Coal Bed Methane in India: Difficulties and Prospects

Abstract

To meet the rapidly increasing demand for energy and faster depletion of conventional energy resources, India with other countries is madly searching for alternate resources like coal bed methane (CBM), shale gas, gas hydrate. CBM is considered to be the most viable resource of these. The present paper discussed about the prospect of CBM as a clean energy source, difficulty involved in production of CBM, enhanced recovery techniques. In this regards, one Indian coal field is selected and gas content is determined by analyzing the collected samples.

Full text

International
Journal of Chemical Engineering and Applications, Vol. 2 , No. 4 , August 2011
Abstract—To meet the rapidly increasing demand for
energy and faster depletion of conventional energy resources,
India with other countries is madly searching for alternate
resources like coal bed methane (CBM), shale gas, gas hydrate.
CBM is considered to be the most viable resource of these. The
present paper discussed about the prospect of CBM as a clean
energy source, difficulty involved in production of CBM,
enhanced recovery techniques. In this regards, one Indian coal
field is selected and gas content is determined by analyzing the
collected samples.
Index Terms—CBM, CO2 Sequestration, Global Warming,
Methane Recovery, Gas Content, Clean Energy, Singareni
Coal Field.
I. INTRODUCTION
Depletion of conventional resources, and increasing
demand for clean energy, forces India to hunt for
alternatives to conventional energy resources. Intense
importance has been given for finding out more and more
energy resources; specifically non-conventional ones like
CBM, shale gas & gas hydrates, as gas is less polluting
compared to oil or coal. CBM is considered to be one of the
most viable alternatives to combat the situation [1]. With
growing demand and rising oil and gas prices, CBM is
definitely a feasible alternative supplementary energy
source.
Coalbed methane is generated during coalification
process which gets adsorbed on coal at higher pressure.
However, it is a mining hazard. Presence of CBM in
underground mine not only makes mining works difficult
and risky, but also makes it costly. Even, its ventilation to
atmosphere adds green house gas causing global warming.
However, CBM is a remarkably clean fuel if utilized
efficiently. CBM is a clean gas having heating value of
approximately 8500 KCal/kg compared to 9000 KCal/kg of
natural gas.
It is of pipe line quality; hence can be fed directly to
national pipeline grid without much treatment. Production
of methane gas from coalbed would lead to de-methanation
of coal beds and avoidance of methane emissions into the
atmosphere, thus turning an environmental hazard into a
clean energy resource.
As the third largest coal producer in the world, India has
Manuscript received June 26, 2011; revised July 16, 2011.
Corresponding author: K. Ojha, Department of Petroleum Engineering,
Indian School of Mines, Dhanbad-826004
(e-mail:keka_ojha@yahoo.com)
B. Karmakar Department of Petroleum Engineering, Indian School of
Mines, Dhanbad-826004 (e-mail: geobibhas @gmail.com)
A. Mandal, Department of Petroleum Engineering, ISM Dhanbad-
826004(e-mail: mandal.a.pe@ismdhanbad.ac.in)
A. K. Pathak, Department of Petroleum Engineering, ISM, Dhanbad-
826004, (e-mail:akhilendra_pathak@yahoo.co.in)
good prospects for commercial production of coal bed
methane. Methane may be a possible alternative to
compressed natural gas (CNG) and its use as automotive
fuel will certainly help reducing pollution levels.
India is one of the select countries which have undertaken
steps through a transparent policy to harness domestic CBM
resources. The Government of India has received
overwhelming responses from prospective producers with
several big players starting operations on exploration and
development of CBM in India and set to become the fourth
after US, Australia and China in terms of exploration and
production of coal bed methane.
However, in order to fully develop India's CBM potential,
delineation of prospective CBM blocks is necessary. There
are other measures like provision of technical training,
promotion of research and development, and transfer of
CBM development technologies that can further the growth
of the sector.
India lacks in CBM related services which delayed the
scheduled production. Efficient production of CBM is
becoming a real challenge to the E & P companies due to
lack in detailed reservoir characterization. So far, the most
investigations have been limited to measurement of
adsorption isotherms under static conditions and is deficient
in providing information of gas pressure-driven and
concentration-driven conditions. More care should be taken
on measurement of porosity and permeability also. To
produce more methane from the coal enhanced technology
like CO2 sequestration may be implemented. This process
can not only reduce the emission of this gas to atmosphere,
will also help in extra production of methane gas [2].
