INTRODUCTION TO ENERGY RESOURCES
Atomic Minerals and Fossil Fuels
R. DHANA RAJU
Former Associate Director
Atomic Minerals Directorate for Exploration and Research
Department of Atomic Energy, Govt. of India, Hyderabad – 500 016
and
Honorary Visiting Professor, Dept. of Applied Geochemistry,
Osmania University, Hyderabad – 500 007
6-3-124, Hastinapuri, Sainikpuri P.O., Secunderabad – 500 094
E-mail: [email protected]
CONTENTS
Part I – Atomic Minerals
Introduction
Radioactivity
Radioactive Minerals
Exploration for Radioactive Minerals
Major Deposit-types of Radioactive Minerals, with Indian Examples and Resources
High-tech Industrial Applications, supported by U, Th, Rare Metals and Rare Earths
Part II – Fossil Fuels
Coal - Lignite
Introduction
Classification and Constituents
Origin, Source Materials and Conditions of Accumulation-Formation
Uses
Major Producing Countries
Indian Scenario
Coal Bed Methane
Future Strategy
Oil – Natural Gas
Introduction
Constituents, Types and Properties of Oil
Origin of Oil and Gas
Features of Occurrence of Oil and Gas
Features of Oil-finding, Drilling and Production
Natural Gas and other Associated products
Uses of Oil and Gas
Indian Scenario
Future Strategy
Epilogue
Keywords: Atomic Minerals, Radioactivity, Radio-elements, Fossil Fuels, Coal- Lignite-Coal
Bed Methane, Oil-Natural Gas-Gas Hydrate, Indian Deposits, Uses.
Part I - ATOMIC MINERALS
1.0. INTRODUCTION
Atom is the smallest particle of matter that has the characteristic chemical properties of an
element. It has three fundamental subatomic particles, viz., proton, having unit positive
charge and mass number 1; neutron, having neutral charge and mass number 1; and electron,
having unit negative charge and negligible mass. Protons and neutrons of atom are
concentrated in central nucleus that has positive charge and almost all of the mass of the
atom. Because extra-nuclear electrons are equal in number to nuclear protons, atom is neutral.
Atomic energy is produced by fission (splitting of the radioactive-elements like uranium) or
by fusion (like colliding and fusing of two deuterons to form helium) of atomic nuclei, with
matter being converted into energy in either process.
Mineral is a naturally occurring inorganic substance, with fixed range in chemical
composition, and is usually obtained by mining. Atomic minerals are the minerals of radioelements – mainly Uranium (U) and Thorium (Th) -- and those in which these radio-elements
are in minor to trace amounts. These radio-elements are associated with major contents of
Rare Metals (RM) like niobium-tantalum (Nb-Ta), beryllium (Be), lithium (Li), zirconium
(Zr), etc., and Rare Earth Elements [REEs; lanthanum (La) to lutetium (Lu)]. As the radioelements exhibit the characteristic property of radioactivity (see below for details), the atomic
minerals are also generally known as radioactive minerals. Salient aspects of atomic minerals
are presented in Part I. These aspects include the following: (a) Radioactivity, naturally
occurring radio-elements, decay-series of Thorium and Uranium, their distribution in the
Earth’s crust and in important rocks types, their determination and radioactive anomaly, (b)
Atomic (Radioactive) Minerals, important geochemical processes governing their formation,
primary and secondary radioactive minerals, their location, diagnostic properties for their
identification and photomicrographs of important ones, (c) multi-disciplined methods for
exploration of atomic minerals, (d) type-deposits of atomic minerals in the world, with Indian
examples and resources, and (e) hi-tech applications of Uranium-Thorium (including the 3stage Nuclear Power Programme of India), Rare Metals and Rare Earths. A few selected
readings are suggested at the end for readers interested in knowing more details about atomic
minerals.
