CNG is often confused with LNG. The similarity is that both are forms of natural gas that has been stored. The main difference is that CNG is stored and transported in compressed form, while LNG is stored and transported in liquefied form. CNG has a lower cost of production and storage compared to LNG as it does not require an expensive cooling process and cryogenic tanks. CNG requires a much larger volume to store the same mass of fuel and the use of very high pressures. LNG projects require large investments along with substantial natural gas reserves and are economically viable for distances longer than 3000 miles. Compressed natural gas technology provides an effective way for shorter-distance transport of the gas and is economical for much smaller reserves due to the much smaller investment in infrastructure required. Indeed, the CNG technology is aimed at monetizing offshore reserves, which cannot be produced because of unavailability of pipeline or because the LNG option is very costly. The CNG technology is easy to deploy economically for distances up to 2500 miles with less requirements for facilities and infrastructure. At distances above 2500 miles the cost of delivering gas as CNG becomes essentially the same as the LNG whereas the disparity in the volumes of gas transported by the respective technologies and market demands play the deciding role for using the technology and thus LNG which takes far less volume usually becomes more economic then. LNG requires large reserves of natural gas near the facilities to support a LNG project and get acceptable returns capital investment. LNG also requires large demand at the user site to justify the vast investments required. Satisfying small demand markets and monetizing small reserves are the two things that the transport of CNG natural gas is intended to target. Indeed, CNG technology can be used readily for the transportation of gas from smaller and marginal fields with small throughputs. The technology is simple and can be easily brought into commercial application. In comparing CNG with LNG the same transporting ship real-volumetric capacity is used. However, in making the comparison it is worth remembering the disparity in the actual standard volume of the gas transported. For the same ship volume, LNG transports 2.1 Bcf of natural gas compared to a maximum volume of 1.2 Bcf transported as CNG. Another factor in the choice between CNG and LNG is the pace of the project deployment. Typically LNG projects require at least 4 to 5 years from the planning stage to the delivery of first cargo. CNG projects can be commissioned in a period from 30 to 36 months beginning with the project design, planning and construction of the required infrastructure and delivery of the first cargo. CNG can also be a solution to monetize stranded reserves of natural gas. There are several large reserves of natural gas in the world that would justify an LNG project, however, due to political risk factors, these same reserves are also considered stranded. In such cases, CNG may transport this stranded natural gas, avoiding the necessity of expensive land-based LNG facilities. CNG carriers do not require a regasification facility near populated markets, natural gas from CNG tankers can be offloaded through an offshore mooring buoy and transported to shore through a sub-sea pipeline. Using a turret mooring buoy, CNG carriers can offload miles away from populated areas. The loading of CNG can be performed using offshore mooring buoys as well. By using a submerged mooring buoy outside of territorial waters (12 miles), CNG can be delivered virtually anywhere. Public safety will not be a concern when the ship is beyond the horizon as it would be for LNG. Whereas LNG has a strong point in its capability to transport larger volumes of gas in each trip, its inability to market stranded reserves makes CNG very attractive for smaller reserves and smaller users. LNG is more suitable for the long distance transports of gas. Another way of applying the CNG technology is in conjunction with LNG. It can work as a complement for a LNG project because CNG can serve as a temporary solution for reserves that can eventually support a LNG project.
