Anway, you're missing the SHIPDUDE point.
It's as logical to turn your oil rigs into armored concrete battle islands as it is to build a giant slab-sided nuclear battlecruiser to protect them!
Iranian oil rigs were only involved in military action because they were in the chokepoint of Hormuz.
Look at the map of Brazil - there may be a difference but I'm terrible at geography!
People aren't going to cross the ocean and invade oil rigs D-day style! If the oil crisis is so bad that people are taking over rigs, they'll look like this:
Honestly trucks would be a better defense than an inherently offensive "BCGN."