Jour. Geol. Soc.

India (2023) 99:99-104

https://doi.org/10.1007/s12594-023-2271-7

ORIGINAL ARTICLE

Investigation on Barail Formation Coals of Upper Assam with

Reference of Coal Bed Methane (CBM)
Prasun Banik1,*, Ranjan Phukan2, Ranjan Kumar Sarmah3 and Minati Das2
1
Department of Petroleum Engineering, DUIET, Dibrugarh University, Dibrugarh - 786 004, India
2
Department of Petroleum Technology, Dibrugarh University, Dibrugarh - 786 004, India
3
Department of Applied Geology, Dibrugarh University, Dibrugarh - 786 004, India
E-mail: prasunbanik@dibru.ac.in*; r.phukan@dibru.ac.in;

Received: 21 February 2022 / Revised form Accepted: 1 August 2022

© 2023 Geological Society of India, Bengaluru, India

ABSTRACT 1992). FTIR may be a demonstrated explanatory method to uncover

Coal is liberally accessible energy resource utilized by mankind carbohydrogenated arrangement (aromatic and aliphatic) and
for its comfort. Though economical it still has unfavorable impact heteroatomic functions (basically oxygenated) in addition follow of
on the environment. Presently underground coal a source of minerals. Literature reveals its importance in prospect evaluation of
methane gas confined within the seams known as coal bed methane coal bed methane gas also (Geng et al., 2009; Deepak Singh Panwar
(CBM) attracts due to its purity and environment friendly. FTIR, et al., 2017; Harinandan Kumar et al., 2021).
UV visible spectroscopy, XRD, solid state NMR are well known X-ray diffraction (XRD) study on coal structure and mineral
spectroscopic instruments used to analyze complex coals chemical composition had been carried out by others (Nelson, 1954; Cartz et
structures and its consequences on methane gas source. In the al., 1956; Diamond, 1958; Grigoriew, 1990: Wertz, 1998; Maity and
present research virgin coal samples from Barail Formation Mukharjee, 2006; Saikia et al., 2007; Kalkreuth et al., 2013). There
are examined by FTIR and XRD to assign various functional are reported studies of Indian coals on a different aspect of utilization
groups and minerals present separately. Proximate and ultimate using FTIR and XRD technique by a few research groups (Manoj et
analyses are correspondingly conducted to know its organic and al., 2008; Manoj, 2014; Manoj, 2016; Saikia et al., 2009; Das et al.,
inorganic constituents. Results reflect the low moisture content 2016). There exist reports that mineral matters have adverse effect on
and moderate fixed carbon quantity progresses with depth. FTIR sorption capacity of coal similar to moisture and ash content (Faiz et
studies uncover presence of aromatic and aliphatic functional al., 2007).
sets; prerequisite of hydrocarbons generation. Coal seam at depths The present study is carried out on coal samples from exploratory
of 740-846 m is favorable for economic methane gas production. wells drilled within the CBM block of upper Assam, India. The coal
These are promising pre-requisites of coal to be an unconventional samples from the Barail Formation are characterized using FTIR and
resource. There is abundance of quartz, kaolinite and mon- XRD data. The proximate and ultimate examination of coal has in
tmorillonite; traces of pyrite and siderite too are observed from addition been decided. The work includes the first assignment of
XRD spectral investigation. functional groups available in sample structure using FTIR
spectroscopy and the second XRD data analysis to assign
INTRODUCTION various minerals present. Examination is additionally carried out to
Coal is heterogeneous, physically and chemically complex understand samples methane gas promise as an unconventional
sediment available on earth crust occurring in different parts of the resource.
world (Haenel, 1992; Myers, 1982; Gorbaty and Ouchi, 1981). Usually
one of the foremost inexhaustible prudent conventional energy GEOLOGICAL SETTING
assets accessible; nowadays optimistic unconventional clean energy Basically the coal field of upper Assam and its abutting locale
resources too within the frame of coal bed methane gas trapped in drop interior the Schuppen belt of Assam (Evans, 1964). This is often
underground coal seams. In spite of the fact that coal is in utility for frequently parceled of the sedimentary basin known as Assam-Arakan
several decades still its chemical structure draws analysts to know it at basin, an amalgamated shelf-slope-basinal framework. The shelf
its fullest (Marzec, 2002). Coals of different rank and depositional portion spreads throughout the Dhansiri valley and Brahmaputra valley
backgrounds have different chemical configurations and structures. amid the Naga foothills then the Mikir slopes. On the shelf to basinal
Different spectroscopic strategies such as UV- visible spectroscopy, slant, the hinge region lies underneath the Naga Schuppen belt. The
FTIR, XRD investigation, solid-state NMR are in use for coal basinal portion (geosynclinals) is encompassed by way of Mizoram,
characterization. Manipur, Tripura plus Cachar fold belts.
Coal primarily comprises of organic and inorganic constituents; Upper Assam coal field sub-surface geology appears that the
contain nitrogen, sulphur and follows of mineral matter. Presence of Tertiary deposits superimposing the basement are delicately folded
sulphur, oxygen and nitrogen in functional groups along with aromatic into anticlines plus domes with moderate to low dipping limbs
structures are part of organic constituents (Mahadevan, 1929; 1930; influenced by frequent faults with a throw extending up to 200 m. The
Mitra, 1953); aromaticity increases with rank (Sobkowiak and Painter, Disang Formation (Eocene age) form the base of upper Assam coal

