1.COALBED METHANE EXPLORATION AND EXPLOITATION_DPS.pdf

COALBED METHANE EXPLORATION AND
EXPLOITATION
PROJECT SUBMITTED
IN PARTIAL FULFILLMENT OF THE REQUIREMENT
FOR THE AWARD OF THE DEGREE OF
Master of Science
in Geology
SUBMITTED BY
DHIRENDRA PRATAP SINGH
UNDER THE GUIDANCE OF
Dr. H. Singh
Scientist, Methane Emission and Degasification
Central Institute of Mining and Fuel Research, Barwa Road,
Dhanbad.
DEPARTMENT OF GEOLOGY,
VINOBA BHAVE UNIVERSITY, HAZARIBAGH,
JHARKHAND.
SEP-2009

ACKNOWLEDGEMENT
We take this opportunity to express our profound gratitude and record our sense of obligation
to the following individuals who helped us directly or indirectly in accomplishing our training
on “Exploration of Coal bed Methane (CBM) “at Central Institute of Mining and Fuel Research
(CIMFR) Dhanbad, Jharkhand from 13th
September to 14th
October 2009.
We are greatly thankful to Dr V.C.BARLA Head, department of Geology and Dr. H.N.Sinha
for providing all the administrative support to undergo this training.
We are also very thankful to Dr. Amalendu Sinha, Director, CIMFR, Dhanbad and Dr.
B. Kumar (scientist in-charge HRD) for providing all the necessary facilities at CIMFR
Dhanbad for completion of successful training. We render our deep sense of gratitude and
sincere thanks to Dr. A. K. Singh (Scientist and Head, Methane Emission and Degasification)
for giving us the opportunity to work as summer trainees under his meticulous guidance. We
express our great thanks to Dr. Harendra Singh, Scientist, Dr. Vinod A. Mendhe, Scientist and
B.K. Mondal, Technical Officer who really took interest in our project work.
During our project work we received a lot of help and knowledge from Mr. Shyam Nath
Hazari and Mr. Rupesh Kumar Sahu, Project Assistants and all supporting staff of methane
emission and degasification department our special thanks to them as well.
Last but not the least we express our deep thanks to all who directly or indirectly helped
us in the completion of our project. We also thank our parents and friends for their support
throughout the training.

ABSTRACT
Coal is a natural gift bestowed by Mother Nature. Coal being formed by biochemical
decomposition of plants by microorganism consist of methane as a byproduct. Once known to
be miner’s fury this hydrocarbon gas can be successfully exploited nowadays. Coalbed
methane is the name termed for methane found mostly in adsorbed state on coal along with
some impurities such as carbon dioxide and nitrogen.
CBM is more potent than its counterpart natural gas as it contains 98% methane whereas natural
gas contains 85-90 % methane. Extraction of CBM becomes more meaningful in gassy mines
where it serves the dual purpose of safety to miners as well as extraction clean fuel.
An attempt has been made to estimate gas content in different ranks of coal and different seams.
The main methodology for this purpose is estimating the gas in stipulated coal sample by direct
method and certain indirect method such as Kim method, adsorption isotherm method. Central
Institute of Mining and Fuel Research (CIMFR) is engaged in finding the gas content of the
coal seam in Jharia and other major coalfields across India. The amount of gas adsorbed
depends on many factors such as rank, moisture content, temperature and pore structure.
Estimation of gas involves three phase viz lost gas estimation, desorbed gas and residual gas.
CBM finds a variety of application, it is good substitute of coal for power generation and may
be used in place of natural gas.
Correct estimation of CBM in coal seam is crucial so as to exploit it profitably and use this
clean fuel in every sphere of life.

CONTENT
SL. No. Page. No.
1. Introduction 1
2. Formation of CBM 2
3. Geological Controls on CBM 4
4. Methane Retention in Coal Beds 5
4.1 Factors Affecting the Methane Retention in Coal 6
5 Flow Mechanism in Coal Bed Reservoir 7
6 What is Unconventional about CBM Production 9
7 Difference Between CBM and Natural Gas 9
8 Estimation of In-Situ-Gas content 10
8.1 Direct Method for In-Situ-Gas Content 10
8.2 Estimation of Gas Content by Indirect Method 14
9 Physico-mechanical Property of Rock 21
10 Proximate Analysis of Coal 34
11 Gas Chromatography 35
12 Coal Petrography 40
13 Drilling for CBM Exploration 43
14 CBM Site Visit 48

1
1. Introduction
Coalbed methane (CBM) is natural gas found in coal. CBM is composed mostly of methane
(CH4) but may have minor amounts of nitrogen, carbon dioxide and heavier hydrocarbons like
ethane. It forms naturally as a byproduct of the
geological process that turns plant material in to
coal.
Coal is sedimentary rock which is formed due
to biochemical decomposition of plant materials
by bacterial activity and succeeding
metamorphic transformation. The process of
formation of coal is known as Coalification
process. During Coalification process, large amount of gases are generated which is known as
Coalbed gas. Among these gases methane is principal and dominated gas. So coal bed gas is
known as Coalbed Methane. When methane is mixed with air, it is called firedamp.
Methane is an odorless, colorless, tasteless and nontoxic gas. It is half the density of air and
when mixed with air in the range of 5.4-14.8 % by volume, it is explosive. This explosive
mixture is also defined as firedamp. The difference between the typical natural gas and CBM is
that the natural gas consists of 85-90% methane, whereas CBM contains 97% of methane.
CBM is considered an unconventional form of natural gas because the coal acts both as the
source of the gas and the storage reservoir. As well, the gas is primarily adsorbed on the
molecular surface of the coal rather than stored in pore space, as occurs in conventional gas
reservoirs. If the CBM gas ever naturally migrates out of a coal seam and becomes trapped in
adjacent porous rock, it is no longer considered CBM but deemed to be conventional gas.
CBM occurs in coal pores in three states: Adsorbed, Free State and Dissolved state. Most of the
gases are generated in the early biogenic stage which is escaped due to poor gas retention
capacity of low rank coal and shallow depth of burial. Gases produced during thermogenic stage
could not migrate due to high pressure regimes and remain stored in the coal.
The gas adsorbed within coals is held there mostly by pressure. If the pressure is reduced, the gas
is released from the coal and free to flow to a well. The amount of gas liberated from a given
coal seam is a function of many factors, such as the chemical composition of the coal, the
geological history of the coal, and whether the coal had been previously depressured. The gas
content of a coal can be estimated by collecting drilling samples and measuring the volume of
gas released as a function of pressure in a laboratory.
Porosity of coal matrix provides space to adsorb the gas into the internal surface of the coal.
There are two types of pressure on coal seam by which methane gas is retained in coal: confining
pressure and hydrostatic pressure. "Methane remains in a coal seam as long as the water table is
higher than the coal”. The coal bed must be dewatered before the gas will flow. For gas
Methane 97.00%
Ethane 00.53%
Carbon dioxide 00.84%
Nitrogen 1.600%
Hydrogen 0.019%
Helium 0.047%

2
extraction pressure should be reduced. Since confining pressure can not be reduced so we reduce
hydrostatic pressure by dewatering. During extraction of gas, we follow several processes like
Drilling, Geophysical Logging, Casing, Cementation, Perforation, Hydro fracturing, and
Dewatering and Gas Production.
2. Formation of CBM
Coal is a sedimentary rock progressively developed during biochemical decomposition of plant
substance by microbes generated in peat swamps and succeeding metamorphic transformation.
Chemically two substances, cellulose and lignin that predominates in plants and constitute entire
structure of wood, contribute significantly to the formation of coal. Both cellulose and lignin are
complex, high molecular weight compounds made essentially of carbon, hydrogen and oxygen.
With increasing time, temperature and pressure, plant material progresses through various stages
of Coalification from peat to lignite, sub-bituminous and ultimately to anthracite.
As thermogenic stage advances, the percentage of oxygen is progressively decreased due to loss
of water resulting in
increased percentage of
carbon. Hydrogen
percentage remains almost
constant until coal attains
carbon percentage of 92%.
The progressive
transformation of woody
material in to peat and
subsequently to higher
rank of coal is determined
by geologic time. Various
theories have been
postulated to explain the
physical and chemical
changes during
Coalification. Many of
them relied on the
formation of methane,
carbon dioxide, carbon monoxide and water as the products of devolatilization during
Coalification. Mechanistic theories proposed are as under:
Parr (1906)
(C6H10O5)5 ® C22H20O3 + 5CH4 + 8CO2 + CO + 10H2O
Cellulose Bituminous Methane Carbon Carbon Water
Coal dioxide monoxide
Parr (1909)
3C12H18O9 ® C22H20O3 + 5CH4 + 8CO2 + CO + 7H2O
Ligno- Bituminous Methane Carbon Carbon
Cellulose Coal dioxide monoxide Water

3
As much as 250 m3
of gas is generated for each tonn of coal while maturation from lignite to
anthracite. Most of the
gases generated in the
early biogenic stage
escaped due to poor gas
retention capacity of low
rank coals and shallow
depth of burial. Gases
generated in the
thermogenic stage could
not migrate as a result of
high-pressure regimes and
remained stored in the
coal. Most available
Coalbeds have in-situ gas
contents of 1-20 m3
/t.
The quantity of enclosed gas is dependent on the physical properties of the coal seams, such as
hardness, content of mineral matter and structure of the coal seams, etc.
In general, the denser and harder is the coal the greater is the quantity of occluded gas. The
amount of occluded gas in coal is dependent on various factors, such as temperature, pressure,
pyrite content or fusain contents etc. It has been shown that under pressure coal adsorbs more
gases.
There are two principal contaminants in methane - CO2 & N2. Both are formed from the
decomposition of organic material and should be expected at some levels in all coal bed
methane. Nitrogen emission begins as Ammonia (NH3) near the end of the high volatile
bituminous stage. It is found as only minor constituents because its molecular size is very small
(3 Angstrom) and it escapes from the system more rapidly than other gases.
CO2 is a principal constituent of early thermogenic gases. CO2 is commonly a relatively minor
and extremely variable constituent in the produced gas. Due to its molecular size it migrates
rapidly as a gas. CO2 is highly soluble in water which facilitates its mobility. Approximately one
volume of CO2 will dissolve in one volume of fresh water at earth’s surface conditions at 20
degree centigrade.
At 300 atm. and 100 degree centigrade, conditions equivalent to a coal bed methane reservoir,
about 30 volumes of CO2 (STP) will dissolve in that same one volume of water. Generally
methane and CO2 occur in coal in inverse proportion i.e. when methane predominates, the CO2 is
less and when CO2 content is more methane appears in small quantities. This is due to the fact
that CO2 is formed by the oxidation of methane. As a result, with progressive oxidation, the
quantity of methane decreases, while the quantity of CO2 increases. Due to high pyrite content
the amount of CO2 in a coal seam may increase because pyrite absorbs oxygen when moist, and
the absorbed oxygen produces water by combining with hydrogen; also CO2 by combining with
carbon. Hydrogen sulfide (H2S) is found in coal seams in trace amount because it is the last
constituent of natural gas to form (starting at about 100 °C).

