Page 57 - Oil and Gas Production Handbook An Introduction to Oil and Gas Production

Gas metering is similar, but instead,
analyzers will measure hydrocarbon
content and energy value (MJ/scm or
BTU, Kcal/scf) as well as pressure
and temperature. The meters are
normally orifice meters or ultrasonic
meters. Orifice plates with a diameter
less than the pipe are mounted in
cassettes. The pressure differential
over the orifice plate as well as
pressure and temperature is used in
standard formulas (such as AGA 3
and ISO 5024/5167) to calculate
normalized flow. Different ranges are accommodated with different size
restrictions.

Orifice plates are sensitive to a buildup of residue and effect on the edges of
the hole. Larger new installations therefore prefer ultrasonic gas meters that
work by sending multiple ultrasonic beams across the path and measure the
Doppler Effect.

Gas metering is less accurate than liquid, typically ±1.0% of mass. There is
usually no prover loop, the instruments and orifice plates are calibrated in
separate equipment instead.

LNG is often metered
with mass flow meters
that can operate at the
required low
temperature. A three
run LNG g metering
skid is shown above.

At various points in the
movement of oil and
gas, similar
measurements are
taken, usually in a more
simplified way.
Examples of different
gas types are flare gas, fuel gas and injected gas where required accuracy is
2-5% percent.

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