Pashin, J.C., 2004, Geologic heterogeneity and coalbed methane production - experience from the Black Warrior Basin, in Warwick, P.D., ed., Selected presentations on coal-bed gas in the eastern United States, U.S. Geological Survey Open-File Report 2004-1273, p. 61-92. Geologic Heterogeneity and Coalbed Methane Production – Experience from the Black Warrior Basin 1 By Jack C. Pashin 2 Opening Points • Numerous geologic factors, including stratigraphy, structure, coal quality, and hydrology influence coalbed methane production in the Black Warrior basin of Alabama. • Producing coalbed methane requires a different paradigm that is used for conventional reservoirs. • The Black Warrior basin is an operationally mature basin in which extreme geologic heterogeneity influences gas and water production from coal. 1 Modified from unpublished short course notes from Short Course #4, Coalbed methane potential in the U.S. and Mexican Gulf Coast, Gulf Coast Association of Geological Societies/Gulf Coast Section SEPM – 52 nd Annual Convention, Austin, TX, October 30, 2002. 2 Geological Survey of Alabama, Tuscaloosa, AL
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Pashin, J.C., 2004, Geologic heterogeneity and coalbed methane production - experience from the Black Warrior Basin, in Warwick, P.D., ed., Selected presentations on coal-bed gas in the eastern United States, U.S. Geological Survey Open-File Report 2004-1273, p. 61-92.
Geologic Heterogeneity and Coalbed Methane Production – Experience from the Black Warrior Basin1 By Jack C. Pashin2
Opening Points • Numerous geologic factors, including stratigraphy, structure, coal quality, and hydrology influence
coalbed methane production in the Black Warrior basin of Alabama.
• Producing coalbed methane requires a different paradigm that is used for conventional reservoirs.
• The Black Warrior basin is an operationally mature basin in which extreme geologic heterogeneity influences gas and water production from coal.
1 Modified from unpublished short course notes from Short Course #4, Coalbed methane potential in the U.S. and Mexican Gulf Coast, Gulf Coast Association of Geological Societies/Gulf Coast Section SEPM – 52nd Annual Convention, Austin, TX, October 30, 2002. 2 Geological Survey of Alabama, Tuscaloosa, AL
10 mi
JEFFERSON
TUSCALOOSA
BIBB
HALEGREENE
WALKER
FAYETTE
CityGas pipelineCBM fieldPower plantDeep mine
INFRASTRUCTURE
Tuscaloosa
Birmingham
Alabama
INDEX MAP
Jack Pashin
Jack Pashin
Figure 1. Infrastructure associated with coalbed methane fields in the Black Warrior basin of west-central Alabama.
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Peter Warwick
Peter Warwick
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62
Coalbed MethaneProduction
Gas Content
Coal Quality
Stratigraphy
Hydrodynamics
Geothermics
Structural Geology
GEOLOGIC CONCEPTS
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Jack Pashin
Figure 2. Major geologic concepts associated with coalbed methane production.
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63
BLUECREEK
COAL BEDMedium volatile
bituminous
Top
Base
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Jack Pashin
Figure 3. The Blue Creek coal bed is the principal mining target in the Black Warrior basin and was the original focus of coalbed methane operations.
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Maximum flooding surface
Gamma ray logGR
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Figure 4. Graphic log of the Duncanville core showing upper Pottsville coal zones from which coalbed gas is produced.
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Peter Warwick
Peter Warwick
ShaleLithareniteQuartzareniteCoalLimestone
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Jack Pashin
Figure 5. Stratigraphic model of an idealized Pottsville depositional cycle in the Black Warrior basin.
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B'Southeast
BNorthwest
0
0
500
1000
1500
2000 ft
10 20 30 mi
L. Boyles
U. Boyles
FayetteBlack CkReamMary LeeGillespy
CurryPratt
CobbGwin
Utley
Brookwood
B
B'
Index map
POTTSVILLECYCLE STACKING
Marine shaleQuartzareniteCoal zone
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Figure 6. Cycle stacking patterns in the Pottsville Formation of the Black Warrior basin in Alabama.
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FAULTING AND FRACTURING
Coalunderclay
Sandstone
Sandstone
Shale
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Figure 7. Flow of water in Pottsville coalbed methane reservoirs is exclusively through natural fractures, including cleats, joints, and shear fractures.
