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unwanted components such as hydrogen sulfide and carbon
dioxide. These gases are called acids and sweetening /acid
removal is the process of taking them out.
Natural gas sweetening methods include absorption
processes, cryogenic processes; adsorption processes (PSA, TSA
and iron sponge) and membranes [21]. Often hybrid combinations
are used, such as cryogenic and membranes.
Gas treatment could also include calibration. If the delivery
specification is for a specific calorific value (BTU per scf or MJ
per scm) gas with higher values can be adjusted by adding an inert
gas, such as nitrogen. This is often done at a common point such as
a pipeline gathering system or a pipeline onshore terminal.

Oil and Gas Storage, Metering and Export
The final stage before the oil and gas leaves the platform
consists of storage, pumps and pipeline terminal equipment.

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 [17].
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.

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