Hmmm, i dont know anything specific about the Shell compounds in Nigeria, however I would say that care needs to be taken if you are travelling to any foreign country. Yes, I know that in the news recently there have been kidnaps, however people should look at the bigger picture - there are kidnaps in england.
if your serious about the job offer, you need to do lots of research into the area and the job itself - no where is completely say, but if you employ common sense and lots of research, there isnt anything else you can do to make yourself anymore safe!
I know friends who have visited Nigeria and know a number of Nigerians, the culture, food, and friendliness of the natives is overwelming, they are so welcoming and the experience would be wonderful.
Good luck :)