4
3. Geological Controls on CBM
Geology of the area affects and modifies mainly the generation, retention and transportation
mechanism of coal seams. Therefore study of geological parameters on coal seams is very
necessary for the development of CBM. There are a lot of factors that affects the CBM
development. The important among these are as follows:-
Depositional condition: When higher concentration of plant materials is deposited in the
basin, coals are formed. There may be two type of origin of coal; in- situ and drifted. In-
situ coal contains biogenic gas as well as thermogenic gas while drifted coal contains
thermogenic gas. With the help of isotope analysis one can know that whether the gas is
thermogenic of biogenic.
Climate: Warm and humid climate of sub- tropical region is most suitable for the
formation of coal.
Structural activity: If area is tectonically unstable then the coals are mostly faulted and
jointed. Large scale faults are harmful because it provides path for the escape of gas from
the coals.
Thickness and depth of coal: Thick coal seams contain more gas content than the thin
coal seams. As the depth of coal seams increases the pressure of overburden on the seams
increases, due to which adsorption capacity of coal increases. Thus gas content is directly
proportional to the depth of coal seams.
Rank of the coal: Rank is the compositional maturity of the coal. High rank coals have
higher maturity. The rank is based on volatile matter, fixed carbon, heating value, coking
power, etc. High rank coals have higher adsorption capacity and vice versa.
Petrography of coal: Coal is mainly composed of macerals. There are three maceral
groups- Vitrinite, Liptinite and Inertinite. The vitrinite coals have more micropores
containing higher gas quantity. Inertinite have least gas quantity.
Temperature and Pressure: If temperature of the reservoir is high, then methane
adsorption capacity is low and vice versa. On the other hand methane storage capacity
increases with pressure.
Dual porosity of coal: Coal bed has natural porosity which has macropores and
micropores in cleats systems. But after some secondary deformation secondary porosity
develops in the coal seams.
Adsorption: In adsorption, molecules of one substance are present in higher
concentration at the surface of other substance. For example, methane is adsorbed by the
coal. The material upon whose surface the adsorption takes place is called adsorbent
while the molecular species that get adsorbed are called adsorbate.
There are two types of adsorption:
o Physical adsorption: If the forces of attraction existing between adsorbate and
adsorbent are Vander wall’s forces, the adsorption is called physical adsorption.
This type of adsorption is also known as physisorption or Vanderwaal’s
adsorption. Since, the forces existing between adsorption and adsorbate are very
weak; therefore, this type of adsorption can be easily reversed by heating or by
decreasing the pressure.
o Chemical adsorption: If the forces of attraction existing between adsorbate and
adsorbent are almost of the same strength as chemical bond’s the adsorption is
called chemical adsorption. This type of adsorption is also known as

5
chemisorption or Langmuir adsorption. Since, forces of attraction existing
between adsorbate and adsorbent are very strong; therefore, this type of
adsorption cannot be easily reversed.
Cleat system: Cleats are the fractures in the coal seams. It provides path for the flow of
gas within the coal seams. If the coals have higher porosity and permeability due to
cleats, then gas can easily flow. Thus higher cleats density is profitable for the
development of CBM.
Hydro -geological Condition: Coals found at the lower and intermediate depths, are
generally contains aquifer but coal seams found below seven hundred meters depth are
mostly dry and absence of water. Good aquifers hamper the rate of production and also
increase the duration of dewatering and finally the cost of production.
4. Methane retention in coal beds
Methane is retained in coal seams in three states:
1. Adsorbed state
2. Free gas state
3. Dissolved in solution
1. Adsorbed state – Maximum (98%) methane retention in coal beds is in the form of
adsorbed state. The methane adsorption generally takes place at high pressure. Methane
(adsorbate) is adsorbed on the surface of the coal bed (adsorbent) and their molecules are held
together by a weak force of attraction i.e., Vanderwaal’s force.
Adsorption is totally different from absorption phenomena. Absorption takes place on the surface
at low temperature. It is chemical phenomenon and there is always a strong bond between the
atoms.
In contrast of it adsorption takes place at depth and high temperature & pressure. It is physical
phenomenon and there is no bond between the molecules of methane & coal except a weak force
of attraction.
2. Free gas state – In this state methane molecules are present in the pore spaces instead of
coal surface. The pores in coal may be of three types:
 Macro pores (size > 50nm)
 Meso pores ( size, 2-50nm)
 Micro pores (size < 2nm)
All these three pores are primary pores and it is less important for methane retention than
secondary pores like fractures & joints (cleat system).
Classification of pores according to their average width has been proposed by “Dubinin”
 Micropores (pores of width below 20A0
)
 Macropores (pores of width above 200A0
)
 Transitional or Intermediate pores (pores width between 20A0
and 200A0
)
3. Dissolved in solution – Some methane molecule is found dissolved in solutions present
in the pore spaces of coal. Its amount is very-very less than the gases present in adsorbed state &
Free State.

6
4.1 Factors affecting the methane retention of coal
There are number of factors which affect the gas storage capacity of coal such as coal rank, coal
type, mineral matter content, moisture content, temperature and pores.
Coal rank: Rank defines the level of compositional maturity of the coal. As Coalification
process progresses, the rank of the coal increases. The carbon content and vitrinite
reflectance are also increased with coal rank. But as rank of the coal increases the
moisture content, volatile matter and ash content decrease. Coal rank is often considered
to be the main parameter affecting the methane adsorption capacity. Adsorption capacity
increases with coal rank.
Coal type: coal type refers to those characteristics, which are initially determined by the
nature of the ingredient matter, the condition of deposition, and extent of operation of the
first or biochemical process of coal making. The features of coal type include variation
macroscopic banding, microscopic maceral composition and mineral matter content.
Maceral composition influences methane generation .e.g. Liptinite macerals are hydrogen
rich and generate more methane than Inertinite (oxygen rich) macerals. Coal type affects
on methane sorption. Inertinite coal having low and medium rank are found to have
higher adsorption capacities than vitrinite rich coals, where as at higher rank both coal
adsorb similar amount. Vitrinite rich coals have found to have greater adsorption capacity
than Inertinite over a wide range of ranks. Methane adsorption capacity and Desorption
rates vary significantly between bright and dull coal types. Bright coal has a greater
adsorption capacity but lower diffusion rate than dull coal from the same seam.
Consistent variation in pore size and distribution account for these effects with bright
coal having a large number of smaller microspores than the equivalent dull coal from the
same seam.
Mineral matter content: The inorganic constituents in the coal are the mineral matter
content that acts as a diluents, which reduces methane storage capacities. The
predominant minerals like carbonates and clays block the coal microspores which
includes fractures and cleats, reducing gas flow rates. It was observed that increase in ash
content decreased the adsorption capacity of the coal.
Moisture content: moisture content is rank related variable, which influences the storage
capacity of methane in coal directly. The effect of moisture on gas adsorption capacity is
inversely related. It is reported that 1% increase in moisture content may reduce the
adsorption capacity by 25% and 5% moisture may reduce 65% of adsorption capacity .
Methane adsorption decreases with increasing moisture content up to critical moisture
content. Moisture present in excess of the critical value has no further effect on methane
adsorption. This critical value was found to be related to the oxygen content of the coal.
Temperature: Temperature influences the sorption capacity of coal, as sorption is an
activated energy process. A linear relationship has been observed with increasing
temperature for a given rank coal. An increase in temperature of 10 degree centigrade
lo0wers the adsorption capacity by about 1cc/g.
Pores: Pores in coal are developed during Coalification process and are classified as
micro (<2nm), meso (2-50nm) and macro-pores (>50nm). The pore volume of coal takes
a U-shaped trend with increasing coal rank. It decreases to a minimum at around 85-90%
carbon content followed by increase with increasing rank. The decrease in pore volume in

7
low rank coal is the result of collapse of primary macro and meso pores due to physical
compactness and later due to plugging by higher hydro carbon generation. Secondary
porosity is developed with deplugging and depolarization of the coal, but this is further
destroyed in the meta-anthracite with graphitization. Increasing pore volume provides
greater storage capacity for gas in coal.
5. Flow Mechanism in Coal Bed Reservoir
A unit of coal can be taken as a cube which is bounded by butt (secondary) and face (primary)
cleats as shown in figure.
Within the cube, a network of micropores and interconnecting capillaries leads to the
thoroughfare of the bounding cleats. According to literature, the movement of gas in coal has
three distinct stages,
 Desorption of the gas from coal surfaces due to decrease in the pressure.
 Diffusion through the coal matrix from a zone of higher concentration to the cleat
system.
 Flow of gas through the coal seam cleat network under Darcy’s flow conditions.
1) Desorption Phenomenon: In this phenomenon methane molecules detach from the
microspore surfaces of the coal matrix and enter the cleat system where methane
molecule exist as a free gas. The desorption isotherm defines the relationship between the
adsorbed gas concentration in the coal matrix and the free gas presents in coal cleat
system. In the desorption stage the desorption isotherm is the link between the flow in the
matrix systems (where flow is controlled by concentration gradient) and flow in the cleat
system (where flow is controlled by pressure gradient). The relationship between gas
concentration and pressure is a nonlinear function i.e. generally defined by the Langmuir
equation.
2) Diffusion Mechanism: In this process, there is random molecular motion from high
concentration to low concentration. Here methane molecules desorbs from the matrix into
the coal cleat system in response to methane concentration gradient. Diffusion of gas
through the micropores of coal is described by Fick’s law.
Matrix
blocks in
coal

8
3) Darcy’ flow: After local diffusion of gas through the micropores of the coal, the
transport of gas occurs in fracture and cleats.
The fluid flow in the cleat system can be described by Darcy’s law. Darcy’s law relates the flow
rate in the reservoir, as fractures in a coal seam to the pressure drop across the reservoir using a
proportionality constant i.e., permeability. In general, following are the assumptions made while
applying the law –
 A single phase fluid of constant viscosity completely fills the connected pores
volume of the porous medium.
 A condition of viscous or laminar flow exists throughout the complex inner
prestructure of the porous medium.

