Performance testing of a novel F ibre Optic based vortex flow meter

‘Smart Flow’in high pressure wet steamin high pressure wet steam

R. Jansen, TNO, The NetherlandsJ. Golliard, TNO, The NetherlandsC. Staveley, Smart Fibres Ltd, UK

W. Schiferli, Shell, The NetherlandsA. Znotins, Shell, Canada

by

Content

• Market need• The solution

– Measurement principle– Test results Air/Water (water wet air)– Test results Air/Water (water wet air)– Test results Wet steam (condensed steam)

• Conclusion• Way forward

Market need

• Availability of a cost-effective solution for permanent flow and quality monitoring

• of steam injected into steam injection wells• of steam injected into steam injection wells

• using specific advantages fibre optic sensing

Solution; combination of:

• Existing principle, vortex meter ; – Proven technology– Robust and low cost

• Fibre Optic (FO) sensing element;– Implemented existing FO architecture– Using specific advantages of FO

Vortex meter principle

• Vortex shedding behind bluff body• Shedding frequency linear to flow velocity

U velocity

Strouhal number

D

USrf 0=

velocity

bluff body diameterVortex shedding frequency

Fibre Optic Vortex Meter

Fibre Optic (FO) Element

• FO sensor inside vane

• Fibre Bragg Grating (FBG)

• Reflected wavelength varies

with strain (and temperature)with strain (and temperature)

Alternating bands of high and low refractive index

Multiplexing

FBG Sensors

Measured parameters

Vortex shedding

peak

Mechanical eigenfrequency

vane

Required d ynamic range : > 2500 Hz

Test result single phase gas

Performance two phase flow?

• Gas hold -up– actual gas velocity increases– also known as ‘over reading’

• Possible interference liquid layer• Possible interference liquid layer• Presence of droplets:

– in the flow near the vortex meter– deposited on the shedder bar

Expected Flow regimeS

uper

ficia

l liq

uid

velo

city

[m

/s]

In surface steam pipelines

Superficial gas velocity [m/s]

Sup

erfic

ial l

iqui

d ve

loci

ty [

m/s

]

Two clear mechanisms

Based on experiments:• Interference liquid layerquality factor vortex shedding

-3dB

width

vortex

• Droplets changing the effective gas densityShift in mechanical eigenfrequency

3dB-f ∆= v

vp

fQ

Test results two phase

Wet steamAir/water

Test results air/water

Air only (no water)

Liquid hold-up (quality factor)

Liquid hold-up (mech. eigenfr.)

Test results wet steam

Dry Steam

Wet steam test conditions

0.6

0.8E

ntra

ined

fra

ctio

n [-

]

40 bar80 bar120 bar

0 5 10 150

0.2

0.4

True Usg [m/s]

Ent

rain

ed f

ract

ion

[-]

Actual steam vapor flow

The measured vortex shedding frequency is translated to a vapor flow rate:• Assuming single phase gas• Using measured steam quality (based on • Using measured steam quality (based on

the vortex peak quality factor)• Known liquid hold-up based on two phase

flow simple model (derived from OLGA)• Assuming two phase flow to calculate the

(corrected) actual vapor flow rate

Assuming single phase flow

40

60(m

easu

red-

refe

renc

e)/r

efer

ence

[%

] SteamQuality < 0.98

0 5 10 15-20

0

20

True Usg [m/s]

Err

or(m

easu

red-

refe

renc

e)/r

efer

ence

[%

]

Known quality & simplified model

10

20(m

easu

red-

refe

renc

e)/r

efer

ence

[%

] SteamQuality < 0.98

0 5 10 15-20

-10

0

True Usg [m/s]

Err

or(m

easu

red-

refe

renc

e)/r

efer

ence

[%

]

Measured quality (quality factor)

Assuming two phase flow using:Measured quality & simplified model

0

10

20(m

easu

red-

refe

renc

e)/r

efer

ence

[%

]

0 5 10 15-30

-20

-10

0

True Usg [m/s]

Err

or(m

easu

red-

refe

renc

e)/r

efer

ence

[%

]

Conclusions wet steam

High steam quality (>0.98) errors in flow:• less than 3% for velocities above 7 m/s• between 2 and 7 m/s errors less than 5%

Lower steam qualities (<0.98) errors in flow: • increased to 60% without correction• With steam quality correction :

– less than 10% for velocities above 7 m/s– between 2 and 7 m/s less than 20%

Way forward

Test performance under field conditions:• Steam tests only covered ‘end of life’ field

conditions in Shell Canada• No (affordable) test rig can deliver such high flows• Bench mark field test: steam test separator

Mature and further validate technology:• Test robustness current algorithms field conditions • Improve current algorithms to reduce steam

quality errors down to +/- 10% (currently +/- 20%)

Back-up slides

• Slide 30: Over-reading as function of XLMSame plot as shown in slide 23

• Slide 31: Measured steam quality taken into account field conditions Shell Canada (Usg > 7 m/s). field conditions Shell Canada (Usg > 7 m/s). Note: Nominal field velocities (10 < Usg < 15 m/s)

Assuming single phase flowOver Reading versus XLM

Wet gas region0 XLM < 0.3

Measured quality (quality factor)Usg > 7 m/s (field conditions)

error lines +/- 20%