Though, presently, CO2 is not an implemented much
because of high cost. But the necessity to reduce greenhouse
gas emissions has provided a dual role for coalbeds - as a
source of natural gas and as a repository for CO2.
In the present investigation, Singareni coal field has been
selected as the study area. Samples have been collected
from various locations & depths. Standard methods have
been followed to characterize the collected coal samples and
evaluation gas reserve.
II. GLOBAL AND INDIAN SCENARIO
Global: The largest CBM resource bases lie in the former
Soviet Union, Canada, China, Australia and the United
States. However, much of the world’s CBM recovery
potential remains untapped. In 2006 it was estimated that of
global resources totaling 143 trillion cubic meters, only 1
trillion cubic metres was actually recovered from reserves.
This is due to a lack of incentive in some countries to fully
exploit the resource base, particularly in parts of the former
Soviet Union where conventional natural gas is abundant.
Coal Bed Methane in India: Difficulties and Prospects
Keka Ojha, B. Karmakar, A. Mandal, and A. K. Pathak
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The United States has demonstrated a strong drive to utilize
its resource base. Exploitation in Canada has been
somewhat slower than in the US, but is expected to increase
with the development of new exploration and extraction
technologies. The global CBM activities are shown in Fig.1.
The potential for supplementing significant proportions of
natural gas supply with CBM is also growing in China,
where demand for natural gas was set to outstrip domestic
production by 2010 [3].
India: India is potentially rich in CBM. The major coal
fields and CBM blocks in Indian are shown in Fig 2. The
Directorate General of Hydrocarbons [4] of India estimates
that deposits in major coal fields (in twelve states of India
covering an area of 35,400 km2) contain approximately 4.6
TCM of CBM [5]. Coal in these basins ranges from high-
volatile to low-volatile bituminous with high ash content (10
to 40 percent), and its gas content is between 3-16 m3/ton
(Singh, 2002) depending on the rank of the coal, depth of
burial, and geotectonic settings of the basins as estimated by
the CMPDI. In the Jharia Coalfield which is considered to
be the most prospective area, the gas content is estimated to
be between 7.3 and 23.8 m3 per ton of coal within the depth
range of 150m to 1200 m. Analysis indicates every 100-m
increase in depth is associated with a 1.3 m3 increase of
methane content [6].
Fig 1. Global CBM activities
In India, commercial CBM production is yet to be started
in full pace. Few E&P companies like ONGC Ltd., GEECL
and Essar Oil have started production, but field
development is yet to be completed.
Fig. 2. CBM Blocks in India (DGH, India)
III. MATERIALS AND METHOD:
A. Sample collection and characterization
Coal samples were collected from Dorli- Bellampalli coal
Belt of Singareni coalfield, Andhrapradesh, India. Samples
are collected from various seams of the bore holes at
different locations.
TABLE I. PROXIMATE ANALYSIS RESULT
BH.N
o.
Seam Avg.
Depth
(m)
M% Ash (%) V.M.
(%)
FC (%)
BH1 I 427 3.76 26 32.50 37.74
431 3.01 24.94 32.75 39.30
II 498.3 3.04 26.59 26.30 44.07
499.7 3.38 22.82 31.62 42.18
503 3.12 17.03 30.46 49.39
III 541 3.53 22.65 23.30 50.70
BH2 I
369 2.95 23.00 28.96 45.10
371 2.46 45.99 25.45 26.01
II 435.5 3.43 25.17 33.61 37.79
435.5 3.72 15.39 27.68 53.21
443.5 3.15 10.52 40.26 46.07
III 456.5 3.82 11.15 31.11 53.92
TABLE II. ELEMENTAL ANALYSIS OF THE SAMPLES
Avg. Depth
(m)
C H N S O
427 54.66 4.09 1.76 0.68 9.05
431 57.49 4.12 1.63 0.66 8.15
498.3 57.47 3.79 1.69 0.59 6.83
499.7 59.42 4.22 1.73 0.55 7.88
503 66.17 4.34 1.57 0.57 7.2
541 61.89 3.77 1.59 0.43 12.17
369 44.38 3.94 1.79 0.54 8.72
371 38.44 2.91 1.48 0.49 8.23
435.5 56.36 4.12 1.67 0.51 8.74
438.5 67.68 4.31 1.71 0.55 6.64
443.5 70.24 5.07 1.66 0.63 8.73
456.5 71.01 4.58 1.69 0.60 7.15
Caprock of each seam is mainly made of coarse to very
coarse grained sandstone, greyish all over. The depth under
study varies from 369m to 541m.
