(Reuters) - Norway's Statoil has sold its remaining 15.5 percent stake in the Azeri gas project Shah Deniz to Malaysia's Petronas for $2.25 billion, the latest in a string of asset sales made to shore up returns to shareholders.

Like other oil majors, Statoil has been selling assets to protect margins eaten up by rising costs and, in recent weeks, falling oil prices. It reduced its stake in Shah Deniz in December last year.

Monday's deal also includes Statoil's stakes in a South Caucasus pipeline company and two other firms. Its second-quarter production from the Shah Deniz field was 38,000 barrels oil equivalent per day, it said.

"The divestment optimizes our portfolio and strengthens our financial flexibility to prioritize industrial development and high-value growth," Lars Christian Bacher, Statoil's head of development and production activities outside Norway, said in a statement.

The Shah Deniz field is operated by BP. The other partners are TPAO, SOCAR, Lukoil and Nico.

The venture is seen by the European Union as a key means to wean itself off its dependence on Russian gas, and the hope is that it will supply 20 percent of European Union needs in the long-term thanks to proven gas reserves estimated at 1.2 trillion cubic meters.

After the transaction, Statoil will still have an 8.56 percent stake in the ACG field in Azerbaijan which is operated by BP and a 20 percent stake in the Trans Adriatic Pipeline (TAP), which will transport Azeri gas to European markets.

Statoil declined to comment on how much profit, if any, it will make from the sale of the stake to Petronas, which is dependent on approval from authorities.

"The process has been going on for a few months", said Statoil spokesman Knut Rostad. "We continuously make assessment and have proven an ability in recent years to create value through portfolio optimization."

The transaction is expected to close in early 2015, although for accounting purposes the effective date will be set at Jan. 1 2014.

Statoil shares closed at 158.3 crowns on Friday.