My first story was like that, but I changed it because I couldn’t make the story work rationally. Specifically I needed a metabolic ‘oxidizer’ to be present along with the food (oil/refined products) not just the ‘food’ supply. In other words, the bacteria needed an abundant source of oxygen or sulfur in order to metabolise the oil(s). I couldn’t create (for my story) (a) a plausible analog of the (anaerobic) lactic acid cycle (what gives you cramps when you are out of shape cardiovascular-wise) so the bacteria COULD derive food energy from oil in the absence of an ‘oxidizer’ or hydrogen acceptor, and (b) couldn’t work out the chemical-bond energy mechanism for a self-sustaining demon bug metabolism.
I wasn’t willing to go forward with “magic happens here” as the mechanism for the bacteria to consume stores of oil. BUT i did work it out where the oil stores could be contaminated with nasty demon bugs and cause problems! Since it didn’t work, really, I wrote the second story. I got a B/A cuz my creative writing teacher thought it was too technical to be entertaining. Tell that to Tom Clancy ;-)