Oct 18 (Reuters) - Schlumberger Ltd, the world's largest oilfield services company, reported a 20 percent rise in quarterly profit as global drilling activity remained buoyant.

Net income rose to $1.71 billion, or $1.29 per share, in the third quarter, from $1.42 billion, or $1.07 per share, a year earlier.

Revenue rose nearly 11 percent to $11.61 billion.