Natural gas, like most other commodities, can be stored for an indefinite period of time. The exploration, production, and transportation of natural gas takes time, and the natural gas that reaches its destination is not always needed right away, so it is injected into underground storage facilities.
These storage facilities can be located near market centers that do not have a ready supply of locally produced natural gas. Traditionally, natural gas has been a seasonal fuel. That is, demand for natural gas is usually higher during the winter, partly because it is used for heat in residential and commercial settings.
Stored natural gas plays a vital role in ensuring that any excess supply delivered during the summer months is available to meet the increased demand of the winter months.
Natural gas in storage also serves as insurance against any unforeseen accidents, natural disasters, or other occurrences that may affect the production or delivery of natural gas.
Base Load vs. Peak Load Storage
There are basically two uses for natural gas in storage facilities: meeting base load requirements, and meeting peak load requirements. As mentioned, natural gas storage is required for two reasons: meeting seasonal demand requirements, and as insurance against unforeseen supply disruptions.
Base load storage capacity is used to meet seasonal demand increases. Base load facilities are capable of holding enough natural gas to satisfy long term seasonal demand requirements.
Types of Underground Storage
Underground natural gas storage fields grew in popularity shortly after World War II. At the time, the natural gas industry noted that seasonal demand increases could not feasibly be met by pipeline delivery alone. In order to meet seasonal demand increases, the delivering capacity of pipelines (and thus their size), would have to increase dramatically.
However, the technology required to construct such large pipelines to consuming regions was, at the time, unattainable and unfeasible. In order to be able to meet seasonal demand increases, underground storage fields were the only option. As mentioned, there are three main types of underground natural gas storage facilities.
This storage facility used a depleted natural gas well that had been reconditioned into a storage field. In the United States, the first storage facility was developed just south of Buffalo, New York.
By 1930, there were nine storage facilities in six different states.
Prior to 1950, virtually all natural gas storage facilities were in depleted reservoirs. The most prominent and common form of underground storage consists of depleted gas reservoirs.
Depleted reservoirs are those formations that have already been tapped of all their recoverable natural gas.
This leaves an underground formation, geologically capable of holding natural gas. In addition, using an already developed reservoir for storage purposes allows the use of the extraction and distribution equipment left over from when the field was productive.
Aquifers are underground porous, permeable rock formations that act as natural water reservoirs. However, in certain situations, these water containing formations may be reconditioned and used as natural gas storage facilities.
As they are more expensive to develop than depleted reservoirs, these types of storage facilities are usually used only in areas where there are no nearby depleted reservoirs.
Aquifers are the least desirable and most expensive type of natural gas storage facility for a number of reasons. First, the geological characteristics of aquifer formations are not as thoroughly known, as with depleted reservoirs.
A significant amount of time and money goes into discovering the geological characteristics of an aquifer, and determining its suitability as a natural gas storage facility.
Underground salt formations offer another option for natural gas storage. These formations are well suited to natural gas storage in that salt caverns, once formed, allow little injected natural gas to escape from the formation unless specifically extracted.
The walls of a salt cavern also have the structural strength of steel, which makes it very resilient against reservoir degradation over the life of the storage facility.
Essentially, salt caverns are formed out of existing salt deposits. These underground salt deposits may exist in two possible forms: salt domes, and salt beds.
Salt domes are thick formations created from natural salt deposits that, over time, leach up through overlying sedimentary layers to form large dome-type structures.
Shipping and Transportation
The transportation of liquefied natural gas(LNG) refers to any movement or shipping of natural gas while in its liquid form. The two major methods of transporting LNG are by pipeline and vessel.
LNG flows efficiently through pipelines so is a preferred method of transporting natural gas. Most LNG pipeline infrastructure takes the LNG between liquefaction facilities and storage facilities, from storage facilities to tankers, and from tankers to re-gasification facilities.
LNG is much denser than compressed natural gas (CNG). This means that much higher amounts of gas are able to be transported for the same volume flow.
The downside is that LNG pipelines are difficult and costly to construct. As LNG requires a temperature of -160°C (-260°F) to remain in its liquid form, significant insulation must be incorporated into LNG pipelines in order to maintain this low temperature and ensure no re-gasification occurs.
This normally includes a combination of mechanical insulation, for example glass foam and a vacuum layer. This complex insulation system makes LNG pipelines significantly more difficult and expensive to manufacture than standard natural gas pipelines. (3)
Liquefied natural gas vessels
The majority of worldwide LNG exports take place at an intercontinental level, meaning that shipping LNG across the ocean is often required. This is done with the use of an LNG vessel or LNG ship, which transports large quantities of LNG between export and import terminals.
Several types of LNG vessels exist in the industry today, with the main one being referred to as an LNG tanker.