American Society of Mechanical Engineers (ASME), Apr. 2014, by John Kosowatz.
https://www.asme.org/engineering-topics/articles/energy/hydro-fracturing-continues-to-impress

"Hydraulic fracturing continues to feed the boom in U.S. energy production, building on greater efficiencies in drilling that generate more productive wells. The boom has pushed energy prices lower, allowing the U.S. to better compete in energy-intensive markets such as steel and chemicals. As the industry evolves, researchers say even better tools and techniques are being developed to exploit shale oil and gas, and producers are relying on different skill sets to find and tap unconventional plays."