Sylva handed his resignation letter last week to President Buhari, who doubles as petroleum minister, and stopped coming to the office, said two sources who did not want to be identified.
They said he would be seeking the ruling All Progressives Congress ticket to run for Bayelsa governor in party primaries scheduled to take place on April 14.
Sylva served as governor of Bayelsa for one full term between 2008 and 2012. At the time, he was a member of the People's Democratic Party, which was then in power at the federal level but is now in opposition.
Appointed junior oil minister in August 2019, Sylva oversaw major reforms in the oil sector, including the passing of legislation that overhauled the sector's fiscal regime in a bid to spur investment.
During his time as minister, Nigeria's oil output fell to its lowest in decades due to crude theft and pipeline vandalism. Angola overtook Nigeria as Africa's biggest oil producer and exporter for a few months last year.
Sylva could not be reached for comment and the petroleum ministry declined to comment.
