Oil and gas facilities provider Petrofac has acquired an additional 11.9% stake in Nigerian production and development firm Seven Energy International for $75m.The investment brings Petrofac's interest in the company to 24.5% (on a fully diluted basis), after the initial 12.6% stake was purchased in November 2010 for $100m."Since the initial investment, Petrofac has provided experienced personnel to assist with the delivery of Seven Energy's key existing projects, and continues to provide active engineering and procurement support," the statement said.Seven Energy had gross assets of $528m as at 31 December 2009, and reported a pre-tax loss for the 2009 financial year of $52m."We are making good progress and the knowledge and exposure we have gained during the course of the last six months has resulted in the identification of additional potential prospects for the group," according to Gordon East, managing director of Petrofac's Production Solutions division.---BC