Flow measurement is more then using a flow meter. This presentation held during the European Flow Measurement Workshop in 2017 highlights some of the things you need to think about when building a metering system gas or liquid flow.

1. Making the most of on-site work by
starting with a proper paper review
Erik Smits – Senior Metrologist Liquid Flow and volume at VSL (6th April 2017)
Making the most of on-site work by
starting with a proper paper review

2. Pages with headers in red are
added in the pdf version for online
publication for clarity!

3. Introduction, purpose and limitations of this
presentation
A (metrological) paper review of a metering system can include
many review aspects like design of pipe work, calculations done
by the system, measurement uncertainty evaluation. The focus
for this presentation is manly on the following items:
- How can we pre-calculated the measurement uncertainty for
gross volume (as an example) to be sure that the requested
accuracy and/or tolerance(s) for the LACT system is achieved?
- Do we update the pre-calculated values at the moment that the
system is operated? Do we maintain updated calculation
during the lifecycle of the system?

4. Review of a LACT system
- Customer: WFMS, Texas, USA
- Review of measurement design,
calculations and other aspects in
accordance with the API Manual of
Petroleum Measurement Standards
- Measurement uncertainty evaluation
according JGCM 100: 2008 (GUM)
- Review of the selected instruments and flow
computer specifications, calibration certificates,
verification certificates and/or test reports

5. The Lease Automatic Custody Transfer System
- Crude oil and water (other?)
- Maximum flow rate of 55000 bbl (8744 m3) per day
- 20% to 70% water is expected
- Operational conditions: viscosity oil ± 4 Cst and API gravity
± 14, temperature 100 ˚F and pressure 800 psi
- 3 Metering lines with 6” PD flow meters and a maximum flow
rate of 27500 bbl/day
- WFMS – 10” Pipe Prover (Straight Calibrated Section)
- Sampling system, inline density meter
- Flow computer (calculating net volume at 60 ˚F)
- Temperature and Pressure transmitters

8. Metering runs according API MPMS chapter 6.1

9. Pipe prover according API MPMS chapter 4 (1)

10. Pipe prover according API MPMS chapter 4 (2)

11. What are sources/aspects we calculated for?
- Instruments
- Calibration, not correcting for calibration results
- Drift ,shifts, turn down ratio’s, wear (short and long term)
- Behavior at changing environmental conditions in and outside of pipe (short and
long term)
- Other depending on type of instrument
- Fluids
- Density, viscosity, pressure, temperature
- Composition and pollutants
- System
- Design pipe lengths, sizing, distance between meters and prover, etc
- Pulsations, vibrations, noise
- Calculations mass balance, volume at reference conditions etc
- Other depending on the system

12. What is available for the calculation?
- Commercial software
- Online tool from NFOGM (Norwegian Society for oil and gas
measurement)
What about the system?
What about changing conditions?
What about other sources of
uncertainty not related to the calculation?

13. How for example to review the gross volume
calculation of the LACT system?
- Start by checking how the calculation is done.
In most cases the flow computer is used
- Find out if the calculations are done according the selected
standards, regulations and/or contract
For example API or OIML
- If you perform the uncertainty evaluation yourself check
whether your tool is using the same calculation model as the
flow computer of the system

14. What kind of information do we need to collect
for the measurement uncertainty evaluation? (1)
- Instruments
- Calibration certificates, verification certificates and/or test reports
During a first paper review these might not be available
- Data sheets, manuals and other information supplied by the manufacturer
that specify what circumstance influences the instrument (short and long
term)
- White papers, studies, information from user work groups (like WIB in NL)
and other information that identify possible uncertainty sources in your
system
- Fluids
- Property specifications like density, viscosity, vapor pressure, etc
- Operational conditions in the pipe (pressure and temperature)
- Environmental conditions through the year
- Composition (in case of the example oil-water mixture)

15. What kind of information do we need to collect
for the uncertainty measurement evaluation? (2)
- System
- Design elements like pipe lengths, diameter, reducers, conditioners, etc
- Flow and system aspects like swirl, vibration, pulsation, noise, etc
- Standards and regulations
- Calculations and uncertainty evaluation and fixed given sources
- Constants (e.g. expansion coefficients)
- Correction factors and their boundaries
- Requirements (e.g. the repeatability of the flow meter)
- The maximum allowed tolerance of the system and the individual
components in the system

16. For example the these instruments in the
LACT system
- The PD flow meters
- The pipe prover
We need to evaluate all instruments in the system in the way
mentioned in the slides before as they can equally contribute to
incorrect measurement.

17. The 6” PD flow meter (1)
- What information is available?
- Meter specification for linearity +/- 0.15%
- Test report linearity +/- 0.04%
If not correcting standard uncertainty 0.08%
- Repeatability 0.005%
- Uncertainty of the test?
- What information is missing?
- Viscosity dependency
- Changing of the water cut
- Effect of temperature
- Long term stability (e.g. wear)

18. The 6” PD flow meter (2)
- What information is available?
- Meter specification for linearity +/- 0.15%
- Test report linearity +/- 0.04%
If not correcting standard uncertainty 0.08%
- Repeatability 0.005%
- Uncertainty of the test?
- What information is missing?
- Viscosity dependency
- Changing of the water cut
- Effect of temperature
- Long term stability (e.g. wear)

19. The 10” pipe prover
- What information is available?
- Base volume from prover calibration report
- API MPMS range repeatability <0.02%
- Due to the Straight Calibrated Section we can
expect smooth sphere operation
- Repeatability of the sphere detectors (product sheet)
- The volume in the pipe work between the outlet
of the PD flow meters and the first sphere detector
- What information is missing?
- The measurement uncertainty from the pipe prover calibration.
We need to do an extra evaluation using the data from the water draw and
the certificates of the test measures, pressure and temperature instruments

20. Use all information for the uncertainty evaluation
With the information we have collected we can start the pre-
calculation and check if we will achieve the requested accuracy
and/or tolerance(s) for the LACT system
Make an estimation of the sources for which information is
missing.
If an uncertainty evaluation is performed very early in the
project it can be the basis for a change in the design, in the
instrument tolerances or even for the selection of different
instruments.
Still we are missing information in the example that we can only
obtain when the LACT system is operated. It might be that after
a few years the LACT system does not meet the design
specification anymore. So what do we do?

21. Update the measurement uncertainty frequently
with new obtained data, calibration results etc…
When the LACT system is in operation we regularly get new data that
we can use for updating the uncertainty calculation
For example proving data of the PD meters. We can make control
charts and see what the real changes are. If we plot or keep more
data then just meter factors we can maybe predict a better re-
calibration period.
We know from experience that some PD meters are very good
thermometers. If we know temperature effects on the meter factor we
might need to include a source of uncertainty for it. We can also set a
parameter for proving if the temperature changes more than a pre-set
value
During operation we might find new sources that add (significantly) to
the measurement uncertainty. Do we than still meet our requirements?

22. What to remember?
- If all measurements are “perfect” what are we doing here
today?
- When we know our measurements and we can trust the data
that it produces we can take the correct decisions and
subsequently control financial risks
- By review and pre-calculation we have a better
understanding of what is possible with a measurement
system
- Updates need to be made when important information
and data changes

24. VSL
PO Box 654
2600 AR Delft
The Netherlands
T
F
E
I
+31 15 269 15 00
+31 15 261 29 71
info@vsl.nl
www.vsl.nl
P 24
Thanks to the team at WFMS for
sharing the information from the
review project for the LACT system.
www.wfmsinc.com
fsmits@vsl.nl