In the past, "compensated" salt caverns have operated with a compensating
liquid, such as brine to displace a stored liquid, such as crude oil,
when the stored liquid is needed on the surface. Virtually all of the
stored liquid in a compensated salt cavern can be expelled from the salt
cavern when it is filled with the compensating liquid. In the past,
"uncompensated" salt caverns have been used to store gases, such as
natural gas. Uncompensated caverns operate without any compensating
liquid; instead they rely on pressure. Some of the stored gas (cushion
gas) must always be left in an uncompensated salt cavern. This invention
breaks with convention and uses a compensating liquid in a salt cavern to
store gases which is a technique believed to be previously unknown.
"Cushion gas" is not required because the compensating liquid displaces
virtually all of the gas in the salt cavern.