It's not every day that a company writes a check for $15 billion in an effort to save money. That's a pretty astronomical number, but it does represent the cheaper option for several companies looking to tap offshore gas fields for liquefied natural gas, or LNG, production. Laying underwater pipelines for hundreds of miles can be expensive, especially when the gas and condensate contains large amounts of seawater and sediment. This heavily skews the economic competitiveness of large offshore reserves around the world to the "noncompetitive" category.

Why bring the gas to the liquefaction facility when you can bring the facility to the gas?

Royal Dutch Shell (RDS.A) aims to get around the high costs of developing offshore gas fields by building a floating liquid natural gas, or FLNG, facility. This is not a fanciful idea by a large multinational company with too much time on its hands: Construction has already begun on the $12.6 billion Prelude FLNG facility. It could mean big things for the future of natural gas.

All ideas start off as crazy
Shell's Prelude FLNG facility (67.5% interest) will be the world's largest, producing 3.6 million metric tons (mtpa) of LNG, 1.3 mtpa of condensate, and 0.4 mtpa of liquid petroleum gas each year. If building a massive floating facility sounds ridiculous, that's because it is. And how massive is massive? Try 488 meters long. That's about 50% longer than a Nimitz-class aircraft carrier (the world's largest), more than four times longer than a soccer field, the same size as the Taipei 101 Tower, and just plain ginormous. The floating giant will displace the same amount of water at six Nimitz-class aircraft carriers. Yet despite its massive size, Prelude will have just 25% of the footprint of a similar-sized onshore facility.  

The capacity will represent only about one-third the capacity of the Sabine Pass facility being constructed by Cheniere Energy (LNG 0.96%) and Total (TTE 1.72%). However, this should not be looked at through a lens that focuses solely on capacity. Prelude is writing an important chapter in world energy supply -- the kind that isn't factored into long-term energy predictions. As we'll see, the facility can be useful long after the gas field becomes uneconomical.

Source: Royal Dutch Shell.

Prelude FLNG will be moored about 200 kilometers off the northwestern coast of Australia and will open up a steady supply of gas to the high-priced Asian markets. The facility won't have to be brought back to port for inspection for 25 years -- not even during the strongest typhoons imaginable (famous last words).

How it works
The FLNG facility will float 250 meters above its target gas field, extract the riches from beneath the sea floor, clean and process the natural gas into LNG and other liquids, store them in the massive tanks located under its deck, and then offload the booty to LNG carriers that come cruising on by. Engineers have created a system that uses cold water from the ocean floor -- at the rate of 50 million liters per hour -- to help cool the LNG tanks. Ocean water is nowhere near the -162 Celsius needed to liquefy natural gas, but it will save millions of dollars and valuable deck space while protecting the facility's cargo from ambient temperatures.

Green LNG
This engineering marvel will eliminate hundreds of miles of pipelines and alleviate traffic in some of Australia's busiest ports. It also keeps traffic away from Australia's Great Barrier Reef, which adds more than $6.4 billion to the country's GDP each year. Decades from the now, when the gas field is depleted or no longer economical, the ship can float over to the next big offshore opportunity. It could also mine smaller reserves that are not economically recoverable by other means, perhaps including valuable methane hydrate deposits.  

An industry shift?
While a handful of multinational companies such as Gazprom and Petronas are planning or building their own FLNG facilities, several high-profile projects opted out at the last minute. Chevron (CVS 1.49%), ExxonMobil (XOM 1.15%), and Shell were initially considering floating facilities for their massive Gorgon and Wheatstone projects but ultimately decided against it. However, the fields are so massive -- expected to triple Australia's LNG capacity -- that there will be plenty of opportunities for future FLNG capacity. That's especially true given Shell's presence, which was responsible for nudging the group toward FLNG in the first place.

INPEX and minority partner Total are building a hybrid FLNG facility for its Browse Basin project. The facility will extract and clean natural gas offshore before shipping it 885 kilometers to an onshore processing facility. Condensate and other liquids will be available for offloading to carriers offshore. Browse will have twice the capacity of Prelude, but will cost 2.7 times as much to build. With a final price tag of $34 billion, perhaps Shell is onto something.   

Foolish bottom line
Although it seems unlikely that all offshore gas deposits will be developed by FLNG facilities in the future, innovations from Shell will ensure that costly onshore facilities aren't the only option on the table. Not only does Prelude represent a discount to a similarly sized onshore facility, but its lifetime can also be extended well beyond that of the initial gas field. That could be a major selling point for companies with large offshore reserves scattered across the globe and give Shell the upper hand in partnering with new projects. This could be as big of a game-changer for the company -- and investors -- as it is for the industry.