It's very hard to keep all of your oil derricks intact during a game as a simple 3/4 pyro/siege cadre rush of the derrick will end its life way before you could save it. Unless off, you are playing a subversive faction.
Not only that, but Oil Derricts give 1k upon capturing them, then puny 20$ every few seconds. If you capture more than one, you either send a few soldiers to all of them, or concentrate your defenders at only a selected few, unless you wish to spend more on defending the derricts that what they give, Either way, the attackers have the edge. If you spread out your forces, they will be vanquished by a concentrated attack. If you concentrate your own forces, then your undefended derricts get destroyed easily. I believe this was the reason why in vanilla, one could build around tech buildings.