Why do you think so few Americans work for SLB? Most Americans I met who work for SLB have ZERO desire to work in the training center and furthermore most see SLB as a stepping stone to an operator. Most Americans in my location are not getting fired, but actually quitting on their own accord whether it be for going back to school for graduate studies or changing industry because they had enough of the SLB bull.
The USA has plenty of industry besides the Oilfield when compared to most other countries whether it be first/developing or third world. In most countries SLB operates, the Oilfield is the only industry in town. So many foreigners from these less developed places will jump hand over fist to get to the USA.
It's easier to keep a foreigner, yes they are hard working, but also if they dont work that hard, they lose their visa and have to go back to wherever they came from. SLB has more control over these individuals. Schlumberger encourages dual careers/families/and expats for a reason. These people have more to lose.
Dont despair, you live in a country with plenty of opportunity whether you decide to stay in the oilfield or jump into another industry. Be adaptable and be willing to take a risk, even if it does mean making less. Schlumberger is a great company...but ask yourself for who? The employee or the investor?