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PRATTSTRUCTURE
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Figure 8. Structural contour map of the top of the Pratt coal zone in the Black Warrior coalbed methane fields. See Figure 3 for index map.
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Contours relative to mean sea level.
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Peter Warwick
inferred detachment
Holt Lakehalf graben
Strip Mine grabenSexton Springhorst
Franklin Hill half graben
Elev. (ft)
SL
-1000
-2000
-3000
No vertical exaggeration
ASouthwest
A'Northeast
0
0
1 km
1 mi
Gwin coal zone
DEERLICK CREEK STRUCTURE
A
A’
Index mapDeerlick
Creek Field
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Figure 9. Structural cross section of thin-skinned horst-and-graben system in Deerlick Creek Field.
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ADSORPTION ISOTHERMS, BLACK WARRIOR BASIN
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Figure 10. Isotherms showing variable sorption performance of Pottsville coal for three gases. Isotherms run by University of British Columbia.
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Peter Warwick
0
500
1000
1500
2000
2500
3000
3500
4000
Gas content (ft3/t, ash-free)
200
400
600
800
1000
1200
1400
1600
OAK GROVE FIELDRock Creek core C-3
(Malone and others, 1987b)
CEDAR COVE FIELDSOMED Duncanville core(Levine and others, 1989)
Gas content (ft3/t, ash-free)200 400200 400 600 0
r2=0.80r2=0.60
GAS CONTENTVS. DEPTH
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Figure 11. Plots of gas content versus depth showing heterogeneous distribution of coalbed gas in the Black Warrior basin.
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COALQUALITY
This may not be theworld’s best coalbed
gas reservoir
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Figure 12. Intensely pyritized coal with mineralized fractures suggests that coal quality affects reservoir properties.
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MARY LEERANK
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Figure 13. Map of coal rank in the Black Warrior coalbed methane fields.
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RANK CROSS SECTIONS
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Figure 14. Cross sections showing coal rank in the Black Warrior basin. See Figure 15 for location.
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hvAmvSORPTION AND RANK
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Figure 15. Relationship between coal rank and sorption capacity in the Black Warrior basin.
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Jack Pashin
Figure 16. Maps of ash content contrasting the Mary Lee and Utley coal beds in Blue Creek Field.
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SORPTION AND ASH
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Figure 17. Relationship between sorption capacity and ash content and sorption capacity of coal in the Black Warrior basin.
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Jack Pashin
Figure 18. Relationship of methane sorption to temperature in a San Juan basin coal.
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60
70
80
90
100
110
120
130
140
150
160
0 1000 2000 3000 4000 5000 6000
Depth (ft)
Bottom-holetemperature (°F)
y = .009x +74.9
n=889r2 = 0.66 Supercritical
bottom-hole conditions(normal hydrostatic pressure)
TEMPERATURE-DEPTH PLOT
Jack Pashin
Figure 19. Temperature-depth plot for coalbed methane wells in the Black Warrior basin showing variation of geothermal gradient.
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GEOTHERMALGRADIENT
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Figure 20. Map of geothermal gradient in the Black Warrior coalbed methane fields.
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TDS < 3,000 mg/L
5 mi
Blue Creekanticline
Eastern limitCretaceous
Oak Grove
CedarCove
Brookwood
White OakCreek
Blue Creek
DeerlickCreek
FRESH-WATER PLUMES
Jack Pashin
Figure 21. Location of fresh-water plumes in the Mary Lee coal zone, which are fed by recharge along the upturned southeast basin margin.
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.93
.94
.95
.96
.97
.98
.99
1
-54 -52 -50 -48 -46 -44 -42 -40d13C1 (ppt)
Drynessindex
Deerlick Creek fieldBrookwood fieldOak Grove fieldMississippian conventional
Sapropelic(waxy)source
Humic(woody)source
Biogenicsource
Thermogenicsource
GAS COMPOSITION
Jack Pashin
Figure 22. Comparison of composition of conventional and coalbed gas in the Black Warrior basin.
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Freshwaterhydrostatic gradient
(0.43 psi/ft)
normal tomoderate
underpressure
Extemeunderpressure
0
250
500
750
1000
1250
1500
1750
2000
2250
2500
0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500
0.19 psi/ft
Depth (ft)
Pressure(psi)
n=1072
PRESSURE-DEPTH PLOT
Jack Pashin
Figure 23. Pressure-depth plot showing bimodal pressure regime in the Black Warrior coalbed methane fields.
