UPDATE 2-Chile's ENAP says signs 10 mln barrel oil deal

* Oil shipments due to begin in August

* Twice monthly shipments of 400,000 barrels (Adds background on Petroecuador, byline)

By Rodrigo Martinez

SANTIAGO, July 16 (Reuters) - Chilean state oil company ENAP said on Thursday it had signed a deal with its Ecuadorean counterpart, Petroecuador, to buy almost 10 million barrels of crude oil per year.

The first twice-monthly shipment of 400,000 barrels is due to arrive in Chilean ports in August, ENAP said, adding that the contract would guarantee imports of about $53 million per month at current prices.

Energy-poor Chile imports almost all the crude and natural gas it uses. Last year, ENAP was forced to step up purchases of crude and diesel to make up for restrictions in the natural gas supply from neighboring Argentina.

A drought also increased demand for fuels to generate energy as hydroelectric output fell.

Leftist Ecuadorean President Rafael Correa said last weekend his OPEC-member country had signed a deal to sell crude oil to China for which Ecuador would soon receive an advance payment of $1 billion.

Petroecuador currently produces about 260,000 barrels a day in the Amazon jungle, but Correa has vowed to invest heavily to increase the company's output.

Ecuador's government is struggling to inject liquidity into the resource-rich country's economy after export revenues fell in the first half of the year due to low oil prices. (Additional reporting By Alexandra Valencia in Quito; Writing by Eduardo Garcia; Editing by Christian Wiessner)