Not particularly devastating. Will average to about 1/25th of the Australian 2019-2020 bushfires.
So in terms of environmental damage from fires, I'm going to define a new unit: "A Black Summer." This is the environmental damage done from the Australian bushfire season that bridged 2019-2020, which we've titled "The black summer" locally.
"A black summer" put out 830 million tonnes of CO2, killed 445 people from smoke inhalation, hospitalised 4000 people, killed 3 billion animals, resulted in AUD 2.2 billion in insurance claims, hit productivity to the cost of about $20 billion.
There's also "1 Australian Black Summer" which is 1 black summer divided over the land area of Australia.
Lets first convert your disaster to Black Summers.
How much oil is out of the ground and in ships / tankers / refineries / storage tanks? The sum total of global strategic oil reserve, which is the best figure I could find for all the oil between extraction and consumption, is 4.1 billion barrels (650,000,000 cubic meters). If production stopped tomorrow, we have 41 days of oil on hand, 1.4 billion of which is government controlled reserves, the rest is stockpiled at refineries or on ships.
If all this is burnt, this handy EPA calculator allows me to calculate how much CO2 is emitted - it's 0.43 metric tonnes per barrel.
Multiply it out and you get 1.763 billion tonnes of CO2 emitted, which is basically 2 Black Summers. This will be stretched over the following days or even weeks as the fires slowly burn (much is underground with limited oxygen to combust through the rail gun holes), similar time frame as the reference Black Summer.
So the total environmental cost can be summarised as:
- 1.7 billion tonnes of CO2.
- ~1000 people dead from smoke inhalation.
- ~8000 people hospitalised.
- 6 billion animals die.
- 4.4 billion AUD (~\$3 billion USD) in insurance claims.
- $40 billion AUD (~\$30 billion USD) in smoke-based damaged to economic output.
That's.... not as bad as one might think, right?
This makes sense... All that oil was going to be burnt by cars and trucks and planes over the following few months anyway. It's been a little more compressed in time, and burning fossil fuels is bad for the environment anyway, but it wont be devastating on its own. No nuclear winter or anything.
You've got double the disaster of the Australian bushfire season diluted over the entire earths surface. Australia is about 2% of the worlds land area, so twice as bad in total, spread over 50 times the area. Average it out - I calculate this as approximately 1/25th as bad as the Australian Bushfires per unit of land.
Using SI prefix notation of milli being 1/1000th, your disaster from igniting all the worlds oil refineries and storage is 40 milli-Australian-Black-Summers.
Honestly that's the end of the interesting analyses. But you did ask about local affects too.
I don't think the local affects are really that notable environmentally, at least compared to the oil spills we're used to seeing in the media. Remember the oil wont spread as far because it'll be consumed in a fireball. The larger the oil spreads, the more surface area to interact with oxygen and the faster it burns.
Some petroleum by-products don't burn easily. I'd normally worry about them getting into the water table, but with millions of litres of liquids burning in a close area vaporising everything within 10s of meters, including normally non-flammable products, it's almost all going to be burnt. Many of these obscure products are "not flammable, but combustible", meaning if you try hard enough, they'll burn.
Surrounding the refineries will be a black scorch mark maybe 100m in the direction of the prevailing winds directly caused by the fire, but the secondary fires ignited by this firestorm will disguise any notable direct environmental damage outside the refinery perimeter. Expect a nearby bushfire and surrounding buildings to be torched.
Almost everything spilt will get burnt in that firestorm so you wont have the images of ducks covered in crude oil or the shiny black beaches 100s of km away - it'll just be a thick smoke cloud for a few days, then sooty black covering everything for a few weeks, and then washed away in the next rains leaving a scared blackened landscape, with nature starting to regrow within a year.
5 years later it'll look like a ruin with normal vegetation and wildlife around it. A trained eye may spot the fire history in the shape of the vegetation, but it'll look fine to you and I.