1.1. RADIOACTIVITY
Radioactivity is discovered in 1896 by Henri Becquerel (Fig. 1) and Pierro and Marie Curies
(Fig. 2). It is the property, possessed by certain elements of high atomic weight like Radium
(Ra), Thorium (Th) and Uranium (U), of spontaneous emission of radiations of alpha (α)
(42He2+) particles, beta (β) (high energy electrons, accompanied by neutrinos) particles and
gamma (γ) (high energy, short wavelength x-rays) rays due to the disintegration of the nuclei
of the atoms, e.g., 238U decays finally into 206Pb. These radiations are capable of penetrating
opaque bodies and can affect a photographic plate, even when separated by a thin sheet of
1
metal. Alpha particles have lower velocity, smaller penetrating power than other radiations
with their direction slightly changed by magnetic field. Betas are faster than alphas and their
direction is changed markedly by magnetic field. Gamma rays have the greatest penetrating
power, with velocity almost that of light, and their direction is not changed by magnetic field.
As the atoms of radioactive elements are not stable, they disintegrate at a definite rate,
measured by their half-life. The half-life of an element is the time required for radioactive
decay of one half of its mass. Each radioactive element has a characteristic half-life, a
constant that cannot be changed by any known means. By disintegration, elements of lower
atomic weight are produced from those with higher atomic weight. This constitutes a
“disintegration series”, in which the final element is a non-radioactive element.
Radioactivity may be induced in certain elements that are not normally radioactive, by
exposure to the action of bombarding particles as protons, deuterons or neutrons. By this, a
new species of radioactive atom, usually of short life, is, thus, formed, e.g., 90Sr and 137Cs.
Fig. 1. Henri Becquerel (18521908), the discoverer of
‘Radioactivity’. (Source: ‘The
Nuclear Age’ , by Jacques
Leclercq; Publisher: Le Chene, p.
16, 1986).
Fig. 2. Pierre and Marie Curies at work in their Laboratory. (Source:
Nuclear Age’ , by Jacques Leclercq; Publisher: Le Chene, p. 16, 198
1.1.1. Naturally-occurring Radio-Elements
Of the nearly 100 elements in the Periodic Table, only three, viz., Uranium [U - Atomic
Number (Z) – 92], Thorium (Th, Z – 90) and Potassium (K, isotope of mass no. 40, 40K,
constituting 0.012% of K) are the naturally occurring `Radio-Elements’. They generate,
respectively, 0.73, 0.20 and 27 x 10-6 calories/gm/year of radioactive heat in the Earth’s
lithosphere. This heat partly contributes to the Earth’s convection process that accounts for
much of its internal dynamic activity. Of these three elements, the content of U and Th in the
Earth and in different major rock types is generally very low, being in the range of a
few parts per million (ppm) or gram/ton (g/t).
Uranium and thorium are the members of the actinide (Ac) series. In the Periodic Table, U is
the first member of Group VI B and Th is the last element in Group IV B. Although both Th
2
and U are markedly oxyphile (close affinity to oxygen, amongst anions), they have also
biophile tendency. Due to this, they concentrate in organic compounds like humus, coal,
petroleum and bitumen. Thucolite is a mixture Th, U and C (carbon).
Thorium (Th), with atomic number 90, has 6 isotopes. Of these, the most abundant and
longest lived is 232Th that decays in a series of stages to yield ultimately 208Pb (Table 1). It
has a half-life of 1.39 x 109 years. The isotope, 232Th absorbs slow neutrons and is converted
to 233U. This, in turn, is fissionable and, hence, can be utilized as a nuclear fuel in breeder
reactors. This indeed is the third stage of India’s 3–stage nuclear power programme. Only one
principal oxidation state of thorium, viz., Th4+, is of importance. Th4+ undergoes extensive
interaction with water (hydrolysis) at pH >3.
