Jennifer Ayre, Swinton Technology by Oil and Gas Focus Group Meeting Weds 11 th May 2011, Norwich Prognosis and Venturi Meters (wet gas application)

Jennifer Ayre, Swinton Technology

by

Oil and Gas Focus Group MeetingWeds 11th May 2011, Norwich

Prognosis and Venturi Meters (wet gas application)

DP Meter Diagnostics – the Theory

One Meter body

P1

t1 t2

DPt

Simplified Venturi meter diagram

Traditional flow rate prediction equation

Traditional DP


One Meter body

P1

t1 t2 t3

DPt

Additional downstream tapping

, 3 DP readings


One Meter body, 3 DP readings

P1

t1 t2 t3

DPt

DPppl

DPr

Recovered DPPermanent

Pressure Loss


One Meter body, 3 DP readings

P1

t1 t2 t3

DPt

DPppl

DPr‘Permanent Pressure Loss’ flow rate prediction equation

‘Recovered DP’ flow rate prediction equation


One Meter body, 3 DP readings provides:

3 flow rate predictions!

Flow coefficients found during meter calibration



3 DP ratios

DP ratios found during meter calibration



3 flow rate predictions

AND

3 DP ratios



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3 flow rate inter-comparisons

comparable uncertainty



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3 DP ratio comparisons (actual v calibrated)

comparable uncertainty



DP pair flow rate comparison

DP ratio comparison

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6 diagnostic results (and comparable uncertainties)



DP pair normalised flow rate comparison

normalised DP ratio comparison

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3 PAIRS of normalised diagnostic results

Correctly operating meter: each result between -1 and +1

(x1,y1)(x2,y2)

(x3,y3)(-1,-1) (1,-1)

(1,1)(-1,1)


One Meter body, 3 pairs of normalised diagnostic results, plotted on a Normalised Diagnostic Box (NDB)

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x - normalised flow rate comparison

y -

norm

alis

ed D

P r

atio

co

mpa

rison

(-1,-1) (1,-1)

(1,1)(-1,1)

DP Meter Diagnostics – Prognosis

Live Field Trials: BP and ConocoPhillips, Orifice meters

North Sea Flow Measurement Workshop Paper 2010

Now a commercially available system (software + I/O gathering)

Can we utilise the Prognosis system (designed and proven for single phase flows) to provide real time monitoring and indication of change in liquid loading of wet gas?

Petronas Carigali Metering Team challenge...

Not before considered

Challenges When Measuring Wet Gas

• The ‘apparent’ wet gas flow rate must be ‘corrected’ using a correlation method – requires a spot check to determine the liquid flow rate and Lockhart Martinelli parameter

• Wet gas is a hostile environment for transmitters – integrity of DP readings is a big issue– Saturated DP transmitters are common– Transmitters often damaged – drift– Water ; hydrates, salt deposits and scale often

block impulse lines

Petronas Carigali Offshore Platform

100 km North-West of KotaKinabalu, Sabah, East Malaysia

• Operating since 2004

• The platform has 4 Venturi meters measuring wet gas

• Throughput averaging 30 mmscf/d per flow line

• Hydraulic workover campaign - Production increase from 30 mmscf / d to 72 mmscf / d on two of the flow lines

Petronas Carigali Offshore Platform

Petronas Wet Gas Application

• New 6”, 0.7 beta ratio Venturi meter to replace one existing

• DP Meter Diagnostic solution (Prognosis) applied to new Meter to help identify when liquid loading changes

• Tracer dilution + wet gas correlation to correct the apparent gas mass flow rate


Meter to be replaced


• New 6”, 0.7 beta ratio Venturi meter to be dry gas calibrated

• And wet gas tested

to find Discharge Coefficient (Cd) + all diagnostic parameters

to prove wet gas performance in line with accepted theory

to assess the suitability of the Prognosis solution for detecting change in liquid loading

Dry Gas Calibration and Wet Gas Tests CEESI Colorado

Dry Gas Calibration

CEESI air blow down facility

Reynolds number of up to 20,000,000

Dry Gas Calibration - Results

Meter flow coefficients found during calibration

Discharge Coefficient = 1.014 (+/-1%)


Meter DP Ratios found during calibration

PLR = 0.067 (+/- 4%)

Flow Coefficients DP Ratios Parameter Uncertainty Parameter Uncertainty Cd = 1.014 x = 1% PLR = 0.067 a = 4% Kr = 1.047 y = 1% PRR = 0.9335 b = 1% Kppl = 2.205 z = 1.5% RPR = 14.03 c = 3.5%


All found to be constant with low associated uncertainties

Reading of all 3 DPs during calibration enabled identification of all diagnostic parameters

