Covariation of carbon and hydrogen isotopic compositions in natural ...
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<strong>Covariation</strong> <strong>of</strong> <strong>carbon</strong> <strong>and</strong> <strong>hydrogen</strong> <strong>isotopic</strong><br />
<strong>compositions</strong> <strong>in</strong> <strong>natural</strong> gas: separat<strong>in</strong>g biogenic,<br />
thermogenic, <strong>and</strong> abiotic (<strong>in</strong>organic CO2 reduction) sources<br />
Robert C. Burruss<br />
Christopher D. Laughrey<br />
U.S. Department <strong>of</strong> the Interior<br />
U.S. Geological Survey<br />
PA Department <strong>of</strong> Conservation <strong>and</strong> Natural Resources<br />
PA Geological Survey
“I believe <strong>in</strong> <strong>natural</strong> gas as a clean,<br />
cheap alternative to fossil fuels.”<br />
“Natural gas is cheap, abundant<br />
<strong>and</strong> clean compared to fossil fuels.”<br />
- Nancy Pelosi on Meet the Press, August 2009
Correlat<strong>in</strong>g <strong>natural</strong> gases <strong>in</strong><br />
groundwater, shows, <strong>and</strong> seeps to<br />
subsurface accumulations or to<br />
possible source rocks can be difficult:<br />
• A range <strong>of</strong> processes affect gas composition<br />
• A limited number <strong>of</strong> variables were used to<br />
characterize gas <strong>in</strong> the past
Stable isotopes <strong>of</strong> <strong>carbon</strong> <strong>and</strong><br />
• C1 – C5<br />
• Provide maximum<br />
possible <strong>in</strong>formation<br />
on:<br />
– Orig<strong>in</strong><br />
– Mix<strong>in</strong>g<br />
– alteration<br />
<strong>hydrogen</strong>:
Goals<br />
• Dist<strong>in</strong>guish gas sources<br />
– Thermogenic<br />
– Biogenic (microbial)<br />
– Abiotic CO 2 reduction, Fischer - Tropsch reactions<br />
• Identify alteration processes<br />
– Mix<strong>in</strong>g<br />
– Raleigh fractionation<br />
• Consistency with theoretical k<strong>in</strong>etic models<br />
• Use all possible measurements
Outl<strong>in</strong>e<br />
• Basics<br />
– Gas generation processes<br />
– Isotope fractionation <strong>in</strong> hydro<strong>carbon</strong>s (HC)<br />
• St<strong>and</strong>ard displays <strong>of</strong> HC isotope data<br />
– Bernard plot<br />
– Schoell plot<br />
– Chung’s <strong>natural</strong> gas plot (NGP)<br />
• Examples <strong>of</strong> source, mix<strong>in</strong>g, alteration<br />
– North Slope, Appalachians, New Engl<strong>and</strong><br />
• Conclusion: 13 C <strong>and</strong> 2 H on all HC gases yield more<br />
<strong>in</strong>formation, <strong>and</strong> therefore stronger <strong>in</strong>terpretations
Nomenclature<br />
δ = Rx - R ( std ) x 1000<br />
Rstd δ units: parts per thous<strong>and</strong>,<br />
per mil or ‰<br />
Where:<br />
Rx = 13C/ 12C or 2H/ 1H (also D/H) <strong>in</strong> sample<br />
<strong>and</strong><br />
Rstd = ratio <strong>in</strong> st<strong>and</strong>ard: 13C/ 12C, PDB; 2H/ 1 Rstd = ratio <strong>in</strong> st<strong>and</strong>ard: C/ C, PDB; H/ H, VSMOW<br />
α A-B = R A<br />
R B<br />
α A-B = K 1/n<br />
Where K is the equilibrium constant for the exchange<br />
reaction for n atoms exchanged
Organic Reaction Facies
THE MAJOR SOURCES OF<br />
HYDROCARBON NATURAL GASES:<br />
• Methanogenic<br />
bacteria<br />
• All types <strong>of</strong> kerogen<br />
• Coal<br />
• Oil <strong>in</strong> source <strong>and</strong><br />
reservoir rocks
Sources <strong>of</strong> <strong>natural</strong> gas:<br />
• The major nonhydro<strong>carbon</strong> gases - CO 2, H 2S,<br />
<strong>and</strong> N 2 – are formed by both organic <strong>and</strong><br />
<strong>in</strong>organic processes. Associated He <strong>and</strong> Ar<br />
orig<strong>in</strong>ate <strong>in</strong> both the crust <strong>and</strong> mantle.<br />
• All known commercial hydro<strong>carbon</strong> gas<br />
accumulations are biogenic <strong>in</strong> orig<strong>in</strong>:<br />
– Decomposition <strong>of</strong> organic matter <strong>in</strong> the earth’s crust<br />
– No known commercial abiogenic methane<br />
accumulations exist based on stable isotope<br />
measurements.