0016-7622/2023-99-1-99/$ 1.00 © GEOL. SOC. INDIA

 Table 1. Generalized Stratigraphic progression in the area
Formation Age Thickness Lithology
(m)
Alluvium Recent 200 - 250 Medium to coarse grained unconsolidated sandstone with thin inter-beds
of dark / bluish grey clay.
Dihing Pliocene 0 - 200 Coarse pale blue green, feldspathic sandstone with brown clay and stone
beds.
Girujan Miocene 0 - 200 Variegated clay, pale blue green sandstone, silty clay.
Tipam Miocene 40 - 100 Sandstone, sandy clay, variegated clay, coaly streaks, conglomerate
Tikak Parbat 300 - 500 Greyish to yellowish white sandstone, mudstone /claystone with economic
Formation coal seams.
Barail Baragolai Oligocene 1600 - 3500 Oligocene somewhat blue dark mudstone, sandstones, thin coal strata and
Group Formation carbonaceous shales.
Naogaon 3000 Tough enormous medium grained sandstone, long slender fragments of
Formation shales with sandstone alterations.
Disang Eocene 3000 Grey to black shale and splintery in nature, pale blue to green, indurate,
flaggy, finely bedded sandstone
Unconformity
Basement

filed while the Tertiary section has a thickness of more than 13,000m. X-ray diffractometer Type Ultima IV (Rigaku). Working parameters
The generalized stratigraphic progression of the zone is given in Table were as given: start angle: 3.015 & stop angle: 100.0; step angle: 0.03
1. The Tikak Parbat portion of the Barail Formation in Oligocene period with measuring time: 0.5; target: Cu (Fe-filtered). The Goniometer
has at least four feasible coal strata within the basal coal bundles radius (R) is 240 mm through the equatorial angle subtended at example
appearing between 723m and 1067m. in detector slit (β) is 1°. The proximate investigation was done
following BIS standard 1350 (Part-I) and elemental analysis were done
MATERIALS AND METHODS in CHNS analyser (Euro EA Basic). The outcomes of the proximate
The methodology adopted for present work is shown in Fig.1. In and ultimate examinations is given in Table 2.
the present study, the virgin coals of Barail Group of Oligocene age
were collected from two core wells bored through exploration drilling. RESULT AND DISCUSSIONS
The samples were ground to -200 mesh and utilized it for FT-IR, XRD
Proximate and Ultimate Analyses
and other investigations.
The spectra utilized in receiving the basic properties of coal were The information of proximate analysis and ultimate analysis are
acquired from the Fourier-transform infrared (FTIR) spectrometer fitted given in Table 2 (Prasun Banik, 2020). Fixed carbon changed from
by an attenuated total reflectance (ATR), Model FTIR Bruker. The 24.2 to 38.48% in borehole 1 and 42.28 to 52.71% in borehole 2. An
spectra were detailed within the run of 4000~650 cm-1. addition in fixed carbon with coal strata depth was recognized. This
XRD information were developed utilizing computer-commanded drift affirms developed porosity and methane gas sorption ability.