9
Here, the Darcy’s equation is given by:
Q= -KA (dh/dl)
Where, Q = vol. of fluid flow through the column in unit time.
K = Hydraulic conductivity (a constant)
A = cross-sectional area of the column
L = length of the column
dh/dl = hydraulic gradient
Here, negative sign indicates that the flow is in the direction from higher head to lower head.
6. What is unconventional about CBM production?
CBM wells differ from conventional gas wells because a reservoir depressurization step is
needed during development to release the gas from the coal matrix and make it flow to a well.
The depressurization can be accomplished by allowing free gas within the naturally occurring
cracks and fractures in the coal to flow to the surface, or by pumping out any natural fluids
occupying the connected cracks and fractures. This fluid can be formation water and/or free gas.
The cracks and fractures in the coal also provide the pathways for the CBM to migrate to the
production wells. Coals usually have a blocky set of natural fractures called Cleats, which form
during coal formation. Provided they are not filled by minerals or squeezed shut by geological
processes. The cleats provide the natural pathways through the coal for CBM production. It is
common process to stimulate a well to assist CBM production through artificial hydraulic
fracturing, commonly called “Fracing”. Fracing involves pumping large volume of fluids
(commonly nitrogen) in to the well bore to create fractures that allow better contact between the
well and the natural coal seam cleats.
7. Difference between CBM and Natural Gas
The geological evolution of coal bed reservoirs is essentially similar to that of
conventional hydrocarbon reservoirs. The basic difference between the two reservoirs is the
mechanism of ‘entrapment of reservoir gases’. Other important differences are tabulated below:
CBM (Unconventional) NATURAL GAS (Conventional)
Low pressure reservoir High pressure reservoir
Two phase flow - water and gas Single flow - only gas
It follows Fick’s law and Darcy’s law It follows only Darcy’s law.
It has dual porosity It has only single porosity.
Hydro fracturing process takes place May or may not be necessary (after
depletion occurs then only)
Low permeability High permeability
Organic reservoir Inorganic reservoir
Micropore system and cleat system Macropore system.

10
Source rock and reservoir rock are both
same
Source rock and reservoir rock are
different
Gas emission can be controlled Gas emission can’t be controlled
Instruments used are new and are modified
with requirement
Instruments used are well established
Low risk involved High risk involved
8. Estimation of In-Situ-Gas content
Coal gas reservoir deliverability is a function of the amount of gas -in -place and the gas
storage and movement characteristics. To reliably estimate these values, we must know in-situ-
gas content and desorption gas behavior. Desorption describes the physical mechanisms by
which gas is released as due to reduced reservoir pressure.
There are two methods for estimation of gas content.
 Direct method
 Indirect method
8.1 Direct Method for In-Situ-Gas Content……………..
This method was suggested by Diamond and Levine (1981) and adopted by USBM. The gas
content of coal is determined by measuring the gas released from a sample of coal taken from the
seam. A recovered sample is placed in sealed canister i.e. desorption canister.
When coal samples are recovered from a well bore, some gas content is lost during sampling
i.e. before gas content measurements. This gas is called Lost Gas (Q1). Amount of gas released
in desorption canister is known as Desorbed Gas (Q2).Some gas is still present in the sample
which is known as Residual Gas (Q3).
Direct method involves following components:
 Sampling of coal cores
 Lost gas estimation (Q1)
 Measurement of Desorbed Gas (Q2)
 Determination of Residual Gas (Q3)
 Total Gas Volume (Q)
Sampling of Coal Cores: A person must be present at the site during sampling. For calculating
the total gas content, the person must record the exact time of when coal bed was encountered,
start of coal retrieval and lapsed time until the sample is sealed in the sample canister.

11
Lost Gas Estimation (Q1):
The volume of gas released from a sample before it is placed in a canister, is known as Lost
Gas. The amount of Lost Gas depends upon the following factors:
 Drilling medium
 Time required for retrieving, measurement & describing the core and finally sealing the
sample in the canister.
The shorter the time required for collecting the sample and seals it into the canister, the
greater the confidence in the lost gas calculation. In general, because of its speed, wire line
retrieval of the core is preferable to conventional coring. If air or mist is used as a medium
during drilling, it is assumed that coal begins desorbing gas immediately upon penetration by
core barrel. If medium is water/mud, desorption is assumed to begin when the core is halfway
out of the hole; that is, when the gas pressure is assumed to exceed that of hydrostatic head.
The lost gas can be calculated by graphical method based on the relationship that for the first few
hours of emission, the volume of gas given off is proportional to the square root of the desorption
time. A plot of the cumulative emission after each reading against the square root of the time that
the sample has been desorbing ideally would produce a straight line.
For lost gas calculation, following information must be known:
 Drilling Medium
 Time coal bed encountered (A)
 Time core started out of hole (B)
 Time core reached surface (C)
 Time core sealed in canister (D)
 Lost gas time calculation
Image showing Desorption canister

12
Lost time = (D-A), if air or mist is used
Or, = (D-C) +
2
B
C 
, if water/mud is used
Table for calculation of lost gas graph
Reading
(S.No.)
Time (in
am or pm)
Time since
sample placed in
canister (in min)
sq. root of (time in
canister + lost
time) in min
Gas
released
(in cc)
Total gas
(in cc)
Measurement of Desorbed Gas (Q2):
A portion of total sorbed gas is released from a sample into desorption canister is known
as Desorbed gas (Q2). Measured gas volume is reported at standard temperature and pressure
conditions. Desorbed gas is measured by Water Displacement Method first described by
Bertard et al. (1970) and later refined by Kissell et al. (1973).
Description of apparatus: - The given experiment is known as Water Displacement
Method. It consists of: Desorption canister, copper tube, water beaker, connecting pipes, glass
burette, iron stand and a reservoir.
The Desorption canister is filled with coal sample fitted with pressure gauge. The desorbed gas
comes out from desorption canister through the pipe, passes through water beaker which
maintains ambient temperature and is collected in the burette. Inside the water beaker, the pipe is
connected with copper tube. The desorbed gas pushes the level of water mixed with methyl
orange in the burette. The displaced methyl orange is collected in the reservoir. The volume of
Apparatus for water displacement method

13
displaced methyl orange gives the volume of desorbed gas. This is repeated for several times
until the sample stops to desorb any more gas or constant reading is obtained.
The observed data are presented in tabular form to compute Q2 as follows:-
Date
(dd/mm/yy)
Time
(minute)
Ambient
temp.
(in °C)
Ambient
pressure
(inch/mm)
Canister
temp.
(°C)
Desorbed
volume
(ml.)
Cumulative
Desorbed
volume (ml.)
Total (Q2)
=...
Determination of Residual Gas (Q3):
After determination of Q2, the coal sample is weighed and then kept into air tight
cylindrical iron/steel vessel. The air tight vessel contains one brass rod fixed inside it and other
brass rod is free to grind the core samples below 200 mesh BSS size. The air tight steel vessel is
filled with inert gas (nitrogen) to avoid adsorption of oxygen initially present in the vessel by the
crushed coal. The volume of residual gas released on crushing is measured by same water
displacement method as applied for desorbed gas volume.
Total Gas Volume (Q):
The Total gas volume is calculated by the following formula:
Gas Content (cc/g) Q =
W
Q
Q
Q 3
2
1 

Where, Q = gas content
Q1 = lost gas
Q2 = desorbed gas
Q3 = residual gas
W = weight of the sample
Coal crushing mill for residual gas content determination (developed by CIMFR)

14
Sorption Time (T):
Sorption time is defined as the time requires to recover 63.2% of methane gas from core
sample. Sorption time characterizes the desorption rate of gas from the coal.
 In low rank coal, sorption time is low i.e. high gas desorption rate and increase in
cumulative gas production.
 Sorption time is only determined when (Q1 + Q2)> Q3.
If (Q1 + Q2) < Q3, then sorption time is not determined.
8.2 Estimation of Gas Content by Indirect Method……….
There are several indirect methods for estimation of gas content. Convectional indirect
methods for estimating gas content require sorption isotherm testing and analysis as well as
knowledge of reservoir pressure and temperature. Some indirect methods are given below:
1. Using Adsorption Isotherms
2. Kim’s Method
3. Bulk density logs method
8.2.1 Using Adsorption Isotherm
By preparing an isotherm curve we can estimate the maximum volume of adsorbed gas on the
sample with respect to overburden pressure. Also we can estimate maximum volume of desorbed
gas from the sample due to release in overburden pressure. The whole process is pressure
dependent. This method is based on Langmuir’s Hypothesis. According to this hypothesis, “the
concentration of gas sorbed depends on the pressure”.
Steps involved in adsorption isotherm:
i. Preparation of coal sample
ii. Equipment used
iii. Measurement of void space
iv. Experimental procedure for adsorption isotherm
v. Significance of adsorption isotherm
vi. Controlling parameters for adsorption isotherm
i. Preparation of coal sample
Coal is crushed and size between -0.60 to +0.40mm is obtained by sieving method. 80gm
of obtained crushed coal is weighted in mettler’s balance.
Weight of crushed coal = (wt. of crushed coal + wt. of empty dish) – (wt. of
empty dish) gm
Now the 80gm coal is put in an oven at 500
C for about 1 hr. coal is taken out from
the oven and put in a dessicator to cool. Now weight of the coal is again taken. To
bring the coal at equilibrium moisture, distilled water is mixed with it to make it
saturate.
 For bituminous coal 5-10ml water is mixed
 For lignite coal 2-5ml water is mixed

