Queiroz Galvao Exploracao e Producao 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 to half that by 2020, QGEP said in a statement.

The 13.5 billion cubic meter P2 natural gas reserve estimate is equal to 85.2 million barrels of oil equivalent (BOE).

The Manati field is 45 percent owned by QGEP. Brazil's state-run oil company Petroleo Brasileiro SA owns 35 percent and is the field operator, Brazilian-Canadian oil company Brasoil owns 10 percent and Chile's Geopark owns 10 percent.

Because of maintenance and other factors, actual production in 2015 will average about 5.5 million cubic meters a day, QGEP said.

The certification, which is dated Dec. 31, 2014, came up with the following production potential curve through 2026:

Year Production Potential Mln Cubic Meters/Day

2015 6.0

2016 6.0

2017 5.4

2018 4.4

2019 3.6

2020 3.0

2021 2.4

2022 2.0

2023 1.6

2024 1.3

2025 1.1

2026 0.9

Source: QGEP