US oil giant Chevron and state-controlled YPF unveiled plans tospend another $1.6 billion to develop Argentina's Vaca Muerta shale formation foroil and gas projects.The investment comes on top of $1.2 billion Chevron agreed to spend last year for ashale pilot project.The second phase of exploration calls for drilling 1,500 wells across 395 squarekilometers (150 square miles) in the hopes of producing 50,000 barrels of oil perday and three million cubic meters of gas per day."The agreement between YPF and Chevron is the most important ever reached thusfar for non-conventional hydrocarbon resource development in the country," YPFsaid in a statement.Vaca Muerta, in the southern Patagonia region, is a huge deposit that ranksArgentina second in the world for shale gas reserves and fourth for potential shaleoil reserves.After many years of being self-sufficient, Argentina has recorded an energy deficit inrecent years that reached $9 billion in 2013.The growing energy bill is worrisome because the country is losing reserves in itscurrency.In a bid to regain autonomy, Buenos Aires is relaunching production and targetinglarge investments by foreign firms.