How are underground storage cavities created inside salt domes?

Underground storage cavities are created inside salt domes through a process known as brine solution mining.1

The procedure begins by drilling a borehole into the salt formation and lining it with protective casing. Once the well is established, fresh water is injected into the salt mass to dissolve the halite (rock salt), creating a brine solution that is then extracted from the cavity.1

Various injection techniques are used to control the shape and growth of these caverns:
* Top and Bottom Injection: Water is injected at one point and brine is withdrawn from another, creating distinct geometries such as "morning glory," "pear," or barrel shapes.1
* Controlled Growth: To manage the cavern's dimensions, operators may inject oil or air into the well. Because these substances are lighter than water and brine, they float to the top of the cavity, acting as a barrier that inhibits upward growth while allowing the cavern to expand laterally.1

These resulting cavities are highly valued for storage due to the inherent impermeability of the salt.2