The document discusses reservoir simulation of coal bed methane (CBM). It begins with an introduction to CBM, explaining how gas is stored in coal seams and produced through desorption, diffusion through micropores, and flow through fractures. The document then discusses reservoir simulation software Comet3, which uses dual-porosity modeling to simulate gas and water production from CBM reservoirs. The author conducted a simulation of a single well producing from 5 coal seams, presenting input parameters, results graphs of gas and water production rates over time, and conclusions on well spacing effects.

1. CBM RESERVOIR SIMULATION
BY
JAMEEL AKBAR
H.T.No.:12H11A27BH
Department of Petroleum Engineering
Al-Habeeb College of Engineering & Technology
1

2. CONTENT
• Coal Bed Methane (CBM)
– Introduction
– Conventional v/s Unconventional Reservoir
– Mechanism of gas flow
– Langmuir Isotherm
• Reservoir simulation
– Introduction
– Comet3
– Uses of Reservoir Simulation
– My work
• Results
• Conclusion
2

3. Coal bed methane
Introduction
• Coal Bed Methane (CBM) is the gas which is created during the formation
of coal and is trapped within a coal seam by formation water.
• CBM is a form of natural gas that is trapped inside coal seams.
• CBM is generated either from a biological process as a result of microbial
action or from a thermal process as a result increasing heat with depth of
coal.
• The gas is stored in two ways within coal
- The majority of gas is adsorbed on coal matrix.
- Methane also occurs as free and dissolved gas in cleats (natural
fractures) and pores within the coal.
3

4. • CBM is generally more than 95% methane and is often marketed as green
fuel, as it contains no sulphur compounds such as hydrogen sulphide.
• Ground water is associated with the gas
- The hydrostatic pressure often serves to contain most of the sorbed
gas in the coal.
• CBM is chemically identical to other sources of gas, but is produced by
Unconventional methods.
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5. Conventional v/s Unconventional Reservoir
• Reservoir requires source rock, seal,
trapping mechanism, and favorable
timing of migration.
• Reservoir usually has adequate
porosity and permeability.
• Reservoir acts as its own source
• Reservoir has extremely low matrix
permeability
SealReservoir
Seal
Source
Wet Reservoir
5

6. Mechanism of gas flow
1. Desorption of the gas from the coal surface inside
the micropores
2. Diffusion of the gas through the micropores
3. Darcy flow through the fracture network to the
wellbore
6

7. Langmuir Isotherm
• To describe the adsorption of gases on a solid
Gs= Gas storage capacity, SCF/ton
P = Pressure, psia
VL = Langmuir volume constant, SCF/ton
PL = Langmuir pressure constant, psia
Fa = Ash content, fraction
fm = Moisture content, fraction
7

8. Diffusion of gas through micro pores
• Diffusion of gas through the micro pores of coal is
described by Fick’s law
Where
c = gas concentration
t =time
D = effective diffusion coefficient
r = radial distance from centre of particle
8

9. Darcy’s flow through fractures
• Flow of gas and water in the cleat or fracture
system is described by Darcy’s law.
q= -kA * (dP/dx)
Where
K= Permeability
A= Area
P= Pressure
x= Thickness of the formation
9

10. Reservoir simulation
• It is an area of reservoir engineering in which computer
models are used to predict the flow of fluids (typically Oil, Gas
& Water) through a porous media in order to more effectively
develop and produce petroleum resources.
• The tool used in this process, a reservoir simulator, is a set of
simplified equations that describes flow in reservoirs.
• The simplified equations in the simulator (material balance
and Darcy’s Law) are applied to each of the many small
elements of the reservoir model called grid blocks.

11. Reservoir simulation
• Simulations using only one block to represent the reservoir
are called tank models. Injection or production wells may be
placed in these blocks corresponding to their location in the
real reservoir.
• Here we are using Comet3 reservoir simulator.
11

12. Comet -3
• COMET3 is a three-dimensional, three-component, two-
phase, single, dual or triple porosity simulator for modeling
gas and water production from desorption controlled
reservoirs (coal and shale).
• For modeling gas and water production from coal beds,
COMET3 is used as a dual porosity.
• COMET3 utilizes both Cartesian (x-y-z) and radial (r-θ-z)
coordinate systems for multi-well problems.
12

13. • The reservoir or coal bed is at a constant uniform
temperature.
• A pseudo steady-state flow condition exists at all times
between matrix and fractures
13

14. • The reservoir is divided
into number of grid
blocks.
• Each gridblock in the
simulator is assigned a
set of reservoir
properties, including
thickness, permeability,
porosity, etc.
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15. Data Needed for Simulation
15

16. Uses of reservoir simulation
• Better understanding and management of reservoir
• Optimization of well spacing
• Field economics
• Implementation in field development
• History matching and Production forecasting with more degree of
accuracy
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17. My Work
A single well data of 5 coal seams was taken
and studied for the CBM parameters and was
simulated as per the requirements
17

