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Measurement Data: from Well to Awarenesswww.SpiritIT.com

GERG-2008 & AGA-8 UNCERTAINTY

By Han van Dal

h.vandal@SpiritIT.com

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UNCERTAINTY U95%

SYSTEMATIC ERRORS (NOTICED OR UNNOTICED ?)

Hardware failures

Wrong setup / configuration

Faulty data entries

Fixed / frozen input values

Wrong software version

Power resets / reboots

Proving / valve issues

Sampling / lab analysis issues

Failing As-found validations

Calculation failures

...

RANDOM ERRORS

Measurement and analysis reproducibility

Calibration uncertainty

Lab analysis uncertainty

Calculation uncertainty

...

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GAS COMPRESSIBILITY EQUATIONS

Natural gas compressibility = Real gas faktor

= correction on ideal gas law

1873 Van der Waals Equation Of State

1940 Benedict Webb Rubin equation (BWR)

(Soave) Redlich Kwong (SRK)

Lee Kesser (LK)

Peng Robinson (PR)

1962 AGA NX-19

1982 NX-19 PTB G9

1991 S-GERG (AGA-8 Gross Method)

1992 AGA-8 (AGA-8 Detailed Method)

2004 GERG-2004 (later GERG-2008)

Source : COMPRESSIBILITY OF NATURAL GAS - Jeffrey L. Savidge ISHM 2000

Applies for AGA-8 Region 1

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AGA-8 BOUNDARIES

Source: AGA Transmission Measurement Committee Report No.8

NX-19-40..+115C

350 bar

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OVERALL UNCERTAINTY WITH AGA-8 U95%= 0.1%

Source: NFOGM 2003 'Handbook for uncertainty calculations Ultrasonic fiscal gas metering stations'

NORWEGIAN SOCIETY FOR OIL AND GAS MEASUREMENT

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http://www.nfogm.no/http://www.nfogm.no/

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OVERALL UNCERTAINTY WITH AGA-8

DETAILED INPUT LEVEL

Relative Relative

Given Relative Confidence Level Type of Standard Sensitivity Relative

Input variables Uncertainty (probability distr.) Uncertainty Uncertainty Coefficient Variance

MODEL UNCERTAINTY1)

Gas compressibility factor at l ine conditions (Z) 0.1 % 95 % (normal) A 0.05000 % 1 0.00000025

Gas compressibility factor at s tandard conditions (Z0) 0.052 % 95 % (normal) A 0.02600 % 1 6.76E-08

ANALYSIS UNCERTAINTY

Line conditions 0.16 % Standard A 0.16000 %

1 0.00000256

Standard conditions 0 % Standard A 0.00000 %

Gas compressibility calculation Sum of relative variances, (EZ0/Z)2

2.8776E-06

Relative Combined Standard Uncertainty, E Z0/Z 0.001696

Relative Expanded Uncertainty (95% c onfidence level, k=2), k EZ0/Z 0.3393 %

1) Re. model uncertainty: AGA-8 uncertainty used for the model uncertainty of Z (line conditions)

ISO 6976 uncertainty used for the model uncertainty of Z0 (standard reference conditions)

Z at line conditions: Fill in AGA-8 uncertainty (option)

Z at std. conditions: Fill in AGA-8 uncertainty (option) Z at std. conditions: Fill in ISO 6976 uncertainty (option)

EMU - USM Fiscal Gas Metering Station

Gas compressibility uncertainty

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0.3

Source: NFOGM 2003 'Handbook for uncertainty calculations Ultrasonic fiscal gas metering stations'

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OVERALL UNCERTAINTY WITH AGA-8 U95%= 0.3%

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Source: NFOGM 2003 'Handbook for uncertainty calculations Ultrasonic fiscal gas metering stations

www.nfogm.no section Handbookshttp://gasmetering.azurewebsites.net

http://www.nfogm.no/http://www.nfogm.no/http://gasmetering.azurewebsites.net/http://gasmetering.azurewebsites.net/http://gasmetering.azurewebsites.net/http://gasmetering.azurewebsites.net/http://www.nfogm.no/

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AGA-8 UNCERTAINTY

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Source: AGA Transmission Measurement Committee Report No.8

Uncertainty = ? %

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AGA-8 UNCERTAINTY

Optimized for pipeline quality natural gas in Region 1

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0.2 .. 0.5%

GERG-2008 UNCERTAINTY

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Source: AGA Transmission Measurement Committee Report No.8

