I think the shortest fair answer is there are no special prerequisites beyond a general, high-school-level education in maths and science.
It's a difficult question to answer directly, because petroleum geoscience is a very broad field including:
- Geology: the study of sedimentary basins, especially sources rocks, reservoirs rocks, and structural geology (folds, fractures, faults). Mostly involves making systematic observations, mapping, and data interpretation.
- Geophysics: remote sensing of geology using various physical measurements, such as gravity, electromagnetics, and seismic waves. Involves lots of computers and digital analysis, and quite a bit of maths and applied (especially signal processing and linear algebra).
- Various other rather niche areas (at least in terms of the number of specialists around) such as geochemistry, palaeontology, mineralogy, field geology, and so on.
It's so broad that I daresay you can find an area that would appeal to almost anyone with an interest in science. If you're more quantitative (interested in maths and computing), then you'll find lots of friends in geophysics, but there are plenty of highly quantitative geologists and geochemists (and arguably those fields are more in need of nerds than geophysics is).
I think it's fair to say that most petroleum geoscientists started with a general degree in geology, geophysics, or some related discipline, perhaps followed it up with a post-graduate degree, then got a job in petroleum. They didn't train in petroleum geology per se.
This may or may not be relevant to your situation, but you should know that petroleum geoscience is in decline as a discipline. Maybe that means there will be opportunities in the future, but right now and for the foreseeable future it means that there's a lot of under-employed earth scientists. If finding a job is your main motivation, my unsolicited personal advice would be to downplay the 'petroleum' aspect, stick to pure sciences and skills, and maybe look at other areas of applied geoscience, such as mining, geothermal (very small), or geospatial (GIS, basically).