Oil was discovered in the Ninian field, which lies 240 miles north-east of Aberdeen, in 1974, with production starting in 1982.
The Canadian company said that its decision to invest in the field was triggered after the Treasury awarded it a tax break under the “brownfield allowances” introduced by Chancellor George Osborne last year.
James Edens, CNR International’s managing director, said: “As a result of this investment, we forecast that the company’s North Sea production will increase in the coming years.
“With the assistance of the brownfield allowance, we are now able to embark on this phase of Ninian’s late life extension programme, realising remaining reserve potential and extending field life.”
CNR, which employs about 400 people in Scotland, awarded a £119m contract in March to Aberdeen-based energy services firm Wood Group to continue supplying staff for the Ninian, Murchison and Tiffany fields for the next three years, extending a deal signed in 2005.
News of the investment came as Aberdeen-based oil driller Xcite signed a deal with support services firm Amec for the development of its giant Bentley field in the North Sea.
Meanwhile, a quarterly survey from trade body Oil & Gas UK found that companies remain “optimistic” about the outlook for the industry, with contractors benefiting from “the record investment in the UK continental shelf”.