Gas Character Anomalies Found in Highly Productive … · Gas Character Anomalies Found in Highly Productive Shale Gas Wells Kevin Ferworn John Zumberge. Jackie Reed, Reed Geochemical

Gas Character Anomalies Found in Highly Productive Shale Gas Wells

Kevin FerwornJohn Zumberge

Jackie Reed, Reed Geochemical Consulting

Stephen BrownGeoMark Research

Houston, TX

Oct. 2008

Oct. 2008Shale Gas Presentation

Presentation Outline

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• Description of carbon isotopes and the differences between Biogenic and Thermogenic gases.

• Sample collection (from the mud stream and cuttings) during drilling.

• Ethane Isotope “rollover” suggests in-situ gas cracking and more productive wells.

• Mud Gas Isotope “reversals” indicate over-pressured shales.

• Differences between Mud (Free) and Cuttings (Adsorbed) Gases as permeability and fracturing markers.


After OGJ May, 2003

Carbon Isotopes

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Dry and Wet Gas Compositions

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Carbon Isotope Ratios

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after M. Schoell


Mud GasSampling

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GASTRAP

MUD SYSTEM

SAMPLING MANIFOLD

FID DETECTOR

STANDARD GASCHROMATOGRAPH

MUD LOG CHART

SAMPLE CHAMBER(ISOTUBE)

ISOTOPE CHART

GASTRAP

MUD SYSTEM

SAMPLING MANIFOLD

FID DETECTOR

STANDARD GASCHROMATOGRAPH

MUD LOG CHART

SAMPLE CHAMBER(ISOTUBE)

ISOTOPE CHART


Gas Sampling for Isotopes

Mud Gas SamplingManifold

Isotube for Mud Gases

Isojar forCuttings Gases

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Mud Gas Interpretive Plots-70

-60

-50

-40

-30

-20-50 -40 -30 -20

Ethane Carbon Isotope, δ 13C (‰ )

Met

hane

and

Pro

pane

Car

bon

Isot

ope,

δ13

C (‰

)

Methane vs. Ethane

Propane vs. Ethane

The maturity calibrations are developed from rock analyses for different regions and basins.

High Maturity

Medium Maturity

Low Maturity

High Maturity

Medium Maturity

Low Maturity

-80

-70

-60

-50

-40

-30

-200 5 10 15 20 25 30

Gas Wetness, C2+ (mole %)

Met

hane

Car

bon

Isot

ope,

δ13

C (‰

)

Bacterial Gas

Associated Gas

Oil

Mixed Bacterial / Thermogenic Gas

Post MatureDry Gas

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Gas Isotope / Maturity “Rollover”

• Ethane and Propane isotopes “Rollover” in increasingly high maturity Shale Gas wells

• Behavior is also observed in Fayetteville, Woodford, Haynesville, Appalachia, portions of the Rockies and Horn River Basin (Canada).

• These wells appear to be among the most productive shale wells.– In-situ cracking makes more smaller molecules increasing fluid pressure.– Organic material becomes more brittle – increased Kerogen porosity and permeability– Appearance of “bubble pores” increasing permeability

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Barnett Shale Ethane Isotope “Rollover”

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Ethane Carbon Isotope vs. Gas Wetness

-45

-41

-37

-33

-29

-25

0 5 10 15 20 25

Gas Wetness (C2+)

Etha

ne C

arbo

n Is

otop

e

Normal IncreasingMaturity Trend

Ethane IsotopeReversals in

Mature EasternBarnett Gases

C2 Isotope“Rollover”


Ethane Isotope Reversals

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“Isotope Rollover” evidence via In-situ Gas Cracking

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Gas iC4 / nC4 Ratio vs. Gas Wetness

0.0

0.5

1.0

1.5

2.0

2.5

0 5 10 15 20 25

Gas Wetness (C2+)

iC4

/ nC

4 R

atio

Normal IncreasingMaturity Trend

In-situGas

Cracking

C2 Isotope“Rollover”


Initial Monthly Gas Production vs. Gas Wetness

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Gas Production DataLee #2H, Johnson County, TX

0

20,000

40,000

60,000

80,000

100,000

120,000

Aug-04 Feb-05 Sep-05 Mar-06 Oct-06 Apr-07 Nov-07 Jun-08 Dec-08

Mon

thly

Pro

duct

ion

(msc

f)

Initial Rate ~ 110,000 mscf

Stable Rate ~ 12,000 mscf


Initial Monthly Gas Production vs. Wetness

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Initial Production vs. Gas Wetness

0

50,000

100,000

150,000

200,000

250,000

0 5 10 15 20 25

Gas Wetness (C2+)

Initi

al P

rodu

ctio

n (m

scf/m

onth

) C2 Isotope“Rollover”C2 Isotope“Rollover”


Stabilized Monthly Gas Production vs. Wetness

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Stabilized Production vs. Gas Wetness

0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

0 5 10 15 20 25

Gas Wetness (C2+)

Stab

ilize

d Pr

oduc

tion

(msc

f/mon

th)

C2 Isotope“Rollover”C2 Isotope“Rollover”

Wells without Isotope “Rollover”are never the best producers.

Some “Rollover”Wells are poorerproducers due tolow TOC and/orpermeability –

fracturing issues.


Total Organic Carbon Map

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Highly mature gaseswith Isotope “Rollover”

but low TOC.Less Productive Wells.


Haynesville vs. Barnett Production

• Early reports of Haynesville production rates are 2 to 3 times better than comparable Barnett wells.

• Similarities include…– Total Organic Carbon (TOC)– Source Maturity– “Rollover” Ethane and Propane Gas Isotopes

• A possible difference for Haynesville wells is the presence of significant overpressure

• An Isotope “Reversal” in a Mud Gas Isotope log suggests little leakage from the Haynesville to shallower formations.