18. Input parameters
Depth Seam 1: 2924.35
Seam 2: 3215.12
Seam 3: 3643.69
Seam 4: 4172.03
Seam 5 : 4485.20
Ft
Thickness Seam 1. 20.506
Seam 2. 18.213
Seam 3. 59.65
Seam 4. 28.992
Seam 5. 22.077
Ft
Model dimensions 13x13x5
Permeability 12.75
11.05
8.925
6.800
5.100
Md
Casing ID 4.9 Inch
18

19. Porosity 0.0224
0.0198
0.0153
0.0125
0.0107
Langmuir volume 17.47
28.52
20.83
24.06
18.05
Scf/ft3
Langmuir pressure 567.7
567.7
567.7
567.7
567.7
psi
19

20. Gas content 9.64
10.20
13.08
16.45
12.62
Scf/ft3
Reservoir temp. 120 F
Reservoir pres. 1266.092
1392.147
1577.717
1806.488
1942.091
psi
Simulation time 10950 days
skin -2.5
20

21. Results of the Simulation
After running of simulation file we got desired parameters like Gas
production rate, Water production rate. We illustrated one simulation
file of 40, 80 & 120 acre of drainage area for production forecast and
following graphs are plotted accordingly
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22. Gas production rate
0
2000
4000
6000
8000
10000
12000
14000
16000
18000 1
9
17
25
33
41
49
57
65
73
81
89
97
105
113
121
129
137
145
153
161
169
177
185
193
201
209
217
225
233
241
249
257
265
273
281
289
297
305
313
321
329
337
345
353
Gas Production Rate, M**3D
Gas Production Rate, M**3D
Gas Production Rate, M**3D
Time
Gas
Production
Rate(scf/ton)
22

23. Water production rates at 40m3/day at drainage area
40, 80 and 120 acre
water
produ
ction
rate
Time in months
0
5
10
15
20
25
30
35
40
45
1
9
17
25
33
41
49
57
65
73
81
89
97
105
113
121
129
137
145
153
161
169
177
185
193
201
209
217
225
233
241
249
257
265
273
281
289
297
305
313
321
329
337
345
353
H2O Production Rate, M**3D
H2O Production Rate, M**3D
H2O Production Rate, M**3D
for 40 acre
for 80 acre
for 120 acre
23

24. Cumulative gas production
0
10000000
20000000
30000000
40000000
50000000
60000000
70000000
80000000
90000000
100000000
1
9
17
25
33
41
49
57
65
73
81
89
97
105
113
121
129
137
145
153
161
169
177
185
193
201
209
217
225
233
241
249
257
265
273
281
289
297
305
313
321
329
337
345
353
Cum Gas Production, M**3
Cum Gas Production, M**3
Cum Gas Production, M**3
Gas
prod
uctio
n
rate
(scf/t
on)
Time in months 24

25. Conclusions
• The Gas peak rate of 40 acre reaches early as compared to 80 acre
followed by 120 acre. The reason behind this is that the reduction in the
pressure causes the 40 acre well to achieve the early peak rate of gas
production
• 120 acre well spacing the peak rate of gas will come at later stage than
the other two but the cumulative gas production of that well will be
greater than the other two well spacing’s.
• If the water production rate was increased , we will achieved an early
peak rate of gas production but however there is a limiting factor of
pumping capacity of pump which could slow down our water production
rate and hence the gas production rate.
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26. References
1. Coal bed methane-fundamental concept- K. Aminian, Petroleum &Natural Gas Engineering
department West Verginia University.
2. A Guide to Coalbed Methane Reservoir Engineering
3. Smith, James T., Pressure Transient Testing: Design and Analysis, Lubbock, Texas (1987) .
4. Horne, Roland N., Modern Well Test Analysis, Petroway, Inc., Palo Alto, California (1990) .
5. Barrenblatt, G.E., I.P. Zheltov, and I.N. Kochina, “Basic Concepts in the Theory of Seepage
of Homogeneous Fluids in Fissured Rocks,” J. Appl. Math. Mech, 24 (5), USSR (1960).
6. Warren, J.E. and P.J. Root, “Behaviour of Naturally Fractured Reservoirs,” Society of
Petroleum Engineers Journal (September, 1963).
7. Mavor, M.J. and H. Cinco-Ley, “Transient Pressure behaviour of Naturally Fractured
Reservoirs,” SPE Paper 7977, presented at the 1979 California Regional Meeting of the
Society of Petroleum Engineers, Ventura, California (April 18-20, 1979).
8. Perrine, R.L., “Analysis of Pressure Build-up Curves,” Drilling and Production Practices,
American Petroleum Institute (1956).
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27. Questions?
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28. Thank You
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