial facilities, then maybe civil economic infrastructure.

But in this case oil economic infrastructure could go to the top of the list at any time. Probably better to capture/blockade rather than destroy, for several reasons.