Transocean Ltd. said it expects to book an after-tax charge of between $300 million and $325 million as it moves to dispose of four rigs. The cuts come as plunging oil prices have wreaked havoc in the industry. The U.S. oil-rig count fell to 866 last week, the 14th straight week of declines, according to Baker Hughes Inc. The rig count hadn’t fallen below 1,000 since June 2011. Last month, the Switzerland-based company, which boasts the world’s largest fleet of offshore drilling rigs, logged a $992 million charge to correct the value of its contract drilling business. Transocean, whose chief executive abruptly resigned last month , has seen its corporate credit slashed to junk by one of the three credit-rating firms with the other two indicating possible downgrades. The company had spent billions of dollars to expand its fleet just before oil prices collapsed. It has since tried to […]