01 December 2000
Pass the salt . . . hold the oil
The Strategic Petroleum Reserve (SPR) created more than 50 new storage caverns through a technique called solution mining. Solution mining begins with a well drilled into the salt dome. Pumped fresh water enters the salt formation to dissolve the salt. As the salt dissolves, the pump pushes the brine out of the cavern into deep disposal wells or into the Gulf of Mexico.
As more injected fresh water enters, the cavern grows in size. Regulating the flow of fresh water at different depths controls the caverns' shape and size. It takes about seven barrels of water to create enough space to hold one barrel of crude.
A typical SPR cavern holds 10 million barrels of crude oil and has a diameter of 200 feet and a height of 2,000 feet. This is enough space to hold the New York World Trade Center.
The roofs of most of these caverns are more than 2,000 feet below the surface. At these depths, the surrounding salt is under such pressure that any cracks that may occur will close almost instantly. This self-healing phenomenon makes the deep salt caverns geologically stable.
When crude oil enters the cavern's top, it causes a displacement of the brine at the bottom. The brine then flows up through pipes to the surface and out to its ultimate destination.
To withdraw crude oil, pressurized fresh water enters the cavern at the bottom, which pushes oil to the surface and out.