For the last few years Darwin has repeated on a grand scale an experiment that is being conducted throughout Australia: what happens to a town when it becomes the site of a mega infrastructure project?

In the next few years the outcome of this experiment will start to become clear.

In 2012 the Japanese company INPEX announced it would go ahead with an ambitious and massively expensive plan to extract "hydrocarbon liquids" (mostly natural gas) from an underwater basin north of Western Australia and then process the gas largely in Darwin.

INPEX at a glance Up to 50 wells will be drilled into the Browse Basin coast of WA

Up to 50 wells will be drilled into the Browse Basin coast of WA A semi-submersible platform called the CPF will extract the hydrocarbon liquids

A semi-submersible platform called the CPF will extract the hydrocarbon liquids The floating production storage and offloading (FPSO) vessel stores the natural gas condensate and compresses the remainder

The floating production storage and offloading (FPSO) vessel stores the natural gas condensate and compresses the remainder Condensate shipped directly to buyers from the FPSO

Condensate shipped directly to buyers from the FPSO Compressed gas sent to Bladin Point via the 889km subsea pipeline

Compressed gas sent to Bladin Point via the 889km subsea pipeline Bladin Point processes gas to make liquefied natural gas (LNG) and liquefied petroleum gas (LPG), also known as propane and butane

Bladin Point processes gas to make liquefied natural gas (LNG) and liquefied petroleum gas (LPG), also known as propane and butane Gas shipped to Japanese and Taiwanese utility companies from Bladin Point

The Ichthys project, as it was officially named, would cost $US34 billion.

At least a third of that money would be spent on the Bladin Point gas processing facility on a peninsula in Darwin harbour.

The chief minister at the time, Paul Henderson, described it as a "game changer" that would "underpin our economy for the next 40 to 50 years".

But others were more wary, warning of the risk of an economic collapse after construction had been completed and the transient workers had gone to jobs elsewhere.

Bladin Point is now less than two years away from completion.

Economists fear a looming bust.

"A huge construction cliff is quickly approaching for the Territory," the Deloitte business outlook report for March 2015 said.

"The likelihood that a matchingly large project gets the go-ahead to help continue to drive growth once construction on Ichthys begins to wind down is now much less."

3,500-bed workers camp could be dismantled

Last week, in a rare event, INPEX conducted a tour of the Bladin Point construction site for the media, as well as senior management including Louis Bon, the project's Perth-based Managing Director.

"It's probably one of the biggest projects in progress at the world at the moment," he said.

"This project is three or four projects. We have the LNG plant here, the pipeline, and then you have the offshore portion.

"And with the offshore portion we have a huge platform - the Central Processing Facility (CPF) - and a huge Floating Production, Storage and Offloading (FPSO) facility.

"Each of them could be a project by itself in some areas of the world."

The massive infrastructure, however, translates to only a few hundred long-term jobs.

Up to 8,000 will be employed at Bladin Point by September, but this figure will be radically cut to 300 once the project shifts form the five-year "construction phase" to the 40-year "operations phase".

INPEX's Perth-based general manager of external affairs, Bill Townsend, who also took part on the tour, described this as a "logical transition".

"The construction jobs are relatively short-term," he said. "A different skill set is required to operate the plant."

"These construction jobs will finish and then we'll have the operations jobs. For the longer term there's opportunities in maintenance support for the project."

INPEX, he said, had tried to be sensitive to its "social footprint".

But it was clear the transition to the "operations phase" would involve great upheaval.

He said the almost brand new 3,500-bed Darwin camp built for INPEX workers would revert to the NT Government.

"In the most extreme scenarios," he said, "we would dismantle the site and rehabilitate it."

Meanwhile, for the length of the operations phase lasting 40 years, four carriers per week will export the processed gas to overseas buyers.

All the gas the project is estimated to produce in these 40 years — about 8.4 million tonnes per annum — has already been sold to Taiwanese and Japanese utilities.

INPEX the last of the Australian gas giants

Among other records, the Ichthys project (which in Darwin is often simply referred to as INPEX) includes the largest semi-submersible platform in the world, represents the largest ever Japanese overseas investment, the largest ever project financing ($20bn), and the longest subsea pipeline in the southern hemisphere (889km).

In a sign of the times, INPEX has been largely eclipsed by the Gorgon project of Western Australia's north-west shelf, which has a higher capital expenditure, as well as the series of LNG projects near Gladstone in Queensland which combined are worth more than INPEX.

