You can't be employed on an oil rig until you've completed courses in fire-fighting and survival. Potential employers would only consider paying for someone to go on these courses if they had a shortage of applicants for jobs. Otherwise you'd have to go through these courses at your own expense before applying for jobs.
More details are here:
http://www.learndirect-advice.co.uk/helpwithyourcareer/j obprofiles/profiles/profile1099/
Aberdeen is the main base for the UK oil industry so you might be able to find out about potential employment opportunities by phoning Aberdeen JobCentre on 01224 618000. (You might also try Great Yarmouth JobCentre on 01502 403200).
Chris