Some are small (like the Co-Op refinery in Saskatchewan) and some are massive (like all those Gulf Of America ones that Keystone XL was supposed to connect to) so in terms of capacity it's a very small fraction.

Also: literally no refinery operates at 100% capacity. Most run at about 60% afaik. The XL pipeline's flow wouldn't have required a single new refinery, they'd easily absorb the (iirc) 600,000 more barrels a day from Alberta's tarsands.

So those 800 were probably doing the work of 650, and losing 2 wouldn't change a thing. Except for that country or company, obviously! I mean in terms of global supply.