Some estimates say that 90% of earth's oil is in shale rock.
Maybe, but we can't use it without killing the planet. We've already burned too much oil.
Petroleum has many uses that don't involve burning it as fuel.
It's the extraction process that's the problem with shale, moreso than the burning of the gas.
According to this Wikipedia page[0], 81% of every barrel of oil is used for fuel. Although dropping to 1/5th size is not the same as going away, it won't be a very enjoyable ride. The picture might get even worse for petroleum as a chemical precursor once the economies of scale supported by fuel use go away.
Yes and no. Yes there are a lot of uses, but they amount to a small amount of our current oil use. If I read https://www.eia.gov/tools/faqs/faq.php?id=41&t=6 right 75% of crude oil is burned directly as fuel.
edit: note that my numbers are different than the wiki below. I suspect that is because of a difference in what counts for what...
Shale oil and oil shale are different things. You're talking about oil shale, which the US has a ton of, but it is not currently economically viable, but could be in the future. Shale oil is different and is recovered by hydraulic fracturing. It can be economically viable depending on the quality of the deposit.