Fig. 1. Flow chart of the methodology followed.

100 JOUR.GEOL.SOC.INDIA, VOL.99, JAN. 2023

 Table 2. Results of Proximate and Ultimate analysis (Prasun Banik, 2020) Table 3. Band Assignments of the most noticeable peaks within the FTIR
spectra of coal samples collected from Bore Hole 1.
Bore Depth M A VM FC C H S
Hole (m) % % % % % % % Bands (cm-1) Assignment References
No.
3690-3696 & Clay minerals Manoj (2016), Manoj et al.
739.6 3.3 31.4 33.7 31.6 52.647 4.179 0.462 3611-3622 (kaolinite and Illite) (2008), Georgakopoulos
740.5 4 14.09 43.43 38.48 48.547 4.215 0.471 et al. (2003)
BH1 744 4.28 25.6 37.07 33.05 53.940 4.098 0.459 3019-3085 Aromatic Nucleus/ Manoj (2016), Suping, Yao
746 4.2 39.1 32.5 24.2 62.327 4.163 0.518 C-H stretch vibration et al. (2011)
832.2 4.63 1.62 42.66 51.09 68.919 5.334 2.792 2914-2920 Aliphatic -CH2 Manoj (2016), Georgakopoulos
837 5.19 1.66 40.44 52.71 81.976 4.967 2.359 asymmetric stretch et al. (2003), Suping, Yao
BH2 839 5.42 5.15 47.15 42.28 62.182 5.053 2.678 vibration et al. (2011)
846 4.84 1.64 40.81 52.71 67.829 5.113 0.521 2853.72 Aliphatic -CH2 Suping, Yao et al. (2011)
847 3.8 1.1 48.1 47 58.866 4.630 4.630 symmetric stretch
vibration
Comparative perception can be found in Laxminarayana and Crosdale 1593.24-1612.70 Aromatic ring stretch Manoj (2016), Suping, Yao
(1999). Volatile matter changed from 24.2 to 38.48% within a depth or Aromatic nucleus et al. (2011)
of 739 m to 847 m. (C=C)
The ash content changed from 14.09 to 39.1% (Borehole 1) and 1430 - 1443 Methylene groups/ Manoj (2016), Manoj et al.
ranged between 1.1 to 5.15% in Borehole 2. Thus the lower ash content CH3/CH2 chain (2008)
is perceived at depth. Additionally low ash content of Borehole 2 1033, 1031 Silicates (Si –O Manoj et al. (2008)
coal samples affirms the higher hydrocarbon content. The moisture stretching) Georgakopoulos et al. (2003)
content varied from 3.3 to 5.42%. The low moisture content 900 -700 Aromatic structure Manoj (2016), Saikia et al.
demonstrates a reasonable fraction of hydrocarbons in coal strata. (2007)
The ultimate analysis revealed that the rate of carbon changed
from 48.547 to 81.976 % and hydrogen changed from 4.098 to 5.334
percent. These deviations show the existence of vitrinite macerals and The C=C groups, which ought to be set between C-O and C=O groups,
methane gas. were not found, since low-rank coals have high oxygen constituent
and these groups nearly masked the C=C assemblies (Manoj, 2016;
FTIR Study Suping Yao et al., 2011). The peaks at 3019 -3085 cm-1 may be due to
In order to assign various functional groups, FTIR spectra of coal the aromatic nucleus (C=C) or C-H stretching vibration. Low-intensity
samples are presented in Table 3 & 4 for samples of Borehole 1 & aromatic bands were perceived in the locale 700 - 900 cm-1 (Saikia et
Borehole 2 respectively. The representative spectra are shown in Fig.2 al., 2007; Manoj, 2016).
(for Borehole 1) and Fig.3 (for Borehole 2). In all coal samples sharp intense peaks were observed at 1300 –
1000 cm-1 area. Peaks were due to the presence of both functional
FTIR Spectral Analysis of Borehole 1 Samples groups and mineral matter making it hard to assign. Peaks in the area
Weak absorption bands are observed at 3,611 – 3,622 cm-1 and 400 -1100 cm-1 indicate the pesence of quartz, montmorillonite,
