After reading your question, I presumed you are very confused.
1) Your preference should be to join Oil operator company such as Shell, BP, Chevron etc. , but not Service company such as Schulumberger, Halliburton, Baker hughes etc..
2) As you have Petroleum engineering degree, you have option to join Operator company in various roles- Petrophysicist, Completion engineer, reservoir engineer, wellsite geologist, drilling engineer etc. But what you get, depends on company requirement. Do not be very specific at this stage. See what option you have and what job offers you have at the end of your degree.