Natural gas storage
Natural gas storage refers to the storage of natural gas until needed by electricity suppliers and other consumers. Natural gas can be stored both underground and in tanks above ground in liquid form. The rapid increase in the production of natural gas, due in part to the practice of fracking, has led to increased scrutiny regarding how and where natural gas is stored.
In order for natural gas to be stored indefinitely, a certain amount of gas must remain in the storage unit to maintain necessary pressure levels. The amount of gas that must remain in the reserve and the amount that can be withdrawn vary depending on the characteristics of the storage unit.
Below are some definitions of storage measures used within the industry.
- 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 currently being stored.
- Base gas, or cushion 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- Working gas is the amount of gas inside a storage unit that can be withdrawn and sold.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). Injection capacity varies as changes occur in the pressure within the reservoir, total gas in storage, and other factors.
- Deliverability is how much natural gas can be withdrawn from a storage unit per day. Deliverability is also measured in millions of cubic feet per day (MMcf/day) and varies according to the same conditions as does injection capacity.
Base gas is the reservoir of natural gas that is needed to maintain adequate pressure inside a storage unit. In the U.S. once natural gas has been mined it is often stored in depleted oil or natural gas fields close to where it will be consumed. Natural gas can be stored in salt caverns, aquifers and mines. The amount of base gas needed in a reservoir varies based on the type of storage unit, the contractual agreement between natural gas providers, and utilities and regulations.
The image to the right shows the different types of natural gas storage facilities used in underground storage.
- Depleted oil and natural gas fields are the most common storage centers in the U.S. because of their availability and relatively low cost. Depleted oil and gas reservoirs are widely available anywhere that oil and gas production has occurred. Additionally, depleted fields are cost-effective storage units because much of the infrastructure needed for delivery to consumers already exists and only needs to be converted.
- Salt caverns can also be used to store natural gas. They require a low amount of base gas for storage, meaning less gas must remain in the unit to make it an adequate storage facility. Salt caverns do require quite a bit of construction to store natural gas adequately. Salt caverns are located in Northeast, Midwest and Southwest United States.
- Aquifers can also be used to store natural gas. Before storage can happen the aquifer must be protected with "an impermeable cap rock." Aquifers can be more expensive places to store natural gas because of this rock cap, additional monitoring and performance requirements. Aquifers can also be expensive because they require larger amounts of base gas to maintain adequate pressure. Most aquifer storage units are located in the Midwest.
- Abandoned mines have been used at least once in the U.S. to store natural gas.
Above ground storage
Liquefied natural gas, or (LNG), is natural gas that has been sufficiently cooled, such that it can be stored in liquid form. Insulated storage tanks, such as those pictured to the right, can keep LNG cool enough to prevent it from evaporating. There are local, state and federal regulations that dictate how LNG can be stored.
Owners and operators
The U.S. Energy Information Administration identified four types of owners and operators of natural gas storage facilities.
- Interstate pipeline companies principally operate underground storage facilities and pipelines that cross state lines. The Federal Energy Regulatory Commission oversees these operators.
- Intrastate pipeline companies are similar to interstate pipeline companies, but they also serve end-use consumers and operate pipelines within one state.
- Local distribution companies (LDCs) have focused on using underground storage units to serve consumers. A recent round of deregulation at the federal level has allowed some LDCs to lease a portion of their storage capacity to third parties.
- Independent storage service providers are private companies, often smaller ones, that have begun providing storage services as the market for natural gas-fired power plants has grown.
Below is a list of LNG related ballot measures across the United States.
- U.S. Energy Information Administration, "The Basics of Underground Natural Gas Storage," August 2004
- 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