Prognosis Response to Dry Gas

Baseline Single Phase Diagnostic Results

All single phase flow calibration data plotted on mass on NDB

Low DPppl (relative to the other 2 DPs) means more scatter of points that includeDPppl

Pipe ID set too high at 14.63cm (schedule 80)Approx measurement error -2.5%

Prognosis Response to Wrong Pipe ID (wrong schedule)

Actual pipe ID 13.9725cm (schedule 120)

Pipe ID set too small at 13.18cm (schedule 160)Approx measurement error +4.4%

Throat diameter too low at 3.7507” (9.5268cm)Approx measurement error -6.6%

Prognosis Response to Wrong Throat Diameter

Actual throat diameter 9.7808cm (3.8506”)

Throat diameter too high at 10cmApprox measurement error +6.1%

Cd set too low at 0.995 (ISO Nominal Discharge Coefficient!) Approx measurement error -1.9%

Prognosis Response to Wrong Cd

Actual Cd 1.014 (+/-1%)

Cd set too high at 1.041 Approx measurement error +2.7%

Illustrates need to have meter calibrated to find correct Discharge Coefficient

Wet Gas Testing

CEESI wet gas flow loopFluid: natural gas and a light hydrocarbon liquid (exxsol D80 - kerosene substitute)

Wet Gas Parmeters

DR = gas to liquid density ratio (dimensionless representation of pressure)

Frg = gas densimetric Froude number

(dimensionless representation of flow rate)

XLM = Lockhart Martinelli parameter (dimensionless representation of liquid loading)

Wet Gas Definition: gas and liquid flow such that 0< XLM < 0.3Petronas wet gas application: XLM ≈ 0.02

Wet Gas Testing Conditions

0 ≤ XLM ≤ 0.12

DR = gas to liquid density ratio (dimensionless representation of pressure)

Wet Gas Testing Conditions

DR Pressure (bar)

Flow rate

(m/s)

Frg

0.034 35 3.3 1.30.034 35 4.3 1.70.078 75 5 1.40.078 75 7.4 2.00.078 75 9.7 2.7

Pressures of 35 bar and 75 bar Gas flow rates up to 12 m/s

Frg = gas densimetric

Froude number

(dimensionless representation

of flow rate)

Wet Gas Testing – Meter ResponseThe higher the liquid loading (XLM), the larger the over-reading

The larger the pressure (DR), the lower over-reading

Petronas meter wet gas data agrees with established theories

Wet Gas Testing – Meter ResponseThe higher the Xlm the higher the PLR

The higher the Pressure (DR) the less an increase in PLR

Petronas meter wet gas data agrees with established theories

Wet Gas Testing – Meter Response

Hence monitoring PLR can indicate shifts in liquid loading and instigate a new spot check (a well established technique)

The Petronas meter is performing in agreement with established theory and in line with all published data

What is Prognosis response to wet gas and change in liquid loading?

Prognosis Response to Wet Gas

Point closest to origin (XLM = 0.005, DR = 0.078, Frg = 2.7)

All Petronas meter wet gas test data plotted on NDB

VERY sensitive, even at very low liquid loadings

0.005

0.010

0.020

0.049

0.099

XLM

All data from density ratio (DR) 0.034, gas densimetric Froude number (Frg) 1.7


As the liquid loading increases, the ‘DPt & DPppl’ point moves further away from the NDB.

Same with other two points but not as noticeable

Same trend for all other DR and Frg data sets

0.005

0.010

0.020

0.049

0.099

XLM


Very sensitive to small change in liquid loading

Monitoring this point offers a real time check on the liquid loading of the wet gas flow

But NDB is dwarfed and too small for any practical use

Non zeroed wet gas point

Zeroing of Prognosis Response to Wet GasWet gas point, DR = 0.078, Frg = 2.7, XLM = 0.005

Zeroed wet gas point, Z = 0.0606

Z factor (Z = PLRact – PLRcal ) is used to remove the effect of the current wet gas condition

‘zero’

‘Zeroing’ means no need for operator to closely monitor co-ordinates. Can simply have an alarm when points move ‘outside the NDB’

XLM = 0.010, Z = 0.0606

XLM = 0.005, Z = 0.0606

Zeroing of Prognosis Response to Wet Gas

DR = 0.078 and Frg = 2.7

Previously ‘zeroed’ wet gas results (XLM = 0.005)

Diagnostic response to liquid load increase( new XLM = 0.010)

Xlm = 0.01, Z = 0.0924

Xlm = 0.005, Z = 0.0924

Zeroing of Prognosis Response to Wet Gas

The pattern of the points as they move outside of the NDB indicates if the liquid loading has increased or decreased

DR = 0.078 and Frg = 2.7Wet gas results (XLM = 0.010) ‘zeroed’ using Z = 0.0924

Subsequent DECREASE in liquid loading (XLM = 0.005)

