Natural gas storage
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Natural gas storage involves the storage of natural gas until it is used as energy. Natural gas is stored underground and in tanks aboveground in liquid form. As of November 2015, there were 385 active natural gas storage facilities in the United States (excluding Alaska and Hawaii).[1][2][3]
Natural gas is usually held in underground facilities, which can include depleted reservoirs in oil or natural gas fields, aquifers, and salt caverns. Natural gas can also be stored as a liquid in aboveground storage tanks. A certain amount of gas must be in a storage unit to maintain necessary pressure levels. The amount of gas in the reserve and the amount that can be withdrawn vary depending on the characteristics of the storage unit.[1][4][5]
Underground storage
Underground facilities are used according to their physical characteristics and various economic considerations. For example, an underground storage site may be selected based on its capacity to hold gas for future use or the rate at which gas can be withdrawn for use. The majority of underground facilities used in the United States are depleted oil or natural gas fields. These sites are generally close to areas where natural gas is consumed. Operators at an oil or gas field can use existing wells and pipelines to store natural gas.[1]
Aquifers (bodies of permeable rock that can contain or transfer groundwater) can become natural gas storage sites if impermeable rock caps are placed on sedimentary rock formations. Aquifers have a similar geology to depleted oil and gas fields, but an aquifer generally has less flexibility as a storage system for injecting and withdrawing natural gas. They are primarily used in the midwestern United States.[1]
Salt caverns (caverns developed in an underground salt layer to store natural gas) are developed in salt dome formations. These caverns have high injection and withdrawal rates compared to other storage sites. Though salt cavern construction is generally of higher cost in terms of working gas capacity than depleted oil and gas fields, costs (of each thousand cubic feet of gas) are generally lower if the gas is injected or withdrawn several times each year. Salt caverns are found throughout the United States, though most are found in the Gulf Coast region.[1]
Ownership and regulation
Interstate pipeline companies, intrastate pipeline companies, independent storage providers, and local distribution companies are the primary owners and operators of underground natural gas storage facilities. According to the U.S. Energy Information Administration, approximately 120 entities operated 385 active underground storage sites in the United States (excluding Alaska and Hawaii) as of November 2015. Storage facility owners and/or operators may or may not own the stored natural gas, which can be held under lease with natural gas shipment companies, local distribution centers, or end-users that also own the gas. The entity that owns or operates an underground facility will generally determine how the facility's storage capacity will be used. States primarily regulate natural gas storage facilities involved in intrastate commerce while the Federal Energy Regulatory Commission primarily regulates storage facilities involved with interstate commerce.[1]
Aboveground storage
Liquefied natural gas (LNG) is natural gas that has been cooled so it can be stored in liquid form. Insulated storage tanks, such as those pictured to the right, keep LNG cool to prevent evaporation.[6]
Terms
Below are descriptions of terms related to underground storage facilities.[1]
- Total gas storage capacity is the maximum amount of natural gas that can be stored.
- Total gas in storage is the total amount of gas being stored in a given unit.
- Base gas is the reservoir of natural gas that is needed to maintain adequate pressure inside a natural gas storage unit.
- Working gas is the amount of gas inside a storage unit that can be withdrawn and sold.
- Working gas capacity is the total gas storage minus the volume of base gas.
- Injection capacity is how much natural gas can be added to a storage unit per day. Injection capacity is measured in millions of cubic feet per day (MMcf/day).
- Deliverability is how much natural gas can be withdrawn from a storage unit per day. Deliverability is measured in millions of cubic feet per day (MMcf/day).
Natural gas storage from 2011 to 2017
The image below shows working underground storage of natural gas from January 1, 2010, to February 17, 2017. Natural gas storage increases beginning in warmer months (March and April) as less natural gas is used. Storage decreases beginning in colder months (such as October and November) as more gas is used, primarily for heating.[7]
See also
Footnotes
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 U.S. Energy Information Administration, "The Basics of Underground Natural Gas Storage," November 16, 2015
- ↑ WAMC Northeast Public Radio, "Gas Storage Adds To Fracking Controversy In Upstate," July 3, 2013
- ↑ The Business Journals, "Controversial natural gas storage plan goes to PUC," July 1, 2010
- ↑ U.S. Energy Information Administration, “Glossary B,” accessed January 24, 2014
- ↑ Oil and Gas Journal, "Base and working gas: getting the most out of storage," June 9, 2003
- ↑ California Energy Commission, "Frequently Asked Questions About LNG," accessed May 22, 2014
- ↑ U.S. Energy Information Administration, "Lower 48 States Natural Gas Working Underground Storage," accessed February 24, 2017
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