How far do oil prices have to fall to throttle the US shale boom?

Vox tries to explain How far do oil prices have to fall to throttle the US shale boom?

"But in 2014, oil prices have been crashing, with the price for West Texas Intermediate crude falling from $100 per barrel in July to below $70 in early December. That's partly because there's so much new oil coming out of the US and Canada, and partly because demand in Europe and Asia is weakening."

"Yes, most everyone agrees that falling prices will constrain US and Canadian oil production to some extent. The International Energy Agency (IEA) has forecast that US shale production will grow more slowly if current prices persist (though the agency still expects output to rise another 955,000 barrels per day in 2015). But estimates of the exact impact can vary widely. Saudi Arabia is predicting — and hoping — that the US boom will largely fizzle out at these prices. Other onlookers think drillers will remain surprisingly resilient."

It's hard to estimate breakeven prices.

"One reason for the wide range is that it's difficult to generalize about even an single region like the Bakken, where more than 100 companies are operating. Each of these operators can have wildly differing costs. They're using different methods to drill with varying levels of success. Some companies are operating in marginal geological formations. Some firms have hedged against falling prices. Others have taken on a lot of debt. This means different operators have different tolerances for lower prices. There are other factors to consider, too. Many companies have already sunk lots of money into acquiring land and permits and may decide to continue drilling anyway, even if prices drop."