Chemical and isotopic tracers 

natural gas and formation watenatural gas and formation wate

fractured shales

Jennifer McIntosh, Melissa Schlegel, Brittney B

Department of Hydrology & Water Resourc

University of Arizona, Tucson AZ

EPA Technical Workshop Feb 24-25, 2011
Outline of Presentation

1

) What is the chemical and isoto

p g ic si

gnature of fo

waters and natural gas in fractured shales?

2) How does it compare with shallow drift aquifers, 

coalbeds and other deep geologic formations? coalbeds, and other deep geologic formations?
Illinois Basin-Case Study

- 3 organic-rich formations: glacial drift, Penn. coal, & Dev. fractured shale- organic

-rich Ordov Shale not part of rich Ordov. Shale, not part of

this study

500 20 kmm

Schlegel et al. (in press, 2011, Geochimica et Cosmochimica Acta)
Illinois Basin-Case Study

- microbial methane in all 3 units- thermogenic methane in shale and coal thermogenic methane in shale and coal

500 20 kmm

Schlegel et al. (in press, 2011, Geochimica et Cosmochimica Acta)
Illinois Basin - water & gas sam

ShallPennDev. Lime

9New data (white symbols): Schlegel et al. (in press)9Previous data (black symbols): McIntosh et al., 2002; Strąpo

ć et al., 2007, 2008

al, 1988
1000000

Fingerprint of natural gases

100000

Shallow AquifersHigh C1/C2, no C3 Coals

10000

100

1000 

10 Shallow aquifers

Penn. Coals

1

-80 -75 -70 -65 -60 -55 -50 -

δ13CCH4 (ä PDB)

Dev. Shale Thermogenic gas

δ CCH4 (ä PDB)

9In general, 3 organic-rich units have different gas compositions (C1/C2+C3) and 

9Cannot distinguish thermogenic from microbial CH4 in Dev. Shales using carbon 
Differences in C isotopes of g

Shallow aquifers

Penn. CoalsDev. Shale

9Microbial methane from shallow glacial drift, coalbeds and fractured shales all p

isotope fractionation line of ~1.05 to 1.09, except for a few coal samples influencoxidation/sulfate reduction (Strapoc et al., 2008), and one outlier glacial drift sam
Differences in C isotopes of g

Shallow aquifers

Penn. CoalsDev. Shale

ThermogThermog

9Thermogenic gas in Penn. coalbeds is distinct from microbial gas, with lower 

δ1

δ13C-CH4 values.

9Thermogenic gas in the Dev. fractured shales contains very little CO

2 (<0.1 mo
Differences in C isotopes of g

Shallow aquifers

Penn. CoalsDev. Shale

Shallow Aquifers

Coals

9Microbial CH

4 from shallow aquifers, coalbeds, and fractured shales have distin

values, which corresponds to increasing fractionation of CO

2 reservoir during CO

9C isotopes of CH4 and CO

2 may be used to distinguish sources of methane.
Differences in H isotopes of gas/

Shallow aquifers

Penn. CoalsDev. Shale

ThermTherm

9

δD-CH4 not useful in distinguishing gas sources; Microbial CH

4 from shallow aq

and fractured shales have similar 

δD-CH4 values.

9Major difference is in H isotope values of formation waters - related to meteoric 
Fingerprint of formation water

0

Coals

GMWL

Bbm

-20

m

60

-40 Shale-80- Shallow aqu

Penn. CoalsDev. Shale

Shallow Aquifers

-10 -8 -6 -4 -2 0 

δ18

OH2O (ä 

9In general, formation waters associated with fractured shales are more enriche

than shallow (drinking water) aquifers9Isotopic composition of coal waters overlap fractured shales and shallow aquife
10000 000

Salinity differences in fluids

1000.000

10000.000

Coals

100.000

h 

1.000

10.000 Sha

0.100 Shallow aqu

Penn. Coals

Dev Shale

0.010

0.0001 0.0010 0.0100 0.1000 1.0000 

Br- (mM)