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HYDROSTATICPRESSURE
Jack Pashin
Figure 24. Map of hydrostatic pressure gradient determined from water levels in gas wells of the Black Warrior coalbed methane fields.
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r2 = 0.83n = 1,140
0.1
1
10
100
1,000
10 100 1,000 10,000100,000
1,000,00010,000,000
Cumulative water production (bbl)
Peak waterproduction
(Bpd)
PRODUCTIVITYMEASURES
r2 = 0.83n = 1,140
10 100 1,000 10,000100,000
1,000,00010,000,000
0.1
1
10
100
1,000
Cumulative gas production (Mcf)
Peak gasproduction
(Mcfd)
Jack Pashin
Figure 25. Relationship of peak and cumulative fluid production values in the Black Warrior coalbed methane fields.
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0
1
2
3
40 1 2 3 4
r 2 = 0.02n = 1,140
Peak water production (Bpd)
1
10
100
1,000
10,000
Log peak water production
Log peak gasproduction
1 10 100 1,000 10,000
Peak gasproduction
(Mcfd)
PEAK GAS VS. PEAK WATER PRODUCTION
Jack Pashin
Figure 26. Scatterplot showing lack of correlation between peak and gas water production in the Black Warrior coalbed methane fields.
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1
10
100
1000
0 10 100
log Net CompletedCoal Thickness
log Peak GasProduction
n=450r2=0.00
0 1 2
0
1
2
3
Net CompletedCoal Thickness (ft)
Peak GasProduction
(Mcfd)
PEAK GAS PRODUCTION VS. COAL THICKNESS
Jack Pashin
Figure 27. Scatterplot showing lack of correlation between peak gas production and net completed coal thickness in the Black Warrior basin.
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-800
-600
-400
Oak GroveMine
2 mi
3 km
1
01
0
1
1
2Peak gas production>300Mcfd
OAK GROVE GAS PRODUCTION
-500-600
-600
-700
Jack Pashin
Figure 28. Map showing concentration of productive gas wells along a synclinal axis in Oak Grove Field. Structure contours (ft below sea level) on
Jack Pashin
top of Mary Lee coal bed.
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-300
2 mi
3 km
1
01
0
1
1
2
Peak gas production >300 McfdPeak gas production 150-300 Mcfd
Normal faultContour interval = 25 ft
Franklin Hillhalf graben
Sexton Springhorst
Strip Minegraben
Holt Lakehalf graben
DEERLICK CREEK GAS PRODUCTION
-400
-200
-100
-300
-300
-200
-200-200
-100
Jack Pashin
Figure 29. Map showing concentration of exceptional gas-producing wells in two half grabens in Deerlick Creek Field. Structure contours on top of
Jack Pashin
Gwin coal zone.
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-300
Peak water production >750 BpdPeak water production 250-750 Bpd
Normal faultContour interval = 25 ft
Franklin Hillhalf graben
Sexton Springhorst
Holt Lakehalf graben
2 mi
3 km
1
01
0
1
1
2
Strip Minegraben
DEERLICK CREEK WATER PRODUCTION
-400
-200
-100
-200
-200
-300
-300
-200
-100
Jack Pashin
Figure 30. Map showing concentration of exceptional water-producing wells in two half grabens in Deerlick Creek Field. Structure contours on top of Gwin coal zone. Compare with Figure 29.
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CONCLUDING THOUGHTSCONCLUDING THOUGHTSCBM reservoirs in the Black Warrior basin areCBM reservoirs in the Black Warrior basin are
characterized by heterogeneous stratigraphy, structure,characterized by heterogeneous stratigraphy, structure,and coal quality.and coal quality.
This heterogeneity has a strong effect on sorptionThis heterogeneity has a strong effect on sorptioncapacity, gas content, basin hydrology, and reservoircapacity, gas content, basin hydrology, and reservoir
performance.performance.
Similar factors affect CBM potential in otherSimilar factors affect CBM potential in othersedimentary basins, but differing geologic factors posesedimentary basins, but differing geologic factors pose
basin-specific challenges.basin-specific challenges.
Jack Pashin
Figure 31. Concluding thoughts.
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