Wall Street Journal: A series of bankruptcies and closures is sweeping across the oil industry as dozens of hydraulic-fracturing companies, many of which are small, privately owned and just a few years old, are at risk from low oil prices, Alison Sider reports. Small start-ups began to challenge the oil-service giants in 2008, as American wildcatters embraced frackingthe process of blasting a slurry of water, sand and chemicals down a well to break apart densely packed rock, unlocking trapped oil and natural gas. There...