The origin of some natural gases in Permian

through Devonian Age Systems in the

Fred Baldassare

Appalachian Basin & the relationship to incidents

of stray gas migration

Fred Baldassare

Senior Geoscientist

p p re ared for

Technical Workshops for Hydraulic Fracturing Study

Chemical & Analytical Analytical Methods Methods

February 24, 2011

1
Methane is the Principal Hydrocarbon found in Permian

through Devonian age strata and in all stray gas

investigations

2
STRAY GAS IN
• As the allegations of hydraulic fracturing causing

contamination of groundwater supplies received the of various media outlets, the link to stray natural gascontamination contamination of aquifer aquifer systems systems created created by hydraul

hydraul

fracturing was simultaneously made, inexplicably...

• I ii nvestigations of stray natural gas i id nc en

Pennsylvania reveal that NO incidents of gas migration migration were caused by hydraulic hydraulicfracturing of the Marcellus shale.
Methane in gas phase

Gas migration in the subsurface occurs principally by advectivetransport from areas of hi hg pressure to areas of low pressure and isinfluenced by temporal changes in:

‐ Barometric pressure

‐ Soil/bedrock porosity, permeability

Methane dissolved in water

/ p y, p y

‐ Precipitation ‐ Pore water

Methane dissolved in groundwater in the shallow aquifer system is

not uncommon in certain areas of the Appalachian Basin...generally,it does not represent the same threat as gas phase methane, and

sh ld ou not be eval d uate the same as methane gas in or around abuilding.Solubility ~ 26‐32 mg/l at atmospheric p , ressure, however, solubilityin water is proportional to pressure. Every foot of water exerts .43

psi or 2.31 feet of water is under 1 psi. With increased hydrostatic

pressures, dissolved methane concentrations in the groundwater

can greatly greatly exceed its solubility solubility, and may represent represent a threat toindoor air spaces.

5
Incidents of stray combustible gas ar

recent occurrences.

Potential Sources Include:

 Naturally occurring gas seeps

 Abandoned, recently drilled & operating gas wells

 Ab d d an oned & operating coal mines

 CBM wells

 Natural gas storage fields

 Natural gas pipelines

 Abandoned & operating landfills

 Naturally occurring sh ll a ow f f ormations/aquifers

 Buried organic matter Drift gas
7
Thermogenic: C1 – C6 hydrocarbons generated. Formed during th

alteration of organic materials.

 A itd ssociated & non‐associtd a e Type I (lacustrine), II (marine), & III (woody) kerogen

 Early mature

 Mature

 Late Mature Overmature

Microbial: C1 – C3 hydrocarbons generated. Formed by the bacter

decomposition of organic matter.

 CO2 reduction

 Met yh l‐type fe e tat o ermentation
Various researchers have determined by examination of stable hydrogen and c

of methane methane that there are common hydrogen hydrogen and carbon isotopic isotopic composition

composition

thermogenic gas associated with coal and natural gas, drift gas, and other near

microbial gases (Craig, 1953; Coleman and others, 1977; Deines, 1980; Schoell

Claypool, 1981; Schoell, 1983; Whiticar,1986; Wiese and Kvenvolden, 1993; Cole

Baldassare and Laughrey, 1997; Kaplan and others, 1997; and Rowe and Muehle

Osborn and McIntosh McIntosh, 2010). Stable carbon isotope compositions are expressed as the ratio of 12C to 13C 

compared with that of the international standard ...expressed as per mil (pthousand, o/oo) and expressed as δ13C values as follows:

δ13C ‰ = [(13C/12Csample ‐ 13C/12Cstandard) / (13C/12Cstandard)] * 1

International standards:

carbon: Pee Dee Belemnite ( ) “PDB”

hydrogen: Standard Mean Ocean Water (“SMOW”)
In general:

Microbial methaneacetate fermentation (marsh gas & landfill gas)

 δ13C1:  ‐40 to ‐62 o/oo δD:   ‐270 to ‐350 o/oo

Microbial methane

CO2 reduction (drift gas) δ13C1:  ‐62 to ‐90 o/oo δD: ‐180 to ‐240 o/oo

Thermogenic methane δ13C1:  ‐26 to ‐50 o/oo δD:    ‐110 to ‐250 o/oo
Isotopic mass‐balance calculations to determine the fraction

member gases can be used to define mixing

Bernard GraphRevesez, et al., 2010
Differentiation of thermogenic gases

-30-25

g

-35

δ13C (o/oo)

