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How Is Natural Gas Stored in a Salt Dome?

Natural gas has been an important fuel for decades, used primarily in homes and businesses to generate heat. While natural gas production is consistent all year, demand for heating is concentrated in the cold months. This makes it necessary to find ways of storing gas in bulk to meet peak-season demand. Underground storage in depleted gas fields, aquifers or salt domes is a safe and practical option.

Types of Underground Storage
- There are three forms of underground storage used for natural gas. The first is once-productive gas fields that have been exhausted. Not only are they well-proven holding grounds for the gas, they come equipped with all the necessary infrastructure to pump it back out again. In areas where these are not available, gas can also be stored in an aquifer. This is an area of porous rock beneath a "cap" layer of impermeable rock. Salt domes are the smallest of the underground storage areas, and they take advantage of natural salt formations.
Salt Domes
- Salt domes are areas where naturally occurring salt deposits form in the shape of an inverted bowl or irregularly rounded column. These can be hollowed out by pumping water into the middle of the deposit and pumping out the dissolved brine until the cavity is suitably large. Gas is then pumped in to fill the resulting reservoir. The salt deposits are impermeable to the gas, encasing it securely.
Salt Domes vs. Other Underground Storage
- Salt domes are the smallest of the three underground storage systems for natural gas. In one important respect, however, they are the most efficient of the three. Any storage facility must maintain enough gas to provide a necessary minimum of pumping pressure. That base amount of gas is referred to as pad gas, base gas or cushion gas, and it is not available to the storage operator for sale. Salt domes only require one-third of the total volume of gas to serve as cushion gas, compared to 50 percent in a depleted field or as much as 80 percent in an aquifer.
Other Advantages of Salt Dome Storage
- Because of their relatively small size, salt dome storage facilities are not able to provide the base amounts of gas required for a major urban center. However, they can be brought online in as little as one hour, a much shorter time than other storage facilities. This makes salt domes ideal for meeting peak-system needs in times of high demand, complementing existing supplies. In times of emergency or natural disaster, salt domes would also be able to deliver gas much more quickly than other storage facilities.

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