ABUJA, Sept 22 (Reuters) - The Nigerian government expects the country to produce 1.88 million barrels per day of crude oil in 2022 and will use a benchmark oil price of $57 per barrel for its budget planning, according to a document approved by the Senate on Wednesday. The Medium-Term Expenditure Framework (MTEF), a crucial part of the annual budget preparation cycle, also showed projected GDP growth of 4.2% and inflation of 13% in 2022. (Reporting by Camillus Eboh, writing by Estelle Shirbon; Editing by Kevin Liffey)