15
Again it is put under the dessicator with dilute K2SO4 at the bottom to maintain relative
humidity inside the dessicator. The whole set up is put under an air incubator which
maintains a constant temperature of 500
C. The reading is taken at interval of 24hr till the
coal attains equilibrium moisture. For this several times the coal is soaked in water and it
is kept in dessicator and then in air incubator. It is done till coal stops to acquire any more
moisture. Now the sample preparation is complete.
ii. Equipment used
The equipment used in the experiment is consisted of a water bath to maintain the
isothermal condition, panel for controlling the flow of gas, reference and sample cells for
storing gas and coal samples, heater for maintaining the required temperature, pressure
transducer to record the drop in pressure and vacuum pump is used to evacuate the
system.
iii. Measurement of Dead volume
The volume which is not occupied by the sample is known as dead volume. It is determined by
non-adsorbing gas usually helium, which is an inert gas and has the smallest molecule that can
enter easily into the micro-pores of the samples.
High pressure adsorption-
desorption isotherm
Vacuum pump
Air Incubator

16
For determination of dead volume, equilibrated moisture coal sample is put into the sample cell.
Dead volume is determined by evacuating and then filling the reference cell with helium at a
high pressure of 5000KPa and allowing it to equilibrate at reservoir temperature. Helium is then
admitted to sample cell from reference cell. Leave the setup for one hour to allow for
temperature equilibrium in the sample cells and a drop in pressure is recorded. Dead volume is
calculated by measured drop in pressure.
iv. Experimental procedure for adsorption isotherm
 After determination of dead volume, valves to reference cells, sample cells and vacuum lines
are opened.
 The whole system is now evacuated for about 45 min.
 Valves to vacuum pump and sample cells are then closed and valves to reference cells are
opened.
 The methane gas introduced into the sample cells at a known lowest at 500 k after
determination of dead volume, valves to reference cells, sample cells and vacuum lines are
opened.
 The whole system is now evacuated.
 Valves to vacuum pump and sample cells are then closed and valves to reference cells are
opened.
 The methane gas introduced into the sample cells at a known lowest at 500 KPa.
 Valves to reference cells are closed and temperature is allowed to equilibrate with water bath
for one hour.
 Now valves to sample cells are opened and methane gas is slowly admitted to sample cells at
500 KPa.

17
 Leave the whole setup for at least one hour for temperature equilibrium in the sample cell.
 A drop in pressure is recorded.
 Increase the pressure in the reference cell to the next pressure step by adjusting the regulator
on the gas cylinder.
 Repeat the steps at increasing pressures up to 8000 KPa.
 The above procedure is repeated by decreasing pressures up to 500 KPa from 800KPa.
 The necessary data obtained by whole process is put in excel software for the calculation of
adsorption-desorption isotherm.
v. Significance of adsorption isotherm
 Determination of critical pressure
 Recoverable amount of gas
 Determination of Langmuir pressure (PL) & Langmuir volume (VL)
Recoverable amount of gas : To start the desorption , we have to reduce the pressure of
coal seam from PS to PA and further a certain limit we can’t reduce the pressure of
the reservoir. This limit is called Abandoned Pressure and corresponding volume is
called Abandoned Volume, which is unrecoverable i.e., we can’t exploit the 100%
of the gas contained in the coal seam.
% Recovery = 100
_
_
x
Volume
Gas
Total
VAB
VA 
Where, PS = pressure of overburden on coal seam
PA = corresponding pressure of volume VA
VA = actual volume of gas adsorbed in coal seam
VAB = abandoned volume
PAB = abandoned pressure

18
In actual practice we can exploit only 30-50% of total adsorbed gas volume due to
technical problems.
Determination of Langmuir pressure (PL) & Langmuir volume (VL):
Langmuir pressure (PL): Gas adsorption capacity of the coal increases with
increase in pressure, but after a certain pressure the adsorption capacity is stopped.
The value pressure of pressure at which the adsorption capacity stopped is called
Langmuir pressure.
Langmuir volume (VL): The volume of gas in coal at the half pressure of the
Langmuir pressure is called Langmuir volume.
vi. Controlling parameters for adsorption isotherm
 Nature of coal
 Ash content
 Amount of moisture present
 Temperature
 Pressure
Adsorption is directly proportional to pressure & rank of the coal and is inversely
proportional to ash, moisture & temperature.
Application of Adsorption Isotherm:
Adsorption isotherm is used-
 To know the saturation level of coal.
 To know the critical desorption pressure.
 To know the abundant reservoir pressure.
 To calculate the recovery factor.
 To forecast recovery of gas by reducing hydrostatic pressure of the reservoir.
 To calculate total recoverable gas from the well.
 To calculate the age of the well.
 To know the economic viability of the well.
8.2.2 Kim’s Method for estimating methane content of Bituminous Coalbeds from
adsorption data
The Bureau of Mines estimated the methane content of a coal, which depends primarily upon
rank and pressure, from the adsorption equation:
V = kPn
Where, k and n are constants related to rank and vary with temperature. By incorporating
corrections for moisture, ash and temperature, and estimating pressure and temperature as a
function of depth, the methane content of coal in place can be estimated from the following
equation:

19
V =
100
)
%
%
100
( ash
moisture

(0.75) [ko (0.096h) n
o – 0.14(1.8/100 + 11)]
The amount of gas in coal is adsorbed on the internal surface of micropores. The amount of gas
that a coal can adsorb varies directly with pressure and inversely with temperature. The
relationship between the volume of gas adsorbed by the coal, and pressure and temperature can
be described by the equation:
V = koPn
o – bT
Where,V = volume of gas adsorbed, in cubic centimeter per gram of
Moisture and ash – free coal;
P = pressure, in atmosphere;
T = temperature, in degree centigrade;
ko= a constant, in cubic centimeters per gram per atmosphere;
no= a constant;
and, b = a constant, in cubic centimeters per gram per degree centigrade.
The values of ko and no depend upon the rank of the coal, and can be expressed in terms of fixed
carbon (FC) to the volatile matter (VM):
Plotting a graph between logV v/s logP we get a straight line. ko Is determined by
measuring the intercept on y-axis. no is determined by the slope of the straight line
The temperature Constant b is measured by plotting a graph between V v/s T (At constant
Pressure) .It is a straight line having negative slope. The slope of the straight line determines the
temp. Constant b.
Log
V
Log P
no is the slope
ko
The graph between log P and
Log V for determining ko & no

20
ko = 0.8 FC/VM + 5.6,
and no = 0.315 – 0.01 FC/VM
Or no = 0.39 – 0.013 ko
Pressure and temperature are functions of depth. At a given depth, the pressure P is usually
assumed to equal the hydrostatic head given by the equation:
Phyd = 0.096h,
Where P is expressed in atmospheres and h is the depth, in meters.
For most high-rank coals, the minimum volume of methane adsorbed on wet coal is between 55
and 85 % of the volume adsorbed on dry coal. In general, the reduction in gas-adsorption
capacity is greater for lower rank coals.
REMARK………………
Kim’s method is not suitable for CBM as we estimate high gas content in mines but we do not
encounter the same amount so it is a loss. But, this method is used in estimating the safety of
mines.
CONCLUSION……….
The gas-adsorption capacity of coal depends upon pressure, temperature and rank. Since pressure
and temperature are functions of depth, the gas content of most coals can be estimated from rank
and depth or calculated from the general adsorption equation. In some cases, factors such as high
moisture content, low pressure gradient, and anomalous temperatures should be considered in
evaluating the accuracy of the gas-content estimation. The estimates of Coalbed gas content
derived from adsorption data provide reasonable preliminary figures and can be developed using
readily available data.
8.2.3 Bulk Density log
Another indirect method involves estimating gas content from calibrated bulk density well logs.
Relationship between core-determined gas content and ash content allow such calculations
.Because gas sorbed only on the coal fraction, an inverse correlation exists between core gas and
Volume
adsorbed,
cc/gm
Temperature, o
C
b is the slope
Graph between Adsorbed volume
& temperature for determining
temperature constant b.

21
ash content data. Core ash content can be mathematically related to high resolution bulk density
well log data because ash content usually has the greatest influence on coal bed reservoir density
.Thus, when you have representative in-situ gas content data available, you can estimate gas
content from bulk density well log data.
9. Physico-mechanical Property of Rock
This was carried out at Rock Testing Division Laboratory of Technological Block at CIMFR
campus. We were guided by Mr. John Burguhain Under the supervision of H.O.D. Dr. Santosh
Kumar Singh.
Following tests are done in this laboratory:
Physical Properties:
 Density (dry density, saturated density and bulk density)
 Porosity (apparent porosity)
 Permeability (by using liquid permeameter & gas permeameter)
Mechanical Properties:
 Uniaxial compressive strength
 Triaxial compressive strength
 Tensile strength (by Brazilian method)
 Point load test
 Young’s modulus & Poisson’s ratio
 Slake durability index
 Cerchar hardness
 Cerchar abrasiveness
 Protodyaknov strength index
Density (Physical Property)
The density of the coal sample was determined by caliper technique as per IS norms. The volume
of the sample was calculated from several caliper readings for each dimension. Each caliper
reading was accurate to ± 01mm.
ρ =
V
M
Where, ρ = dry density in gm/cc
M =dry mass of the sample in gm
V = volume of the sample in cc
Porosity (Physical Property)
Porosity is a measure of how much of a rock has open space. This space can be between grains
or within cracks or cavities of the rock.
Porosity of a rock is a measure of its ability to hold liquid. Mathematically,

