Isotopic Analysis of Compounds in Low Concentration in Australian

Report
Isotopic Analysis of Compounds in Low
Concentration in Australian Natural Gases
Using CF-GC-IRMS Systems
Junhong Chen and Chris Boreham
Isotope and Organic Geochemistry Team at GA
Isotopic Analysis of Compounds in Low Concentration in Australian Natural
Gases Using a CF-GC-IRMS System
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
Isotopic Analysis of Compounds in Low Concentration in Australian Natural
Gases Using a CF-GC-IRMS System
Instruments
•
13C/12C, 15N/14N
analysis:
Thermo Finnigan-MAT 252 (253) GC-C-IRMS System
with ConFlo III (IV) interface
Isotopic Analysis of Compounds in Low Concentration in Australian Natural
Gases Using a CF-GC-IRMS System
Instruments
• D/H:
Thermo Finnigan Delta Plus XL GC-TC-IRMS
System (TC – High Temperature Conversion)
Isotopic Analysis of Compounds in Low Concentration in Australian Natural
Gases Using a CF-GC-IRMS System
Analytical Conditions (δ13C and δD)
GC conditions:
• GC columns:
Varian, coating: PoraPlot Q; 25m x 0.32mm (ID),
0.25m.
• 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
Isotopic Analysis of Compounds in Low Concentration in Australian Natural
Gases Using a CF-GC-IRMS System
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
Isotopic Analysis of Compounds in Low Concentration in Australian Natural
Gases Using a CF-GC-IRMS System
Analysis for C1, CO2 and C2
Reference
44
Compositions (mol%) :
C1: 85.67
CO2: 2.03
C2: 6.47
Standard C1
45/44
30°C; 200:1
40l, 3 injections
30°C; 25:1
150l, 2 injections
C2
C1
BF C1
BF C1
CO2
CO2
C2
C2
CO2
Isotopic Analysis of Compounds in Low Concentration in Australian Natural
Gases Using a CF-GC-IRMS System
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.
Isotopic Analysis of Compounds in Low Concentration in Australian Natural
Gases Using a CF-GC-IRMS System
230°C
GC
oven temperature programming
45/44
20°C/min
30°C
44
C2
C3
Split ratio 25:1; inject 200μl
BF:170-360s
n-C4
i-C4
i-C5 n-C
5
200
Injection time
400
600
800
1000
Time (s)
Isotopic Analysis of Compounds in Low Concentration in Australian Natural
Gases Using a CF-GC-IRMS System
45/44
44
C2
C3
n-C4
i-C4
i-C5 n-C
5
200
400
600
800
1000
Isotopic Analysis of Compounds in Low Concentration in Australian Natural
Gases Using a CF-GC-IRMS System
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.
GC-IRMS m/z 44 trace of C4 and C5 hydrocarbons
n-C4
i-C4
Split ratio: 25:1
Injection volume: 200µl
neo-C5
i-C5
n-C5
Isotopic Analysis of Compounds in Low Concentration in Australian Natural
Gases Using a CF-GC-IRMS System
GC-IRMS m/z 44 trace of neo-C5
Split ratio: 25:1
Inject volume: 8ml
neo-C5
BF
BF
i-C4, n-C4, i-C5 and n-C5 are back flushed (BF)
Isotopic Analysis of Compounds in Low Concentration in Australian Natural
Gases Using a CF-GC-IRMS System
neo-Pentane and biodegradation
n-pentane
iso-pentane
neo-pentane
Biodegradation Difficulty
Isotopic Analysis of Compounds in Low Concentration in Australian Natural
Gases Using a CF-GC-IRMS System
Neo-C5: application to gas correlation
C1
C2
C3
i-C4
n-C4
neo-C5
i-C5
n-C5
-10
d13C (o/oo)
-20
-30
-40