Table 1. The Thorium – 232 (4n) decay series___
Element Isotope
Decay Constant (s-1)
Half-life
Radiation
_________________________________________________________________
Thorium
Radium
Actinium
Th232
90
88Ra
228
228
Ac
89
Thorium
90
228
Radium
224
88Ra
Rn220
Radon
Polonium
Lead
Bismuth
Th
86
Po
84
216
212
82Pb
Bi
83
212
212
Polonium
84
Thallium
208
81Tl
Lead
Po
Pb
82
208
1.39x1010 y
1.58x10-18
α, SF, γ
3.30x10-9
6.7 y
β, γ
-4
6.13 h
β, γ
3.10x10
1.91 y
-8
1.15x10
α, γ
3.64 d
2.20x10-6
α, γ
55.3 s
1.30x10-2
α, γ
0.158 s
10.64 h
60.5 m
-7
3.04x10 s
3.1 m
α
4.30
1.80x10-5
-4
1.90x10
6
2.30x10
3.70x10-3
β, γ
β, α, γ
α
β, γ
stable
_____________________________________________________________
SF: spontaneous fission
Uranium (U), with atomic number 92, is composed of 3 principal isotopes, viz., 234U
(0.0054%), 235U (0.720%) and 238U (99.275%). 235U, with a half–life of 0.713 x 109 years,
and 238U, with a half–life of 4.51 x 109 years, decay in a series of steps to yield ultimately
207
Pb and 206Pb, respectively (Tables 2 and 3). 235U undergoes fission (Fig. 3) with slow
neutrons and can sustain a chain reaction (Fig. 4) with release of enormous amount of energy.
235
U, on increased content from 0.72% to about 2.5–3%, constitutes the enriched fuel
for light water nuclear power reactors such as the Tarapur reactor. 238U, like 232Th,
absorbs slow neutrons to form 239U. This, in turn, decays to 239Pu (Plutonium) that can
sustain a fission reaction and, thus, can be used as nuclear fuel, like the one used in
many heavy water-moderated nuclear power reactors, such as at Kota, Narora,
Kakrapar, Kaiga etc. Of the oxidation states of U, U4+ and U6+ are of interest. U5+, as
(UO2)+, may be present in some natural waters and environments with a low oxidation
potential. The hexavalent state as the uranyl ion (UO2)2+ is the most stable oxidation
state. In nature, it is commonly reduced to the U4+ (UO2 – uranous) state and
precipitated as the oxide, UO2. Depending upon the availability of various ligands, U in
U6+ state precipitates as a member of complex hydrated oxides, hydroxides, silicates,
phosphates, arsenates, vanadates, molybdates, sulphates, selenites, tellurites and
carbonates,.
3
4
Fig. 3. Fission of
18, 1986).
235
U. (Source: ‘The Nuclear Age’, by Jacques Leclercq; Publisher: Le Chene, p.
Fig. 4. Chain reaction of U. (Source: ‘The Nuclear Age’, by Jacques Leclercq; Publisher: Le
Chene, p. 18, 1986).
Table 2. The Uranium – 235 (4n+3) decay series
______________________________________________________________________
Element
Isotope
Half-life
Decay constant(s-1)
Radiation
_____________________________________________________________
Uranium
Thorium
U235
231
Th
90
Protactinium 91Pa
Actinium
Thorium
0.71x109 y
92
25.6 h
231
3.4x10 y
227
Th
90
α, γ
6.50x10
β, α, γ
-7
18.7 d
223
β, γ
-13
10-9
21.6 y
α, SF, γ
-6
7.40x10
4
227
89Ac
3.10x10-17
4.35x10
-4
α, γ
22.0 m
5.20x10
β, α, γ
Radium
223
88Ra
11.4 d
7.04x10-7
α, γ
Radon
86
Rn219
4.0 s
0.17
α, γ
Francium
Astatine
Polonium
Astatine
Bismuth
Fr
87
At
85
215
84Po
215
Bi
215
Bi
211
83
Bismuth
83
84
Pb
Thallium
81
Lead
82
1.28x10
α, β
1.8x10-3 s
3.80x102
α, β
10 s
8.0 m
Po211
82
54.0 s
-2
-4
At
85
Polonium
Lead
219
211
Tl
β
-3
α, β, γ
2.15 m
5.35x10
0.52 s
1.32
4.8 m
Pb207
α
-3
6.90x10
1.44x10
36.0 m
207
3
α, γ
-4
β, γ
-3
β, γ
3.20x10
2.40x10
stable
_________________________________________________________________________
SF: spontaneous fission.
