overstay in china for one year

I am a Nigerian, and overstayed in China for one year now. I want to surrender myself at Shanghai and pay the fine of CNY 10,000. Will I be detained after paying the fine? I consulted some people and they said i might be detained after paying the fine. Pls how true can this be? Whats your advice and also how long can i get the exit visa after paying my fine?