No oil was taken out of the global supply chain
The area ISIS took control of reduced oil production from ~300,000 BPD to ~50,000. The global oil supply was reduced by their actions.
If you want to control these oil prices world wide, start working to control the price of FOOD. Might be a whole different ball game.
What you're not accounting for above is the 100,000+ bpd ISIS was reportedly selling at the discounted price of $25 per barrel.
Of course we also have no idea how much more oil was being sold at $25 a barrel under the guise of ISIS or who was really doing the selling... only that shortly there after the price of oil worldwide plunged toward $25.
That looks very much like the proverbial straw that broke the camel's back for oil pricing.