-Tissot <strong>and</strong> Welte, 1984)
-Howell <strong>and</strong><br />
others, 1993
Generation <strong>of</strong> gases from organic<br />
matter with <strong>in</strong>creas<strong>in</strong>g temperature:<br />
• Diagenesis:<br />
– microbial methane generation<br />
up to ~ 50°C<br />
– ~ 20% methane <strong>in</strong><br />
conventional reservoirs<br />
– Important <strong>in</strong> some shale<br />
reservoirs <strong>in</strong> the Michigan <strong>and</strong><br />
Ill<strong>in</strong>ois bas<strong>in</strong>s<br />
• Primary crack<strong>in</strong>g:<br />
– thermal crack<strong>in</strong>g <strong>of</strong> kerogen<br />
<strong>and</strong> coal to generate methane<br />
– ~25% to 40% <strong>of</strong> gases<br />
• Secondary crack<strong>in</strong>g:<br />
– thermal crack<strong>in</strong>g <strong>of</strong> oil<br />
– ~40% to 55% <strong>of</strong> gases<br />
• Metagenesis?<br />
- Hunt, 1996
Microbial Gas Generation<br />
• Biogenic vs. microbial or<br />
bacterial gas<br />
• C1/(C2 + C3) >> 100<br />
• δ13C1 < 60 permil<br />
• δDC1 < 150 permil<br />
• Covariance <strong>of</strong> δD values <strong>of</strong><br />
formation water <strong>and</strong> CH 4<br />
• Alkal<strong>in</strong>ity <strong>of</strong> associated formation<br />
water (> 10 meq/kg)<br />
• Positive δ 13 C <strong>of</strong> DIC (> 10<br />
permil)<br />
• Microbial fermentation<br />
• CO 2 reduction
Microbial Gas Generation
CHO Reactions <strong>in</strong> Crustal Rocks<br />
Crack<strong>in</strong>g <strong>of</strong> sedimentary OM:<br />
[(C xH y)-CH 3 ] Kerogen ---> CH 4 + C xH (y-1)<br />
[(C xH y)-C 2H 5 ] Kerogen ---> C 2H 6 + C xH (y-1)<br />
Anthracite grade:<br />
C20H4 ---> 19C + CH4 C C20H 20H 4 + 2H 2H2O 2O ---> 17C + 2CH 4 + CO 2<br />
Graphite buffered, metamorphic fluids:<br />
2C + 2H 2O = CH 4 + CO 2<br />
Fischer-Tropsch Type:<br />
CO 2 + 4H 2 = CH 4 + 2H 2O<br />
2CO 2 + 7H 2 = C 2H 6 + 4H 2O<br />
nCO 2 + (3n+1)H 2 = C nH 2n+2 + 2nH 2O
Schoell (Whiticar) diagram<br />
From Whiticar, 1999
Bernard diagram
10000<br />
1000<br />
C 1/C 2+<br />
100<br />
10<br />
δ 13 C Methane vs Gas Dryness<br />
Microbial<br />
Gas hydrate<br />
dry<strong>in</strong>g effect<br />
1<br />
-90 -80 -70 -60 -50 -40 -30 -20<br />
δ 13 C<br />
Thermogenic<br />
Gubik<br />
Simpson<br />
Tarn<br />
Umiat<br />
West Sak<br />
Wolf Creek<br />
Alp<strong>in</strong>e<br />
E. Barrow<br />
Kalubik<br />
Kuparuk<br />
Po<strong>in</strong>t MacIntyre<br />
S. Barrow<br />
Walakpa<br />
Endicott<br />
Liberty Unit<br />
Prudhoe Bay<br />
Prudhoe Lisburne Pool<br />
Individual Wells
1000<br />
100<br />
C 1/C 2+<br />
10<br />
1<br />
Bernard plot<br />
-60 -55 -50 -45 -40 -35 -30 -25 -20<br />
δ<br />
13 C1<br />
TBR<br />
LSRA<br />
Lee Cty, VA<br />
Rome Trough/Homer<br />
Swan Crk, TN<br />
L&B, 98<br />
J,D, &K, NYS
Methane Isotopic Composition<br />
δ 13 C<br />
-65 -55 -45 -35 -25<br />
-350<br />
-300<br />
-250<br />
δδD<br />
-200<br />
-150<br />
-100<br />
Microbial<br />
