Fewer and fewer oil exploration and production companies are declaring bankruptcy. But more oilfield service companies are. So far this month, only one North American E&P firm filed for Chapter 11 protection, according to data released on Tuesday by the Dallas law firm Haynes & Boone. That’s down from two in September, three in August and four in July. But it’s been an especially tough few months for service companies. As crude prices began crashing in 2014, drillers started idling rigs. That led to fewer jobs for the companies that make their money helping producers pump oil and gas. Moreover,...