Kōrero: Engineering on the sea floor

Whārangi 3. Drilling the Māui gas field

Ngā whakaahua me ngā rauemi katoa o tēnei kōrero

In 1969, one of the largest gas fields yet discovered was found on New Zealand’s doorstep. The Māui gas field, as it came to be called, lay about 30–50 kilometres offshore from Taranaki in open ocean. At the time, however, it was one of the most adverse environments ever to be considered for gas extraction. The engineering problems were immense – new technology was required, under tight deadlines.

Environmental challenges

The Māui field lies kilometres beneath thick sedimentary rocks that are 110 metres below the water’s surface. The area is exposed to Southern Ocean swells and Tasman Sea storms. Measurements obtained during exploration suggested that the production platform which sat above the sea must be able to endure waves up to 22 metres high and wind gusts of 260 kilometres per hour. The field is near active faults, so the tower, rising 275 metres from the sea floor, has to be capable of withstanding earthquakes up to magnitude 8.

The pipelines that carry oil and gas to the shore are 610- and 254-millimetres in diameter and covered in concrete. They cross underwater beds of boulders the size of small cars, dumped by catastrophic fluid avalanches (lahars) from the volcanic cone of Mt Taranaki. Supports and protective rock embankments had to be built to buttress the pipes between mounds of boulders.

Māui A platform

After many trials in appalling weather, the Māui A platform was completed and functioning in 1979. Since then it has produced about 80% of New Zealand’s gas and oil.

In stormy seas

The Māui A oil and gas tower was built in a Japanese dry dock. Two tugs then towed it 8,400 kilometres to New Zealand. The voyage was easy compared with the task of upending and pinning the tower to the sea floor in rough weather. In 1976 New Zealand experienced its worst summer weather for 25 years. Experienced oil workers based at the tower began to rate the Tasman Sea as more inhospitable than the treacherous northern North Sea.

Māui B platform

As the flow of gas and condensed light oil began to run out at Māui A, another part of the field, richer in light oil, was brought into production. 1993 saw the construction of the un-manned Māui B platform. It is 15 kilometres further offshore than Māui A, and has pipelines linking the platforms and running to shore. However, this platform’s days are also numbered. Other fields in the same area have been explored, and some of these off the north and south Taranaki coasts are to be exploited in the late 2000s.

Drilling other fields

The technology to develop shallow offshore gas fields is now well established, but drilling deeper fields is a challenge. Economic gas and oil reserves have not yet been found elsewhere around New Zealand (outside of Taranaki). Although gas in the form of ice-like hydrate seems to be widespread under the continental slope to the east of the North Island, no one has yet devised a way to exploit these deposits.

Me pēnei te tohu i te whārangi:

Keith Lewis, 'Engineering on the sea floor - Drilling the Māui gas field', Te Ara - the Encyclopedia of New Zealand, http://www.TeAra.govt.nz/mi/engineering-on-the-sea-floor/page-3 (accessed 14 December 2019)

He kōrero nā Keith Lewis, i tāngia i te 12 Jun 2006