Companies are proposing to build or expand three large underground natural gas storage facilities in salt caverns in Mississippi and Texas to supply a rapidly growing LNG industry and to use gas generators to back up the use of wind and solar power.  

The three storage projects – by Enstor Gas in Mount Olive, Mississippi; Golden Triangle Storage in Beaumont, in East Texas; and WhiteWater Midstream in Pecos County, in West Texas – would together add about 58 billion cubic feet of underground natural gas storage capacity, or about 8 percent more than the amount currently stored this way in the United States.

Energy companies in the U.S. have been storing natural gas (methane) beneath the ground in rock salt formations since at least 1951, with occasional leaks and explosions over the decades. Underground storage projects have been expanding in recent years because of increased demand from liquefied natural gas (LNG) terminals and alternative energy industries.

Salt caverns are created by drilling a hole into a naturally occurring underground rock salt formation called a “salt dome” between layers of sedimentary rock. Companies then inject water to dissolve the salt and pump out the saltwater solution. This leaves behind an empty space that can be filled with natural gas or other petroleum products. Companies withdraw fuel from the cavern by pumping in water, forcing the petroleum product upwards.

One side effect of storing gas in salt caverns is the leakage of methane, which is a potent greenhouse gas, and they are occasionally the sites of explosions and other accidents, according to a report in Oil & Gas Science and Technology Revue.

A salt cavern gas storage facility in Hutchinson, Kansas, was the site of a deadly explosion in 2001.  A leak of natural gas from the Yaggy salt cavern storage field allowed methane to move upward to the surface through abandoned wells. This fed explosions in the small town of Hutchinson that killed two people and forced the evacuation of 191 homes.

Among other examples, in 2020, in Mississippi, a significant leak at a salt cavern natural gas storage facility called the Petal Gas Storage Station released nearly 5,000 metric tons of methane.  That’s as much climate-warming pollution as 140,000 metric tons of greenhouse gases (carbon dioxide equivalent tons) – or the equivalent of 32,320 average cars driving for a year -- over a 100 year time horizon.

In 2004 in Liberty County, Texas, an accident at the Market Hub Partners Moss Bluff Storage facility meant that about six billion cubic feet of methane gas escaped from the cavern and burned before dying out.

The environmental group Earthworks warns on its website of the potential risks from storage facilities being inadequately regulated and over-used, leading to leaks and accidents. “Owners of (underground storage) facilities may be filling them to maximum capacity, resulting in very high pressures and a higher chance of leaks and explosions,” the organization states.

The demand for more storage space for gas has been rising in recent years, in part because the growth of wind and solar power creates a market for backup power provided by natural –gas-fired power plants that can turn on quickly if the wind dies or thick cloud cover reduces solar power generation.  

The rapid expansion of Liquid Natural Gas (LNG) export terminals has also created more demand for underground gas storage, because companies must store the gas before they supercool and liquefy it to ship overseas.

“Natural gas salt dome storage is undergoing a revival along the Gulf Coast as LNG exports and renewables raise demand and prices for the flexible storage option,” a recent article in Natural Gas Intelligence, an industry publication, explained.  

The Houston-based Enstor company, which is planning to expand underground gas storage facilities in Mississippi, cited the LNG industry’s need for more storage as the reason several new caverns are being built now, after about a decade of status quo.

"The market has changed dramatically and materially on multiple fronts, including pipeline shipments of U.S. natural gas to Mexico, continuing growth of U.S. gas-fired power generation nationwide, and the launch and rapid growth of U.S. LNG exports, which have made the United States the number-one exporter of LNG in the world,” said Enstor CEO Paul Bieniawski. “It is very clear that now is the time to increase gas storage capacity, and we are thrilled that our application to expand the Mississippi Hub Storage facility is currently in front of FERC."

The three projects currently proposed in Mississippi and Texas are:

• Enstor Gas, LLC, which owns the Mississippi Hub Storage facility in Mount Olive, Mississippi, is planning to more than double the storage capacity of the facility between 2028 and 2031. The hub already has three salt caverns with about 22.4 billion cubic feet of gas storage. The company has announced plans create three more salt caverns, each with 10 billion cubic feet of storage capacity, while also adding another 3.5 billion cubic feet by expanding the size of two of its existing salt caverns, along with infrastructure like gas compressor units, water wells, saltwater disposal wells, and pipeline equipment.  
• In Beaumont, Texas, Golden Triangle Storage, owned by Caliche Development Partners II, has proposed an expansion at its 90-acre salt-dome natural gas storage site, aiming to just about double its working gas capacity. The site currently has two salt caverns and a total working gas capacity of 14 billion cubic feet.  The expansion involves developing two new salt dome natural gas caverns that will add 14.4 billion cubic feet of storage capacity, along with new well pad sites, pipelines, and additional access roads. Construction is predicted to be underway by July 2024 and ready for service by April 2026.  
• In West Texas, an expansion project by WhiteWater Midstream is planned at the Waha Gas Storage facility in Pecos County. WhiteWater acquired the Waha storage hub from Enstor in 2021, creating Waha Gas Storage, LLC, to supply gas to the nearby Agua Blanca and Whistler pipelines. The site already has six salt caverns, and five additional caverns are already permitted but have not been developed. Once fully developed, WhiteWater Midstream says the site will be able to store about 10 billion cubic feet of natural gas

Lead photo: A LNG tanker ship with storage tanks in the background. Photo by iStockphoto.