Most oil rig workers do not need qualifications. It is hard physical work and working hours tend to be 12 hour shifts on a 24 hour shift rota. They would tend to work 2-3 weeks on the oil platform and then have the same time back on shore. It can be physically demanding, cold, wet and tiring.
To apply you would need to take a look at websites of oil rig companies. You may also find jobs advertised on job boards online.