3,690 – 3,696 cm-1. This usually represents illite and kaolinite minerals. kaolinite and illite groups of clay mineral (Saikia et al., 2007; Manoj
The same has been reported by Georgakopoulos et al., (2003) for low et al., 2008; Manoj, 2016).
rank Greek coals and by Manoj et al., (2016) for Indian coals. Within
the aliphatic stretching locale, (2,800- 3,000 cm-1) there are distinctive FTIR Spectral Analysis of Borehole 2 Samples
peaks at 2853.72 cm-1 and 2,914 -2920 cm-1 which are assigned to The sharp intense band at 2839.29 – 2841.60 cm-1 and 2959.49 –
symmetric and asymmetric –alkenes -CH2 extending individually. 2979.53 cm-1 show valency oscillations of –CH2 and –CH3 aliphatic
Especially in low-rank coals, the intensity peak at 2920 cm-1 is found compounds separately (Manoj, 2016). Aliphatic -CH3 symmetrical
to be uncommonly small since a portion of the alkane–CH hydrogen stretching vibration is shown by the peak at 2877.26 cm-1 (Manoj,
is replaced by hydroxy–OH compounds (Georgakopoulos et al., 2003; 2016).
Manoj et al., 2008; Manoj, 2016). A number of C-O-R and C=O functional groups is uncovered by
Fujii et al., (1970) calculated the specific extinction coefficients the presence of high-intensity peaks in the 1800 – 1000 cm-1 area
(K) at 1605, 2920, 3030 cm-1 band of twelve Japanese coal samples (Manoj et al., 2008; Manoj, 2016). The band at 1359.41 cm-1 and
from anthracite to lignite. These bands were allotted to C=C aromatic, 1369.67 cm-1 appear in low-rank coals, is on account of extending
aliphatic –CH3 and aromatic –CH groups respectively. The intensity modes of methyl -CH3 and methylene –CH 2 groups. The frail
of the bands gives the amount of carbon in the samples. The intensity band (1035 – 1010 cm-1) is due to the C-O stretching of phenolic
increases slowly as coal rank expanded up to 86.2% carbon and after compounds and the silicate minerals as indicated in the coal tests
that diminishes with the increase of coal rank. In exceptionally low- (Manoj et al., 2008; Georgakopoulos et al., 2003).
rank coals the intensity of 2929 cm-1 is found to be exceptionally little Band areas 1694.79 – 1702.14 cm-1 and 1580.70 - 1606.23cm-1
since the extent of the alkyne –CH3 hydrogen is replaced by hydroxyl seen within the larger part tests may be assigned to the carboxyl
groups (Georgakopoulos et al, 2003; Suping Yao et al., 2011; Manoj, C=O and C=C stretching correspondingly (Manoj et al., 2008; Manoj
2016; ). 2016; Suping Yao et al., 2011). Starsinic et al. (1984) ascribed the
The weak wide bands perceived at the section 1430 – 1443 cm-1 band at 1695 cm-1 to carboxyl compounds, haply ketones. Similar
can be assigned to elongating styles of methylene bridge CH2< groups conclusion was made by Supaluknari et al. (1998) while examining
present in the sample (Starsinic M et al., 1984; Manoj et al., 2008). spectra of Australian brown coals. It was detailed the groups at 1695
The intensity of the peaks in the 100 -1800 cm-1 section revealed and 1605 cm-1 were in oxygen-rich brown coals, while in superior
the dominance of C=O and C-O-R functional groups. This zone of rank coals in the midst of small oxygen the absorption at 1605 cm-1
oxygen-containing functional groups has band peaks at 1593.24 – edit up as a bear on the 1695 cm-1 band (Supaluknari et al., 1998). The
1612.70 cm-1, which is assigned either to C=O or C=C aromatic ring. strong band at 1695 cm-1 is ascribed essentially to carboxylic acid