22
% Porosity =
volume
rock
total
rock
in
space
open
_
_
_
_
_
X 100%
Porosity is more difficult to define in the case of coal, where it constitutes a more or less integral
part of the coal structure. This is not exactly measurable. Porosity is the volume fraction of coal
that may be occupied by a particular fluid. This includes everything from large fractures, visible
to the unaided eye, down to intramolecular interstices beyond the resolution of the most powerful
electron microscopes. Porosity is not a fixed property of coal, but varies for different molecular
probes, all of which sorbs to some degree on “Internal surfaces” in the coal structure. Porosity is
measured in percentage.
Boyle’s Law is used to calculate the pore volume of the sample.
Boyle’s law describes the inversely proportional relationship between the absolute
pressure and the volume of a gas, the temperature is kept constant within a closed system.
The mathematical equation for Boyle’s law is:
pV = k
Where, p denotes the pressure of the system
V is the volume of the gas
K is a constant value representative of the pressure and volume of the
system.
Classification of coal pores: Generally coal has dual porosity i.e. micro pores
(capillaries and cavities of molecular dimensions) and macro pores (cracks, cleat, fissures,
vacant cell limens in fusinite, etc.) Some classifications of porosity of coal are given below.
 Classification based on size of pores: On the basis of size pores can be classified into
three types.
 Micropores (<2 nm)
 Mesopores (2-50 nm)
 Macropores (>50 nm)
 Genetic classification: Coal pores may be grouped into a number of genetic categories.
a) Intramolecular porosity ( occurring on an angstrom to nanometer scale ),
b) Phyteral porosity (derived from plant precursors and occurring on the scale of microns
to hundreds of microns),
b) Thermally generated pores (ranging up to tens of microns in dimensions),
c) Fractured porosity (on the order of microns in width and ranging anywhere from
microns up to meters in length and height).
Coal pores can be further classified into primary and secondary porosity. The primary pores
are incorporated into the coal structure during deposition while secondary pores are formed
during late stage of Coalification.
Fundamental Importance of Porosity in Coal Bed Reservoirs: Porosity is the most
critical fundamental characteristic of coal bed reservoirs. The bulk of the natural gas recoverable
from coal bed reservoirs is stored in the Micropore system; and the macro porous network of
fracture. Porosity provides the pathways through which reservoir fluids flow to the production
well. A good Coalbed reservoir must provide both a well-developed, accessible Micropore
structure & well developed unobstructed fracture porosity. Limitations of the former will reduce

23
the gas storage capacity of the reservoir, whereas limitations of the latter will adversely influence
gas flow and production
Permeability (Physical Property)
Permeability of coal is very important for commercial flow rate of methane. Permeability is a
measure of the ease with which fluid can move through a porous rock. Like porosity,
permeability also is not exactly measurable. It is affected by many parameters, e.g. the frequency
of natural fractures, their interconnections, degree of fissure aperture opening, direction of butt
cleat & face cleat, water saturation, burial depths & in-situ stresses. If pores are not connected
then the rock is not permeable.
Permeability is measured in a permeameter by determining the pressure drop (P1-P2) from a
fluid of known viscosity (μ) and flow rate (Q) across a rock sample of known cross-section area
(A) and length (L). Permeability (K) is then determined by “Darcy’s Equation”,
K =
A
P
P
L
)
2
1
(
Q


A good reservoir has good permeability & the permeability of natural cleat system vary from
impermeable to >100 md. Cleats are the fractures & joints in coal seam which are formed as a
result of Coalification process.
There are two mechanisms for the origin of cleat formation in coal:
Endogenetic cleat: This is formed during the process of physical changes in the
properties of coal during the metamorphic process. Coal matter undergoes density
changes and a decrease in its volume. These processes are associated with the changes in
the internal stress system, compaction and desiccation, and the formation of cleat planes.
Exogenetic cleat: This is formed as a result of the external stresses acting on the coal
seam. These include tectonic stresses, fluid pressure changes, folding and development of
tensile stresses to which the coal seam is subjected during various time periods.
Endogenetic cleats are normal to the bedding plane of coal and generally occur in pairs.
There are at least two sets of near perpendicular fractures that intersect the coal to form an
interconnected network throughout a coal-bed. These two fracture systems are known as face
Darcy flow in cleat

24
cleats and butt cleats. The shorter butt cleat normally terminates at a face cleat, which is the
prominent type of cleat.
Cleat spacing greatly influences coalbed methane permeability. Cleat spacing is related to rank,
petrographic composition, mineral matter content, bed thickness, and tectonic history. In general,
at any given rank, closer cleat spacing is associated with brighter coal, less mineral matter, and
thinner beds. This correlation means that most medium and low –volatile coals will have good
permeability if the cleats are open. Permeability can be low to non-existent in semi-anthracite
and anthracite coals because of the destruction of the cleat.
Mineral fillings in cleat may also lead to low permeability. If a large proportion of the cleats are
filled, absolute permeability may be extremely low.
Cleat system and process of gas transport in Coalbed methane reservoirs
Matrix blocks in coal

25
Coals with bright lithotype layers, with a high percentage of vitrinite macerals, have greater
amount of cleats than dull coals. Common understanding is that cleats are formed due to the
effects of the intrinsic tensile force, fluid pressure, and tectonic stress. The intrinsic tensile force
arises from matrix shrinkage of coal, and the fluid pressure arises from hydrocarbons and other
fluids within the coal. These two factors are considered to be the reasons for Endogenetic cleat
formation.
On the other hand, the tectonic stress is regarded as extrinsic to cleat formation and is the major
factor that controls the geometric pattern of cleats. Face cleats extend in the direction of
maximum in situ stress, and butt cleats extend in the direction of minimum in situ stress which
existed at the time of their formation. This is why regular cleats are formed in face and butt pairs.
In general three sets of cleats are present in coal: face, butt and sometimes curvi-planar cleat
direction, which intersect both face and butt cleat as shown in the Figure.
Cleat spacing generally influences coal bed methane permeability. Cleat spacing is
related to rank, petrographic composition, mineral matter content, bed thickness, and tectonic
history. In general at any given rank, closer cleat spacing is associated with brighter coal, less
mineral matter and thinner beds. This correlation means that most medium and low volatile coals
will have good permeability if cleats are open. Permeability can be low to nonexistent in semi
anthracite and anthracite coals because of the destruction of the cleat. Mineral fillings in cleat
may also lead to low permeability. If a large proportion of the cleats are filled, absolute
permeability may be extremely low.
Klinkenberg, Shrinkage, and Stress Effects on Permeability
The effect of gas pressure on the permeability is explained by Klinkenberg effect (eq.1). When
pressure declines in coal seams as a consequence of production of water and gas, permeability
changes because of three mechanisms: Klinkenberg effect, matrix shrinkage, and effective stress.
Two of these mechanisms increase permeability, and the third one reduces permeability.
The Klinkenberg effect increases effective permeability of methane at low pressures (Patching,
1965). Flow of a gas through the cleats of coal is described by the Darcy equation which includes
the assumption that the layer of gas closest to the fracture walls is stagnant and does not move. In
conventional sandstone reservoirs as well as coal reservoirs, slippage of the adjacent layer does
occur at low pressures to give a higher flow rate than would be calculated by Darcy’s law, that is,
the Klinkenberg effect. In the coalseams pressures are likely to be lower than conventional
reservoirs, especially as production approaches abandonment, making the Klinkenberg effect
more important in coal.
Curvi-planar cleat

26
The correction of permeability for the Klinkenberg effect on gases flowing through porous media
at low pressures is described by equation-2.
)
1
(
p
b
k
k 
  (1)
Where, k= corrected permeability
k = permeability at high pressure
b = slippage factor
p = mean pressure
At very high pressures, the permeability is denoted by k. At low pressures, equation -2 shows
that slippage increases effective permeability of the gas linearly with reciprocal pressure.
The phenomenon is illustrated in Fig.-4 where the permeability of a porous rock to hydrogen,
carbon dioxide, and nitrogen increases linearly with reciprocal pressure as pressure is decreased
from a common value for all three gases at an initially high pressure (Harpalani and
Schraufnagel, 1990).
The coal matrix shrinks as gases desorbs which causes an enlargement of the adjacent cleat
spacing (Gray, 1987). The effect increases with adsorbate affinity for the coal. For example, the
effect is greater for desorption of CO2 than for methane because of the stronger affinity of the
coal for CO2.
Klinkenberg effect on permeability (after Harpalani and Schraufnagel, 1990)

27
Above figure shows the net effect of methane desorption on the volumetric change in a coal. In
collecting data for above figure, Harpalani used the non adsorbing helium to isolate the effect of
grain compressibility (Harpalani and Schraufnagel, 1990). The effective shrinkage is a sum of
the two phenomena (Gray, 1987). Thus, shrinkage with desorption increases the production rate
of methane through enhancement of permeability by widening the cleat apertures.
Water production reduces pressures in the cleats. As pressure declines, the increasing effective
stress acts to close the cleats and to reduce permeability (Puri and Seidle, 1991). A schematic of
the cleat contraction after water removal is given in Figure below. It is seen that the phenomenon
acts in opposition to the shrinking of the matrix in its effect on permeability.
Therefore in above figure, it becomes evident that the permeability of the coal seam is a dynamic
property of the three mechanisms affecting permeability during production, one decreases
permeability and the other two increase permeability. It is hypothesized that matrix shrinkage
and the Klinkenberg effect increase permeability as production proceeds: effective stress
decreases permeability.
Desorption of methane shrinks the coal matrix
(After Harpalani and Schraufnagel, 1990)
Effective stress and desorption effects on cleat dimension

28
Harpalani studied the dynamic permeability in the laboratory. Figure below gives the combined
effects of the Klinkenberg phenomenon, the matrix adsorption swelling, and the cleat contraction
from increasing effective stress (Harpalani and Schraufnagel, 1990). The Langmuir adsorption
curve of methane is superimposed on the data in Figure below.
One can see from Figure below that as pressure is decreased from 1000 psi, the three parameters
are interactive. Two of them (matrix deswelling and the Klinkenberg effect) tend to increase
permeability while the third (cleat contraction) has a negative impact and dominates at the higher
pressures. The positive effects of matrix deswelling dominates cleat contraction at the point on
the Langmuir isotherm at about 1000 psi in which desorption accelerates; the greater volumes of
methane desorbed in that process of the isotherm for a unit pressure drop emphasizes the positive
effects of deswelling.
The permeability curve of above figure is fitted with equation-3 by Harpalani
2
CP
p
b
A
k 

 (3)
where, k= effective permeability
A, B, C = constants
P = operating pressure
At low pressures, where
P
B
>CP2
, the equation reduces to the form of the Klinkenberg
relationship of equation-2. At high pressures where the term CP2
is dominant in the equation, the
importance of a low effective stress is indicated (Harpalani and Schraufnagel, 1990).
Permeability changes with production (after Harpalani and Schraufnagel, 1990)

