I think the most important is knowing what the company is all about. Get on the webpage (www.slb.com) and deep dive into their culture, the type of work they do, how is the company internally segmented, how do they make money, etc. Get familiar with the different programs they have, one of my favorites for example is SEED. Mention you're familiar with some of those, so they know you did your homework. SLB is looking for proactive leaders, so don't be shy about sharing all you know about them.
During my interview with recruitment, their focus was mainly on two things 1. my ability to work in harsh conditions (in my case the Middle East) and 2. my ability to work under pressure (they stressed on this because you will be interacting with clients). They were happy to hear that I showed interest in the environment, from being an electrical engineer and also sharing with them that my father was a geologist. My advice would be to show that you've had exposure (whatever that may denote) and that you are physically up for the challenge. Schlumberger is very diverse, and they want to make sure they choose the right people that won't jeopardize their own relationship with their clients.
Learn about the company and its different segments of actuation inside the oil business.
Your curriculum, courses, major, training are great, but they want to know if you can learn something new fast enough to solve a problem that might not be expected on a daily routine.
They like people that can face challenges with simple and safe solution. As a field engineer in remote locations you might not have all the resources at hand when an unexpected problem happens. So have in mind some extra curriculum activities that demonstrate it as Mission Trips for example.
You will meet a lot of people from different nations. Knowing another language, and some travelling abroad experience is something that they might appreciate.
Problem solving skills, team working, time management are some of the skills that a Field Engineer at Schlumberger needs to have.