Researchers have highlighted potentially significant errors in the calculation methods that are widely used to account for the effects of temperature and pressure on the density of hydrocarbons.
“We have a research project underway which has shown that errors become significant when large differences in temperature and pressure are involved,” says Principal Consultant, Dr Norman Glen, whose team has found errors of about 0.25%. “We are currently quantifying the inaccuracies for a range of oils and conditions and believe that the results will have significant implications for real-world operating conditions.”
“0.25% is the limit on uncertainty for the measurement of oil for fiscal purposes in the UK,” explains Norman. “If a company is introducing a substantial percentage of this uncertainty through inaccurate density calculations then it won’t come in under its overall uncertainty threshold.”
The calculations Norman and his team are studying are based on American Petroleum Institute (API) figures and are widely used to take into account temperature and pressure differences in measurement systems that measure different aspects of flow at different locations. An example of this would be in systems that have a flow meter and a densitometer in different locations.
The calculations are also used to convert density at operating conditions to standards conditions. This has implications in a range of situations. For example, if a compact prover is used to calibrate a device and this is operating across an extended range of temperatures and pressures then the limitations in the calculations highlighted by Norman’s team could cause significant errors. The research is scheduled to be finished in March 2017.
