* Largest energy project in Israel's history
* Leviathan gas seen on Israeli market by end 2019
* Project operated by U.S. group Noble Energy (Adds Noble, Delek comments, details)
By Tova Cohen and Ari Rabinovitch
TEL AVIV, Feb 23 (Reuters) - Developers of the Leviathan natural gas field have approved a $3.75 billion investment (FID) in the first phase of the largest energy project in Israel's history, they said on Thursday.
The reservoir, located 100 km (62 miles) west of Haifa, was discovered in December 2010. Its $3.75 billion budget follows $1 billion that has already been invested in exploration, appraisal and planning activities.
According to a development plan approved by the government in 2016, the project will be completed in less than three years and gas will be available to the Israeli market by the end of 2019.
Texas-based Noble Energy owns 39.7 percent of Leviathan, while Delek Drilling and Avner Oil Exploration, subsidiaries of Israel's Delek Group , each hold 22.7 percent. Israel's Ratio Oil holds 15 percent.
Ratio shares were up 2 percent in afternoon trade in Tel Aviv, while Delek Drilling and Avner were 1 percent higher.
The first stage of work will involve drilling four production wells at an average depth of around 5 km below sea level. These will produce about 12 billion cubic metres (bcm) of gas annually, which will double the volume of gas available to the Israeli market.
"This is a day of good tidings for the economy and people of Israel. This move will provide gas to Israel and promote cooperation with countries in the region," Prime Minister Benjamin Netanyahu said on Twitter.
The gas from Leviathan will be transported through two underwater pipes 120 km in length to a processing and production platform situated 10 km offshore.
The processed gas will be piped from the platform, through a northern entry pipeline that will be connected to the national gas transmission system of Israel Natural Gas Lines.
"Developing Leviathan and pursuing more export agreements, coupled with supply to the domestic market, will ensure energy security for Israel and will add to Delek Group's stability," said the company's chief executive, Asaf Bartfeld.
Noble, the group's operator, said its share of the bill was $1.5 billion. It plans to fund phase one with operating cash flows from the nearby gas field Tamar, as well as east Mediterranean portfolio proceeds. Regional portfolio proceeds received to-date total about $575 million, it said.
Noble said it was also securing access to a financing facility for additional funding flexibility.
Noble projects operating cash flow for the first year following Leviathan's start-up to be at least $650 million net. (Editing by Jason Neely and Mark Potter)