Diesel will run on mostly anything if it’s running… including methane in the air intake, so you need to think quickly when presented with a generator that keeps running after cutting the fuel

Oil leaking around a turbocharger rotor seal also makes for good diesel fuel, if you define "good" as an exciting uncontrolled disassembly of the engine.

Crude oil from various wells has properties varying from ‘thick, stinky, corrosive goo’ to ‘explosive, barely liquid, bubbly mess’. Also, rigs need to be careful about ignition sources, as methane leaks can be a common emergency condition for some wells/crude.

It’s not the type of thing that using directly is economically feasible, even for emergency situations.