Shell's Pohokura natural gas field in north Taranaki is to undergo a $70 million facelift this summer.
Pohokura - which cost $1 billion to develop - supplies 40 percent of New Zealand's gas.
Shell New Zealand chairman Rob Jager said the project involved routine maintenance and would offer substantial contracts for local suppliers, while providing work for about 250 people.
The jack-up rig Ensco 107, which has been moored at Port Taranaki since July, will be located alongside Pohokura to house workers, store equipment and provide heavy lift capability during the project.
Shell expects work to start before the end of the year and to be completed in the first quarter of 2016.