Playing around with Shetlander's 2nd photograph in Photoshop uncovers a rather large soot / oil mark extending from the left hand engine to the tail rotor.
The engines do burn a lot of oil normally- the air oil separator is not very efficient so oil mist tends to find its way into the exhaust area, where it is cooked sufficiently to make it a black mess - but not sufficiently to burn it off.
The latest engine mod state has an improved separator and so a cleaner exhaust, but this is by no means implemented in the whole N Sea fleet.