Example: Wet Gas, Xlm = 0.05, Approximate measurement error +15%Apparent gas flow rate = 1.15 x Actual gas flow rate Wet gas DP = 1.32 x Dry gas DP ((1.15)^2 = 1.32 )→Saturated DPs are common

DP Transmitter Integrity Issues

Saturated DP → negative bias in flow rate predictionIncreased PLR → too high liquid loading assumed (apparent flow rate ‘over-corrected’)

Traditionally NO WARNING SYSTEM for false DP readings

Huge potential for mis-measurement

Solid points: Non-zeroed ‘wet gas’ data (XLM = 0.05) . Hollow points :same data but saturated traditional DP

Actual DPt =135.5 barSaturated DPt = 124.4 bar

Saturated DP Transmitter Example

Effect of saturated DPt is dwarfed by effect of wet gas on NDB

BUT.... Prognosis has ability to detect this!

Any true DPs must agree with first law of thermodynamics!

91.8 bar + 43.6 bar = 135.5 bar Compared to traditional DP of 124.4 bar

+8.9% Difference in measured and inferred traditional DP’s

Saturated DP Transmitter Example

DPr + DPppl = DPt

Automatic check performed by Prognosis software (typically an alarm is raised if difference > 1%)

Saturated DP Transmitter Example: Dry Gas

Solid points: dry gas data

Hollow Points: same data point but saturated DPt

Error in any of the three DPs displays a distinct pattern on the NDB – Clear WHICH DP reading is in error

Dry OR Wet gas: Prognosis makes a simple check of this sum and can detect any false DP reading

DPr + DPppl = DPt

Summary

• During both dry gas calibration and wet gas testing, the Petronas meter was proven to be repeatable and to behave in line with accepted theory and published data

• Prognosis system performed as expected and identified simulated errors during the dry gas calibration

• During the wet gas testing the Prognosis system was shown to be VERY sensitive to liquid flow in gas flow

Summary• Zeroing of wet gas diagnostic results allows easy

detection of change in liquid loading and pattern of results determines increase or decrease

• AS LONG AS THREE DPs ARE BEING READ Prognosis will also alert the user as soon as any of the DPs is in error due to saturation / damage / blocked impulse lines

• When measuring dry gas, Prognosis can identify WHICH DP is in error

Realisation

Real time monitoring of system health

Clear indication when liquid loading changes

PLUS - Simple yet powerful check on DP accuracy

Field Data I/O

Flow Computer

Including additional DPs

Petronas Application of Prognosis System

PC running Prognosis Software

Petronas Field Experience

Planned Installation Date

July 2011

Petronas view“Petronas are delighted to be pioneers of this new DP Meter diagnostic technology and can see huge benefits in measuring wet gas. Benefits above other methods of monitoring wet gas are clear as Prognosis can identify when there is a Saturated DP transmitter as opposed to a change in liquid loading hence reducing ‘false alarms’ which would otherwise wrongly predict a change in liquid loading.”

Deverapalli Vijay, Petronas Carigali

Centrica Ensign Project

Prognosis for:3 x 6” Venturi Meters1 x 10” Venturi Meter

Potential wet gas issues!

Calibrations found all diagnostic parameters fit to Reynolds number with low uncertainties

Centrica Ensign Project

Calibration results

6” meter no.1Diagnostic Parameter Uncertainty

(+/-)

Cd = 1.007+(1e-9)*R 0.65%

Kr = 1.097-(1e-9)*R 1.00%

Kppl = 0.433-(3.6e-9)*R 0.65%

PLR = 0.147+(1.6e-9)*R 1.60%

PRR = 0.847-(1e-9)*R 0.50%

RPR = 4.74-(6.2e-8)*R 1.60%

6” meter no.2Diagnostic Parameter Uncertainty

(+/-)

Cd = 0.994+(8e-10)*R 0.45%

Kr = 1.09-(1e-9)*R 0.80%

Kppl = 0.409-(4e-9)*R 0.45%

PLR = 0.159+(2e-9)*R 1.00%

PRR = 0.836-(1e-9)*R 0.90%

RPR = 5.32-(6.3e-8)*R 1.10%

Centrica Ensign ProjectMeter no.1 using calibration results for meter no.2:

The Future?

Proven on single phase applications to provide powerful diagnostic information for any DP meter

Proven to provide a method of monitoring liquid loading changes on wet gas Venturi applications AND identify DP measurement errors

Establish magnitude of DP measurement error based on given information and pattern of results

Thank YouQUESTIONS?

Documents

Jennifer Ayre, Swinton Technology by Oil and Gas Focus Group Meeting Weds 11 th May 2011, Norwich Prognosis and Venturi Meters (wet gas application)