SPR Storage Sites

Salt caverns along the Gulf Coast have been used for storage for many years by the petrochemical industry. When the U.S. Government decided to create the Strategic Petroleum Reserve in the mid-1970s, it acquired previously created salt caverns to store the first 250 million barrels of crude oil. This was the most rapid way to begin securing an emergency supply of crude oil following the oil shocks of the 1970s. To stockpile oil beyond the first 250 million barrels, the Department of Energy created additional caverns.

Salt caverns are carved out of underground salt domes by a process called “solution mining.” Essentially, the process involves drilling a well into a salt formation, then injecting massive amounts of fresh water. The water dissolves the salt. In creating the SPR caverns, the dissolved salt was removed as brine and either reinjected into disposal wells or more commonly, piped several miles offshore into the Gulf of America. By carefully controlling the freshwater injection process, salt caverns of very precise dimensions can be created. For every barrel of crude oil to be stored in the SPR’s caverns, it takes approximately seven barrels of raw water to create the storage space.

Besides being the lowest cost way to store oil for long periods of time, the use of deep salt caverns is also one of the most environmentally secure.  Rock salt exhibits extremely low porosity and permeability, plastic deformation characteristics, and self-healing characteristics, at the subsurface depths that the caverns are located.  It is these self-healing characteristics which will almost instantly close any microcracks, should they develop in the walls of the salt caverns.

The fact that oil floats on water is the underlying mechanism used to move oil in and out of the SPR caverns. To withdraw crude oil, fresh water is pumped into the bottom of a cavern. The water displaces the crude oil to the surface. After the oil is removed from the SPR caverns, pipelines send it to various terminals and refineries around the nation.