The coal samples were first crushed, ground and sieved
through 72-BSS mesh openings. Proximate analyses of the
samples were performed using muffle furnace as per the
standard method. The equilibrium moisture content of the
samples was determined using the standard test method
[ASTM D 1424 – 93]. Ash contents of samples were
estimated in accordance with the ASTM D3174-04 and
elemental composition of coal samples were determined
using CHNS Analyzer (Elementar Vario EL III- CHNS
analyzer). The results of the proximate and elemental
analyses are shown in Table I and Table II respectively.
IV. RESULTS AND DISCUSSIONS
From the results it was observed that the ash content
varies from 10.52% to 26.59% except one sample that
showed an irregularly high ash content of 45.99%.
Proximate analysis of the investigated coal samples reveal
that the moisture content (M %) varies from 2.46% to
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3.82%, whereas volatile matter ranges from 23.30% to
40.26% and fixed carbon (FC) content varies from 26.01%
to 53.21%. From elemental analysis (Table II) it is seen that
the fixed carbon percentages varies from 38% to 71 %. In
general it is recognized that the fixed carbon of coal
increases with increase in coal depth which is directly
proportional to the coal maturity and rank [8]. The similar
trend is observed in the present study also as shown in Fig 3
and Table I.
A. Gradation of coal under study:
The value of vitrinite reflectance ( %) gives idea about
the coal rank and grade. In the present study, the vitrinite
reflectance (Ro%) is calculated by using the formula by Rice
[9] using the data from approximate analysis. The formula is
as follows:
% = -2.712 × log (VM) + 5.092 (4)
The % varies from 0.45% to 0.88% (Table III).
From the proximate analysis and value of vitrinite
reflectance (Ro) varies from 0.45 to 0.88%. Hence, the coal
samples under study belong to sub-bituminus to bituminous
rank.
300 350 400 450 500 550 600
20
25
30
35
40
45
50
55
60
y = 0.1397x - 19.20
R² = 0.852
Fixed Carbon (%)
Depth, M
field data
linear fit
Fig. 3. Variation of fixed carbon with depth
B. Estimation of Methane Content
Most of the gas in the coal is adsorbed on the internal
surface of micropores and varies directly with pressure and
inversely with temperature. The relationship between the
volume of adsorbed gas with pressure and temperature
based on the moisture and ash content of coal samples was
estimated by Kim’s empirical equation [10].
Kim’s correlation:
The estimated methane gas content is shown in Table II.
From estimated gas content data, it is observed that the gas
content varies from 5 m3/ tonne to 9 m3/ tonne as against the
economic viability of 8 to 15m3/ tonne. The values of gas
content increase with increase with depth as the maturity &
rank of the coal also enhanced (Table II). However, from
the result it is seen that the gas content is at the lower
economic limit. This may be due to less maturity of the coal
and less depth.
TABLE III. ESTIMATED GAS CONTENT
BH.No. Seam Avg.
Depth (m)
Fixed Carbon (%) Gsaf, cc/g Ro
(max)
BH1 I
427 37.74 7.28 0.65905
431 39.30 7.47 0.65276
II 498.3 44.07 7.36 0.81164
499.7 42.18 7.67 0.68109
503 49.39 8.34 0.70994
III 541 50.70 7.77 0.88335
BH2 I
369 45.10 7.71 0.74693
371 26.01 5.32 0.83209
II 435.5 37.79 7.39 0.63106
435.5 53.21 8.48 0.77821
443.5 46.07 8.94 0.4587
III 456.5 53.92 9.00 0.6938
C. Relationship between Total Gas Content and Non-
Coal content (ash + moisture content):
Since it is generally true that methane is not adsorbed
onto non-coal material, ash and moisture values can be used
to make appropriate corrections on the total measured gas
contents. Gas content is seen to increase with depth, and
bituminous coals are associated with the highest gas
contents, followed by sub bituminous coals. Cross plot of
Gas Content versus non- coal content (ash + moisture
content) is shown in Fig.4.
