I had an on-campus interview the day after meeting Schlumberger at the school career fair. It was a fairly casual interview where it felt they were mostly scoping out if you could handle the extreme work environment that they put their employees through. Afterwards, I went to the second round interview. During this interview, they flew candidates from across the country to a location in Texas. We were put into small groups prior to the interview process to prepare presentations to give to the full group (30-ish people). The group portion went from 6pm-4am and was a mix of presentations, team building activities, questions, etc. During the second day, we visited a drilling site and had the opportunity to ask many questions about life in the field. I would not say the interview was difficult. It was more that they were testing are ability to be personable under low-sleep/slightly stressful conditions and that you were willing to work the long hours required by the job.