Oil-services giant Schlumberger said Thursday it would cut 11,000 more jobs as its first-quarter earnings tumbled after low crude prices forced it to cut drilling. Schlumberger chief executive Paal Kibsgaard said the latest round of cuts was caused by a severe decline in North American land drilling and by reduced investment by oil companies overseas. Thursday's job cuts were announced on top of 9,000 layoffs already planned in January. Schlumberger currently employs 115,000 around the world. "In spite of the detailed preparations we made in the fourth quarter, the abruptness of the fall in activity, particularly in North America, required us to take additional actions during the quarter," Kibsgaard said. The oil services company, whose clients include ExxonMobil, BP and other major firms, took a $390 million charge in concert with the job cuts.