There are engines ( Nat Gas & Diesel ), generators, compressors, pumps, cranes, electric motors, vessels, meters (oil, water & gas), piping, burners, tanks, electronics & iron on a production platform. As far as the engines, generators, compressors, pumps, cranes, vessels, burners & tanks go that would be mechanical engineering. At least here in the states we call it mechanical engineering. Maybe in the UK or Canada they call it Machinery Engineering, Eh?