CANNES, France—Matt Damon said on Friday he had immersed himself for weeks in Oklahoma with oil rig workers for his role as a disoriented American who travels to France to help his jailed daughter, in a new film loosely inspired by the real-life Amanda Knox case. Damon said he spent time driving around and living with the so-called roughnecks in Oklahoma to grasp his character’s mindset in “Stillwater”. “Being invited into their homes, into a backyard barbecue, a guitar comes out and they start singing church songs. It’s a very specific place.. and very different to where I grew up,” Damon told a news conference after “Stillwater” held its red carpet premiere at the world’s biggest cinema festival. “It was really eye-opening for me.” In the film, which was screened out of the festival’s main competition, Damon plays oil worker Bill Baker, who travels to Marseille, France to visit his estranged …