Subsea gas energy and quality measurement using ultrasonic flow meters

International trading of natural gas is based on high-precision, traceable,
and accredited fiscal flow metering systems and international pipeline
transmission infrastructures. Norwegian O&G industry is today moving towards subsea solutions for fiscal allocation metering, to replace today?s
topside metering systems. Gas is traded on basis of energy flow rate. Thus,
in addition to the volumetric flow rate, the energy and quality parameters
(QP) of the gas need to be measured. Traditional methods used topside
cannot be used in subsea systems. An industrial solution to this challenge is
mandatory and urgent.

The objective of the research project is to develop necessary scientific
basis and technology components, as a fundament to - in a follow-up
industrial project - realize traceable and accredited gas energy and quality
measurement by ultrasonic gas flow meters (USMs) in subsea fiscal
metering systems. The approach is based on use of the sound velocity
(VOS) measurement already available in relevant USM technologies.
However, no method is available today to ensure necessary traceability and
accreditation of this VOS measurement.

The work includes development of a measurement method and a laboratory
high-pressure VOS measurement cell for gas, as a basis to achieve
high-precision calibration of the USM?s subsea VOS measurements.
Secondly, it includes further development of an already operational
VOS-to-QP algorithm to ensure - from measurements available from the
USM and the metering system - high-precision and accredited calculations of
the energy and quality parameters under subsea gas operational conditions.

The results of the project will serve as a necessary fundament to enable
accredited and traceable subsea measurements of the USM?s VOS reading,
as input to an accredited and traceable VOS-to-QP algorithm, which ?
together with the already accredited USM volumetric flow measurement ?
provides the gas energy flow rate with accredited fiscal accuracy.