Underground storage of natural gas
■ Locations Grijpskerk and Langelo, The Netherlands
Underground storage of natural gas
Sufficient natural gas for everyone, all the time. Whilst this may appear to be the most normal thing in the world, it is not the case.
Natural gas reserves are being depleted and the reservoir pressure needed to produce natural gas is declining too. This is why
Nederlandse Aardolie Maatschappij B.V. (NAM) operates two underground gas storage facilities, at Grijpskerk and Langelo (in the
Norg field). These storage facilities guarantee the supply of natural gas when demand is extraordinarily high, for example during
periods of extreme winter cold.
Natural gas is the prime energy source of the Netherlands. This is why underground gas storage facilities were set up at
Approximately 50 per cent of all energy consumed in the Grijpskerk and Langelo, from where large volumes of gas can
Netherlands comes from natural gas, and the Groningen be produced without delay. This ensures the supply of sufficient
gasfield is one of the world’s largest. Moreover, natural gas is volumes of natural gas to the Netherlands under any circum
being produced from around two hundred smaller fields both stances.
onshore and offshore in the Dutch sector of the North Sea.
What does this look like?
Why store gas? A gas storage facility might be imagined to be a hollow space
The rate at which natural gas is consumed in the Netherlands underground, but this is not the case. The gas in the storage
fluctuates from day to day. Demand for natural gas is low dur facility is stored in the same location as where natural gas was
ing the summer and high during the winter. Sufficient pressure formerly held. Natural gas is found in porous rock, locked up
is essential for natural gas production, so that enough gas in the pores with a maximum diameter of 0.1 mm between
flows to the earth’s surface. However, the Groningen field has the grains of sandstone. The sandstone layer largely occurs at
already yielded so much natural gas that its reservoir pressure depths of between 2500 and 4000 metres. Above this there
is no longer adequate to provide everyone with natural gas on is an impermeable layer, usually a thick salt bed, that prevents
time during peak demand, e.g. during extremely cold periods. the natural gas from escaping through the rock strata.
Gas production Gas injection
7 7 12
10 5 4 5 5
3 1. Gasfield: porous sandstone
2. Impermeable layer
3. Safety valve
5. Shut-off valve
6. Pressure control valve
7. Air coolers
8. Gas-drying unit
9. Liquid separation unit
10. Water and condensate storage
2 11. Gas filters
approx. 3000 m. 12. Gas meters
deep 13. Compressor
Schematic representation of natural gas storage.
Six adsorption towers each weighing 325,000 kg and with a wall thickness of 18 cm are located at both sites.
This layer is often several hundred metres thick. A borehole will a separate building, brings the natural gas to the right pressure
have been drilled through the upper layers at some point, via for injection (up to 330 bar). Because the temperature of natu
which natural gas was produced. Dedicated equipment and ral gas increases when the pressure increases, cooling units
pipework make it possible to pump back (inject) natural gas are used to reduce this. The compressor is driven by an electric
into the reservoir through this well. motor. The electricity needed for this comes from a 110,000
Volt underground highpower line. When the compressor
The principle is operating at full speed, the motor runs at 38 Megawatt,
NAM uses two almost empty gasfields to store natural gas that roughly half the daily electricity consumption of a town the size
are especially suited to this task. During the summer, natural of Groningen. One compressor can inject a maximum 12 mil
gas from other fields, for which there is no demand, is injected lion cubic metres of natural gas each day.
into the storage facility. This increases the reservoir pressure
of the storage facilities so that they can produce natural gas Producing natural gas
as required during the following winter. Natural gas stored at When natural gas is produced from a field, it must first be
Grijpskerk is intended primarily for industrial purposes. This is dried. This is again the case when it is produced from gas
also referred to as highcalorific gas, which means a relatively storage. Liquids that naturally occur in the natural gas are re
large amount of heat is released per cubic metre of gas. The moved. These liquids are water and natural gas condensate (a
natural gas stored at Langelo is intended primarily for domestic gasolinelike hydrocarbon). The first step in the drying process
use, and is known as lowcalorific gas. Domestic and industrial involves reducing the temperature of the natural gas by means
equipment are adjusted for the use of specific qualities of gas. of coolers. This makes it possible to remove most of the liquid
Gas for domestic use comes from the Groningen field, which is from the natural gas. The natural gas is then passed through
why it is also referred to as Groningen quality. Natural gas from drying towers or ‘adsorption towers’. These are filled with silica
various fields is blended to form this quality and ensure the same gel granules, as in the silica gel sachets placed in electronic
composition is always delivered to domestic customers. appliances and other consumer products to absorb moisture.