29
Permeability and Porosity Measurement facilities at CIMFR, Dhanbad
Gas/Liquid Permeameter/ Porosimeter system is highly rapid, accurate and non-destructive
measurement of permeability and effective porosity of core samples. A computer data
acquisition system automatically calculates the permeability and porosity, and records the data
saving it to a spreadsheet file. Test core of varying diameters can be easily accommodated by
switching core holder internal parts. Cores are easily and quickly inserted and removed by
screwing the end plugs. Maximum confining (overburden) pressure is 10,000 psig (68.9 Mpa) at
room temperature and maximum flowing (pore) pressure through the core sample is 2500 psig
(17.2 Mpa) at room temperature. With the low-pressure (100 psig full scale) inlet pressure
transducer installed for porosity testing, maximum pore pressure is 100 psia (0.69 Mpa absolute
or 0.85 psig or 0.59 Mpa).
Single-phase gas permeability is measured with the steady-state method. Helium or Nitrogen gas
is injected through the core sample via a pressure-reducing gas regulator and a metering valve. A
core holder and confining-pressure pump are used to apply uniform confining (overburden)
pressure to the sample. A gauge-pressure transducer measures inlet pressure to the core sample.
The pressure drop across the core sample is measured with one of three calibrated mass flow
meters which have voltage output signals. A thermocouple measures the flowing temperature
(ambient temperature) of the gas meters. The computer software automatically calculates
permeability of the core sample using the differential pressure, gas flow rate, gas viscosity, core
dimensions, and temperatures.
A pulse-decay Permeameter is also included in this system. It operates as a separate, independent
instrument, with its own software and hardware to measure permeability of a core sample. It is
an unsteady-state Permeameter designed to measure permeability in the range of 1 millidarcy
(md) to 10 nanodarcy (10 nd). The steady-state permeameter designed to measure permeability
in the range of 1 md to 10 Darcy’s.
Porosity measurement begins with calibration of the inlet pressure transducer; using its quick,
simple and highly accurate shunt calibration feature (The porosity measurement does not use the
differential pressures, the flow rate or the temperature). Then the volumes of the different
sections of the plumbing system and of the reference chambers are measured by calibrating them
against the known pore volumes of the calibration test plugs. A core sample is placed in the core
holder and the reference chambers and transducer plumbing (both of known volume) are
pressurized to approximately 100 psia (0.69 Mpa a absolute). Opening the core holder inlet valve
releases some of the gas into the core and core holder plumbing dead volume. The equilibrium
pressure which results is measured. Helium (He) is the preferred gas to use for porosity testing,
since it minimizes the adsorption of gas on the grain surfaces.

30
Uniaxial compressive strength (Mechanical Property)
Procedure for sample procedure:
a) Test specimen was right circular cylinder having a height to diameter ratio of 2.0.
The diameter of the specimen was related to the size of the largest grain in the
rock by the ratio of at least 10:1.
b) The ends of the specimen were flattened to within 0.05mm and were parallel to
each other within 0.002 D, where D is the specimen diameter. The ends of the
specimen were perpendicular to the axis of the specimen within 0.001 radians (3.5
min).
c) The sides of the specimen were smooth and free from any abrupt irregularities
and straight to within 0.3 mm (0.012 inch) over the full length of the specimen.
d) The diameter of the test specimen was measured to the nearest 0.01mm by
averaging two diameters measured at right angles to each other near the upper-
height, mid-height and lower-height of the specimen. The average diameter was
An expert giving required shape
to the core by cutting machine
A polishing machine
Photographic view of whole
core permeameter and
porosimeter at CMRI,
Dhanbad

31
used for calculating the cross-sectional area. The height of the specimen was
determined to the nearest 0.01mm.
e) Load on the specimen was applied continuously at a constant stress rate such that
failure occurred within 10 minutes of loading. Alternately the stress rate was
within the limits of 0.5-1.0 MPa/sec.
Note: For the testing of compressive strength, the sample was such made that the length
of the cylindrical sample was double to that of the diameter of the sample. This sample
was placed under UNIVERSAL TESTING MACHINE and pressure was continued to
exert until the sample broke. The load at which sample was broken was the FAILURE
LOAD.
Calculation:
The Uniaxial compressive strength of the specimen was calculated by dividing the
maximum load carried by the specimen during the test by the original cross-sectional area.
σ =
A
F
Where, σ = Uniaxial compressive strength in kg/sq.cm
F = failure load in kg
A = cross-sectional area in sq.cm
Uniaxial tensile strength (Mechanical Property)
This Uniaxial tensile strength of rock samples was determined by the indirect Brazilian Tensile
strength Test as per IS norms.
Universal rock testing machine
at CIMFR, Dhanbad

32
Procedure for sample procedure:
a) Test specimen was right circular cylinder having a height to diameter ratio of 0.5.
The diameter of the specimen was related to the size of the largest grain in the
rock by the ratio of at least 10:1.
b) The sides of the specimen were smooth and free from any abrupt irregularities.
c) The diameter of the test specimen was measured to the nearest 0.1mm by
averaging two diameters measured at right angles to each other of the specimen.
The average diameter was used for calculating the cross-sectional area. The height
of the specimen was determined to the nearest 1.0mm.
d) Load on the specimen was applied continuously at a constant stress rate such that
failure occurred within 15 to 30 seconds. Loading rate was 200N/s.
Calculation:
The Uniaxial tensile strength σt was calculated by,
σt = 0.636 х
Dt
P
Where, σt = tensile strength in kg/sq.cm
P = load in failure in kg
D = diameter of the specimen in mm
t = thickness of the test specimen in mm
Deformability characteristics (Mechanical Property)
The sample preparation and test procedures for determination of Young’s Modulus of and
Poisson’s Ratio comprise of the following steps:
a) The length to the diameter ratio of the specimen was 2. The diameter of the
specimen was related to the size of the largest grain in the rock by the ratio of at
least 10:1.
b) The ends of the specimen were flattened within 0.05mm and did not depart from
perpendicularly to the axis of the specimen by more than 0.001 radian (3.5 min)
or 0.05mm in 50mm.
c) The sides of the specimen were smooth and free of any abrupt irregularities and
straight to within 0.3mm (0.012 inch) over the full length of the specimen and the
dimension of the specimen did not varied by more than 0.2mm over the length of
the specimen.
d) The diameter of the test specimen was measured to the nearest 0.01mm by
averaging two diameters measured at right angles to each other at about the
upper-height, middle-height and lower-height of the specimens. The average
diameter was used for calculating the cross-sectional area. The height of the
specimen was determined to the nearest 0.01mm.

33
e) Load on the specimen was applied continuously at a constant stress rate such that
failure occurred within 5-10 minute of loading. Alternatively the stress rate was
within the limits of 0.5-1.0 MPa/sec.
f) Load and axial and circumferential strains or deformations were recorded at
every spaced load intervals during the test.
Calculation:
Axial strain was calculated from the equation,
εa = Δl/lo
Where, lo = original measured axial length
Δl = change in measured axial length
Diametric strain was calculated from the equation,
Εd = Δd/do
Where, do = original undeformed diameter of the specimen
Δd = change in diameter
The compressive stress in the test specimen (σ) was calculated by dividing compressive load (P)
on the specimen by the initial cross-sectional area (Ao). Thus,
σ =
0
A
P
Tangent Young’s Modulus Et, is measured at a stress level which is some fixed percentage of
the ultimate strength. It is generally taken at a stress level equal to 50% of the ultimate uniaxial
compressive strength.
Poisson’s Ratio V, was calculated as the total diametric strain to the total axial strain at any
given stress level. It is generally taken at a stress level equal to 50% of the ultimate uniaxial
compressive strength.

34
TEST RESULT……………………..
I. Compressive strength, Tensile strength and Density.
S.
No
Dia
(mm)
Length
(mm)
Mass
(gm)
Failure
Load
(kg)
Comp.
Strength
(kg/sq.cm)
Avg.
Strength
(kg/sq.cm)
Density
(gm/cc)
Avg.
Density
(gm/cc)
Thickness
(mm)
Failure
load (kg)
Tensile
Strength
(kg/sq.cm)
Avg.
strength
(kg/sq.cm)
Compressive
Strength
Density Tensile strength
II. Young’s Modulus and Poisson’s Ratio.
10. Proximate Analysis of Coal:
This was done at CIMFR, Dhanbad and we were guided by Mr. P.K. Mandal. For general
purpose proximate analysis is taken into consideration. It includes determination of moisture,
volatile matter, fixed carbon and ash content. The procedures for proximate analysis are rather
empirical, but do not require elaborate costly equipments. As such this analysis is widely used
for industrial purpose and also for grading the coals.
Measurement of Ash content (A)………………
Weight of empty silica dish (x)
Weight of empty silica dish + 1gm coal sample (y)
Weight of y after heating in a muffle furnace at about 800o
C for 1hr (z)
Weight of coal sample = (y-x) gm
Ash % = (z-x) gm X 100%
Measurement of Moisture content (M)……………
Weight of empty moisture bottle (x)
Weight of empty moisture bottle + 1gm coal sample (y)
Weight of y after heating in an oven at 110 o
C for about 1hr (z)
NOTE: weight is taken after cooling the sample in a dessicator for about 45 minute.
Moisture % = (y-z) gm X 100%
Measurement of Volatile Matter (VM)……………
Weight of empty silica crucible (x)
Weight of empty silica crucible + 1gm coal sample (y)
Weight of y after heating it in an oven at 900 o
C for 7 minutes (z)
Volatile matter % = (y-z) gm X 100%

35
Measurement of Fixed carbon (FC)………….
Fixed Carbon % = 100% - (A+M+VM)
11. Gas Chromatography
Chromatography is a phenomenon of separation of mixture of compounds into different
components. In chromatograph a sample is dissolved in a mobile phase (which may be gas or
liquid). The mobile phase is then forced through an immobile stationary phase. The sample is
transported through the column (A narrow tube packed with stationary phase) by continuous
addition of mobile phase; this process is known as Elution.
Gas chromatography is a type of chromatography in which the mobile phase is a carrier gas;
usually an inert gas such as helium or an unreactive gas such as nitrogen and stationary phase is a
layer of liquid or polymer on an inert solid support inside the column. The instrument used to
perform gas chromatographic separation is called Gas Chromatograph (GC).
Mettlers Balance to weight coal
sample up to 4 decimal place
Desiccator
Figure showing external and internal view of Gas Chromatograph

