Towed CNG cargo packages competitive with LNG, pipelines

A transport technology for moving up to two bcf of CNG (compressed natural gas) on a ship over 4,000-mile distances at lower costs than LNG (liquified natural gas) has been claimed by EnerSea Transport, L.L.C. The technology is known as Votrans (volume optimized transport and storage).

A transport technology for moving up to two bcf of CNG (compressed natural gas) on a ship over 4,000-mile distances at lower costs than LNG (liquified natural gas) has been claimed by EnerSea Transport, L.L.C. The technology is known as Votrans (volume optimized transport and storage).

Enersea describes the technology as a virtual sea-going pipeline, comprising long large-diameter pipes contained within an insulated structure, integrated into a ship. The developers say that Votrans improves on previous CNG concepts by combining optimal storage efficiency, the ability to transport both lean and rich gas, an innovative offloading process, and significantly lower (~40%) compression requirements. The latter increases vessel capacities and reduces costs.

Independent engineering, naval architecture, and economic analyses performed by Paragon Engineering, Alan C. McLure Associates, and Groppe, Long & Littell confirm the viability of the technology, according to EnerSea Transport. The firm states that natural gas could be sold into US markets for substantially less than $3/Mcf. This price compares favorably with published LNG average landed costs of approximately $3.50/Mcf.

EnerSea claims other competitive advantages over LNG:

  • Total capital costs are less than LNG
  • Terminal facilities make up less than 15% of total capital cost, compared with more than 60% for LNG, making the technology more flexible and the capital easily re-deployed
  • Minimizes gas losses during processing and transport less than 7%, compared to 20% for LNG.

These advantages provide producers with higher netbacks through cost savings and the ability to access multiple markets. "Natural gas markets throughout the world are experiencing record demand," stated Paul Britton, EnerSea's managing director. "In the US alone, consumption is expected to approach 30 tcf per annum by 2010, a substantial portion of which is predicted to be met by foreign LNG imports.

"Votrans could provide a domestic alternative by delivering Alaskan or deepwater Gulf of Mexico gas more cheaply than proposed pipelines. Because Votrans is effectively a portable pipeline, it can also competitively deliver stranded gas reserves to worldwide markets with increasing natural gas demand." Britton said EnerSea has a development and construction schedule that would allow the initiation of transportation and sales by 2004.

Portable pipeline

The Votrans method involves ship towing CNG cargo packages consisting of long large-diameter pipe structures manifolded together in tiers. In order to maintain temperature over time and distance, the pipe structures are contained within a nitrogen filled and insulated "cold box."

Producers can tailor gas transportation requirements with field production profiles to optimize infrastructure investment. Redeploy-able conversion and newbuild ships have design capacities ranging from 300 MMcf to 2 bcf. The offloading operation and minimal capital investment required for terminal facilities will provide direct access to multiple markets. Offshore offloading operations should reduce permitting issues. Incremental cost to add offloading terminals is minimal when compared to arbitrage associated with access to multiple markets.

All gas conditioning (pressure and temperature) equipment can be located on the platform, at the loading terminal, or on a Votrans ship, thus eliminating a link to an onshore facility.

A redeployable Votrans fleet accounts for 85% of the total capital expenditure and reduces the need for long-term dedicated commitments to justify projects. The capability to transport natural gas liquids produced with associated gas directly from the field results in decreased capital expenditures for field process facilities and provides an opportunity for producers to monetize associated gas, the developers say. Associated gas currently being flared or re-injected for conservation purposes can be transported to market and converted to commercial - proved, developed producing reserves.

Loading system

Votrans uses a proven loading system designed for harsh environmental conditions encountered in typical stranded gas areas of the world. The system maximizes valuable gas reserves delivered to market by reducing product loss associated with processing and transport. Shrinkage is estimated at 93-97%, which includes product used as fuel for compression, transport (200-4,000 miles) and offloading. Ships can be converted to this service or can be designed and built specifically for it.

The system's storage can also be used as cyclic storage on a daily basis, with deliverability similar to salt dome cavern storage. In addition, the system can be used for extended well test applications to eliminate flaring and provide information resulting from long-term reservoir tests that are required to make decisions on deepwater developments.

Patents have been filed in the US and internationally. Phase II concept engineering has been completed by Paragon Engineering and Alan C. McLure Associates. Interface meetings are underway with the US Coast Guard and the (US) Minerals Management Service. EnerSea claims that the firm's principles together have founded and built profitable energy and logistics businesses with more than $1 billion in annual sales. The company plans to complete regulatory approval in principle in 2002 and could initiate service by mid-2004.

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