The flow of oil and gas was turned off by automatic safety valves before the fire started.
The fire soon died out. There was no explosion. Statement from Mariner Energy.
Not sure of what caught fire, but there were 100 or so bbls. of stored oil on the production platform. Perhaps the welding equipment caught the oil on fire, but Mariner said just painting and cleanup were going on. There have been no further announcements.

No injuries. One worker caught without his suit, and seen in the water without it prompting the injury report, but the other workers held him up.
WWL News, CNN News,

All offshore platforms are constantly undergoing sanding, painting and repair, much like ships.

The NOLA superdome will be busy tonight as Tulane plays Southeastern Louisiana in their season opener.