Storage Fields

What are Storage Fields?

Underground natural gas storage can be used to balance the load requirements of gas users. Storage fields are the warehouses that provide a ready supply of natural gas to serve the market during periods of high demand. For example, in the Midwest and the Mid-Atlantic regions, natural gas is primarily used during the winter because many homes are heated by natural gas. To accommodate this load profile, natural gas is injected into storage fields during the warmer months (April - October), and withdrawn in the colder months (November - March). However, since the 1980s, most new power generation equipment has been fired by natural gas, which has created summer peaking requirements for natural gas to accommodate air conditioning loads in many areas of the country. Storage helps to meet peak demand requirements both in winter and in summer.

Types of Storage Facilities

Most natural gas storage facilities in the U.S. consist of underground formations, combined with above-ground equipment. These facilities include wells (injection/withdrawal and observation, water supply, water disposal), wellhead valve assemblies, gathering lines (field lines, headers), metering and compression facilities, dehydration units, generators or transformers, associated electric equipment, roads, sheds/buildings and pipeline pigging facilities. A list of natural gas facilities that fall under FERC. Natural gas storage facilities that are owned and operated by natural gas distribution systems and used to deliver gas to their customers fall under the authority of state regulatory agencies. 

Depleted Oil and/or Gas Fields

Most of the natural gas storage in the United States consists of naturally-occurring oil or gas reservoirs that have been depleted through production. These consist of porous and permeable underground rock formations (usually 1,000 to 5,000 feet thick) that are confined by impermeable rock barriers and identified by a single natural pressure. Typically, this type of field has one injection/withdrawal cycle each year – gas is injected in summer and withdrawn in winter. 

This type of storage facility is normally used for long term or seasonal system supply, although in some instances it is used for peak day deliveries. These formations contain volumes of gas that are permanently stored in the field (called cushion or base gas) that help to maintain the underground pressure required to operate the field. Storage gas is then added to the field. In field storage the base gas is generally about 50% of the total reservoir capacity

Aquifer Storage Fields

This type of storage field uses a permeable rock formation containing water, called an “aquifer.” The nature of the water in the aquifer may vary from fresh water to saturated brine. An aquifer would have a high cushion gas requirement, generally between 50% and 80%, as the water in the portion of the reservoir being used for storage must be displaced constantly. They also have high deliverability rates but are limited to one injection/withdrawal cycle each year. 

Salt Cavern Storage

This type of storage field uses caverns that are leached or mined out of underground salt deposits (salt domes or bedded salt formations). Salt caverns usually operate with about 20% to 30% cushion gas and the remaining capacity as working gas. Working gas can be recycled more than once per year (some up to 10 – 12 times per year), the injection and withdrawal rates being limited only by the capability of the surface facilities. Salt cavern storage has high deliverability and injection capabilities and is usually used for peak deliverability purposes, daily or even hourly. Most of the naturally-occurring salt caverns in the United States lie closer to the producer region—in Louisiana, Texas, and the Gulf Coast.