How deep are they, and what keeps them from leaking? Just curious.
I don’t know the specifics of this facility. But I can give you a comparison of the SPR oil caverns, which are bigger.
http://energy.gov/fe/services/petroleum-reserves/strategic-petroleum-reserve/spr-storage-sites
Strategic Petroleum Reserve caverns range in size from 6 to 35 million barrels in capacity; a typical cavern holds 10 million barrels and cylindrical in shape with a diameter of 200 feet and a height of 2,000 feet. One storage cavern is large enough for Chicago’s Willis Tower to fit inside with room to spare. The Reserve contains 62 of these huge underground 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 Mexico. 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 salt caverns, it took 7 barrels of 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. At depths ranging from 2000 to 4000 feet, the salt walls of the storage caverns are “self-healing.” The extreme geologic pressures make the salt walls rock hard, and should any cracks develop in the walls, they would be almost instantly closed.
An added benefit of deep salt cavern storage is the natural temperature difference between the top of the caverns and the bottom, a distance of around 2,000 feet. The temperature differential keeps the crude oil continuously circulating in the caverns, maintaining the oil at a consistent quality.