0.1%

0.1% -183 .. + 177 C Up to 35 Mpa

0.2 .. 0.5% -213 .. + 427 C Up to 70 Mpa

No limits on composition

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AGA-8 / GERG-2008 : DRY GAS

Methane

83.18

Nitrogen

9.94

Carbon Dioxide

1.79

Ethane

4.05

Propane

0.71

Water 0.00

Hydrogen Sulphide 0.00

Hydrogen

0.00

Carbon Monoxyde 0.00

Oxygen 0.00

i-Butane

0.00

n-Butane

0.23

i-Pentane

0.00

n-Pentane

0.05

n-Hexane

0.05

n-Heptane 0.00

n-Octane

0.00

n-Nonane 0.00

n-Decane 0.00

Helium

0.00

Argon 0.00

NeoPentane 0.00

Sum 100.00

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Relative difference

Z(AGA-8) Z(GERG2008)

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AGA-8 / GERG-2008 : DRY GAS

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AGA-8 / GERG-2008 : SEPARATOR GAS

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Pressure bar(a)

85

Temperature C

24

Total

Liquid

Vapour

C1

mol frac.

0.7302

0.3837

0.8673

C2

0.0786

0.0884

0.0748

C3

0.0431

0.0834

0.0271

nC4

0.0181

0.0472

0.0066

iC4

0.0326

0.0764

0.0153

nC5

0.0117

0.0360

0.0021

iC5

0.0166

0.0470

0.0045

nC6

0.0106

0.0353

0.0009

nC7

0.0209

0.0713

0.0009

nC8

0.0161

0.0559

0.0003

nC9

0.0118

0.0412

0.0001

nC10

0.0097

0.0342

0.0000

Fraction

mol frac.

1.0000

0.2835

0.7165

Fraction

mass frac.

1.0000

0.5174

0.4826

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AGA-8 / GERG-2008 : SEPARATOR GAS

Methane

83.18

Nitrogen

9.94

Carbon Dioxide

1.79

Ethane

4.05

Propane

0.71

Water

0.00

Hydrogen Sulphide 0.00

Hydrogen 0.00

Carbon Monoxyde

0.00

Oxygen 0.00

i-Butane

0.00

n-Butane

0.23i-Pentane

0.00

n-Pentane

0.05

n-Hexane

0.05

n-Heptane 0.00

n-Octane 0.00

n-Nonane

0.00

n-Decane

0.00

Helium 0.00

Argon

0.00

NeoPentane 0.00

Sum 100.00

Relative difference

Z(AGA-8) Z(GERG2008)

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AGA-8 / GERG-2008 : SEPARATOR GAS

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AGA-8 / GERG-2008 : SEPARATOR GAS

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AGA-8 / GERG-2008 : WITH WATER

Methane

82.6

Nitrogen

0.32

Carbon Dioxide

2.01

Ethane

7.41

Propane

4.37

Water

0.5

Hydrogen Sulphide

0

Hydrogen

0

Carbon Monoxyde

0

Oxygen

0

i-Butane

0.83

n-Butane

1.07

i-Pentane

0.31

n-Pentane

0.25

n-Hexane

0.3

n-Heptane

0

n-Octane

0

n-Nonane

0

n-Decane

0

Helium

0.03

Argon

0

NeoPentane

0

Sum

100.00

Relative difference

Z(AGA-8) Z(GERG2008)

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AGA-8 / GERG-2008 : WITH WATER

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AGA-8 / GERG-2008 : WITH WATER

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CONCLUSIONS

AGA-8 IS ACCURATE FOR DRY GAS

as accurate as GERG-2008

also accurate in expanded range

AGA-8 IS LESS SUITED FOR WET GAS

(BOTH HC AND H2O)

calculation failures

increased uncertainty

GERG-2008 IS ACCURATE AND ROBUST

0.1% for both dry and wet gases

no limitation on composition

no calculation failures

10 x CPU time of AGA-8

GERG2008 ALSO FOR LIQUID ?!

liquid density U95= 0.1 .. 0.5 %

online comparison with Coriolis density to

verify well composition ?!

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Measurement Data: from Well to Awarenesswww.SpiritIT.com

THANK YOU FOR YOUR ATTENTION

Questions?