Argentina's state-run energy firm YPF said on Jan. 14 it had signed a preliminary deal worth more than $500 million over three years with American Energy Partners to explore for shale gas in the country's vast Vaca Muerta formation.

In a statement, YPF said the accord involved a pilot project in the Bajada de Anelo block, located in Argentina's Neuquen province that would run until mid 2018.

If the project is continued, Pluspetrol and the province-owned Neuquen Oil and Gas would join the venture, exploring the southern zone of another bock Cerro Areno. A company affiliated to American Energy Partners would take up to a 50 percent stake in both blocks.

Argentina sits atop some of the world's largest shale resources but is a net energy importer after years of under-investment in the country's energy sector.