Darius Rafieyan

Daniel Schreiber, the CEO of a small insurance company called Lemonade, was surprised this summer when he received a strongly worded letter from lawyers at one of the world's biggest telecom companies.

"At some level I knew it wasn't a joke, but it sure sounded like one," he said.

The letter was from Deutsche Telekom, the parent company of T-Mobile, and it accused Lemonade of stealing its trademark.

The shale oil boom that catapulted the U.S. into being the world's largest oil producer may be going bust. Oil prices are dropping amid weakening demand, bankruptcies and layoffs are up, and drilling is down — signs of a crisis that's quietly roiling the industry.

Some of the most successful companies in the oil business are household names — think Exxon Mobil or Chevron. But the boom in shale drilling has been driven by smaller, independent operators. These companies have pushed the limits of drilling technology and taken big risks on unproven oil fields.