Guess there could be enough oil residual in the drilling riser to cause a sheen however I don't know why it would show up at this late date. Oil in that riser would not be effected by the corexit.
I'm wondering if all that oil at the bottom in those underwater canyons once effected by the Corexit is allowing the crude crud to reverse back to it's natural state allowing the release of a "sheen". I dunno, any Geo chemists or physicists here?
"Samples from a sheen in the area of the Deepwater Horizon rig, which exploded and sank more than two years ago, “correlates to oil that originated from BP’s Macondo well,” the Coast Guard said a statement Wednesday night.
The statement gave no indication of any active leak, but said: “The exact source of the sheen is uncertain at this time but could be residual oil associated with wreckage and/or debris left on the seabed from the Deepwater Horizon incident in 2010.”
The statement, from the office of the Federal On-Scene Coordinator, said the sheen – which was first reported to the National Response Center on Sept. 16 by BP and has varied in size, poses no risk to the shore and isn’t feasible to recover. It was approximately 50 miles off the coast of Louisiana.
The Coast Guard, in concert with BP and NOAA, has made assessments of the sheen by aircraft and boat since its discovery. Samples, the statement says, were taken by a Coast Guard unit on Sept. 26 and sent to the Coast Guard Marine Safety Lab in New London, Conn.
One or both of BP, which owned the well, and Transocean, which owned the Deepwater Horizon, may be sent a bill any costs associated with further assessments or operations related to the sheen, the statement said."