-45-40

d13-C1 d 13-C2 d 13-C3 d 13-

A -41.87 -35.04 -29.16B -43.22 -33.39 -30.06

C -42.99 -34.03 -31.07D -41.3 -35.98 -30.23

45

E -41.76 -35.4 -30.49

A B C D E
DIC: Dissolved inorganic carbon

If we have background groundwater quality for an aquifer, DIC analysis will

allow us to determine if methane has been impacted by oxidation or

d di egra ation.

Microbial processes such as CH4 production or CH4 consumption by

oxidation can impart unique isotopic signatures to gases and components of

the associtd a e waters. U i s ng a combi d ne gas and water approach is i tt mpor antfor constraining the origin of natural gas in water wells.

Whiticar, and Faber, 1986, Revesz, et. al, 2010

13
Central & Northern Appalachian Basi

Representative isotope geochemistry datth i ermogenic gases:
-100

ISOTOPE CROSSPLOT

 Themogenic Gas("natural gas" and coalbed methane)

Upper Devonian/

Marcellus (SW PA)

(% )o

Microbial Gas -CO Reduction 2

-200

hane (drift gas)D of Met early thermogenic

δ

Microbial Gas - Fermentation(landfill gases)

-300

y g

( g)

-90 -80 -70 -60 -50 -40 -30 

δC of Methane 13 (% )o Representative Thermogenic gases Central/Northern Appalachian Basin
-100

ISOTOPE CROSSPLOT

 Thermogenic Gas("natural gas" and

(% )o

Microbial Gas -CO Reduction 2

( natural gas and coalbed methane)

-200

hane 

δ

 (drift gas)

2

D of Meth

Microbial Gas - Fermentation(landfill gases)

-300

-90 -80 -70 -60 -50 -40 

δ 13 C of Methane (% )o Southwestern Pennsylvania Private water supply well data

Investigations revealed methane origin as naturally occurring
-100

ISOTOPE CROSSPLOT

 Themogenic Gas("natural gas" and

(% )o

Microbial Gas -CO Reduction 2

( natural gas and coalbed methane)

-200

ane CO Reduction

 (drift gas)

2

D of Metha

Upper Devonian 

(Catskill & unknow

C1 : C2 55 

δ

Microbial Gas - Fermentation(landfill gases)

-300

δ

-90 -80 -70 -60 -50 -40 -30 

C of Methane (% ) Pre-Marcellus well activity

δC13of Methane (%o) Pre Marcellus well activity private water supply wells

Bradford County
-100

ISOTOPE CROSSPLOT

 Themogenic Gas("natural gas" and coalbed methane

566'

(% )o

Microbial Gas -CO Reduction 2

-200

ane 

Upper Devonia

(Catskill & unknow

566' - 916'

566'

916'

770'

CO Reduction (drift gas)

2

D of Metha

δ

Microbial Gas - Fermentation(landfill gases)

-300

D

δ

( g)

-90 -80 -70 -60 -50 -40 -3

(% )

C of Methane 13 Marcellus Gas Well (%o)

Central Bradford County
δC

MarBrad

0

‐55 ‐50 ‐45 ‐40 ‐35 ‐30 ‐25 

δC 13

Upper Devonian

20004000

Seal?

Upper Devonian(Catskill fm?)

40006000

epth (ft)

Marcellus shale

(note isotope reversal)

8000

De(note isotope reversal)

1000012000
δ

MBr

0

‐50.0 ‐45.0 ‐40.0 ‐35.0 ‐30.0 ‐25.0 

δC 13

U D i

2000

seal?

pper Devonian

(Catskill fm?)

40006000

pth (ft)

8000

Dep

Marcellus 

(note isotope 

1000012000
δ

MBr

0

100

‐55 ‐50 ‐45 ‐40 ‐35 ‐30 ‐25 

δC 13

200300

Shallow thermogenic gathroughout sample

400500

pth (ft)

throughout sampleinterval

600700

Dep

Seal?

800900

1000