Within weeks, two low-profile legal disputes may determine whether an unprecedented wave of bankruptcies expected to hit U.S. oil and gas producers this year will imperil the $500 billion pipeline sector as well. In the two court fights, U.S. energy producers are trying to use Chapter 11 bankruptcy protection to shed long-term contracts with the pipeline operators that gather and process shale gas before it is delivered to consumer markets. The attempts to shed the contracts by Sabine Oil & Gas ( SOGCQ.PK ) and Quicksilver Resources ( KWKAQ.PK ) are viewed by executives and lawyers as a litmus test for deals worth billions of dollars annually for the so-called midstream sector. Pipeline operators have argued the contracts are secure, but restructuring experts say that if the two producers manage to tear up or renegotiate their deals, […]