Barrow Island Z56M non-biodegraded
Barrow Island F 82M - moderately biodegraded
Tubridgi-18 - severely biodegraded
-50
Isotopic Analysis of Compounds in Low Concentration in Australian Natural
Gases Using a CF-GC-IRMS System
Neo-C5: application to gas correlation
C1
C2
C3
i-C4
n-C4
neo-C5
i-C5
n-C5
100
50
d2H (o/oo)
0
-50
-100
-150
-200
Barrow Island Z56M non-biodegraded
Barrow Island F 82M - moderately biodegraded
Tubridgi-18 - severely biodegraded
Isotopic Analysis of Compounds in Low Concentration in Australian Natural
Gases Using a CF-GC-IRMS System
Australian sedimentary basins with natural gas deposits
Isotopic Analysis of Compounds in Low Concentration in Australian Natural
Gases Using a CF-GC-IRMS System
Use gas carbon isotope to correlate source rocks
d 13C kerogen = d 13C i-butane (Boreham et al. APPEA)
Isotopic Analysis of Compounds in Low Concentration in Australian Natural
Gases Using a CF-GC-IRMS System
d13C neo-pentane vs i-butane
d 13C kerogen = d 13C neo-C5 + 2‰
-50
-40
-30
-20
-10
0
-20
Terrestrial
-25
13
135C
neod-C
(delta
neo-CC,5 per
(‰ mil)
)
biodegradation
-30
-35
-40
Gippsland
Otway
Bonaparte
Marine
-45
Browse
Carnarvon
-50
Perth
Amadeus
-55
13C i-CC,(‰
i -Cd
4 (delta
4 per)mil)
13
Isotopic Analysis of Compounds in Low Concentration in Australian Natural
Gases Using a CF-GC-IRMS System
N2: A preliminary study
BOC UHP N2 as reference (d15N = -1.5‰)
Oxidisation furnace temperature reduced from 900C to
600C; Reduction furnace still at 630C
The N2 of air (d15N = 0 ‰) was used as the standard
GC oven temperature: 30C
Split ratio: 200:1 to 25:1
Injection volumes: variable
Isotopic Analysis of Compounds in Low Concentration in Australian Natural
Gases Using a CF-GC-IRMS System
GC-IRMS traces of N2
29/28
28, 29
Gas 1: d15N = 0.45‰
stdev = 0.11
Gas 2: d15N = 0.54‰
stdev = 0.12
Gas 3: d15NAIR = -0.37‰
stdev = 0.10
Air N2: d15N = 0.29‰
stdev = 0.09
Isotopic Analysis of Compounds in Low Concentration in Australian Natural
Gases Using a CF-GC-IRMS System
N2 Results:
-7
-6
-5
-4
N15
Delta
d15N
N2(‰)
-1
-2
-3
0
1
2
3
-10
Delta
of 4i-butane
d1313C
C i-C
(‰)
-15
-20
Bowen
Gippsland
Otway
Surat
Bonaparte
Browse
Carnarvon
Perth
Amadeus
Air
biodegradation
-25
Terrestrial
-30
Marine
-35
-40
Isotopic Analysis of Compounds in Low Concentration in Australian Natural
Gases Using a CF-GC-IRMS System
N2 Results:
50
Bowen
Gippsland
Otway
Surat
Bonaparte
Browse
Carnarvon
Perth
Amadeus
45
40
%
NN2
2 mol
mol%
35
30
Air
from ‘air’ in
meteoric water
25
20
15
10
Terrestrial
5
Marine
0
-8
-6
-4
-2
d15
N N2N15
(‰)
Delta
0
2
4
Isotopic Analysis of Compounds in Low Concentration in Australian Natural
Gases Using a CF-GC-IRMS System
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.
Isotopic Analysis of Compounds in Low Concentration in Australian Natural
Gases Using a CF-GC-IRMS System
Thank you!
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
Presentation Contents
• Aim
• Methods and Instruments
• Results and Applications
• Summary
Isotopic Analysis of Compounds in Low Concentration in Australian Natural
Gases Using a CF-GC-IRMS System

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