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The benefits of using controlled reference fluids rather than live hydrocarbon fluids for calibration was highlighted at a recent webinar which attracted participants from around the world.
“The webinar, titled ‘From the Lab to the Field’, looked at the challenge of how to get the best performance out of a meter,” says Principal Consultant, Dr Norman Glen who ran the knowledge transfer session. “My main message was that, by using reference fluids to calibrate a flow meter you get better control. Although reference fluids are not what the system sees in service, our experience shows that this approach along with in-situ testing gives the best results.”
Norman highlighted the rationale and advantages of using controlled reference fluids, including the fact that they are stable, have well-defined properties and that they are generally safe. Although the alternative, live (hydrocarbon) fluids, are representative of what multiphase flow meters (MPFM) experience in service; they are potentially hazardous and unstable, exhibit component transfer between phases and higher uncertainty in their fluid properties.
To underline his point, Norman highlighted Guidance Notes for Petroleum Measurement, produced by the Oil & Gas Authority. These notes state that the use of ‘model’ calibration fluids is “not only far less hazardous to operate but the PVT characteristics of the fluids are likely to be relatively well understood so that it becomes possible to compare the reference measurements with those of the MPFM with minimal additional uncertainty.”
“We used the webinar to highlight lots of other key issues relating to meter implementation, such as good metrology practice and fluid property issues,” Norman adds. “We also highlighted recent relevant developments at NEL. These included the EMPIR MultiFlowMet II project, designed to achieve measurement harmonisation between multiphase flow metrology testing facilities. The webinar produced a number of questions, mainly on calculation and uncertainty issues associated with fluid properties and on how best to account for changes due to temperature and pressure.”
