Shale is in its infancy in the US. There is a tremendous amount of shale oil and gas in North America. No one knows how much.
The US also has a tremendous amount of natural gas.
Undoubtedly, when the need for more supply arises, a lot of shale oil will be found in other parts of the world too.
Solar, wind, hydro, tidal, and geothermal will continue to benefit from innovation and gain energy market share and oil’s importance as an energy source will decline.
Coal went from supplying the majority of electricity in the US to small proportion fairly quickly. Although coal is the cheapest fuel before considering air emission control costs, natural gas is the cheaper overall.
I think offshore oil will have another two or three boom and bust cycles over the next 20 years, but it’s importance as a cost effective energy source is in permanent decline.