Johnny Depp isn’t famous for doing a lot of press for the films he appears in. But the mercurial movie star has promised the producers of “Black Mass” that he’ll play ball this time. Depp (above left), who portrays notorious South Boston mobster Whitey Bulger in the movie, is said to be excited about the film and plans to promote it. (“Black Mass,” based on the book of the same name by former Globe reporters Dick Lehr and Gerry O’Neill, premieres this week at the Venice Film Festival and opens in the United States Sept. 18.) “[Depp] said this is his favorite movie he’s ever worked on,” producer Tyler Thompson of Cross Creek Pictures told The Hollywood Reporter. Asked if Depp’s recent string of flops is cause for concern, Thompson and his producing partner Brian Oliver said no. “It’s a return to form for him, and it’s the type of role you haven’t seen him in in a long time. He and [director] Scott Cooper had amazing chemistry,” said Thompson. Added Oliver: “He’s playing a real-life scary sociopath, and he nailed it. . . . Everyone wants to really see Johnny Depp do this role.”Names can be reached at email@example.com. Follow Mark Shanahan on Twitter @MarkAShanahan.