Page 58 - Oil and Gas Production Handbook An Introduction to Oil and Gas Production

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 a 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 units. On some
floaters, a separate storage tanker is used. Ballast handling is very important
in both cases to balance the buoyancy when the oil volume varies. For
onshore, fixed roof tanks are used for crude, floating roof for condensate.
Rock caves are also used for storage

Special tank gauging systems such as level radars, pressure or float are
used to measure the level in storage tanks, cells and caves. The level
measurement is converted to volume via tank strapping tables (depending
on tank geometry) and compensated for temperature to provide standard
volume. Float gauges can also calculate density, and so mass can be
established.

A tank farm consists of 10-100 tanks of varying volume for a typical total
capacity in the area of 1 - 50 million barrels. Storage or 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 can amount to several
million barrels.

Accurate records of volumes and history are 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 products. This
is for stock control and warehousing requirements. A tank farm management
system keeps track of all stock movements and logs all transport operations
that take place

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