Record-breaking facts and statistics The FPSO has the heaviest anchor chain in the world - each link is one metre tall.

The FPSO has the heaviest anchor chain in the world - each link is one metre tall. Trucks carrying quarry rubble to Bladin Point have travelled 12mn km - or 15 times to the moon and back.

Trucks carrying quarry rubble to Bladin Point have travelled 12mn km - or 15 times to the moon and back. Longest subsea pipeline in the southern hemisphere (889km)

Longest subsea pipeline in the southern hemisphere (889km) CPF is the world's largest semi-submersible platform

CPF is the world's largest semi-submersible platform Browse Basin gas reservoirs were the largest discovery of hydrocarbon liquids in Australia in 40 years

Browse Basin gas reservoirs were the largest discovery of hydrocarbon liquids in Australia in 40 years Largest ever Japanese overseas investment

Largest ever Japanese overseas investment Largest ever project financing ($20 billion)

Largest ever project financing ($20 billion) Offshore and onshore facilities built to withstand a 10,000 year storm without significant damage.

Offshore and onshore facilities built to withstand a 10,000 year storm without significant damage. INPEX estimates it will create tax revenue of $100 bn for the Federal Government

From the centre of Darwin, the Bladin Point gas plant under construction appears as a distant gleam — its presence is felt more through the injection of wealth into local business (INPEX estimates it will spend US$8bn with NT businesses during the construction phase), the tall apartment buildings that have sprung up in the city centre, and the high-vis workers who wait on street corners for private buses to the site.

But at the site this perspective is reversed, and the Northern Territory capital appears dwarfed by the 90m diameter LNG storage silos, the pre-fabricated modules built at fabrication yards in China, the Philippines and Thailand that were shipped to the site in four parts each weighing 5,500 tonnes.

The Bladin Point power plant could power a town three times the size of Darwin.

In addition, as Mr Bon noted, there are also the offshore facilities — the CPF semi-submersible platform currently being built by 6,000 workers in South Korea, the pipe-laying barge of 700 people, the gigantic FPSO that will displace seven times more water than the Titanic.

The fall in global LNG prices — which hit six-year lows in January — has meant large offshore gas projects with massive upfront capital outlays are less viable and more of an investment risk.

After a massive natural gas construction boom in Queensland and Western Australia, there are few new major gas projects in the pipeline.

Unions NT organiser Paul Kirby said he was receiving several calls a week from Gladstone workers in Queensland who were looking to pick up work in the NT as their own projects wound down.

'We need to plan to avoid a boom and bust cycle'

According to INPEX, construction is on schedule, and according to the unions, this has been achieved with "industrial harmony" — without the major industrial action of projects such as Gorgon.

"Some projects in Australia are struggling to be on time," said Mr Bon.

"We want to be the one that will succeed."

As the construction phase nears completion, unions have shifted their focus to securing the "operations phase" jobs for local workers and smoothing out the coming downturn.

"This is a $34-billion project. The Giles and Abbott governments need to plan to avoid a boom and bust cycle," Maritime Union of Australia NT Branch Secretary Thomas Mayor said.

"It's probably one of the biggest projects in progress at the world at the moment," says managing director Louis Bon. ( ABC News: James Purtill )

"If this is done properly, Darwin will be set up for a generation of prosperity.

"But we can't stand back and allow companies to come in, plunder our natural resources and leave nothing behind.

"These natural resources belong to everyone and that's why we'll continue to be front and centre of the public debate and protect the best interests of all Territorians."

But given the scale of job cuts on the horizon, it is not clear what any government may do to avoid the bust.

"INPEX and their contractors have a lot of ground to make up in local employment outcomes, both now during construction and in a few years in the post construction operational phase," Mr Mayor said.

Around the world the Ichthys project employs about 30,000 people.

Within two years it will employ about 700 — the positions will all be in Australia, either in Perth, Darwin or on the Browse Basin rig.

Mr Townsend said about 400 of these 700 positions had already been recruited and "395 of these are Australians" but he would not be drawn on how many of these workers were from Darwin, or how much INPEX would spend in Darwin after construction.

"I've been coming here for last seven years on the project to see how Darwin has been transformed in that time," he said.

"I get off the plane and there's a real vibe about Darwin.

"This is a place where things are happening."