The government wants to complete an undersea inspection of the Tui oil field next month as it prepares for decommissioning of the facility.

The Ministry of Business, Innovation and Employment is seeking bids from firms interested in inspecting and testing the field's five seafloor wellheads and the lines linking them to the floating production and storage vessel Umuroa.

The contract is expected to start by August 3 and be completed, using a remotely-operated vehicle, within three weeks. The actual inspections should only take three to four days.

"This is a critical activity for the development of the demobilisation work programme," the ministry said in tender documents for the work. "As such, the delivery dates of the services in New Zealand are highly important and must be met for MBIE to consider a supplier's quote."

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The government took control of the field in May following the collapse of former operator Tamarind Taranaki. It is budgeting about $155 million for the decommissioning and has hired international specialist Petrofac as a technical advisor and local firm Elemental Group for advice on the project's regulatory requirements.

Earlier ruling

MBIE is working quickly so that the Umuroa, operated by BW Offshore from Singapore, can be released. It has been stuck at the field after the Environmental Protection Authority said in April the vessel could not leave until a full decommissioning plan was in place for the field.

Production from the field was halted in November and the wells shut after a leak was discovered in one of the lines to the Umuroa.

BW had then planned to disconnect the lines from the ship, purge them, cap them and place them on the seabed in line with an earlier agreed disconnection plan. But the EPA wasn't prepared to allow that, citing what it considered to be a lack of information on the state of the Tui wellheads.

MBIE said the first phase of the decommissioning will enable the removal of the Umuroa by making safe the field's subsea assets. All flowlines will be flushed to minimise environmental risks.

At a later date, the wells will be plugged and the other seafloor infrastructure removed. MBIE has previously said that work would likely be carried out over the 2021-22 summer, subject to vessel availability and the completion of planning and consenting processes.

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