Avantages
Schlumberger is a great place to work if one is mobile, ie move from city to city or even country to country every 2-3 years. The international mobility is what attracted me to SLB and it paid off both in experience as well as money. Those not willing to move around have fewer opportunities. Also the "local" compensation packages are not competitive especially when one considers the level of responsibility even lower level employees have. It makes for a very challenging and interesting career but the compensation is not great.
Inconvénients
Whether or not your SLB employment is enjoyable and rewarding will very much depend on your direct manager. Each department is rather independent with managers able to make decisions on their own. A good manager will fight on your behalf (the personnel department is appalling) and a bad one will simply ignore any issues. This means that your experience will never be consistent throughout your career, and even if you do not move around, your manager certainly will.