Dev. Shale Shallow Aquifers

Br (mM)

9Formation waters associated with natural gas in coalbeds and fractured shales 

and Br (and other solutes) relative to shallow (drinking water) aquifers 
40

Fingerprint of formation water

3020

0

10

Shallow Aquifers

-10 Shallow a

Penn. Coa

Dev Shale

-20

0 10 20 30 

Alkalinity (meq/kg)

. Shale

Alkalinity (meq/kg)

9Formation waters associated with microbial CH4 in shales or coalbeds typically 

DIC values (>10 per mil), and variable alkalinities (<5 to 37 meq/kg)9Shallow aquifers have alkalinities <10 meq/kg, and low δ13C-DIC values (<0 pe
40

Fingerprint of formation water

3020

0

10

-10 Shallow a

Penn. Coa

Dev Shale

Basinal brine - no microbial CH4

-20

0 10 20 30 

Alkalinity (meq/kg)

Dev. Shale

Alkalinity (meq/kg)

9Basinal brines not associated with microbial methane have low alkalinities (<8 mδ13C-DIC values (most near 0 per mil)
Summary

9Natural gas (microbial & thermogenic) from shales and coalbe

distinguished from microbial methane in glacial drift aquifers bascomposition and δ13C values of CH4 and CO2.

9Formation waters from Dev. fractured shales can be distinguisshallow glacial drift aquifers using major ion chemistry (Cl, Br, otand stable isotopes ( and stable isotopes (18O 2H 13C) 18O,2H,13C).
Schlegel, M.E., McIntosh, J.C., Bates, B., Kirk, M., Martini, A.M. (in press, 2011) Com

h i d i bi l

f li l i i h i i di 

For more information

geoc

hemistr

y an

d microbi

ology

o

f multiple or

ganic-ric

h reservoir

s in a sedime

evidence for controls on methanogenesis and microbial transport. Geochimica Acta. 

Martini, A.M., Walter, L.M., McIntosh, J.C. (2008) Identification of microbial and ther

component f srom 

Upper 

Devonian blac

k

sh l a e cores,

Illi i no s an

d Mi hi B 

Mi

chigan 

Ba

Association of Petroleum Geologists Bulletin, 92, 327-339. 

McIntosh, J.C. and Martini, A.M. (2008) Hydrogeochemical indicators for microbial m

black shales: Case studies of the Antrim, New Albany, and Ohio shales. In Hil

Curtis J Curtis, J., ed

s, Gas

S

hale in th

e

R

ocky Mountains cky Mountains and Beyond, Rock

y Mountai

Mountai

Geologists 2008 Guidebook, p. 162-174. 

McIntosh, J.C., Walter, L.M., and Martini, A.M. (2004) Extensive microbial modificat

water geochemistry: Case study from a Midcontinent sedimentary basin, Unite

Bulletin vol 116 Bulletin, vol. 116, no. 5, p

p. 743-759.

Martini, A.M., Walter, L.M., Budai, J.M., Ku, T.C.W., McIntosh, J.C., and Schoell, M

production and modifi cation of gases in sedimentary basins: A geochemical caDevonian Shale gas play, Michigan Basin. AAPG Bulletin, vol. 87, no. 8, pp.

McIntosh McIntosh, J.

C., Walte

r, L.M., an

d

Martini, artini,

A.M. (2002) Pleistocen Pleistocen

e

r

echarg

e to mid-co

co

effects on salinity structure and microbial gas generation. Geochimica et Cosmvol. 66, no. 10, pp. 1681-1700.

Martini, A.M., Petsch, S.T., McIntosh, J.C., Schlegel, M., Damashek, J., Miller, S.E., K

Microbial Gas from Unconventional

Reservoirs: The New Alban

y Shale as a c

Research Institute, Report-07122-16. 

Walter, L.M., McIntosh, J.C., Martini A.M., and Budai, J.M. (2001) Hydrogeochemistr

Albany Shale, Illinois Basin. Gas Research Institute, Report-5094.