JOUR.GEOL.SOC.INDIA, VOL.99, JAN. 2023 101

 
Fig. 2. FTIR spectra of Borehole 1 coal sample (Depth-746 m)


Fig. 3. FTIR spectra of Borehole 2 coal sample (Depth-839 m)

whereas moderately weak band at 1670 cm-1 is dur to ketonic oxygen content. Moreover, in 1950, J.K. Brown had seen comparable
configuration. The full absorbance of all the carboxyl groups for the prominent band at 1605 cm-1 and proposed this band to aromatic ether
oxygen rich brown coal was better than those for the superior rank linkages. Low and Glass (1989) allotted the same to aromatic ring
coal samples. The brown coal rich in oxygen (O/C = 0.26) hold a stretch of minor, confined aromatic entities in low rank coals.
small sum of carboxyl group both as acid and esters appeared A pronounced absorption band at 1580.70 - 1606.23 cm-1 in
at low intensity for 1695 cm-1 band compared to brown coal poor in samples is related with C=C aromatic extending vibration. Usually
oxygen (Supaluknari et al., 1998). It can be summarized that coal due to change of C=O to CH2 decreasing oxygen; improved the carbon,
with poor oxygen content show signature by well resolved strong hydrogen and consequently the calorific value (Manoj et al., 2008;
band at 1695 cm-1 compared to coals rich in oxygen and vice-versa Manoj, 2016; Suping Yao et al., 2011).
(Manoj et al., 2008; Suping Yao et al., 2011). Jacky Kister et al., (1998) examining low-rank Gardanne coal
The presence of a weak absorption band within the spectra 1694.79 apportioned a weedy wide leftover absorption band between 1200 to
– 1702.14 cm-1 affirms that the examined coal samples are rich in 1300 cm-1 to C-O bonds of phenol or ether. Landais et al., (1998)
102 JOUR.GEOL.SOC.INDIA, VOL.99, JAN. 2023
Table 4. Band Assignments of the most noticeable peaks in the FTIR spectra
of coal samples collected from Bore Hole 2.
Bands (cm-1) Assignment References
3694.58 – 3695.91 & Clay minerals Manoj (2016), Manoj et al.
3624.94-3661.80 (kaolinite and Illite) (2008), Georgakopoulos
et al. (2003)
3013.02- 3051.80 Aromatic Nucleus or Manoj (2016), Suping, Yao
C-H stretch vibration et al. (2011)
2959.49 – 2979.53 Aliphatic - CH3 Manoj (2016)
asymmetrical stretch
vibration
2877.26 Aliphatic - CH3 Suping, Yao et al. (2011)
symmetrical stretch
(2011)
2839.29 – 2841.60 Aliphatic - CH2 Georgakopoulos et al.
symmetric stretch (2003), Suping, Yao et al.
vibration (2011)
1694.79, 1696.95, Carbonyl stretch Manoj et al. (2008) Suping, Fig. 4. XRD spectra of Borehole 1 coal sample (Depth 746 m) 
1702.14 C=O stretch Yao et al. (2011)

1580.70 – 1606.23 C=C aromatic ring Manoj (2016), Manoj et al.
Table 5. d-values and their assignments of coal samples collected.
stretch or Aromatic (2008), Suping, Yao et al.
 BH1 Coal Samples BH2 Coal Samples
nucleus (C=C) (2011)
1359.41, 1369.67 -CH2 bending Manoj (2016) d (Å) Assignments d (Å) Assignments

