The real problem with oil prices is that demand is weak and hasn't grown as fast as supply. Pretty simple and don't really need anyone to tell us that.
We have limited oil reserves and they would have eventually run out with past trends (however far in the future you believe that to be).
What's happening now is that the high price caused everyone to produce loads of it to cash in on that price, supply soared. Now governments around the world are screwed as they have budgets to run and need to sell more of it to make up for budget shortfalls. Budgets which were made on higher oil prices.
Shale oil prevents OPEC from taking any action to restore revenues instead through price by squeezing the market. Russia won't necessarily coordinate action with OPEC either as they also have serious budget problems. The low price should squeeze the market partially (as in the above post) but governments do have very low lift costs.
https://en.wikipedia.org/wiki/List_of_countries_by_oil_production
The glut will reduce investment in alternative fuels, but technology will advance even without significant investment. It may make fossil fuel demand fall even further because of alternatives or more efficient use of it. In which case, if you hold massive reserves, fill your boots while it lasts.