BUENOS AIRES, April 12 (Reuters) - Argentina’s state-run oil company YPF SA and Schlumberger AG, the world’s top oil services provider, have reached a deal to invest $390 million in the Vaca Muerta shale field in Patagonia, YPF said on Wednesday.

In a letter to the Buenos Aires stock exchange, YPF said a division of Schlumberger would invest the full amount and obtain a 49 percent stake in the 228.5 square kilometer (88.22 square miles) Bandurria Sur concession, where the two companies would develop a two-phase shale oil pilot project. (Reporting by Luc Cohen)