It takes a lot of research to understand the global supply/demand mechanics as well as which firms will succeed/fail under what circumstances. Here is my two cents.
OPEC production is about 40% of global supply. Members like Saudi Arabia and Kuwait benefit from "old school" production that are mostly simple vertical wells tapping into gigantic fairly homogenous reservoirs. These are what people refer to as wells with $10-15/bbl break-even economics. They could over time adjust their budgets (easier said than done) and theoretically adjust to these prices.
Prices could feasibly stay in the $20-40 range if this was the bulk of existing and future production. Keep in mind even ideal conventional wells still decline 5-15% annually but global demand grows 2-3% annually on average via population growth in developing nations. The majority of incremental production over recent years, however, has come from unconventional sources in North America (Canada and the US) and off shore. Heavy oil production, say such as in Canada (topic of my thesis), can accomplished through surface extraction or steam applications such as Steam Assisted Gravity Drainage (SAGD).
Global demand is ~90mm bbls/day with my estimate placing 12.5-25mm bbls/day derived from unconventional plays and enhanced oil recovery (EOR) techniques on mature fields that cannot produce economically under standard reservoir conditions (need some kind of stimulation like refined water flooding or carbon dioxide injection as is common in the prolific Permian basis of west Texas). Very few of these applications are economical at initiation with oil and gas prices where they are now. Operating costs, even deep off shore, may permit existing wells to produce but few firms are initiating new projects like in the past.
The take away from all this is that "cheap" oil cannot be produced at 90mm bbls/day; I doubt much more than 75mm bbls/day is economically viable on a new project basis at prices below $55/bbl Brent. Oil cannot stay this low if demand remains steady unless some technological development revolutionizes oil production at 10 times the extent lateral drilling and hydraulic fracturing have (unlikely). It may, however, take years to work through the inventory glut and excess production that wells already in place will continue to add to the market because the initial drilling costs are sunk and any revenue they can get is better than nothing to keep making debt payments (be it a nation or firm). That doesn't mean it'll return to $100/bbl but it does mean it will be somewhere between where we are now and there.