User blog comment:Kajune/Does Dean require demon blood for Michael to possess him?/@comment-27593090-20151230201510/@comment-27460953-20151230222555

Well it was explained on the archangel page I think, that Raphael chose not to repair his vessel because he didn't care, but Michael did.

Also, Lucifer noticed Sam drank the demon blood and didn't question why, so it's pretty obvious he knew what it was for (to hold him).