Just finished the first three books in the Emergence series by John Birmingham. (Resistance and Ascendance are the next two, and presumably there are more to come).
Birmingham has a real way with words, an eye for the absurd, and a talent for imagining a realistic outcome for an impossible event; and the Dave Hooper novels, of which this is the first, are no exception.
Dave Hooper, safety officer for a deep water, deep drilling oil platform in the Gulf of Mexico is called back from leave due to a problem on the rig - which turns out to be an attack by demons from the underworld who have been imprisoned since Palaeolithic times. Neither the humans nor the demons are prepared for the encounter, nor its consequences.
8/10 - well worth a read.