First of all understand that you should just relax and be yourself. Take a copy of your resume to hand them in case the interviewer didn't bring one. Smile, look the interviewer in the eyes, and make a firm handshake - first impressions matter. As far as the interview itself, if you don't have any O&G experience they will probably focus on trying to understand your personality and what you would bring to the company. Come up with life experiences that showcase the qualities they would look for in an engineering intern. Put yourself in their shoes and think about what qualities they will want from an intern. Be prepared to answer the standard character trait type questions - show you can work with a team, communicate well, determination/perseverence, examples of when you have overcome challenges or obstacles, anything that shows you will exceed the status quo.