Question about Environmental/Petroleum Engineering

How hard is it to become a Petroleum Engineer/Geotechnical Engineer with a B.S. in Environmental Engineering?I will receive a degree in Environmental Engineering from Cornell University (CALS), and Petroleum Engineering is not offered as a program. I did a lot of thinking about my future career, and I realized that I want to pursue an engineering field where I’m not in a cubicle most of the time. That’s why I was directed toward Petroleum/Geotechnical Engineering, so please feel free to offer me other career suggestions based on this. I would prefer to not pursue a masters degree unless of course I was compensated by an employer. I also want to travel a lot and look forward to going to my job and solving problems, where I feel useful and appreciated. Thank you!