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

Pages with headers in red are

added in the pdf version for online

publication for clarity!

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?

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

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

Metering runs according API MPMS chapter 6.1

Pipe prover according API MPMS chapter 4 (1)

Pipe prover according API MPMS chapter 4 (2)

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

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?

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

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)

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

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.

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)

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)

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

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?

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?

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

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