Quotes from the news wire:
Weak industrial data in China and Japan is causing even more demand concerns [for oil], oil may also be seeing some pressure from the fact that the Iraqi army has taken back the city of Ramadi from ISIS forces. ..the crude oil market is also seeing pressure due to talk of Iranian oil coming back on line. Oil Minister Bijan Namdar Zangenesh is claiming that they plan to export 500,000 barrels a day within a week after sanctions are removed.
On the face of it, this executive order should have been bullish if anything to oil, if it impedes oil moving of Venezuela in any way, but Venezuela is such a basket case that people tend to worry about so many other things concerning that country, and that's possibly what caused the market to go down.