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Gas goes underground

Marco Clemente | 20 Jan 2016 | Comments

Remember these?

Love them or hate them, the gas holder (also known as a gasometer) is gradually disappearing from the landscape. This lasting symbol of Victorian ingenuity has been in decline for years as the way we consume and store natural gas has changed, and the land – which is often in prime territory within our cities and towns – is being sold to developers for housing or community usage.

Storing gas has been something that we in the UK, and many other places around the world, have had to do for a long time. Some gas holders have stood since the 1860s and they were being built in the UK into the early 1980s, over 100 years later.

Originally, gas holders stored gas produced from burning coal at an on-site gasworks to be used locally as needed, mainly for street lighting and heating. When North Sea gas was discovered in the 1960s and the UK network infrastructure was overhauled, gas began to come into people’s homes via a high-pressure network as it still does today and use of the gas holders went into decline.

Increasing complexity of gas supply across international boundaries is creating a need for gas storage capacity many times greater than that what exists at present. The development of storage space in underground facilities such as salt caverns, depleted oil and gas reservoirs and aquifers has the potential not only to meet this need but to do so more safely than in smaller, above-ground facilities.

Atkins’ energy storage team offers a specialist underground gas storage service, integrating our traditional planning and engineering skills to provide the capability of investigating, developing and designing storage facilities.

Demands in gas supply can vary due to a number of factors within the energy market – e.g. economic activity, electricity demand, seasonal variations in temperature or if daily supplies are lost due to technical difficulties.

Gas storage is one of the most effective means of providing supply flexibility to the grid over short term peaks or longer periods. Over winter 2013/14 storage withdrawal met 9% of the UK total gas needs, the remainder being met by other supply sources.

There are a number of reasons why we need gas storage and it has various uses:

  • Multi cycle or flexible storage;
  • Seasonal, where gas is injected to storage in summer and is delivered from storage in winter. There tends to be a spread in price of energy delivered between the two seasons;
  • Strategic, where gas is stored to be used in a defined set of unforeseen circumstances;
  • Peak shaving, where gas is stored in a facility with high rate of deliverability that is used to meet high energy demands in a short period of time;
  • System support, where gas storage facilities are located at key points on the network to supply short term back up in the event of a pipeline or compressor failure.

The key characteristics of gas storage are how much volume of gas can be injected, stored and then delivered. Most gas storage facilities are underground in either salt caverns or depleted gas fields.

Depleted gas fields are, unsurprisingly, fields that have produced all of the economically viable natural gas. A depleted gas field is readily capable of acting as a store and is economically attractive because the geological and physical characteristics have already been studied and are known. This in turn makes them cheaper to develop and operate.

Salt caverns are created when water is pumped into salt deposits underground, where the water dissolves the salt (this is known as solution mining) producing brine.

The optimum depth for salt cavern facilities range between 1,000 and 1,500 meters based on various process specific parameters. The process continues until the caverns are the correct size and shape to store gas. After the cavern integrity has been verified, gas is pumped in, the brine is extracted and the gas is stored until required. Salt caverns are useful for storing gas because the gas cannot permeate through the salt. Although they are much smaller than depleted gas fields, salt caverns can be rapidly filled meaning they are very useful for providing a quick response to short term demand increases.

Atkins is currently working with German company DEEP Underground Engineering GmbH at SSE’s Aldbrough and Atwick gas storage sites in East Yorkshire, providing end to end support through the development and execution of projects, in addition to supporting their continuing operation and maintenance, to ensure the reliability of these sites for many years to come.

These two sites are part of the UK gas storage network and combined have eighteen solution mined caverns with a combined capacity of over 500 million cubic metres (mcm); that’s about 30% of the UK’s storage deliverability.

Additionally, Atkins has provided extensive technical support to a number of other UK gas storage sites across the UK including supporting the development of the EDF Energy Hill Top Farm site in Cheshire as Owners Engineer.

Although gas storage currently plays a relatively minor role in the energy mix, it’s an important one. Gas storage is one of the most effective solutions to provide flexibility and security of gas supply.