The company is acquiring an 8% interest in the producing Alba field, 130 miles north-east of Aberdeen, from Japan's Cieco Energy. The deal will add around six million barrels to its reserve base.
While the deal is small scale it reflects the continued enthusiasm of Enquest for an area that has been attracting increased attention from overseas buyers.
Deep-pocketed organisations from countries including China and United Arab Emirates have been buying assets on the UK Continental Shelf to help them meet strong global demand for oil and gas.
Analysts at Jefferies International said Enquest, which has headquarters in London, appeared to have struck a good bargain.
The company will pay only $5.20 (£3.40) per barrel oil equivalent (boe) for reserves compared with an average $13boe in recent deals in the North Sea.
Enquest acquired a 60% holding in the Kraken heavy oil field east of Shetland in three separate deals last year, in which it agreed to pay up to $474m in total.
Experts at Wood Mackenzie have predicted that 2013 will see another year of strong deal activity in the North Sea, after the value of transactions reached a 10-year high of $10 billion in 2012.
The consultancy expects companies to invest more than $60bn, bringing new fields into production and improving existing assets in the North Sea, in the period between 2012 and 2015.
Yesterday, Malcom Webb, chief executive of industry body Oil & Gas UK, said: "In the past six months alone, more than £8bn of new investment and many thousands of new jobs have been announced in projects across the UK Continental Shelf and we know there are currently more in the pipeline for approval."
Mr Webb said tax breaks introduced by the Coalition Government last year had encouraged firms to invest.
"With improvements to the tax regime as a result of better engagement with the Treasury, no fewer than 30 new offshore oil and gas developments were approved in the past 12 months."
The Chancellor previously hiked the tax rate payable on North Sea profits in the 2011 Budget.
Cieco Energy's parent company, Itochu, has interests in other North Sea assets.