American shale companies are starting to tap the brakes on drilling. U.S. oil output remains robust and may still surpass the record annual average of 9.6 million barrels a day, set in 1970. But companies, confronting technological, operational and financial obstacles, are starting to ease up on drilling. The pace of innovation that allowed shale drillers to maintain production even as prices fell appears to be slowing, experts say. The cost of labor and services, meanwhile, is rising in the most popular oil fields, driving up drilling expenses. And companies are facing a backlash from investors , who have grown weary of drillers focusing on growth over profit and insist they live within their means. “There’s always a lot of exuberance,” said Robert Clarke, an analyst with energy consulting firm Wood Mackenzie. “But then something happens that kind of puts the brakes on.” Future oil production is notoriously difficult […]