LNGINDUSTRY

WHY LNG WILL FALL IN LOVE WITH CNGIn the quest to find economic reserves to supply liquefaction

plants, the LNG industry has a nimble new friend:

compressed natural gas (CNG) shipping.

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LNG’s New FriendIan Mallory, Sea NG, Canada, explains how marine CNG

is expanding the transport options of gas producers

In the quest to find economic gas reserves to supply liquefaction plants, the LNG industry has a nimble new friend: compressed natural gas (CNG) shipping.

As global demand for LNG steadily increases, producers are finding that smaller or more distant offshore gas fields could be compelling sources for gas to liquefy – if there were an economic way to transport this gas to on-shore plants or existing gathering systems.

Currently, subsea pipelines are the only method of delivering significant volumes of offshore gas for feedstock to onshore facilities such as LNG, methanol, or gas-to-liquids plants. The effective range of subsea gathering pipelines is usually maximum 400 km. In cases where the distance to the gas field is beyond 400 km – or the seabed too difficult, or the water depth too deep -- a subsea pipeline can quickly become less viable. More pivotal, an installed seabed pipeline system cannot be moved to tap sequentially a series of smaller fields in different locations. For these reasons, producers have been seeking a flexible means to extend their transport reach and unlock more stranded offshore gas.

The advent of the CNG ship removes these restrictions on gathering gas for LNG and other industrial applications: a CNG gathering shuttle has an effective economic range of 2500 km and can be readily re-deployed from one offshore field to another as circumstances require.

Figure 1: Marine CNG enables producers to overcome the limitations of traditional pipelines

Extending reachUnlocking stranded gas with Floating

CNG (FCNG) for smaller fieldsThe CNG gathering shuttle of Sea NG Corporation is a new ship, fully approved for construction by the American Bureau of Shipping (ABS), that deploys a novel solution to load, store and transport natural gas over shorter marine distances. The technology is the Coselle® System, a patented configuration of large pressure containers made with inexpensive, small-diameter steel pipe. It is simple and reliable – and safe, due to the small-diameter size of the gas containment.

The Coselle CNG gathering shuttle is built using normal shipyard construction techniques. The Coselle containers are integrated into the ship like any other ‘block’, and form part of the ship’s structure. South Korea’s leading shipyards have been qualified as builders.

Figure: C112 shuttle ship with Coselle cutaway

Loading and unloading the CNG gathering shuttle of Sea NG is also simple and economic. With its ability to dynamically position and maintain station, the ship can be loaded offshore, using industry standard pipeline gas compression equipment and connectors. Unloading the gathering shuttle at port requires an even smaller footprint: a compact (“scavenging”) compression unit and unloading arm at a finger pier. In circumstances where an absolute minimum shore impact is required, the decompression can be completed on each ship. In circumstances where an absolute minimum shore impact is required, the decompression equipment can be located on each ship.

Three major international corporations have joined with Sea NG to deploy Coselle CNG shipping services worldwide. Enbridge Inc., Marubeni Corporation and Teekay Corporation have joined Sea NG in a strong global alliance to finance, construct and operate the marine CNG projects worldwide.

Coselle CNG and LNG producers: could be good friends.

“ ...producers have been seeking a flexible means to

extend their transport reach and unlock more stranded offshore gas. ”

With the advent of the fully ABS approved Coselle® ship, marine CNG has become an economically viable and flexible option for the transportation of natural gas over water. The use of Coselles (very large pressure vessels made with inexpensive, small diameter steel pipe) dramatically reduces the cost of CNG shipping while offering exceptional safety and simplicity.

Fields smaller than 5 TCF can now be exploited with Coselle CNG ships deployed in conjunction with a conventional gas FPO or a gas platform. A Floating CNG (FCNG) system typically costs less than half of an FLNG vessel for such volumes, as compression is a simpler, cheaper process than liquefaction, and uses less energy in its operation.

Figure: CNG ship with Single Anchor Leg (SAL) Mooring

The FCNG system can sequentially be moved from one smaller field to another, enabling the exploitation of significant gas reserves that would be impractical to access using LNG or pipelines. FCNG should promote the development of new smaller reserves that are located within the 2,500 km economic reach of CNG. Many gas fields once considered stranded may now be considered economically viable and thereby “unlocked” for development.