>I have no idea what the profit margins are but at 10 %...
Profit margins do not give the correct picture, which is rather complex, and involves royalties, multiple layers of taxation, "production sharing agreements, etc.
A good way to look at this is to take production costs (around US$ 20-25 per barrel in Nigeria) from the oil price, giving a margin of say $30/bbl. This should be applied to the entire production, not just the exports, since the country would need to import the oil for domestic needs if it did not produce it. Furthermore, a part of the production costs is internal spending, but there are also profits repatriated, so to keep things simple let's make the rough assumption that these two are roughly equal... this gives the benefits from oil production (at 2.7 mmbbl/d) at about US$80 million per day, or about $30 billion per year.