This link might be useful to your friend:
https://nationalcareersservice.direct.gov.uk/advice/planning/jobfamily/Pages/default.aspx
(I suggest using the list of job fields, at the foot of the page, as he might see something listed there that he wouldn't otherwise have thought of).
That link provides loads of information about career paths and, importantly, provides further links to information about relevant training courses).
However he needs to be aware that the number of people working in the offshore gas/oil industry has fallen dramatically over the years. That's largely because companies are replacing group of rigs (all with their own teams) with automated rigs operating as satellites of a single manned rig. So where they used to need to staff, say, 6 rigs, they now only need to staff just one.
The construction industry might be a better place to look. Although there are still lots of unemployed construction workers, those with highly-specialised skills (such a tower crane drivers) probably find it easier to get work.