Oil-associated<br />
Mixed Microbial<br />
<strong>and</strong> Thermogenic<br />
Cond.<br />
associated<br />
Non-associated<br />
Thermogenic<br />
Gubik<br />
Simpson<br />
Tarn<br />
Umiat<br />
West Sak<br />
Wolf Creek<br />
Alp<strong>in</strong>e<br />
E. Barrow<br />
Kalubik<br />
Kuparuk<br />
Po<strong>in</strong>t MacIntyre<br />
S. Barrow<br />
Walakpa<br />
Prudhoe Bay<br />
Prudhoe Lisburne Pool
Lower Paleozoic gases compared to sources<br />
δ D<br />
δ 13 C, methane<br />
Grugan
Chung, et al., 1988, crack<strong>in</strong>g model <strong>and</strong> the <strong>natural</strong><br />
gas plot (NGP)<br />
• Consider crack<strong>in</strong>g <strong>of</strong> gases from kerogen with homogeneous <strong>isotopic</strong><br />
composition, δ 13 C p<br />
• All gases form by same reaction mechanism<br />
• Parent molecules (kerogen or oil) are structurally similar<br />
• No condensation reactions form gases<br />
K KR - C<br />
KR - C - C<br />
KR - C - C - C<br />
KR - C - C - C - C<br />
KR - C - C - C - C - C<br />
KR - C - C - C - C - C - C<br />
Cm Cp Cn Isotopic composition <strong>of</strong> C Cn δ 13 C n = [δ 13 C m + (n-1) δ 13 C p]/n<br />
Rearrang<strong>in</strong>g:<br />
δC n = -1/n(δC p - δC m) + δC p<br />
Where:<br />
δC p is δ 13 C <strong>of</strong> parent<br />
δC m is δ 13 C <strong>of</strong> l<strong>in</strong>k C<br />
δC n is δ 13 C <strong>of</strong> gas molecule
Natural Gas Plot (Chung, et al.)<br />
ε - -15‰
Ab <strong>in</strong>itio calculations, Y. Tang, et al., 2000, GCA, assum<strong>in</strong>g non-cleaved C is 0 per mil<br />
δ<br />
0<br />
-10<br />
-20<br />
13 Cn<br />
-30<br />
-40<br />
-50<br />
-60<br />
Hexane precursor<br />
300 K<br />
400 K<br />
500 K<br />
600 K<br />
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1<br />
1/C n
North Slope, Alaska: Selective isotope reversals due to microbial oxidation<br />
-25<br />
-30<br />
-35<br />
δ 13 C,<br />
Cn -40<br />
-45<br />
-50<br />
-55<br />
n-pentane<br />
W. Sak #17 (Kup. C)<br />
Prudhoe #15-10<br />
Prudhoe #16-10<br />
W. End Test #1<br />
Sag Delta #8<br />
Sag Delta #10<br />
Mukluk DST4<br />
Prudhoe, Eileen<br />
Prudhoe, Ma<strong>in</strong><br />
Prudhoe, Ma<strong>in</strong><br />
Liberty Unit<br />
n-butane<br />
propane<br />
ethane<br />
Prudhoe Bay Area Gases<br />
methane<br />
0 0.2 0.4 0.6 0.8 1<br />
1/C n<br />
δ<br />
13<br />
Cn -25<br />
-30<br />
-35<br />
-40<br />
-45<br />
-50<br />
-55<br />
-60<br />
West Sak<br />
Tarn<br />
Kalubik<br />
Greater Prudhoe Bay area fields<br />
Kuparuk River<br />
Pt. MacIntyre<br />
Alp<strong>in</strong>e<br />
Prudhoe Bay G.C.<br />
Prudhoe Lisburne<br />
0 0.2 0.4 0.6 0.8 1<br />
1/C n
Reservoir <strong>in</strong>tervals <strong>and</strong><br />
distribution <strong>of</strong> gas reservoirs
Natural gas plot<br />
samples from bas<strong>in</strong>-center LSRA
Natural Gas Plot<br />
Ordovician Reservoirs, Trenton-Black River Fm., NY, PA
Natural Gas Plot<br />
Abiogenic, Kidd Creek gases.
