Nigeria had the highest rate of deforestation in the world in 2005. Apparently a lot of it is really people cutting down wood for fuel and desertification stepping in, so essentially its woods replaced by desert.
As well, govt. doesn't have much regulations on stopping people cutting wood.
I imagine people are burning it to make charcoal they can sell.
it seems a classic self destruction.. people used to know how to live in nature, now you want to live in modern economy.. but it's not there so you destroy nature for a few coins until there's nothing to destroy or live in.
People have to eat, and it's an available way to make money. In other African countries (at least in the East which I'm more familiar with) the government has been trying to combat the charcoal trade. The government in Nigeria has less of a presence though, so it's probably been difficult and not a top priority.
This is all speculation though.
Tribal way of life found ways to eat too. It's the impedance mismatch of global capitalism and secondary countries that caused a partial harmful migration.
Oil.
Nothing I've read on the topic mentions oil extraction as a cause for deforestation in Nigeria, including the Wikipedia link elsewhere in these comments.