U.S. energy producers have cut so deeply into a once-large reserve of oil wells waiting to be turned on they soon may have to resume drilling to keep production from sagging, executives and analysts said. This would mean an increase in spending which could unsettle investors who have benefited from shale companies’ recent prioritization of shareholder returns over ramping up production. Companies, including Diamondback (FANG.O) , Pioneer Natural Resource (PXD.N) and Devon Energy (DVN.N) , for example, have redirected rising cash returns to dividend growth, variable distributions, buybacks, and further debt reduction. Investors, frustrated with years of low returns from the sector, have punished companies that have looked to grow production at the expense of shareholder return and rewarded those that […]