(Reuters) – Chesapeake Energy (CHK.O) said on Thursday it would buy smaller rival Southwestern Energy (SWN.N) in an all-stock transaction valued at $7.4 billion, a deal that would enable the second-largest U.S. natural gas producer to take the top spot. The move extends a recent spate of multi-billion deals in the U.S. energy sector including Exxon Mobil’s (XOM.N) $60-billion Pioneer Natural … Read more