The silica gel granules in the adsorption towers extract the
Filling the gas storage facility remaining moisture from the natural gas. When the granules
The natural gas injected into the underground storage facility are eventually saturated with water, they are dried with the aid
during the summer comes from a trunkline owned by Gasunie. of hot gas (at approx. 300 °C). This natural gas is heated in
Its pressure is approximately 65 bar. A compressor, located in furnaces. Both Grijpskerk and Langelo have six large adsorp
tion towers that are at the heart of the drying the environment. Account is taken of safety
process. in every aspect of the two gas storage facili
When sufficient liquid has been removed from ties. Highintegrity pressureprotection systems
the gas, it can be delivered to Gasunie for enable valves in the production and injection
further transportation. unit to close within two seconds. This is the best
means of guaranteeing plant safety. Both loca
Facts and figures tions have their own control rooms that monitor
Partially depleted gasfields are used to store the entire process of injection and production
gas at Grijpskerk and Langelo. In these fields of natural gas. Safety reports and emergency
the gas was able to flow into the well via pores contingency plans are drawn up for each loca
of the rock, largely under its own natural pres tion. These plans are tested regularly to ensure
sure. The original reservoir pressure in both their effectiveness.
gasfields was more than 300 bar. Billions of
cubic metres of natural gas have been injected Consideration was given to the surrounding
to restore that pressure. The Grijpskerk plant area when developing the locations. Close
comprises a gasinjection unit with a capacity consultations were held with the people living
of 12 million cubic metres of natural gas each in the neighbourhood and licensing bodies to
day. A compressor compresses the gas to the ensure that the facilities would blend into the
desired pressure in two steps. There are two landscape. The locations were constructed in
compressors at Langelo, which means the such a way that the people in the neighbour
capacity of the gasinjection unit can rise to hood endure only a minimum of inconvenience
24 million cubic metres of natural gas each from the facilities’ appearance, noise and light.
day. These stateoftheart compressors can At Langelo the plant was constructed length
compress the natural gas supplied from 55 to wise in relation to the nearby village to make
330 bar. Both sites have a production unit with it less conspicuous. A large green mound was
a capacity of 80 million cubic metres of natural also landscaped between the village and the
gas each day. Each location can currently pro complex. The most conspicuous element at both
duce between 50 and 60 million cubic metres locations is the flare stack, used only when
of natural gas on a daily basis. The gas can necessary to flare off gas for maintenance pur
be produced from and injected into six wells poses. The stacks are tens of metres high. An
at the Langelo facility. The Grijpskerk facility entire park landscape (more than 65 hectares)
comprises ten wells. was developed around the Grijpskerk complex,
including cycle paths and walking trails. The
Safety and the environment Langelo complex even includes an animal trail
Safety is paramount in all NAM’s activities. for the local wildlife.
Safety for the surroundings, the personnel and
A park comprising cycle paths and walking trails has been developed around the Grijpskerk site.
NAM was awarded the ‘Drentse Welstands Langelo are not flared off but reused as gas for
prijs’ (award for town and country planning heating in the gasdrying process.
design in the Province of Drenthe) in 2000 in
recognition of the company’s consideration of The licences granted to the two locations
the environment. According to the adjudicators, guarantee that they comply with the relevant
every conceivable detail had been taken into legislation. For example licences pursuant to the
account when harmonising the plant with the Netherlands Environmental Management Act
landscape. comprise general requirements regarding the
design and maintenance of the installation. Soil
Environment and licences protection measures are detailed, and criteria
A large number of licences are required for are laid down regarding flaring, setting up a
the construction of gas storage facilities. These firefighting plan, surveillance, illumination and
licences guarantee that adequate research a noise abatement plan. This also comprises an
has been conducted into all aspects impacting annual groundwater analysis and reporting on
nature and the environment. The procedure for and notification of any incidents. The locations
the underground storage of natural gas is as en also comply with the Netherlands Surface Water
vironmentally friendly as possible. For example, Pollution Act, which lays down general require
the residual gases discharged at Grijpskerk and ments with regard to surface water protection.
Nederlandse Aardolie Maatschappij B.V.
Nederlandse Aardolie Maatschappij B.V. (NAM) has been engaged in the exploration and pro
duction of oil and more importantly natural gas since 1947. Gas is relatively clean energy; it is the
cleanest fossil fuel on earth. NAM is by far the largest natural gas producer in the Netherlands,
accounting for around 75 per cent of all natural gas produced here. This makes the company a fun
damental provider of energy resources in the Netherlands. This is not as straightforward as it may
seem. Every day, around 1,800 NAM employees work hard to produce the gas our society needs,
doing so safely and in an environmentally friendly manner, both today and in the future. This is how
NAM contributes to reliable and safe energy supplies.
NAM B.V., NAM Communications, PO Box 28000, 9400 HH Assen
Telephone No.: +31 (0)592 368222 www.nam.nl February 2008