I was first contacted by a recruiter who had seen my resume online. After having a phone interview with the recruiter, he passed my name on to an internal recruiter within Schlumberger. After a second phone interview, I was invited to a group interview. They paid for a plane ticket to Shreveport, LA.
The group interview consisted of about 10 people. We were given presentation topics and partners a week in advance. At the interview, we first had a brief introduction to the company by two recruiters. Then everyone did their presentations, and there was a team activity. The recruiters then went into depth about the job. We did a teambuilding activity (build a catapult out of random stuff), and then we were sent to bed.
The next morning, we got on a bus/van thing and drove out to the field site (they provided hard hats, coveralls, boots, goggles, and ear plugs). We first visited an office area and talked to some engineers who showed us some of the equipment. All of the candidates were put in a room with the engineers without the recruiters to ask whatever questions we like without worrying about how they'd sound.
After that, we visited a site where they were actually fracking, and we walked around and saw what was happening, and met some of the engineers in the trailer. That evening the recruiters took everyone out to dinner, and then some people went to a couple of different bars with some of the engineers we met earlier after that. Overall, the interview was relaxed and was definitely geared towards just figuring out if the position was the right fit for you.