In a bid to capitalise on the predicted future market for Compressed Natural Gas (CNG) transportation, Norway’s largest oil and gas company and two of the country’s most significant shipping companies have joined forces in order to pool knowledge and develop new technologies. Statoil, Teekay Shipping and Leif Höegh have jointly established a new company, Compressed Energy Technology AS (CETech) and have already filed a number of patents. CETech’s CNG model has received Approval in Principle from classification society DNV. Market studies suggest that CNG ships are a viable alternative where the size and geographical location of oil and gas fields means transportation is not commercially attractive using conventional or Liquefied Natural Gas (LNG) solutions.
The company has developed two major designs - the first is the CNG Shuttle designed to carry gas only, while the second is a conventional CNG system, but fitted onto an oil shuttle tanker. The CNG Shuttle vessel design will consist of large horizontal pipes capable of carrying gas under high pressure mounted within and on its deck. It is envisaged that these will be relatively large vessels, typically 200-300m long and 40-60m wide. Such vessels could be deployed in a number of ways. They might receive processed gas from a platform, although the presence of a platform is unnecessary. Given the ability to carry out processing onboard the ship, another option is for the gas to enter the ship via an APL loading/unloading system. In this system a buoy connected to the seabed facilities, is introduced into the hull of the tanker where it is mated with the ship’s own reception facilities. After the tanker has been loaded, the buoy would be disconnected, permitting the tanker to sail to its destination - a land terminal or even another offshore installation.
CETech has also recently completed the outline specifications for the CNG Producer, which is essentially a CNG storage unit incorporated with a conventional shuttle tanker. This was developed with support of the Norwegian Research Council and is primarily aimed at applications requiring the simultaneous production of oil and associated gas. Research focused on improving the interface between the ship and pipe system, and in particular how the pipe can be anchored to the vessel bulkhead, is ongoing. In the meantime, a number of designs have been proposed, based on Aframax and Suexmax sized tankers. The smaller unit, based on the Aframax design, would be able to store 60-70 000m3 of oil and 8000m3 of gas. The larger, Suezmax-sized unit would transport 120 000m3 of oil along with a 30 000m3 gas system which would correspond to approximately 6000t. The gas storage facilities would be installed on the deck above the oil. Although there would be enough physical space, this extra weight and volume would change the sailing properties of the vessel itself. It would therefore require a new tanker rather than a conversion. If it is not used for gas production, it could still be used as a conventional oil tanker, which makes it more flexible.