_ 13 C (ä)<br />
-20<br />
-25<br />
-30<br />
-35<br />
-40<br />
-45<br />
-50<br />
Range <strong>of</strong><br />
possible<br />
source rock<br />
δ 13 C<br />
-55<br />
0 0.2 0.4 0.6 0.8 1<br />
Figure 5a<br />
1/C n<br />
<strong>in</strong>creas<strong>in</strong>g<br />
depth<br />
127 o C<br />
possible<br />
endmember<br />
227 o C<br />
butane propane ethane methane<br />
δ 13 C organic matter range:<br />
-34 to -24 ‰<br />
-25<br />
-35<br />
__ 13 C<br />
-45<br />
-55<br />
-65<br />
Figure 5b<br />
Range <strong>of</strong><br />
possible<br />
source<br />
Gases generated from two types<br />
<strong>of</strong> organic matter <strong>in</strong> Middle<br />
Ordovician age source rocks,<br />
Utica/Antes, Appalachian bas<strong>in</strong><br />
<strong>in</strong>creas<strong>in</strong>g<br />
depth<br />
possible<br />
endmember<br />
127 o C<br />
227 o C<br />
butane propane ethane methane<br />
0 0.2 0.4 0.6 0.8 1<br />
1/C n
-32<br />
δ 13 C<br />
ethane<br />
Mix<strong>in</strong>g between OAG <strong>and</strong> Sil. NAG<br />
-37<br />
-42<br />
Sil. NAG<br />
Ord. NAG<br />
Sil. OAG<br />
Ord. OAG<br />
0 0.5 1 1.5 2 2.5 3<br />
1/mol % ethane<br />
-25<br />
-30<br />
-35<br />
13<br />
δ C<br />
ä<br />
13C ethane<br />
-40<br />
-45<br />
Raleigh fractionation <strong>in</strong> Ord. NAG<br />
30% rema<strong>in</strong><strong>in</strong>g<br />
40% rema<strong>in</strong><strong>in</strong>g<br />
Ord. NAG NY<br />
-50<br />
-1.5 -1 -0.5 0 0.5 1<br />
ln mol % ethane<br />
Ord. NAG PA<br />
alpha = 1.015<br />
alpha =1.021
-25<br />
-30<br />
-35<br />
δ 13 δ C<br />
ethan<br />
13C ethan<br />
ethane<br />
Figure 10<br />
-40<br />
-45<br />
-50<br />
Raleigh fractionation<br />
Possible end-member<br />
Mix<strong>in</strong>g<br />
Sil. NAG<br />
Ord. NAG<br />
Sil. OAG<br />
Ord. OAG<br />
-15 per mil<br />
-22 per mil<br />
Mix<strong>in</strong>g<br />
0.0 2.0 4.0 6.0 8.0 10.0 12.0<br />
mol % ethane
-100<br />
-120<br />
-140<br />
δ 2 H C n<br />
-160<br />
-180<br />
-200<br />
Figure 6<br />
C1<br />
C2<br />
-45 -40 -35 -30 -25 -20<br />
δ 13 C n<br />
C3<br />
York<br />
York<br />
York<br />
York<br />
York<br />
York<br />
Drumm<br />
Gillis<br />
Lant<br />
Curren<br />
Hakes<br />
Series12<br />
Series13<br />
Series14
-20<br />
-40<br />
-60<br />
-80<br />
-100<br />
δ D<br />
methan<br />
-120<br />
-140<br />
-160<br />
-180<br />
-200<br />
-220<br />
Possible H/D exchange between CH 4 <strong>and</strong> H 2O<br />
Lee Cty, VA<br />
Swan Creek<br />
Rome Trough, KY<br />
Silurian, OH, PA<br />
Kukersite<br />
L&B, Cambrian, OH<br />
TBR<br />
Possible range <strong>of</strong> δ D<br />
for formation water<br />
Magnitude <strong>of</strong><br />
fractionation at<br />
about 200 to 250 o C<br />
-60 -55 -50 -45 -40 -35 -30 -25 -20<br />
δ 13 C methane
δ 13C vs δ D for C1 to C4 hydro<strong>carbon</strong>s
Low thermal maturity gases<br />
• Are there thermogenic gases with δ13C methane<br />
< -50 ‰ ?