• Isotopic Reversal trend less pronounced in Barnett wells.

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Texas

Arkansas

Louisiana

0 50 100

MILES

N

UpliftSabine

Mex

iaFa

ult

Zone

Current LeasingActivity

Texas

Arkansas

Louisiana

0 50 100

MILES

N

UpliftSabine

Mex

iaFa

ult

Zone




5,000

6,000

7,000

8,000

9,000

10,000

11,000

12,000

13,000

14,000

15,000-40 -35 -30 -25 -20

Ethane Carbon Isotope, δ13C (‰ )

Mea

sure

d D

epth

, MD

(ft)

5,000

6,000

7,000

8,000

9,000

10,000

11,000

12,000

13,000

14,000

15,0000 4 8 12

Wetness, (C2 - nC5) / (C1 - nC5)

Mea

sure

d D

epth

, MD

(ft)

Mud Gas Ethane Isotope “Reversals” (Haynesville Example)

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Bossier / Cotton Valley

Haynesville

Top of Overpressure

“Normal” maturityisotopic trend.


Barnett Shale Sourced Oils in Younger Reservoirs

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Mississippian Barnett Shale SourcePennsylvanian Reservoirs

Barnett Source & Reservoir

Mississippian Barnett Shale SourcePennsylvanian Reservoirs

Barnett Source & Reservoir

Substantial Barnett-SourcedOil in younger reservoirs.


Barnett Shale Stratigraphy

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Montague Wise Parker Hood Erath Mills LlanoCommanche San Saba

Fort Worth Basin North South Cross Section

North SouthMontague Wise Parker Hood Erath Mills LlanoCommanche San Saba

Fort Worth Basin North South Cross Section

North South


Shale Gas Analyses as Permeability Markers

There is a clear isotopic differencebetween Methane from Mud Gases (black squares) and HeadspaceGases (green squares).

• Mud Gas ~ Free / Solution / Lost Gas

• Headspace Gas ~ Adsorbed Gas

Larger differences between Isotube and Isojar isotopes correlate with increased Permeability.

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Methane Isotope Comparison

4,200

4,300

4,400

4,500

4,600

4,700

4,800

4,900-50 -45 -40 -35 -30

Mea

sure

d D

epth

Headspace Gas - IsoJars

Mud Gas - IsoTubes


Nanopores in Maturing Kerogen

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• Reed et al. Texas BEG• Presented by Bob Loucks,

AAPG San Antonio 2008• Submitted for publication 2008

Darker Areas –Higher TOC

Nanopores

~ 10 μm



4,200

4,300

4,400

4,500

4,600

4,700

4,800

4,900-50 -45 -40 -35 -30

Mea

sure

d D

epth


Mud Gas - IsoTubes


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Free Gas – more negative isotopesAdsorbed Gas – more positive isotopes

Poorer PermeabilityGas eventually evolving off cuttingshas more free gas making Methane Isotopes more negative

Headspace Gas

Mud Gas



4,200

4,300

4,400

4,500

4,600

4,700

4,800

4,900-50 -45 -40 -35 -30

Mea

sure

d D

epth


Mud Gas - IsoTubes


GeoMark

BetterPermeabilityGas eventually evolving off cuttings is mostly adsorbed gasHeadspace Gas

Mud Gas

Free Gas – more negative isotopesAdsorbed Gas – more positive isotopes


5,500

6,000

6,500

7,000

7,500

8,000

8,500

9,000

9,500

10,000

10,500-48 -42 -36 -30

Ethane Carbon Isotope, δ 13C (‰ )

Mea

sure

d D

epth

, MD

(ft)

Marcellus Example (with Isotopic Reversal)

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PossibleOverpressure?

“Normal” maturityisotopic trend.

-70

-60

-50

-40

-30

-20-50 -40 -30 -20

Ethane Carbon Isotope, δ13C (‰ )M

etha

ne a

nd P

ropa

ne C

arbo

n Is

otop

e, δ

13C

(‰)

BA

CTE

RIA

L M

IXIN

G

The maturity calibrations arebased on proprietary EOG dataf th B tt Sh l

Ethane vs. Propane

Ethane vs. Methane

%Ro = 2.0

1.5

1.4

1.3

1.2

0.8

1.0

0.9 %Ro = 2.0

1.5

1.4

1.3

1.2

0.8

1.0

0.9

These mature gases (> 2.0 Ro) have Ethane and Propane isotope reversals due to in-situ gas cracking.

-80

-70

-60

-50

-40

-30

-200 5 10 15 20 25 30

Gas Wetness, (C2 - nC5) / (C1 - nC5)

Met

hane

Car

bon

Isot

ope,

δ13

C (‰

)

Bacterial Gas

Associated Gas

Oil

Mixed Bacterial / Thermogenic Gas

Post MatureDry Gas

After M. Schoell


Conclusions

• Shale Gas well performance can be diagnosed with Mud and Headspace isotopic analyses

• Gas and Cuttings samples collected while drilling and quickly analyzed

1. Ethane and Propane Isotope Rollover indicates in-situ gas cracking at high maturities. Increasing maturity and gas cracking creates additional nanopores within the kerogen.

2. Ethane Isotope “Reversals” within a single well demonstrates overpressure / effective seals.

3. Mud (Free) and Headspace (Adsorbed) gas signatures are used as Permeability / Fracturing Markers.

• Early Marcellus Shale examples look promising.

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Documents

Gas Character Anomalies Found in Highly Productive … · Gas Character Anomalies Found in Highly Productive Shale Gas Wells Kevin Ferworn John Zumberge. Jackie Reed, Reed Geochemical