Table 3. The Uranium–238 (4n+2) decay series___________________
Element
Isotope
Decay constant(s-1)
Half-life
Radiation
_____________________________ __ ____________________________
Uranium
U238
92
234
Pa234
Thorium
90Th
Protactinium
91
Uranium
234
U
92
Thorium
230
90Th
Radium
88
Ra226
222
4.51x109 y
4.9x10-10
α, SF, γ
24.1 d
3.3x10-7
β, γ
6.7 h
2.84x10-5
β, γ
5
-14
2.48x10 y
8.9x10
α, SF, γ
8x104 y
2.75x10-10
α, γ
1.35x10-11
α, γ
1622 y
-6
Radon
86
Rn
3.82 d
2.07x10
α, γ
Polonium
218
84Po
3.05 m
3.8x10-3
α, β
Astatine
85
At218
1.35 s
0.51
Bismuth
Polonium
Lead
Bi
83
214
214
84Po
Pb
214
Pb
210
82
Lead
82
Bismuth
210
83Bi
α
-4
19.7 m
5.85x10
α, β, γ
1.64x10-4 s
4.25x103
α
26.8 m
21 y
5d
-4
4.3x10
-9
β, γ
1.05x10
β, γ
1.58x10-6
β
5
Polonium
Po210
138.4 d
5.7x10-2
α, γ
210
Tl
1.3 m
8.85x10-2
β, γ
Tl206
4.2 m
84
Thallium
81
Thallium
81
Lead
Pb
82
206
β
stable _____________________________________________
SF: spontaneous fission
1.1.2. Concentration of U, Th and Related Elements in the Earth’s Crust
The occurrence and concentration of different elements in the Earth depend mainly upon their
geochemical coherence, i.e., elements with similar or comparable chemical properties of
ionic radius, ionic charge, electronegativity etc., occur and concentrate together, just like
birds of the same feather flock together. Thus, U with its charge of 4+ and 6+, and
corresponding ionic radii of 0.89 and 0.73 Ǻ (1 Ǻ = 10-10 meter), and Th with its charge of
4+ and ionic radius of 0.99 Ǻ go together with elements of same or nearly same charge
and/or similar ionic radii. Such elements include Rare Metals (RM: Zr – Hf, Nb – Ta,
Be, Li and Sn) as well as the Rare Earths (RE : La to Lu, Y). During the evolution
of the Earth, much of all these elements, being incompatible with many other elements of
greater abundance, was expelled from the mantle and core, and concentrated in the
shallower crust. Accordingly, the crustal rocks of acid magmatic and their derived products
of sedimentary and metamorphic rocks contain higher concentrations of these elements. The
average abundance of U and Th in the Earth’s crust (upper part) is, respectively, about
2 and 8 ppm, with the value for Th/U being between 3 and 4. Their average
abundance in the deeper parts of the Earth, viz., mantle and core, is much less, since
all the three radio–elements [U, Th and K (40K)] concentrate progressively in the crustal
part.
1.1.3. U and Th contents in the Common Rock Types
In the common rock types, both U and Th prefer (i) acidic (with high silica content of
>62%), especially alkali (K and Na) – rich magmatic rocks; (ii) carbonaceous and
phosphatic sedimentary rocks and (iii) pyritiferous (FeS2) quartz-pebble conglomerate
and low–medium grade (Temperature ~ <350oC) metamorphic rocks of phyllites and
schists, with Th/U value ranging from <1 to 5. Like U and Th, potassium also is
relatively more in the crust (av. 1.2%). Recent investigations indicate 0.12% K in the
Earth's core, as an alloy with Fe. It, thus, contributes some radiogenic heat from core,
with much higher heat from the crust.
1.1.4. Radioactive anomaly is an abnormal content of radioactivity due to relatively higher
(~ > 4 times normal or threshold) contents of either U or Th, or even both in rocks.
Such anomalies are usually located by detecting radiation (usually gamma-sensitive due
to long range of penetration) with instruments, such as the Geiger–Müller (GM) Counter and
Scintillometer in the field, and Gamma–ray spectrometer in the laboratory.