36
Gas chromatography involves a sample being vaporized and injected into the column. The
sample is transported through the column by the flow of inert gaseous mobile phase. The column
itself contains liquid stationary phase (gel fluid).
SAMPLE PREPRATION
For sample preparation we have to consider any of the four times intervals at which desorption of
gas has completed.
1st
sample - First hour desorbed gas sample.
2nd
sample - 16 to 24 hrs disrobed gas sample.
3rd
sample - 45 to 60 hrs desorbed gas sample.
4th
sample - 96 to 100 hrs desorbed gas sample.
The gases present in the first hour sample are O2, N2, CH4, C2H6 and other hydrocarbons.
The gases present in the second hour sample are CH4, O2, N2 (less than 1%) & other
hydrocarbons.
TEMPERATURE OF THE SAMPLE INJECTIONPORT
It is usually about 500
C higher than the boiling pt. of thee least volatile component of the sample
and is generally maintained between 100 – 1100
C.
OVEN TEMPERATURE
It is generally maintain 400
C
CONDITIONING OF COLUMN
For conditioning the column, the carrier gas is allowed to flow for about 3 – 4 hrs and the
required temperature of the column is also maintained.
INSTRUMENTAL COMPONENTS:
1. Carrier gas: The carrier gas must be chemically inert eg: nitrogen, helium,
argon etc. The choice of carrier gas often depends upon the type of detectors
which is used, for example: for TCD (Thermal Conductivity Detector, used
for non-hydrocarbons) the carrier gas is nitrogen while for FID (Flame
Ionization Detector, used for hydrocarbons) hydrogen & air are used as carrier
gas. The carrier gas is generated by generators.

37
2. Sample Injection Port: The sample is injected by injection syringe through a
rubber septum into a vaporized port at the head of the column. The injector
can be used in one of the two modes; split or split less. The injector contains a
heated chamber containing a glass liner into which the sample is injected
through the septum. The carrier gas enters the chamber and can leave by three
routes. The sample vaporizes to form a mixture of carrier gas. A portion of
this mixture passes into the column but most exit through the split outlet.
3. Columns: There are two types of column; packed and capillary (open).Packed
column contains a finely divided inert solid support material coated with
liquid stationary phase.
Capillary columns have internal diameter few tens of millimeters. Capillary columns are of
two types;
Hydrogen gas generator

38
 Wall coated open tubular (WCOT) - It consists of a capillary tube whose
walls are coated with liquid stationary phase.
 Support Coated Open Tubular (SCOT)-In it the inner wall of the
capillaries lined with a thin layer of support material such as diatomaceous
earth, onto which the stationary phase adsorbed.
SCOT is generally less efficient than WCOT.
The column temperature must be controlled within 40-50 degree centigrade. Column
temperature depends upon the boiling point of the sample.
4. Detectors: There are many detectors which can be used in gas
chromatography. Different detectors give different type of selectivity. A non-
selective detector responds to all compounds except carrier gas, a selective
detector responds to a range of compounds with common physical & chemical
property and a specific detector responds to a single chemical compound.
The GC (at CIMFR) is equipped with two types of detectors:-
 TCD (Thermal conductivity detector) - The carrier gas of TCD. is ‘N2’. This gives
the peaks of different gas components.
 FID (flame ionization detector) - Here we ionize the gas (sample) by lighting heat
by using flame. The carrier gas of FID is ‘H2’.
A systematic diagram of Gas Chromatograph

39
For producing H2, distilled water put in H2 generator, which generates H2 by the process of
electrolysis, which separate H2 & O2 from supplied distilled water. GC is also connected with
calibration gas cylinder at the same point from where sample is injected but at different time.
The type calibration gas use depends upon the gas component to be analyzed. Finally the GC
is connected to P.C. (computer) with specific software, which gives two different graphs.
 One of Sample gas and,
 Other of calibration gas.
Detectors can also be grouped into concentration dependent detector and mass flow
dependent detector. The signal from concentration dependent detector is related to the
concentration of solute in detectors. The sample is not destroyed in the process.
Mass flow dependent detectors usually destroy the sample and signal is related to the rate at
which solute molecules enter the detector
STEPS INVOLVE IN THE ANALYSIS OF DIFFERENT GAS COMPONENT BY THE
USE OF GAS CHROMATOGRAPH
STEP 1: Sample is injected at the injection port by help of medical syringe/ auto sampler.
STEP2: The sample mixed with carrier gas, which is then forced into stationary phase.
STEP3: Due to oven temperature the sample (gas) gets vaporized.
STEP 4: Now the sample inters the capillary column by continuous addition of mobile
phase (carrier gas) this process is called Elution.
Flame Ionization Detector

40
STEP 5: After passing through capillary column the sample reaches detection port.
In FID
STEP 6: Now the sample ignited with the present of H2 & air, which ionizes the sample
(gas)
In TCD
STEP 7: The TCD whose carrier gas is N2 helps to produce the peak on the computer.
STEP 8: For collection of data the GC is connected to computer, where we get different
peak area and retention time of gas components, which is compared by the graph
obtained of the calibration gas.
RETENTION TIME
The interval between the instant of injection and detection of the component is known as
retention time. Because this varies with the identity of components, they are utilized for
qualitative analysis.
WHAT INFLUENCES SEPRATION
 Polarity of stationary phase - Polar compounds interacts strongly with a polar
stationary phase; hence have a longer retention time than non-polar column.
 Temperature - More is the temperature the more of the
compound is in the gas phase and hence retention time is shorter.
 Carrier gas flow - If the carrier gas flow is high, the molecule
do not have a chance to interact with the stationary phase. Hence retention time is shorter.
 Column length - Longer is the column, longer is the retention time
and hence better is the separation.
 Amount of material injected. - More is the sample injected, poor is the separation.
High temperature and high flow rate decreases the retention time but also
deteriorate the quality of separation.
The main reason why different compound can be separated this way is the interaction of the
compound with the stationary phase. (Like – dissolves – like – rule). The stronger the interaction
is the longer the compound remains attached to the stationary phase, and the more time it takes to
go through the column (= longer retention time).
12. Coal Petrography
This was carried out at Rock Quality Assessment (RQA) Division, CIMFR, Digwadih Campus,
Dhanbad on 13/10/09. The H.O.D. of RQA Division, Dr. Mrs. Nandita Choudhary permitted us
for analysis of coal petrography under the supervision of Dr. Ashok Singh (Scientist). We were
guided by Mr. Saroj Kumar (SA) and Debadutta Mohanty (Scientist RQA Division).

41
Petrography of coal
The coal petrology or petrographic characterization of coal involves qualitative and quantitative
assessment of macroscopic as well as microscopic constituents. The macroscopic examination is
performed without any aid of instrument but the microscopic assessment requires application of
sophisticated microscopic systems. The petrological examination on coal under the microscope
has become a highly specialized branch of coal science, and has assumed great significance,
because of the many practical application it can offer in the utilization of this important fuel.
Here, I have tried to mention, in a bare outline, the results and practical uses of such study.
Macropetrographic characteristics:
A virtual examination of coal shows that it is not homogeneous throughout its mass but is
composed of a number of bands or layers. They are called the banded constituents of coal. These
bands are termed vitrain, clarain, durain and fusain and they show the following properties:-
Vitrain: - It is brilliantly glossy, jet black coal lithotype with a minimum thickness of 3mm,
uniform in texture, having vitreous luster and breaking with conchoidal fracture. The vitrain
band may split up readily in the fingers in small cube like segments.
Clarain: - It is less bright than vitrain. Clarain is a thinly banded lithotype formed by alternate
laminations of bright (vitrain) and dull bands (durain and fusain). It is less than 3mm in thickness
but cumulative band should have a minimum thickness of 3mm. Clarain band has a silky luster
and does not break with conchoidal fracture.
Durain: - It is the ‘dull’ component of coal with a dull grayish black color and occurring as thick
band. It is quite hard and breaks with an rough, lusterless surface. The texture on the broken
surface is distinctly granular.
Fusain: - Also called ‘mineral charcoal’ is the soft black powdery component of coal occurring
as patches or as wedges. Fusain, like durain, is taken as dull coal. But, unlike durain, fusain on
touching soils fingers. It generally forms a minor fraction of the coal seam, say about 2-5 %.
The macro constituents of coal have widely different physical, chemical and technological
properties within a particular rank range.
Micropetrographic characteristics:
The composition of coal at microscopic scale is described in terms of ‘macerals’ which are
equivalent to minerals in rocks, although there is a great difference between minerals and
macerals. The macerals are organic entities produced under highly variable physico-chemical
conditions from different parts of plants such as woody tissues, leaves, needles, cuticles, spores,
pollens, resins and others. As such, they do not possess any property typical of a mineral. The
minerals, therefore, may be, defined as the humified and coalified products of various parts of
plants. The macerals associations are called microlithotypes.

