By Curtis Williams HOUSTON (Reuters) – Portugal oil and gas firm Galp has asked U.S. regulators to allow it to join BP and Shell’s formal complaints against U.S. liquefied natural gas (LNG) exporter Venture Global LNG, a filing showed on Tuesday. Shell and BP have asked the Federal Energy Regulatory Commission (FERC) to require Venture Global to disclose plant commissioning data to determine why commercial operation at Venture Global’s Calcasieu Pass terminal is stalled. Galp Trading, a unit of Galp Energia, said “no other party can adequately represent or protect its interests,” in the disput…