1.1.5. Determination of Radio–Elements, viz., K, U, Th and total, in a sample from an area
of radioactive anomaly is carried out either by radiometric analysis, using gamma–ray
spectrometry, or chemical analysis. In the gamma–ray spectrometry, the intensity of peaks
of 1.46, 1.76, 2.62 and >0.1 MeV (energy), respectively, from K (40K), U (of its
daughter product, 214Bi), Th (of its daughter product, 208Tl) and total is counted as counts
per second (cps). The contents are obtained by comparing the cps of the samples with
6
those of the standards, containing known quantity of K, U, Th and total of all the
three. Accuracy of such estimates depends on ‘radioactive equilibrium’ in the radioactive
series, as it is based on the measurement of gamma or beta radiation from the daughter
products in the decay series of Th and U (Tables 1, 2), and not directly U or Th, since both
these are alpha-emitters. The decay series is said to be in radioactive equilibrium when the
various daughter nuclei of the family becomes constant, and each bears a fixed proportion to
the parent. Thus, by counting the beta or gamma rays emitted by some of the daughter
products of U or Th, the quantity of the parent in the sample is inferred. Since it is not known
whether the total radioactivity measured in a sample originated from U or Th or both, or from
any other radio-element and whether U in the sample is in radioactive equilibrium, it is
expressed as ‘equivalent (e) U3O8’. This means that the radioactivity of the sample is
equivalent to the radioactivity of a sample which contains the amount of U inferred by the
analysis. In other words, the sample in question should have contained that much actual U3O8
had the U present been in radioactive equilibrium with its daughters and no Th is present.
Thus, eU3O8 value could be less than, equal to or greater than the actual U3O8 content,
depending upon the state of equilibrium of the U-series and/or presence of Th. As daughters
of Th have short half-lives, Th is almost always found in equilibrium. The disequilibrium, if
any, in a sample is due to U. This radioactive disequilibrium is of two kinds, viz., one in
favour of daughter-products of U and the other in favour of parent U. For example, if U gets
leached away from an old deposit, the gamma-activity shows practically no change and the
eU3O8 content will be much higher than the actual uranium content. On the other hand, if U
were deposited recently in a locale, gamma-activity will be very low and the eU3O8 content
of a sample from this deposit will give a value much lower than the actual content of
uranium. In view of these possibilities, it is desirable to analyze uranium content chemically.
It may be noted that U3O8 is a stoichiometric material of U4+O2 + 2 U6+O3, and not a
compound.
Chemical analysis for U is done by various techniques like gravimetry, volumetry,
colorometry and fluorimetry; of these, the last using a laser (laser fluorimetry) is versatile
and normally adopted for even very low concentrations at parts per billion (ppb - 10-9
gm) level, as in water samples.
1.2. ATOMIC (RADIOACTIVE) MINERALS
Atomic or radioactive minerals are discrete minerals of uranium and/or thorium, as
exemplified by uraninite (of U) and thorite (of Th). Besides, they include those in which
either U or Th or both occur in notable quantity, like the minerals of Rare Metals (NbTa, Li, Be, Sn, W etc.) and Rare Earth Elements (REE: La to Lu, Y).
1.2.1. Geochemical Processes in the formation of Atomic (Radioactive) Minerals
Geochemical processes play an important role in the formation of minerals. Geochemistry of
U is more complex than Th. This is due to the following properties and tendencies of U, as a
result of which U interacts and associates with many elements and compounds in complex
ways:
(i) different oxidation states, mainly U4+ and U6+;
(ii) variable large size cell units permitting U4+ substituting for many elements of similar
ionic radii, largely Th and to a limited extent Ca, Zr, Ti, W, Mo, Nb, Ta and REE; the latter is
seen predominantly in accessory minerals in rocks;
7
(iii) U-phases hydrolyze in the presence of solutions;
(iv) high chemical reactivity of U6+, due to which U forms complexes with a variety of anions
in aqueous solutions;
(v) relative solubility of U6+-compounds in aqueous solutions, compared to the relative
insolubility of U4+-compounds; and
(vi) adsorption tendency of U on clay, organic and other particles, or on certain hydroxides of
Fe, Ti, Zr etc.
In view of the above geochemical processes, uranium forms a major constituent in many
minerals of its own. The bulk of them are of U6+-compounds, formed in oxidizing
environment. Only a few are of U4+-compounds, formed in reducing environment. With
increasing oxidation potential, U4+ transforms into U6+, while U6+ changes to the U4+ in the
presence of reductants like sulphides and carbonaceous matter.
