ALGIERS (Reuters) - Algeria plans to drill its first offshore oil well by the end of 2015, having boosted annual refining output to 31 million tonnes at the end of last year, Energy Minister Youcef Yousfi said on Monday. Output was 25 million tonnes when the country launched improvement work at its main refineries in 2012. With that work finished, output rose by six million tonnes in 2014, Yousfi told a forum organized by state radio. He said five new refineries would be built to double capacity by 2020, reiterating previous comments. Algeria exports several refined oil products but also imports petrol and diesel due to growing domestic demand. "We are still developing our capacity to meet citizens' needs," Yousfi said. Zoubida Benmoufouk, head of the refining department at state energy firm Sonatrach, last week said both diesel and petrol output would double to 9 million tonnes and 8 million respectively in 2018. Algeria has been seeking to boost energy output to improve earnings from exports on which the government relies heavily to implement social programmes and fund economic development plans. As part of that goal, Sonatrach aims to drill its first offshore well before the end of this year. "We have finished seismic studies," Yousfi said, adding that new onshore oil and gas fields would also start production in the next few years. Sonatrach has said it will open a new round of bidding for investment in the third quarter of 2015 and promised to improve terms for companies. In the last round in September, just four out of 31 blocks on offer were awarded.