42
Classification of microscopic constituents:
A number of nomenclature systems were proposed from different countries over the years. To
overcome these differences an International committee was formed in 1953 which is presently
known as ‘International Committee for Coal and Organic Petrology (ICCP). The nomenclature
system in current use throughout the world is the Stopes–Heerlen system adopted and published
with some modifications by the ICCP in 1963 and 1971. In this system, the names for macerals
are based on the optical properties of organic constituents viewed under incident light. The
incident light microscopy is recommended because it is the only method through which
quantitative maceral analysis can be performed.
The three important micro constituents of coals (macerals) are grouped as ‘Vitrinite’,
‘Exinite or Liptinite’ and ‘Inertinite’. Each group embraces a set of macerals. These are:
 Vitrinite
 Fusinite
 Semi-fusinite
 Exinite
 Resinite
 Sclerotinite
 Alginate and
 Micrinite
In general, the macerals of one particular group are similar in their origin, mode of
conservation, colour and reflectance but differ in their morphology at maceral and submaceral
levels. In addition, the macerals of each group show close similarity in their chemical
composition, such as Vitrinite rich in oxygen, Liptinite in hydrogen and Inertinite in carbon.
Optical properties:
(a) Vitrinite: The primary constituent of ‘bright’ coal and the principal coal maceral. A
polished sample clearly shows the structure of the woody tissues. In thin sections it is
translucent and shows a light or dark orange colour. The reflectance is highly variable
depending upon the rank of the coal.
(b) Liptinite: Maceral representing the remains of spores and cuticles. These are translucent
and yellow in colour in thin sections. Polished surface shows lows reflectivity in low rank
coals (lignite to medium volatile bituminous coals).
(c) Inertinite: The macerals of this group are considered ‘inert’ because they do not react to
temperature during the entire course of coalification and also during the carbonization
process. Thin sections are opaque and show a cellular structure. Polished surface shows
strong reflectivity.
12.1 APPLICATIONS OF COAL PETROGRAPHY
Presently, four methods are commonly employed for the microscopic examination of coal.
These are:

43
 Maceration technique
 Thin section study
 Polished section study and
 Study of polished thin sections
Each of these methods has its own advantages and disadvantages but all of them are equally
important from the point of view of the study of micro-fossils in coal. However, during training
period, we learned more about the study of thin-section and polished section and its uses.
Therefore, we have tried to put a brief outline on these methods.
Thin and polished section study:
The techniques of studying thin section of coal under transmitted light as well as the study of
polished surfaces of coal under reflected light were developed side by side. Since, coal is opaque
and friable, the preparation of thin sections of coal is comparatively difficult, time consuming
and requires greater skill. Also, it is generally not possible to make thin sections of high rank
coal (Anthracite). Due to its high mineral matter content, preparation of thin sections of Indian
bituminous coals is all the more difficult.
On the other hand, it is quite easy to prepare polished sections of coal. A block of coal (about 2-
5cms cube) is taken from the sample and a surface – usually that is perpendicular to the bedding
plane is polished by first grinding it with carborundum powder and then by finer grades of
alumina powder. If the sample is in powdered form, a briquette is made with molten carnauba
wax or resin and the major surface polished. It takes only about ten minutes to prepare a polished
sections compared with one hour or more for a thin sections.
The advantage of thin section method is that the micro-structures of transparent and semi-
transparent constituents are clearly visible as compared to the polished section method. However,
in thin sections, structures of opaque constituents are not prominent, whereas they are clearly
visible in polished sections.
The difficulties in examining micro-structure in thin as well as polished sections are overcome
by using polished thin sections. In this method instead of covering the surface of a thin section
with a cover glass, it is polished and then viewed alternately under transmitted and reflected
light. This method is very useful in studying the morphology of plant remains.
An understanding of nature and origin of the micro-constituents of coal is the prime object of
coal microscopy. Moreover the petrographic study of coal is of great significance in the study of
the relationship between the content of different macerals in coal and its technological properties.
It has also been found that the maceral of the Exinite group has a higher matter than the maceral
of Vitrinite group, which in turn has a higher volatile matter than those of the Inertinite group.
13. Drilling for CBM exploration
Exploratory holes are drilled to collect the coal sample for estimation of methane gas in the coal
seam. Coal samples are collected from different seam present. The chronological sequence
followed during drilling is as follows-:

44
Drilling: Vertical boreholes are drilled from the surface to the coal seam. According to the extent
of seam different drilling pattern is followed. Directional drilling is also done in many seams if
the seam is dipping constantly. Drilling is same as practiced in oil and gas industry. Fractures
stimulation of vertical well bores is based and applied for medium permeability coals, thin beds
and where multiple coal seams are penetrated. The problem is that most vertical wells are
inefficient due to low gas recovery rates, long term dewatering, the large number of wells needed
to depressurize and limitations of surface access. Horizontal open wells can be used for thick
coal seams, low permeability coals, and in areas where good lateral continuity is present. A
pinnate drainage pattern established by drilling multiple side laterals off a main horizontal lateral
provides maximum CBM production under ideal reservoir conditions.
Horizontal holes are drilled into the coal seam from development entries in the mine. They drain
methane from the unmined areas of the coal seam shortly before mining, reducing the flow of
methane into the mining section. Because methane drainage occurs only from the mined coal
seam and the period of drainage is relatively short, the recovery efficiency of this technique is
low.
Casing and cementation: Large diameter steel pipes called casing is screwed into the well. The
casing stabilizes the well, preventing the sides from caving in & prevents water flow from other
formations into the well. During casing a gap is created between casing pipe & wall of the well.
This gap is filled by cement called slurry at high pressure. Casing is done as the well is being
drilled. The well is drilled, cased, drilled deeper & then cased again The well is first drilled down
to a certain depth with a large diameter bit & then drill string is run out of the well. Large
diameter casing (surface casing) is cemented into the well. The well is then drilled down to the
drilling target & tested. A string of smaller diameter casing (production casing) is then run
through the surface casing into the well and cemented.
Directional drilling and vertical drilling

45
Perforation: Perforation is the process of making contact between the coal seam & bore
hole. It is done by a small diameter steel pipe which is run down the centre of the well. Bore
holes are then made into the casing at the level of the production zone by a perforating gun
with explosive charges. After the explosion by a perforating gun coal seam is fractured and
the connection is made between the coal seam & bore hole.
Hydro fracturing: Hydro fracturing is done by setting a bore hole packer below the casing
depth and expanding it. This isolates the production zone from the rest of the well. Water
mixed with sand is then pumped at high-pressure and high-volume simultaneously through
the water injection pipe. Because of the pressure and flow created, it will cause small, tight
fractures to joints in the rock to open and the water to flow freely, connecting to the nearby
water-bearing fractures and the bore hole.
Figure showing different types of casing

46
Hydro fracturing is done for easy production of methane. Generally coal has very less
permeability (< 3 md) which create problem in CBM production, but for easy production of
methane permeability should be >10 md .
After hydro fracturing water is taken out from the well by which a low pressure zone is created.
Due to pressure difference coal bed methane flows from zone of high pressure to zone of low
pressure.
Dewatering: The basic way of exploitation of CBM is dewatering the coal seam so as to
reduce its pressure. So by reducing the hydrostatic pressure the gas will flow from the seam to
the dewatered area and hence to the surface. There are three methods for exploitation
There are 3 important tools for dewatering:
 Progressive cavity pump (PC pump) - pumping abrasives with progressive cavity,
helical rotor, eccentric screw pumps often used to pump slurries. Helical rotor pumps
(also known as progressive cavity pump, eccentric screw pump, mono pump) use a
spiral rotor to move a chamber full of product through the pump. When moving slurries
it is critical that the rotor wipes the rubber firmly, else fine particles get between the
rotor stator & rip material out.

47
 The Sucker Rod Pump brings underground water and gas to the earth's surface. It is
driven by a motor which turns a flywheel with a crank arm. Attached to the crank arm
is a Pitman Arm which in turn, attaches to the Walking Beam. At the other end of the
walking beam is the Horse head. The Hanger Cable hangs off the Horse head, and is
attached with a clamp to a Polished Rod, which goes through a Stuffing Box and is
attached to the Rod String. At the bottom of the well a Traveling Valve, often just a ball
in a cage is attached to the Plunger at the end of the Rod String. Below that is another
ball in a cage, called a Standing Valve. This pump can lift oil 10,000 feet or more!
 In artificial lift, the oil is pumped up the tubing to the surface. A common artificial lift
technique is a beam pumper or sucker rod pump. An electric motor or gas engine on the
ground causes a steel walking beam to pivot up and down. Attached to the opposite end
of the walking beam is a long, small diameter steel rod called a sucker rod string.
Sucker rods come in twenty five foot lengths that are screwed together to form the
sucker rod string. The sucker rod string runs all the way down the well through the
tubing to the down hole pump on the bottom of the tubing. The walking beam causes
the sucker rod string to rise and fall. This activates the down hole pump which lifts the
oil up the tubing to the surface.
Air lift system
Our team in front of Sucker
Rod Pump at Moonidih CBM
Site, Dhanbad

48
Gas Production: Coalbed methane wells are completed open hole. Using this method,
casing is set to the top of the target coalbed and the underlying target zone is under-reamed
and cleaned out with a fresh-water flush. A down-hole submersible pump is then used to
move water up the tubing; the gas then separates from the water and flows up the annulus.
The natural gas and the water that are produced at individual wells are piped to a metering
facility, where the amount of production from each well is recorded. The methane then flows to a
compressor station where the gas is compressed and then shipped via pipeline. The water
produced is diverted to a central discharge point at a drainage or impoundment. Some of the
produced water is reinjected into nearby aquifers.
14. CBM Site Visit
Date: 15/10/2009, Thursday
Moonidih CBM well No. 3
Moonidih is 20km away from CIMFR, Dhanbad. At this site the borehole drilling was stopped
due to some technical problem and all the equipments for drilling were present at the site. We
were guided by Mr. Ramakrishna (CMPDI, Ranchi). Our faculty Dr. Harendra Singh (Scientist,
CIMFR, Dhanbad) also explained us about the drilling techniques and equipments used.
Moonidih CBM well No. 2
At this site CBM was under production. Coal seam was dewatered by using sucker rod pump
(SRP). The water was stored in a tank and the gas was supplied to another site by the use of
pipelines for the production of electricity. At this site the gas production was 2500m3
/day.
Gas production

49
Then we went to CBM electricity generation station which was nearby to the well no. 2. Here
electricity was generated from the CBM. The electricity generated was being supplied to the
nearby villages and area.
Drilling Rig (CROWN PRINCESS
CE35ODD)
Our team in front of Sucker Rod
Pump with Ram Krishnan sir and Dr.
Harendra Singh
Core Barrel Core Cutting Bit

50
Our Team with our Guide Dr. Harendra Singh in front of Drilling rig
An Electricity Generator

1.COALBED METHANE EXPLORATION AND EXPLOITATION_DPS.pdf

Recomendados

Recomendados

Mais conteúdo relacionado

Semelhante a 1.COALBED METHANE EXPLORATION AND EXPLOITATION_DPS.pdf

Semelhante a 1.COALBED METHANE EXPLORATION AND EXPLOITATION_DPS.pdf (20)

Último

Último (20)

1.COALBED METHANE EXPLORATION AND EXPLOITATION_DPS.pdf