Salt caverns: First fill and storage operation
Filling and operating the caverns
When the solution mining process has ended after about 30 months on average per cavern, the internal casing strings are converted for the subsequent storage operation.
The crude oil pumped into the caverns displaces the brine. The crude oil is then removed from the cavern as required by pumping in seawater or brine to displace the oil.
In the case of gas caverns, the brine remaining in the cavern is displaced during gas first fill by injecting gas into the cavern. The piping through which the brine was displaced to the surface during gas first fill is pulled out of the hole using a “snubbing” technique. The cavern is then ready for operation, and the gas is injected and withdrawn by compressors.
A certain amount of gas at a specific pressure always remains behind in the cavern (the cushion gas) to maintain the pressure conditions in the cavern specified by the rock-mechanical and operational criteria.