Underground Gas Storage

15. October, 2016 News No comments
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   Natural gas is a seasonal fuel – demand for it is usually higher during the winter. The process of exploitation, production, and transportation of natural gas takes time, and it is not always needed right away. The solution for this issues is underground gas storage. It is also used for:

– balancing the flow in pipeline systems,

– insuring against any unforeseen accidents,

– market speculation – producers and marketers use gas storage as a speculative tool, storing gas when they believe that prices will increase in the future and then selling it when it does reach those levels,

– maintaining contractual balance – shippers use stored gas to maintain the volume they deliver to the pipeline system and the volume they withdraw,

and other secondary purposes.

   Natural gas is most commonly held in inventory underground under pressure in three types of facilities. These underground facilities are depleted reservoirs in oil or natural gas fields, aquifers, and salt cavern formations. Natural gas is also stored in liquid or gaseous form in above–ground tanks.  This is the most expensive of all storage options, but this solution is applicable when it is impossible to build other storage facilities near large consumers. Two important characteristics of an underground storage reservoir are its capacity to hold natural gas for future use and the rate at which gas inventory can be withdrawn – called its deliverability rate.

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Depleted gas reservoir

They are the reservoir formations of natural gas fields that have produced all their economically recoverable gas. The depleted reservoir formation is readily capable of holding injected natural gas. Using such a facility is economically attractive because it allows the re-use, with suitable modification, of the extraction and distribution infrastructure remaining from the productive life of the gas field which reduces the start-up costs. Depleted reservoirs are also attractive because their geological and physical characteristics have already been studied by geologists and petroleum engineers and are usually well known. Consequently, they are the cheapest and easiest to develop, operate, and maintain of the three types of underground storage.

Aquifer reservoir

An aquifer is suitable for gas storage if the water-bearing sedimentary rock formation is overlaid with an impermeable cap rock. Although the geology of aquifers is similar to depleted production fields, their use for natural gas storage usually requires more base (cushion) gas and allows less flexibility in injecting and withdrawing. These types of storage facilities are usually used only in areas where there are no nearby depleted reservoirs. They are the least desirable and most expensive type of natural gas storage facility.

Salt formation

Underground salt formations are well suited to natural gas storage. Once formed, they allow little injected natural gas to escape from the formation unless specifically extracted. The walls of a salt cavern also have the structural strength of steel, which makes it very resilient against reservoir degradation over the life of the storage facility. Salt caverns provide very high withdrawal and injection rates relative to their working gas capacity.

How it works

Pumping gas is about injecting it in an artificial gas field using the parameters, specified by the process design. Gas is routed from a trunk gas pipeline to a site for removing solids, then to a gas metering station, and then to a compressor shop, where it is compressed and supplied to gas distribution stations (GDS) via headers. At a GDS, the general gas flow is divided in process lines, to which well loops are connected. Hook-up of process lines allows to measure productivity, temperature, and pressure of gas during an injection for each well.

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Back into the pipe

Extraction of gas from an underground storage facility is almost the same technological process as extraction from gas fields, but there is an essential difference: all active (commercial) gas is extracted within the period from 60 to 180 days. Flowing through the loops, it is received at gas-collecting stations, where it is gathered in a gas-collecting header. From there, gas is supplied to a separation site for the separation of produced water and solids, and then it is routed to a cleaning and drying site. Cleaned and dried gas is routed to the trunk gas pipelines.

gazprominfo.com/articles/gas-storage/

naturalgas.org/naturalgas/storage/

en.wikipedia.org/wiki/Natural_gas_storage

eia.gov/naturalgas/storage/basics/

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