Investors sent a surprising message to U.S. shale producers as crude fell almost 20 percent in August: keep calm and drill on. While most oil stocks have fallen sharply this month, the least affected by the slump share one thing in common: they don’t plan to slow down, even though a glut of supply is forcing prices down. Cimarex Energy Co. jumped more than 8 percent in two days after executives said Aug. 5 that their rig count would more than double next year. Pioneer Natural Resources Co. rallied for three days when it disclosed a similar increase. Shareholders continue to favor growth over returns, helping explain why companies that form the engine of U.S. oil — the frackers behind the boom — aren’t slowing down enough to rebalance the market. U.S. production has remained high, frustrating OPEC’s strategy of maintaining market share and enlarging a glut that has […]