U4+ in natural minerals has predominantly the coordination number 8, i.e., it forms a central
cation, surrounded in equidistance by eight anions (normally oxygen and fluorine), with ionic
radius of U4+ being 1.01 Ǻ. Furthermore, it occurs with coordination number 6, when it has
ionic radius of 0.97 Ǻ (Figs. 5A and B). The U4+-state prevails in magmatic and metamorphic
environments, and gets concentrated in hydrothermal conditions. It forms the principal ore
minerals of uraninite and pitchblende. These two crystallize in cubic system and are of the
formula UO2+x. Pure U4+O2 phase does not exist in nature due to self-oxidation during
radioactive decay.
Uraninite, compared to pitchblende, forms at relatively higher
temperature, has a higher lattice constant (a0 > ~5.46 Ǻ) and lower oxidation state, and
generally contains Th, REE, Pb and other elements. Pitchblende, the fine-grained
(cryptocrystalline), colloform variety of uraninite, has a0 of 5.36 to ~5.465 Ǻ and may
accommodate elements like Ca, Si, Ti and Pb, but rarely Th and REE. Other common U4+minerals formed under reducing environment are coffinite [U (SiO4)1-x(OH)4x] and thucolite
(organic complex containing Th, U and C).
U6+ occurs in minerals in two configurations, viz., as individual ion with coordination number
6 and an ionic radius of 0.80 Ǻ, and as uranyl complex ion. The latter is more frequent and
forms many mineral species in oxidizing environment. The uranyl complex [(UO2)2+]
develops in aqueous solution, as per the following formula:
U4+ + 2H2O ↔ (U6+ O2)2+ + 4H+ + 2e
The uranyl complex displays a linear dumb-bell shaped structure, 3.4 Ǻ long and 1.4 Ǻ
wide, in which U6+ is flanked by two oxygen ions (Fig. 5C). This complex is stable in
oxidizing environments and forms minerals with layered structure of the basic formulae,
A(UO2)(RO4)-.xH2O or B(UO2)(RO4)2-.xH2O,
where, R is P5+, V5+ or As5+, A is K or Na and B is Ba, Ca, Cu, Fe2+, Mg, Pb.
Furthermore, the uranyl ion forms hydrous minerals with MoO4, SO4, CO3, SiO3, SeO3 and
TeO3 as anions and a variety of cations. The cations are not strongly bonded and can be
substituted easily. The H2O component indicates the necessity of a hydrous environment for
the formation of uranyl minerals and their instability when the water gets expelled, for
example at elevated temperatures. In contrast to the uranous (U4+) ion, a diadochic
incorporation of the uranyl complex into other crystal structures is not possible due to the
following two reasons:
8
Fig. 5 A, B and C - Uranium in six-fold coordination with central cation (filled circle, U) surrounded by
six anions (open circles, F); B: Uranium in eight-fold coordination with central cation (filled circle, F),
surrounded by eight anions(open circles, F); C: Dumb-bell shaped uranyl [(UO2)2+] ion.
a) the dumb-bell-shaped morphology is incompatible with the structure of other minerals
constituting complex ions; and
b) the uranyl complex is unstable at elevated temperatures as in magmatic and high-grade
metamorphic environments.
The common uranyl minerals in oxidizin55
g environment are vanadates (e.g., K-bearing carnotite and Ca-bearing tyuyamunite),
phosphates (e.g., Ca-bearing autunite and Cu-bearing torbernite), silicates (e.g., Ca-bearing
uranophane), carbonates and arsenates.
Under ultraviolet light of suitable wavelengths (2537 Ǻ, 3660 Ǻ), some of the uranyl
minerals, especially the yellow, green or greenish-yellow coloured vanadates, phosphates,
carbonates, arsenates and sulphates, fluoresce to variable degree, and emit a yellow-green
fluorescence colour. The non-fluorescent uranium minerals include all uranous minerals
(oxides, silicates, etc.) that are black, brown or drab-gray in colour.
In some phosphate minerals like apatite, U4+ (0.97 Ǻ) replaces Ca2+ (0.99 Ǻ), and the charge
difference between these two is compensated by partial replacement of (PO4) by (CO3) or
(SO4), as shown below:
Ca5 F -1 [(PO4)3]-9 = Ca4 U4+ F-1 (PO4)-9 (CO3)-2
9
Both uranous and uranyl ions are strongly adsorbed by many inorganic and organic
substances, possibly due to their large size and high charge density. Hydrous gels or
hydroxides of Fe, Mn, Ti, Zr, Si, Al and Mo, zeolites, clays, clay-humic complexes and
humic substances adsorb uranium. Sorption capacities of both organic and inorganic matter
appear to rise with increasing pH values to ~ 8.5, with maximum adsorption in the pH range
of 4.5-7.5 for the former and 4.5-7.5 for the latter.
