Southwestern Energy to buy $5.4 bln in assets from Chesapeake

* Southwestern to buy assets in Marcellus and Utica shale fields * Southwestern shares at 2-yr low indicating co is overpaying * Southwestern adds 435 horizontal wells through deal (Adds Breakingviews column link, updates share movement) Oct 16 (Reuters) – Southwestern Energy Co said it would buy some oil and gas assets in the Marcellus and Utica shale fields in West Virginia and Pennsylvania …