As reported by Simon on AvHerald:
A Norwegian Air Shuttle Boeing 787-800, registration LN-LNB performing flight DY-7064 from Oakland,CA (USA) to Oslo (Norway), was enroute at FL370 about 80nm west of Calgary,AB (Canada) when the crew detected an engine (Trent 1000) oil leak and decided to return to Oakland. The aircraft descended to FL360 for the return. About 20 minutes later the crew shut the affected engine down, drifted the aircraft down to FL220 and continued to Oakland for a safe landing on runway 30 about 2 hours after turning around. The airline reported the indications were false.
Return to origin with both engines running a completely understandable decision, but will be interesting to hear their version of the story on why was it considered a good idea to continue after the shut-down
(over high terrain), by-passing several suitable closer alternates (YYC, YVR and SEA all spring to mind).