In contrast to U, Th-mineralogy is relatively simple as only one principal oxidation state of
thorium (Th4+) is of importance. Th commonly replaces Zr in zirconium minerals; Y, Ce and
other REEs in most RE-minerals; and U in certain U-minerals, under conditions of relatively
higher temperatures.
1.2.2. Primary and Secondary Atomic (Radioactive) Minerals
Radioactive minerals are broadly divided into primary and secondary discrete minerals of U
and Th, and nearly 200 such minerals are known. The primary minerals are those formed
directly from magmas, hydrothermal solutions and groundwater. Secondary minerals are
formed due to remobilization of elements from primary minerals, their transportation in
solution and later precipitation due to over-saturation in oxidizing or supergene (surface or
shallow-surface) environment. The most common primary minerals of uranium are
uraninite (pitchblende, if microcrystalline) (oxide), coffinite (silicate) and brannerite
(complex oxide). In these, U occurs mostly in U4+ state, besides some U6+ in pitchblende.
Secondary minerals of uranium occurring in supergene conditions are many (~180) in
which U occurs entirely in the U6+ state. These include various oxides and hydrated
oxides, silicates, vanadates, carbonates, sulphates, molybdates, phosphates and
arsenates, and their complex derivatives. The most common primary minerals of
thorium are thorianite, thorouraninite (oxides) and throite/uranothorite (silicates). A few
secondary (supergene) minerals of Th are known, the most common being
thorogummite.
1.2.3. U- and Th-bearing Accessory Minerals
U and Th in notable contents (≥1%) occur in a large number of rock-constituting
accessory minerals, such as zircon, apatite, allanite, sphene, rutile, monazite and
xenotime. Alpha emission of the uranium may render some of these minerals metamict by
destruction of the internal order of their original crystalline structure (mostly to a limited
degree and very rarely completely). U, as a substitutional ion, occurs in about 20
uranium niobates, tantalates and titanates, the notable ones of which are betafite,
davidite, euxenite, samarskite, columbite–tantalite and pyrochlore.
Important
properties
of
radioactive
contents of U and Th, are given in Table 4.
minerals,
including
their
maximum
Table 4. Some Important Properties of the Common Atomic Minerals ___________
Sl. Mineral
*Up to Colour
No. (Formula) %U %Th
1. Uraninite
88
H
45 Brown 5.5
Specific Crystal
Gravity System
Opaque,
Remarks
Transparent or
Transluscent________________________________
A. Oxides
9-9.7 Isometric Opaque
10
Contains Pb,Zr,REE,N,He,Ar,Ca
Pitchblende
(U4+U6+)O2+x
88
2. Thorianite
44.6
(Th,U)O2
3. Brannerite
43.6
(UCaCeTh) (TiFe)2
4. Fergusonite
7.2
(NbTaTi)O4
-
Black
88 Black
≤ 4 < 6.5 Cryptocry- Opaque
stalline,
Amorphous
6.5 9.3 Isometric Nearly
opaque
4.5 4.5-5.4 Monoclinic Opaque
47.5 Black
(O,OH)6
6.0 Brownish 5.5-6 5.8
black
Tetragonal Sub-transluscent to
Opaque
5. Samarskite
16.6 3.7 Velvet
5-6 5.6-5.8 Orthorho- Nearly
(YCeUCaPb)(NbTaTi)2O6 black
mbic
opaque
6. Betafite
24.5 1.1 Greenish 5
4
Isometric Opaque
(CaNaU)2 (NbTaTi)2 O6(OH) black
7. Pyrochlore- 17.1 5.5 Brown 5-5.5 4.2-4.36(py) -do- Sub-transMicrolite
(reddish/
5.5(Micr) -do- luscent to
[(NaCaCeU)2 (NbTaTi)2 (O,OH,F)7]
opaque
B. Silicates, Phosphates, Carbonates, Vanadates
Th &REE absent;Ca,H2O present
(both with Pb,Ag,Co,Ni,Cu,Fe,
Zn sulphides)
High temperature formation
Refractory
High temperature,(YCeFeU)
refractory
Sn,W in small amounts; high
temperature, refractory
Refractory
Refractory
-do-
8. Coffinite
60.2 - Black
~3.5 ~4.5 Tetragonal Opaque
Low temperature
(USiO4)1-x (OH)4x
9. Thorite
10.1 64.1 Black 4.5-5 4.5-5 Tetragonal Isotropic
(ThSiO4) .
