Commingled multiphase flows – the metering challenge
Multiphase flow measurement has been developing in the oil and gas industry over the last 20 years. When multiphase metering was first introduced, unrealistic claims led to great expectations and ultimately disappointment when the technology failed to meet its initial promise. However, in recent years the technology has developed to a point where multiphase metering is considered as a key enabler in development of many marginal fields.
The technology’s accuracy certainly has improved and it is fair to say that many of the meters being marketed today are more than capable of meeting the levels of accuracy required for operations such as well testing, i.e. up to 20% uncertainty, where approximate performance and repeatability of measurement are the main requirement. However, for allocation and fiscal measurement with required uncertainties of less than 10%, or in some cases below 5%, there is still a challenge.
There are a handful of multiphase meters currently available that can meet the accuracy required for allocation under specific conditions, but so far no multiphase meters are available commercially with less than 5% uncertainty over the full range of conditions.
With more than 1 million production wells around the world, the “per well” market for flowmeters is attractive for meter manufacturers and they are working to improve technology. However, with multiple stakeholders in terms of allocation and fiscal reporting, independent verification of meter accuracy is essential. Furthermore, the current cost of multiphase meters is prohibitive for “per well” metering to become common.
Developing technology
There are a number of factors multiphase meter manufacturers need to research. These include:
- Transparency of accuracy through independent testing
- Uncertainty less than 5%
- More gas volume fraction (GVF) capabilities
- Higher water cut capability
- Lower cost.
Improving reliability, packaging
Accuracy of multiphase flowmeters has been tested by independent specialists TUV NEL over a number of years via joint industry projects (JIPs) funded by a wide range of oil companies including most of the major international operators and meter manufacturers.
There are two keys to accuracy claims that require independent verification: the hardware and the software. Manufacturers claim significant accuracy advances for hardware with improved sensor technology in meters such as nuclear gamma ray detectors and dielectric sensors. In terms of software, manufacturers have worked to refine algorithms to interpret the measured signals and to correct for flow regime effects.
Complete multiphase metering systems need independent verification across a full range of well conditions with varying levels of water cut and GVF. This can be done at a specialist multiphase testing laboratory such as TUV NEL’s facility in East Kilbride, Scotland, which combines a full scale three-phase test separator with single-phase reference meters to provide real time comparisons with multiphase meters on test. (This facility forms part of the UK National Standards for flow measurement).
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Volume 68 Issue 9
September 2008
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