2 million barrels (if tanker was full) is 2% of total world oil demand per day.
That will be quite an explosion!
What about the fertilizer plant in SC on fire. Inside, 600 TONS of ammonium nitrate.
That much liquid didnt explode. Only vapors burn/explode.
I can see a fire getting quickly out of control after a mechanical failure but I dont think the ship exploded. The hull was still intact and it was still displacing water but not for long when they start pumping it full of sea water.