Goldman Sachs estimates that nearly $1 trillion of new projects could be at risk if oil prices remain around $60.
The reality is actually much worse. In general, capex tends to track oil company revenues. Current prices reflect a revenue drop of 40%, and all other things equal, we should expect a 40% drop in capex, which, including maintenance capex, is currently about $1 trillion per year. Thus, the foregone investment would total on the order of $300-400 bn per year, assuming a constant capex / revenue ratio.
Do the math, and that's in excess of $2 trillion through 2020.
Of course, the oil supply will implode in such an event, so such cuts won't come to pass. But the numbers being bandied about are suggestive of just how unsustainable current price levels are.