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Background on underground salt dome storage process
Of the 500 known salt domes in the Gulf Coast region from Mexico to the Florida Panhandle, three are in Franklin Parish.
The Louisiana Department of Natural Resources designates them as the Fort Necessity, Baskin and Crowville domes.
The domes typically originate from a thick bed of salt as deep as four to five miles below surface. They are usually circular in shape and average between one and two miles in diameter.
The formation of a salt dome takes hundreds of years.
Geologically, domes are thought to have been created by the repeated flooding and drying of sea water areas which were then covered with sediments as centuries progressed.
Because the salt is lighter than its surrounding sediments, the salt can rise to the surface.
During the rise of the domes, some are exposed to the surface, and some—like those in northern Louisiana—are likely to trap oil and gas during their rise.
The Jefferson Island salt dome, Avery Island, where Tabasco originated, and Weeks Island in southern Louisiana are examples of salt domes which have risen to the earth's surface.
The three Franklin Parish domes are located in townships and ranges 12 N, 7E; 13N, 8E and 15N, 8E, are near Fort Necessity, Gilbert and Crowville respectively. Each dome is deep a structure and not likely to produce table salt for the food products grown on the surface above the respective domes.
Some of the buried salt, however, will see the light of day in the process of creating a storage cavern for natural gas.
Salt brine is produced by introducing fresh water into the dome and pumping it to the surface. The water melts the rock salt to produce a solution and a cavern for the gas storage.
A large diameter borehole is drilled to about 4-5,000 feet to produce the cavern by water injection and retrieval. The process would be similar to drilling a hole in the ground with a garden hose and then removing the ponded water from the hole.
State and Federal agencies have oversight of the process.
In most cases, the process is approved in stages with a project subject to compliance to conservation and safety regulations.
One of the major areas of concern for regulators is the disposal and use of millions of gallons of salt water.
Salt water, created in the formation of the cavern, is used to force stored natural gas back to the surface and into the pipelines which transport the gas to the final marketplace—which could range from a home gas stove to a large electricity plant.
The creating, storage and transportation of natural gas then becomes dependent on the salt water which is repeatedly injected and withdrawn from almost a mile below the surface. Of course, during the process, natural gas is continually flowing into and out of the storage salt dome.
To imagine the process, think of the New Orleans Superdome buried about 3,000 feet underground with a pipe running to the surface. Water can be injected around the dome to create pressure on the sides to force the air inside the Superdome out of the pipe.
Of course, the entire process is much more complicated and difficult. The entire process can take several years to complete. |
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