According to the document, loadings will fall to 1.81 million barrels per day (bpd) in the month, leaving exports at an 11-month low.
The last time exports were very low was October 2011 when the country was due to load 1.80 million bpd.
The provisional programme compiled by Reuters showed that Nigeria will ship a total of about 55 million barrels of oil in September compared to around 68 million in August.
Lower volumes are due to fewer cargoes of the benchmark Qua Iboe grade which typically exports between 11-12 cargoes but will load just 10 in September.
The Forcados grade will load six cargoes in September compared with eight in August, the programme showed.
Traders said the lower exports were likely to support Nigerian differentials which fell to near two-year lows earlier this month.
Nigeria, Africa;s oil and gas power house, has seen exports at about two million barrels per day so far this year, helped by the Usan grade, which began production in February.