Jeff Franks, Reuters

HAVANA, Oct 12 (Reuters) - The arrival of a Chinese-built drilling rig set to explore for oil in Cuban waters has been delayed again and is not expected to reach the island until the second half of December, sources close to the project said.

The delay is the latest of many as communist-run Cuba awaits the start of a project it hopes will give a shot in the arm to its struggling economic system.

The massive Scarabeo 9, which set sail from Singapore in late August, had been expected in Cuba by early November, but was slowed by problems not unusual for a newly built rig going to its first drilling operations, people close to the project said this week.

The late December arrival means the first well, to be sunk in 5,600 feet (1,700 metres) of water off Cuba's northern coast, may not be started until January, the sources said.

They warned that further delays were possible as the rig makes its journey halfway around the world after it was built in Yantai, China, and completed in Singapore. It was said to be currently off the coast of West Africa, although reports about its location varied.

Cuba had hoped to begin exploring for oil in its part of the Gulf of Mexico several years ago, but the project has been put off by construction delays and other issues.

The high-tech rig belongs to Saipem, the offshore unit for Italy's Eni SpA, and has been contracted by Spain's Repsol YPFfor the Cuba project, which is the island's first major exploration offshore.

It will be used to drill at least three wells, two by Repsol in a consortium with Norway's Statoila unit of India's ONGC, and another by Malaysia's Petronas in partnership with Russia's Gazprom Neft.

After that, plans for the project, which has been cloaked in secrecy, are not clear, but may depend on the success of the first three wells, a diplomatic source said.

If oil is found, it will take at least three years to begin production, said the local manager for one of the companies involved.

BALM FOR CUBAN ECONOMY

Cuban officials have not said much publicly about the offshore exploration, but make it clear in private conversations that oil would help their troubled economy.

Opponents of the Cuban government fear oil will be the salvation of the communist system, which President Raul Castro is trying to preserve with economic reforms. But that will depend in part on how much oil, if any, is found.

Cuba has said it may have 20 billion barrels of oil in its 43,000 square miles (111,370 square km) of the Gulf of Mexico, while the U.S. Geological Survey has estimated 5 billion barrels, the figure more broadly accepted in the oil world.

Cuba oil expert Jorge Pinon, a former president of Amoco Oil in Latin America who is now at Florida International University, said the most likely prospect if oil were found was that it would be a field closer to the USGS estimate.

Owing to the fields and the probability they contain heavier oil, he thinks only 30 percent to 40 percent of the reserves can be produced.

"If they find 5 billion barrels, you take 40 percent of that and it's 2 billion barrels," Pinon said.

The contracts with international partners call for Cuba to get 60 percent of the oil, which based on a 25-year reservoir life, would equate to about 131,000 barrels a day.

That amount may or may not assure the survival of the Cuban system, experts said, but would bring solid economic and political benefits, including a better balance sheet for the cash-strapped island and oil independence.

Cuba now gets 92,000 barrels a day from socialist ally Venezuela to help meet internal demand, but Venezuelan President Hugo Chavez is battling cancer, raising questions about how much longer the program will last.

The Cuban wells have raised environmental concerns because they will be about 60 miles (96 km) from Florida, twice as close to the state as drillers are allowed in U.S. waters.

A blowout like BP experienced last year off the coast of Louisiana could douse both Cuba and Florida with oil.

To alleviate concerns, Repsol will follow through on an offer it made to invite U.S. Coast Guard officials to inspect the rig when it reaches Trinidad and Tobago, sources said.