While I don’t work in the Oil & gas production / drilling side of things, I work in the subsea / offshore construction industry whose biggest client is- you guess it.. Oil & gas.
My experience of it has been mostly good, work is interesting, meet lots of pople etc. However- travel to remote parts of the world is a bit of a double edged sword, as you will see alot of departure lounges, heli bases, offshore supply bases in the middle of nowhere & not much else, its proably better when you are younger & can take time off at the end of a trip to travel, but if you are 41 & have a wife & kids I’m guessing that this wouldn’t be an option.
The quality of the accomodation (my experience is from constuction vessels & barges, not been on too many rigs) is quite variable, from having a room to yourself to having to share a cabin with 3 other people on differant shifts, makes for interesting sleeping patterns. The same goes for the quality of the food as above- Sometimes its great, sometimes you are lucky to see anything green for a month at a time.
Crewchanges can sometimes be a bit hit or miss too- I have done 7 week trips offshore with no end in sight a times, or crewchanges canceled due to weather / problems with the heli / your replacement got drunk & was refused boarding on a plane…
If you have a background in chemistry then that will help, working as a mud engineer would be a possibility (although given that drill mud is a nasty stuff, maybe not!)
What bigjim said about renewables is very true, most of my work over the past few years have been to do with building offshore windfarms.