1029.80, 1035.34, Silicates (Si–O Manoj et al. (2008), 12.34 Kaolinite 12.49 Kaolinite
1038.84 stretch) Georgakopoulos et al. 18.19 Montmorillonite 14.51 Montmorillonite
(2003) 20.77 Quartz 20.84 Quartz
900 -700 Aromatic structure Manoj (2016), Saikia et al. 22.15 Kaolinite 21.36 Kaolinite
(2007) 25.46 Kaolinite 21.83 Montmorillonite
27.75 Montmorillonite 22.08 Montmorillonite
 38.18 Kaolinite 23.75 Kaolinite
observed particular vibration bands at 1165, 1270, 1375, 1435 cm-1 65.48 Quartz 23.88 Quartz
 95.12 Quartz
whereas analyzing infrared spectra of Mesburg, GDR brown coals.
The bands were assigned to C-O extending modes, asymmetric

extending in aliphatic ester (C-O-C), deformation vibration of –CH3
& out of plane bending of –CH2, deformation vibration of –CH3 Figures 4 shows the XRD report from Barail Formation coal of

individually. In addition band 1105 – 1010 cm-1 were assigned to BH1 sample. Similarly minerals of samples at different depths are
Si-O-Si groups in silicate mineral. So also Olson (1998) assigned the determined. Table 5 shows the assignment of minerals against d (Å)

band at 1030 cm-1 to clay minerals while considering Beulah values.
lignite samples.

The asymmetric –CH 2 and –CH 3 bending vibrations are CONCLUSIONS
watched within the display set of coal samples (1400 -1485 cm-1, FTIR study on coal of Barail Formation confirms the existence

1433.66 cm-1, 1421.52 cm-1, 1440.11 cm-1, 1442.78 cm-1, 1446.92 of aliphatic CH2, CH3 structure along with C=C stretch, C=O, C-O
cm-1, 1359 cm-1, 1369.67 cm-1). The peaks at 1103.17, 1051, 1038.84, compounds and minerals such as illite, kaolinite etc. High moisture

1035.34, 1029.80 and 1011.36 cm -1 can be credited to trace and clay mineral content with low carbon content uncover that
minerals related with the samples (Manoj et al., 2008; Georgakopoulos they are low-rank coals. It appears the presence of aliphatic and

et al., 2003). The 700 900 cm-1 regions are apportioned to the low- aromatic hydrocarbons in coal seams produce hydrocarbons from
intensity aromatic band (Saikia et al., 2007; Manoj, 2016).  coal. The presence of inorganic minerals is confirmed at XRD
It is seen that all the tests appear weak absorption bands at 3694.58 spectral investigation. There is presence of quartz, kaolinite and
– 3695.91 and 3624.94- 3661.80. Typically due to mineral  showing montmorillonite; followed by pyrite and siderite. The samples are
the shape of kaolinite clay structure (Manoj et al., 2008; Manoj, 2016; amorphous in nature. The proximate and ultimate analysis confirms
Georgakopoulos et al., 2003). Venkatachalapathy et al., (1991)
 reported its low rank. The analyzed data assures coal bed methane gas asset
the similar perception while characterizing Neyveli lignite samples. such as fixed carbon increments with depth, low moisture content etc.
This can be bolstered by peaks at 1029.80 and 1011.36 cm-1. There is Coal strata depth is ideal to put pump for dewatering and gas
a band at 3438.93 cm-1 which can be due to extendedvibrations of production. This may be asserted after advanced investigation on coal
hydroxyls. This is well reflected in the observations of Chomnanti et of Barail Formation to assess its financial achievability.
al., (1970) and Osawa and Shih (1971) during coal, lignite and oil
shale investigation. Acknowledgments: The authors acknowledged the assistance
provided by the OIL and Dart Energy for providing samples of the
XRD Spectral Analysis study area. The authors would like to acknowledge the Department of
The XRD spectra of the studied samples show that coal samples Pharmaceutical Science and the Central Instrumentation Facility,
are amorphous. The mineral compositions show the dominance of Dibrugarh University, India for facilitating the instruments to carry
quartz and kaolinite. Other minerals determined in the core samples out experiments. The authors are thankful to Prof S.K. Ghosh and
included montmorillonite, pyrite, siderite, calcite. It has adverse effect Miss Nayana Adhikari for the guidane and assistance provided during
on sorption of methane gas in coal. FTIR experiments. Financial assistance was provided by All India

JOUR.GEOL.SOC.INDIA, VOL.99, JAN. 2023 103

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Indian Jour. Phys., v.IV(IV).
Maity, S. and Mukharjee, P. (2006) X ray structural parameters of some Indian
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