Oil and gas production handbook - Process Control and ...

LNG is often metered with massflow meters that can operate at the required low
temperature. A three run LNG metering skid is shown above.
At various points in the movement of oil and gas, similar measurements are taken,
usually in a more simplified variant. Examples are Flare gas, Fuel Gas and Injected
gas where required accuracy is 2-5% percent.
4.4.2 Storage
On most production sites, the oil and gas is piped directly to a refinery or tanker
terminal. Gas is difficult to store locally, but occasionally underground mines,
caverns or salt deposits can be used to store gas.
On platforms without pipeline,
oil is stored in onboard storage
tanks to be transported by
shuttle tanker. The oil is stored
in storage cells around the
shafts on concrete platforms,
and in tanks on floating
platforms. On some floaters, a
separate storage tanker is used.
In both cases ballast handling
is important to balance the
buoyancy when the oil volume varies. For onshore fixed roof tanks are used for
crude, floating roof for condensate. Also rock caverns are used.
Special tank gauging systems such as Level radars, Pressure or Float are used to
measure the level in storage tanks, cells and caverns. The level measurement is
converted to volume via tank strapping tables (dependent on tank geometry) and
compensated for temperature to provide standard volume. Float gauges can also
calculate density, and so mass can be provided.
A tankfarm consists of 10-100 tanks of varying volume for a total capacity typically
in the area of 1 - 50 million barrels. Storage for shuttle tankers normally store up to
two weeks of production, one week for normal cycle and one extra week for delays
e.g. bad weather. This could amount to several million barrels.
Accurate records of volumes and history is kept to document what is received and
dispatched. For installations that serve multiple production sites, different qualities
and product blending must also be handled. Another planning task is forecasting for
future received and delivered product to make sure that the required amount of sold
product is available and that sufficient capacity is reserved for future received
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