UPDATE 1-QGEP says Brazil Manati field holds 13.5 bln cubic meters of gas
(Adds additional certification data, production-potential table) RIO DE JANEIRO, Aug 12 (Reuters) - Queiroz Galvão Exploração e Produção SA said on Wednesday that the Manati offshore oil field in Brazil holds 13.5 billion cubic meters (477 billion cubic feet) of proven and probable, or "P2", natural gas reserves. The reserves, certified by Houston-based Gaffney, Cline Associates, will allow production potential of 6 million cubic meters of natural gas a day in 2015 and 2016, falling t