Eni signed an agreement with the Kazakh government and a consortium represented by Karachaganak Petroleum Operating in Astana in December for the Karachagank field. State company KazMunaiGaz enters the project with a 10 percent stake.
"KazMunaiGaz's entrance represents a significant step forward toward strengthening the cooperation between the parties involved in the consortium," Eni said in a statement.
"In the interim the companies have already started preparatory activities to support future development of the field, which is expected to yield a substantial increase in current production of liquids and gas."
Talks over the government acquisition of shares in Karachaganak were complicated by a tax row with Astana and a consortium that included Eni.
Foreign energy majors took over Karachaganak in the 1990s. It holds roughly 2.4 billion barrels of oil and an estimated 15 trillion cubic feet of natural gas.
Italian prosecutors in May said Eni subsidiary Agip Kco was suspected of offering bribes to the son-in-law of the Kazakh president, through 2007. Bribes through 2007 may have been at least $20 million.