ConocoPhillips’ announcement Feb 21, 2017 that erased 1.15 billion oil-sands barrels, plunging its reserves to a 15-year low.
Source: https://www.bloomberg.com/news/articles/2017-02-23/oil-sands-batter-major-explorers-reserves-as-rout-sinks-value?cmpid=yhoo.headline
Sky is falling.
Shale oil for the win. Shutdown osbu
SEC rules for "Proved Reserves" are very specific and reflect both the quantifiability of the subsurface characterization of the hydrocarbon volumes, the economics of extraction (must have positive cash flow, market, etc), and commitment to develop (e.g. is it budgeted). Its very unlikely that there has been a negative revision in the volume characterization. It's much more likely that lower market commodity prices or higher extraction costs (e.g. dilluant or steam generation for heavy oil fields) have made the projects fall below positive economic thresholds. If commodity prices improve during the year, these projects may be added back in.
It may be raining pretty hard on COP's parade right now, but it doesn't necessarily mean the sky is falling in the long term.