Interviews are often done in group format, and are usually not "interviews" in the formal sense, but observations of how you interact with your assigned group mates.
Our interviewers sent us a topic to prepare a PowerPoint on with other candidates. We worked together via email to put the presentation together and divide up roles. We presented together at the interview along with groups.
Also during the interview, the recruiters gave us toothpics and marshmallows to build a tower. It was a competition with other teams. Again, it wasn't who won, but which candidates could vibe well with their teammates, versus who became negative and started blaming.
Overall, the interview is really about testing your maturity and social IQ. They're looking to see if you can keep your cool under pressure.
Research the company - more than just the website. Learn about Schlumberger's latest news headlines. How are they positioning themselves in the market - what is their strategic plan? Read the company's latest earnings report and generate questions based on what you read. Ask a lot of questions. Communicate your leadership skills/experiences and how you function in a team environment. Schlumberger will send you to a training school during your first few months of employment so you do not necessarily need to know the technological aspect of how the tools work.
Schlumberger is the top oilfield services company in the world and they seek individuals who will help push them forward. Make sure to communicate your desire to learn and how you will provide value to their company mission. The onsite interview is designed to see if individuals are truly interested in the position - the interview will extend nearly 24 hours - onsite/jobsite tour, one on one interview, team building/interactive activities. Be prepared for a long few days. Wireline engineers spend several days straight on a jobsite - and job-sites are most always out in the middle of nowhere.