δ 13 δ C<br />
n<br />
-10<br />
-20<br />
-30<br />
-40<br />
-50<br />
-60<br />
-70<br />
-80<br />
If the CH 4 is microbial, what is the source <strong>of</strong> ethane <strong>and</strong> propane ?<br />
Antrim Gases, Mart<strong>in</strong>i, et al., 2003<br />
0 0.2 0.4 0.6 0.8 1<br />
1/C n
δ 13 C n<br />
-10<br />
-20<br />
-30<br />
-40<br />
-50<br />
-60<br />
-70<br />
-80<br />
Low maturity (microbial C 2?) shallow gases, W. Canada, Rowe <strong>and</strong> Muehlenbachs, 1999<br />
0 0.2 0.4 0.6 0.8 1<br />
1/C n
δ D n<br />
-90<br />
-110<br />
-130<br />
-150<br />
-170<br />
-190<br />
-210<br />
-230<br />
Oils are bio- biodegraded<br />
C 1<br />
<strong>Covariation</strong> δ 13 C <strong>and</strong> δ D<br />
-55 -50 -45 -40 -35 -30 -25 -20<br />
δ 13 C n<br />
C 2<br />
i-C 4<br />
C 3<br />
C 1<br />
Rose Hill #1001<br />
Rose Hill #LE-59<br />
Rose Hill #8708<br />
Ben Hur, Terry 108<br />
Drumm 1<br />
Gillis 1<br />
Lant 1<br />
Curren 1<br />
Hakes 1<br />
Konstant<strong>in</strong>ides 1<br />
Harvey<br />
Lovell
So, what does it mean?<br />
• Carbon <strong>isotopic</strong> reversals <strong>and</strong> <strong>in</strong>creas<strong>in</strong>g 13 C enrichment with depth<br />
imply destruction <strong>of</strong> HC leav<strong>in</strong>g “heavy” residual components.<br />
• H/D <strong>in</strong> methane from deepest samples suggests exchange with<br />
formation water<br />
δ 13 C <strong>in</strong> methane <strong>and</strong> ethane (<strong>and</strong> propane) <strong>in</strong> deepest samples<br />
suggests <strong>isotopic</strong> exchange<br />
δ 13 C <strong>in</strong> methane <strong>and</strong> CO 2 <strong>in</strong> deepest samples suggests <strong>isotopic</strong><br />
exchange<br />
• Apparent H/D exchange <strong>in</strong> CH 4-H 2O <strong>and</strong> 12 C/ 13 C exchange <strong>in</strong><br />
CH 4-CO 2 is consistent with fractionations at T = 200 to 250 o C<br />
• THE LEAP: Isotopic exchange is most efficient when molecular<br />
components undergo chemical reactions, therefore I suggest<br />
that all the gas components are l<strong>in</strong>ked through redox reactions,<br />
probably <strong>in</strong>volv<strong>in</strong>g Fe 2+ /Fe 3+ , for example:<br />
– Comb<strong>in</strong>e CO 2 + 4H 2 = CH 4 + 2H 2O with<br />
2Fe 3O 4 + H 2O = 3Fe 2O 3 + H 2 to get<br />
8Fe 3O 4 + 2H 2O + CO 2 = 12Fe 2O 3 + CH 4
OK, so maybe we are wrong <strong>and</strong> this has<br />
noth<strong>in</strong>g to do with redox reactions<br />
• We would welcome suggestions <strong>of</strong> other<br />
mechanisms to generate the <strong>isotopic</strong> variations<br />
we see.
The End