Moisture and ash content within the coal reduces the
adsorption capacity of methane. Adsorption capacity of
methane decreases with increasing ash and moisture
percentage within the coal. As little as 1% moisture may
reduce the adsorption capacity by 25%, and 5% moisture
results in a loss of adsorption capacity of 65% [11].
0.0 0.1 0.2 0.3 0.4 0.5 0.6
3
4
5
6
7
8
9
10
Y= -10.61x+10.47
R
2
=0.998
Dry Gas Co ntent (m
3
/ton)
Ash + Moisture Content(fraction)
Gsaf, m
3
/ton
Best Fit Line
Fig. 4. Relationship between Total Gas Content and Non- Coal content (ash
+ moisture content)
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V. PRODUCTION OF GAS FROM COALBED.
A. Gas Transportation mechanism in reservoir:
Production of gas is controlled by a three step process (i)
desorption of gas from the coal matrix, (ii) diffusion to the
cleat system, and (iii)flow through fractures [12] as shown
in Fig 5.. Many coal reservoirs are water saturated, and
water provides the reservoir pressure that holds gas in the
adsorbed state.
Flow of coalbed methane involves movement of methane
molecules along a pressure gradient. The diffusion through
the matrix pore structure, and steps include desorption from
the micropores, finally fluid flows (Darcy) through the coal
fracture (cleat) system. Coal seams have two sets of
mode; breaking in tension joints or fractures that run
perpendicular to one another.
Fig. 5. Process of Gas Transport through coal beds [12]
The predominant set, face cleats, is continuous, while the
butt cleat often terminates into the face cleats. Cleat
systems usually become better developed with increasing
rank, and they are typically consistent with local and
regional stress fields.
The size, spacing, and continuity of the cleat system
control the rate of fluid flow once the methane molecules
have diffused through the matrix pore structure. These
properties of the coal seams vary widely during production
as the pressure declines. Coal, being brittle in nature, cannot
resist the overburden pressure with reduction in pore
pressure during dewatering; and fractures are developed. In
addition, hydraulic fracturing is done to increase the
permeability of coal. Because, permeability and porosity of
coal is extremely low for which production rate is also low.
The basic petrophysical properties of coal responsible for
production of methane, e.g. porosity, permeability vary
widely with change in the pore pressure during dewatering
as well as gas production period. Hence, efficient
production of methane from coal bed needs continuous
monitoring of variation in porosity, permeability and
compressibility of coal. The unique features of the coal are
that coals are extremely friable; i.e., they crumble and break
easily. Therefore, it is nearly impossible to recover a
“whole” core. Direct measurement of intrusive properties
like permeability, porosity, compressibility, relative
permeability measurements are very difficult and must rely
on indirect measurement.
In India, ONGC Ltd. has implemented multilaterial well
technology to increase the drainage area and enhance the
production in the Jharia block. But, brittle characteristic of
coal restricts the production at the expected rate.
Moreover, coal is highly compressible (~as high as 2x10-3
psi-1) [13]. Variation of permeability and bottom hole
properties during production requires accurate well test
analysis using correct model. CBM reservoirs are of dual
porosity system, which demands for special models of well
test analysis. So, only static adsorption-desorption study can
not suffice the analysis of coal bed methane production. As
these properties will continuously vary during production,
efficient & economic production of methane from coal bed
requires constant monitoring and analysis of the system by
experienced and proficient persons.
B. Enhanced recovery techniques:
The main hurdle associated with the production of CBM
is the requirement of long dewatering of coal bed before
production. This difficulty may be resolved to some extent
with implementing the CO2 sequestration technology.
Due to higher adsorption affinity of CO2 to coal surface
[7], methane will be forced to desorb from the coal surface
at comparatively high pressure and can reduce the
dewatering time and hence the total project period. Also the
problem associated with variation in coal properties related
to pressure depletion may be alleviated. China, Australia,
USA have been started to implement this technology for
enhanced recovery of CBM gases.
