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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1 Modified from unpublished short course notes from Short Course #4, Coalbed methane potential in the U.S. and Mexican Gulf Coast, Gulf Coast Association of Geological Societies/Gulf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
Coalbed MethaneProduction
Gas Content
Coal Quality
Stratigraphy
Hydrodynamics
Geothermics
Structural Geology
GEOLOGIC CONCEPTS
BLUECREEK
COAL BEDMedium volatile
bituminous
Top
Base
Maximum flooding surface
Gamma ray logGR
ShaleLithareniteQuartzareniteCoalLimestone
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
FAULTING AND FRACTURING
Coalunderclay
Sandstone
Sandstone
Shale
PRATTSTRUCTURE
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
ADSORPTION ISOTHERMS, BLACK WARRIOR BASIN
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
COALQUALITY
This may not be theworld’s best coalbed
gas reservoir
MARY LEERANK
RANK CROSS SECTIONS
hvAmvSORPTION AND RANK
SORPTION AND ASH
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
GEOTHERMALGRADIENT
TDS < 3,000 mg/L
5 mi
Blue Creekanticline
Eastern limitCretaceous
Oak Grove
CedarCove
Brookwood
White OakCreek
Blue Creek
DeerlickCreek
FRESH-WATER PLUMES
.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
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
HYDROSTATICPRESSURE
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)
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
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
-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
-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
-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
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.