I believe that some of these objects are already in the game. I know there's an oil well and, of course, we have a variety of tanks.
Oil refinery, oil field and chemical factory objects would be useful for a number of maps, not just Ploesti. They'd be good for the central Caucasus around Grozny, various Middle Eastern maps, and various synthetic oil plants that German built during the war.
What is needed are:
Oil/gas pipelines - single and multiple pipes elevated and ground level: straight, 90 degree left, 90 degree right, S-bend right, S-bend left, 45 degree left, 45 degree right.
More varieties of oil/chemical tanks - including tall, skinny tanks.
Tank blast walls for various sizes of oil tanks (like in the bottom photo of Korpdorfer's post).
"Mule" type oil pump.
Wooden oil derrick - like in Korpdorfer's big picture.
Several different refractory column objects - like in the Korpdorfer's bottom picture.
Big fires and massive black clouds or smoke columns to simulate burning oilfields/refineries.