VI. CONCLUSIONS
CBM technology is proceeding with good space to prove
itself as a cleaner energy security to India as well as the
World. However, production strategy of methane from
CBM is very much different from conventional gas
reservoir. The study revealed that the coal type, rank,
volatile matter and fixed carbon are strongly influence the
adsorption capacity of methane into the coal bed. With
increasing depth maturation of coal increases and generation
of methane gas also increases. Gondwana basin as the most
prospective CBM field is being developed now. From the
studies, it is observed that Singareni coal field under
Gandowana basin contains low gas Hence, presently it is not
considered for CBM exctraction. However, in future this
field may be considered for methane extraction using
advanced technology and in emergency condition.
Sequestration of CO2 helps in mitigation of global warming,
at the same time helps in recovery of methane gas from coal
bed unveiled otherwise. However, detailed and intensive
studies are required for efficient and economic production
of coal bed methane. India with ~4.6 TCM of methane
reserves in coal bed can enrich its per capita energy demand
by successful exploitation of CBM.
Appendix
BH1= Borehole 1
BH2= Borehole 2
Gsaf = Dry, ash-free gas storage capacity, cm3/g
A = Ash content, weight fraction
wc = Moisture content, weight fraction
d = Sample depth, m (feet/3.28)
= Fixed carbon, weight fraction
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xvm= Volatile matter, weight fraction
Ro= Vitrinite reflectance
ACKNOWLEDGEMENT
We gratefully acknowledge for the financial assistance
provided by Ministry of Coal, Govt. of India (CE/29)
through CMPDI L ·td, Ranchi and Department of
Petroleum Engineering, Indian School of Mines, Dhanbad,
India. Thanks are also extended to all individual associated
with the project.
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[3] World Coal Institute (WCI), (2009),
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[4] DGH : CBM Exploration, Directorate General of Hydrocarbons,
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[5] D.N. Prasad, Personal communication with D.N. Prasad, Ministry of
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from adsorption data,” U.S. Bureau of Mines 1977, RI8245 1–22.
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,
Dr. Keka Ojha, Associate Professor of the Department of
Petroleum Engineering, Indian School of Mines has more
than ten years of research and teaching experience. Before
joining ISM Dhanbad, she has worked as Research Associate
in University of Notre Dame, USA and Lecturer in Heritage
Institute of Technology, Kolkata, India.
She is currently running a number of R&D project in various field of
Petroleum Engineering including Coal Bed Methane, green house gas
emission. Dr. Ojha has about fifty publications to her credit in peer
reviewed national/international journals & conferences.
Dr. A. K. Pathak, Head & Professor of the Department of
Petroleum Engineering has been serving the department as
faculty since 1984. Research area is surface activity of oil
& its fraction and their effect on fluid flow through porous
media. He is actively involved in development of computer
soft wares and expert system on various areas of drilling
system design, Directional drilling and on Horizontal Well
Technology.
He is currently working on various field of Petroleum Engineering
including Coalbed Methane, Surface/ interfacial activity of Crude Oil and
its fractions, Horizontal /Slanted Well Technology.
Dr. Ajay Mandal is presently working as Associate
Professor in the Department of Petroleum Engineering,
Indian School of Mines, Dhanbad. He is the recipient of
Gold Medal in M.ChE. (J.U.) in 1998 and DAAD
Fellowship (Technische Universidad Braunschweig,
Germany) in 2008. Currently Dr. Mandal is carrying out his
research works on gas hydrates, enhanced oil recovery,
coal bed methane, multi-phase flow system, micro-
emulsion etc.
He has published around 40 research papers in reputed peer reviewed
Journals and presented/participated more than 25 National and
International Conferences. He is the reviewer of more than 15 International
Journals in the field of chemical and petroleum engineering. He is currently
handling five major projects sponsored by CSIR, UGC, ISM and Ministry
of Coal. Dr. Mandal is also a member in the editorial board of International
Journal of Petroleum Engineering and section Editor of Journal of
Petroleum Engineering & Technology.
Bibhas Karmakar is a Senior Research Fellow in the
Department of Petroleum Engineering, Indian School of
Mines, Dhanbad. Mr. Karmakar did his M.Sc. from
Presidency College, Kolkata and Master of Technology in
Petroleum Exploration from Indian School of Mines,
Dhanbad, India. His research area is Enhanced Coalbed
Methane Recovery by CO2 Sequestration.
Mr. Karmakar is an active student member of different professional
organization including AAPG, SPE.
260