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.
The research project is made in a cooperation between the University of Bergen (UiB, project leader), NORCE, and the Western Norway University of Applied Sciences (HVL), with Equinor and Gassco in the industry reference group.
Eivind Nag Mosland is from 01 November 2020 employed by UiB as PhD research scholar in the project. Mosland works on mathematical-numerical modelling of acoustic signal propagation in the measurement method being planned for implementation in the measurement cell for VOS in natural gas, as a basis to establish necessary correction methods for systematic errors in the measurements. There are high accuracy requirements e.g. to the influences of acoustic diffraction on the measured transit times, and improved methods relative to the models that are available today in the scientific literature are under development. The work has in 2021 been reported at an international scientific acoustics conference. The second PhD position under the project has been announced, and employment of PhD research scholar will be made in 2022. The progress plan is being revised in coherence with that.
Review of relevant international literature related to precision measurement of sound speed in gas, and acoustic measurement of energy and other quality parameters of natural gas, is ongoing continuously as an integrated part of the work.
In the summer of 2021, a UiB master candidate has completed his master exam as a part of the project, and another candidate is underway with his UiB master thesis work. A master topic under the project has been announced at HVL.
Norwegian O&G industry is today moving towards subsea fiscal allocation measurement of gas. In such metering systems, the energy and quality parameters (QP) of the gas need to be measured, in addition to the volume flow. Traditional methods used topside for partner allocation and sales measurement of gas cannot be used in subsea systems. An industrial solution to this challenge is mandatory, and urgent.
A method is proposed to enable subsea allocation measurement using an ultrasonic transit time gas flow meter (USM). The method is based on using the USM's volumetric flow rate and sound velocity (VOS) readings, for which the required accuracy and traceability of the VOS quantity is obtained using calibration of the USM versus a high-precision and accredited VOS measurement cell. The energy flow rate and the gas quality parameters (QP) are then obtained using a Gas Analyzer algorithm for VOS-to-QP calculation.
In particular, the researcher project addresses development of necessary scientific basis and technology components, as a fundament to realize traceable and accredited gas energy and quality measurement by ultrasonic gas flow meters (USMs) in subsea fiscal measurement of natural gas. This includes:
(1) Development of laboratory high-pressure VOS cell to address scientific research challenges that need to be solved to realize construction of a high-precision VOS cell enabling accredited and traceable calibration of the USM's VOS reading in natural gas;
(2) Development of a full 3D system model for the VOS cell measurement method, to establish necessary and traceable time delay corrections in the measurement method; and
(3) Development of robust Gas Analyzer algorithm for VOS-to-QP calculation for a wide range of gas compositions, with documented accuracy sufficient for fiscal gas flow metering.
The project includes education of 2 PhD and 3 master candidates.
[USM = ultrasonic gas flow meter, VOS = sound velocity, QP = quality parameters.]