How storage facility works
When gas arrives at a storage facility via a pipeline network it first enters a metering station where it is filtered, and the quantity and quality are measured. Injection and withdrawal take place via a number of wells. Where necessary, compressors (compressors with electric drive systems or gas driven turbocompressors) bring the incoming gas up to the right injection pressure. Since compression raises the temperature, the gas must then be cooled before being conveyed to the wellhead and injected into the natural rock formations. Care must be taken not to exceed the original reservoir pressure. The gas is withdrawn when it is needed, and processed for transportation. It must be dried as it will have absorbed moisture in the reservoir. Once it is on specification it enters the grid and is carried to the consumer.
Cushion gas is needed to keep the number of wells and the scale of the surface equipment to a minitmum. Optimising the design of the storage facilities cuts operating costs, reduces the impact on the environment and minimises the disturbance in the vicinity of the surface installations. Some gas is always left in the reservoir as a "cushion", and only the working gas above it is injected and withdrawn.
The cushion gas is a major investment when constructing a storage facility, but pays off because it permits high gas withdrawal rates due to the constant base pressure in the reservoir.
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