Junhong Chen and Chris Boreham Isotopic Analysis of Compounds in Low Concentration in Australian...

Junhong Chen and Chris Boreham

Isotopic Analysis of Compounds in Low Concentration in Australian Natural Gases Using CF-GC-IRMS Systems

Isotopic Analysis of Compounds in Low Concentration in Australian Natural Gases Using a CF-GC-IRMS System

Isotope and Organic Geochemistry Team at GA

Aim

Explore efficient analytical methods of natural gases isotopic composition, especially for those in low concentrations;

Provide new isotope data sets (neo-C5, N2) for natural gas evolution assessments


Instruments

• 13C/12C, 15N/14N analysis: Thermo Finnigan-MAT 252 (253) GC-C-IRMS System

with ConFlo III (IV) interface


Instruments• D/H: Thermo Finnigan Delta Plus XL GC-TC-IRMS

System (TC – High Temperature Conversion)


Analytical Conditions (δ13C and δD)

GC conditions:• GC columns: Varian, coating: PoraPlot Q; 25m x 0.32mm (ID),

0.25m.• Oven temperature:

Isothermal at 30oC for methane, CO2 and ethane; Increased at 20°C/min to 230°C for C3-C5.

• Injector temperature: 150ºC• Split Ratio: 200:1 to 25:1.

Furnace temperatures for δ13C:• Oxidation: 900ºC• Reduction: 630ºC

Furnace temperature for δD: 1400ºC


Injection Requirements (δ13C)

Peak intensity required for reliable results: Trace m/z 44: Min 0.3 V; Max 7V (MAT 252)

50V (MAT 253)• Equivalent to: 0.0064 – 0.15µg (MAT 253:

1.05µg)• Split ratio: 200:1 to 25:1• Injection volume: 30µl – 20 ml• Cryo-trapping: only applied for C1-C3 and CO2 when

large volumes (>200µl) are needed


Analysis for C1, CO2 and C2

Refe

ren

ce

Sta

ndard

C1

CO2

C2

30°C; 200:140l, 3 injections

30°C; 25:1150l, 2 injections

BF C1BF C1

44

45/44

CO2

C2

Compositions (mol%) :C1: 85.67CO2: 2.03C2: 6.47

C1

CO2C2


C2+: manual or programmed?

• Manual: Use timer to remind operator to switch between SF and BF and start GC to increase oven temperature after C2 elutes.

• Programmed: Inject sample at injection time and ‘walk away’: the program automatically switches between SF and BF and start to increase oven temperature at the right time.


Split ratio 25:1; inject 200μl

BF:170-360s

200 400 600 800 1000Time (s)

45/44

44 C2 C3

i-C4

n-C4

i-C5 n-C5

30°C

20°C/min

230°CGC oven temperature programming

Injection time


200 400 600 800 1000

45/44

44 C2 C3

i-C4

n-C4

i-C5 n-C5


C4 and C5

• No need of cryo-trapping.

• C4 and C5 will ‘focus’ at the front end of GC column until oven temperature increased.

• Neo-C5: ―Extremely low concentration in natural

samples. ―Backflushing is needed! ―Routinely analysed at GA.

neo-C5

i-C4

n-C4

i-C5n-C5

GC-IRMS m/z 44 trace of C4 and C5 hydrocarbons

Split ratio: 25:1Injection volume: 200µl


BF BF

GC-IRMS m/z 44 trace of neo-C5

neo-C5

i-C4, n-C4, i-C5 and n-C5 are back flushed (BF)

Split ratio: 25:1Inject volume: 8ml


neo-Pentane and biodegradation

n-pentane iso-pentane neo-pentane

Biodegradation Difficulty


Neo-C5: application to gas correlation

-50

-40

-30

-20

-10

C1 C2 C3 i-C4 n-C4 neo-C5 i-C5 n-C5

d13

C (

o/ o

o)

Barrow Island Z56M non-biodegraded

Barrow Island F 82M - moderately biodegraded

Tubridgi-18 - severely biodegraded


-200

-150

-100

-50

0

50

100

C1 C2 C3 i-C4 n-C4 neo-C5 i-C5 n-C5

d2H

(o/ o

o)

Barrow Island Z56M non-biodegraded

Barrow Island F 82M - moderately biodegraded

Tubridgi-18 - severely biodegraded

Neo-C5: application to gas correlation


Australian sedimentary basins with natural gas deposits


Use gas carbon isotope to correlate source rocks 13C kerogen = 13C i-butane (Boreham et al. APPEA)


-55

-50

-45

-40

-35

-30

-25

-20-50 -40 -30 -20 -10 0

i -C4 (delta 13C, per mil)

neo

-C5

(de

lta

13C

, p

er

mil

)

Gippsland

Otway

Bonaparte

Browse

Carnarvon

Perth

Amadeus

13C neo-pentane vs i-butane

13C i-C4 (‰ )

13C

neo

-C5 (‰

)

Marine

Terrestrial

13C kerogen = 13C neo-C5 + 2‰

biodegradation


N2: A preliminary study

BOC UHP N2 as reference (15N = -1.5‰)

Oxidisation furnace temperature reduced from 900C to 600C; Reduction furnace still at 630C

The N2 of air (15N = 0 ‰) was used as the standard

GC oven temperature: 30C

Split ratio: 200:1 to 25:1

Injection volumes: variable


GC-IRMS traces of N2

29/28

28, 29

Air N2: 15N = 0.29‰ stdev = 0.09

Gas 1: 15N = 0.45‰ stdev = 0.11

Gas 2: 15N = 0.54‰ stdev = 0.12

Gas 3: 15NAIR = -0.37‰ stdev = 0.10


N2 Results:

-40

-35

-30

-25

-20

-15

-10

-7 -6 -5 -4 -3 -2 -1 0 1 2 3Delta N15

De

lta

13

C o

f i-

bu

tan

e

BowenGippslandOtwaySuratBonaparteBrowseCarnarvonPerthAmadeus

15N N2(‰)1

3C

i-

C4 (‰

)

Terrestrial

Marine

biodegradation

Air


N2 Results:

0

5

10

15

20

25

30

35

40

45

50

-8 -6 -4 -2 0 2 4

Delta N15

N2

mo

l%BowenGippslandOtwaySuratBonaparteBrowseCarnarvonPerthAmadeus

15N N2(‰)

N2 m

ol

%

Terrestrial Marine

from ‘air’ in meteoric water

Air



Acknowledgements

We would like to thank Ziqing Hong, Neel Jinadasa, Prince Palatty, Alex Moisis of GA for analysis of gas compositions, which provide necessary information for isotopic analysis.

Phone: +61 2 6249 9111

Web: www.ga.gov.au

Email: [email protected]

Address: Cnr Jerrabomberra Avenue and Hindmarsh Drive, Symonston ACT 2609

Postal Address: GPO Box 378, Canberra ACT 2601

Thank you!

Presentation Contents

• Aim

• Methods and Instruments

• Results and Applications

• Summary


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