Royal Dutch Shell said Friday it completed the sale of its stake in a Nigerian oil field for $737 million as part of a strategic review of onshore assets there.

The company sold its 30 percent stake in oil mining lease 30 to Eroton Exploration & Production Co. Eroton took on in additional stake in the area from subsidiaries of Total and Eni.

"This divestment is part of the strategic review of Shell Petroleum Development Co.'s onshore portfolio and is in line with the federal government of Nigeria's aim of developing Nigerian companies in the country's upstream oil and gas business," the Anglo-Dutch company said in a statement.

The oil mining lease was producing an average 14,000 barrels of oil equivalent per day last year.

Amnesty International expressed frustration with Shell and its Italian counterparts at Eni over the legacy of oil spills in the Niger Delta region. The rights group said the two companies combined reported more than 550 spills in the area last year.

"These figures are seriously alarming," issues director for Amnesty Audrey Gaughran said in a statement. "Eni has clearly lost control over its operations in the Niger Delta. And despite all its promises, Shell has made no progress on tackling oil spills."

Shell in 2013 said the rising operational challenges in Nigeria, including theft of crude by organized gangs and pipeline vandal attacks, had eroded its profit margin by $250 million.