Been in Nigeria for several years and also been in Bonga field. Travel is out of Lagos to Bonga, next to International Airport, Bristows. Lagos airport has improved vastly, no one trying to tap you up for money at immigration, etc. Depending on arrival time, but can be large queues at immigration. Not the same security risk as it used to be. Meet and greet either in baggage hall or just outside. Take mixture of Dollar and Euro. Most hotels will change cash but not all will accept cards. Most hotels used are western chains.
Port Harcourt is a different thing all together. Everyone is on the take, Immigration, Customs etc. I have never handed over any cash to date, just smile and be polite gets you past. Dont leave airport until your escort is with you after clearing customs. Armed escorts every where. Totally different to Lagos.
You will get all the scare mongerers on here, most never been to Nigeria. yes there is risk but that stands all over the world. All the fields have armed security boats.
Enjoy it, once offshore just same as the rest and rainny season will be over then.