Getting employed into any oil companies in Nigeria' starts when you re still in College and University.
The fact of this action is,as your education progresses, you keep, updating your profile, in some cases, they will suggest, courses you can pursue of change to fit into these industries thereby getting keyed in,as first choice during recruitment.Even if their recruitment exercise is done publicly, you will receive invite first.
Let me use Shell as an example, they have the flay of recruiting young graduates, not that they have experience they will be employed under graduate trainees.
Hence if you are still studying or have a ward in secondary school or univeristy, he or she should log into www.shell.com look for regional site, choose Nigeria, first register, then click career, check college, graduate,or undergraduate, fill in required info.Same for exxonmobil,chevron,sclumberger,halliburton,bakerhughes,Elf, NNPC , Cameron, Total,etc.
Then if your are a young fresh undergraduate, visit any of these oil companies sites, register, check job alerts, search for jobs.
After this visit www.linkedin.com, register, create honest profile search for fellow colleaques, connect with many Managing directors,Technical, Operation Managers etc, if they read your profile, and connect with you, pronto you may land a job, because their personal email or their phone number will be reveal to you, in some cases.
If you go premium, Bill Gates to Richard Bronson contacts you will have

thanks

hisable2: thanks

In addition to these, your can also create a resume/cv related blog,and have your finest photo there, update it as often as your acquire any experience no matter how insignificant it might seem.
For instance, I re-painted My family house garage today, if your actually did and post the picture in your blog.
Whenever your read of vacancies, simply refer to your blog and then wait for response.

mr. indigene......tanx, hw u dey?

atitebi: mr. indigene......tanx, hw u dey?

My location weather is very fine to take an evening walk.

One major oil service company known only by few is seadrill www.seadrill.com click career
If you want to pursue a career in this company and real want to undergo some training, you have a chance.
Total, Elf, Mobil depends upon them for crude oil extraction, mud logging etc.
I will encourage any reader of this thread, to destroy the mentality of "what Nigeria now needs is any university degree". which mean as long as you re a graduate, you re walking on a road paved gold. FALSE.
Some university degree Can not fetch you a job throughout your life.
So are you a degree holder in any engineering fields and Science stake out seadrill