Fracking an oil well takes millions of dollars, thousands of pounds of horsepower and dozens of people, but the whole operation can be brought to a halt by a humble grain of sand. Without sand—a crucial ingredient in the hydraulic fracturing process—the U.S. drilling boom would stop. That is why Halliburton Co. set up a new “war room” to track sand shipments by trains and trucks. More than a dozen employees hunker down daily on the first floor of Halliburton’s north Houston office in front of massive screens with real-time maps of railcars transporting sand, live camera feeds of sand mine loading and unloading operations, constantly updated weather conditions and data about sand levels in the company’s storage silos.