10. Zircon
2.7 13.1 Colourless 7.5 4.2-4.86 Tetragonal Transparent Contains HfO2(up to 4%),
(ZrSiO4)
yellow,
sub-translu- REE, produces pleochroic
green
scent,opaque haloes in host minerals
11. Allanite
2.95 4.35 Brown to 5.5-6 3-4.2 Monoclinic Sub-tranProduces pleochroic haloes
(CeCaYTh)2(AlFeMg)3 black
sluscent
in biotite
(SiO4)3(OH)
to opaque
12. Uranophane 55.6
Yellow
2-3 3.81-3.90 OrthorhTransspaMassive,
fibrous (in granite)
[Ca (UO2)2 Si2O7. 6 H2O]
rhombic
rent
13. Xenotime
3.6 2.2 Yellowish 4-5 4.45-4.56 Tetragonal Opaque
HREE,especially Er, in large
(YPO4)
brown, fleamount; U,Th & Si present
sh red, yellow
14. Monazite 0.1 26.4 Hyacinth- 5-5.5 4.9-5.3 Monoclinic Sub-trans- LREE,Th,Si (Th-silicate in
(CeLaNdTh) (PO4,,SiO4) red, Yellowish
parent-tra- solid solution with Cebrown
nsluscent
phosphate)
15. Torbernite 47
Emerald- 2-2.5 3.2 Orthorhom- Transpa- As may replace P; forms in
Cu(UO2)2 (PO4)2.
& Grassbic-Pseudo- rent-Subair at <100oC; dehydrates to
8-12 H2O
Green
tetragonal transluscent meta-variety
16. Autunite 50
Lemon- to 2-2.5 3.1 Orthorhom-, TranspaSecondary in origin; someCa(UO2)2(PO4)2.
Sulphurbic, nearly
rent to tra- times with ores of
10-12 H2O
Yellow
tetragonal nsluscent
Ag, Sn, Fe
17.Meta-uranocircite 47 - Yellow2
3.5
-do-do-doBa(UO2)2 (PO4)2. 8 H2O green
18. Carnotite 55
Yellow
~2
~4
Orthorhombic
As yellow crystalline masses/
K2(UO2)2 (VO4)2. 3 H2O
powder in quartzose rocks
19.Tyuyamunite 54.1 - Yellow Soft 3.7-4.3 -doAs scales, crystalline or
Ca(UO2)2(VO4)2. 5-8 H2O
earthy masses____________
*Data from Boyle (1982). H: hardness (in Moh’s scale)
1.2.4. Location and Identification of Atomic (Radioactive) Minerals
As the Atomic or Radioactive Minerals (RM) usually occur in very low content (<1%) in
rocks, they are difficult to locate and identify by normal megascopic and microscopic
techniques; these are used in identification of rock–forming minerals that occur in major
to minor quantities (>1%). However, the intrinsic property of radioactivity resulting in
11
spontaneous emission of alpha – beta particles and gamma rays of RM is taken
advantage of for their location as well as estimation of the contents of eU, U and Th.
Thus, location of RM in a rock sample is done by the technique of `radioluxography
(RLX)’ or `solid state nuclear detection (SSNTD)’; the latter is a modified and easy
version of the former. In RLX, either an even surface or a thin (polished – thin)
section of a rock specimen is exposed in a dark room for generally about 3 days to a
high – speed (usually 400ASA) photographic film. In this, the film is placed over the
specimen with silver-activated zinc sulphide phosphor screen in between the two,
using rubber bands to hold them together tight. Before exposing, an indicator (U6+bearing solution prepared from uranyl or secondary U–minerals) is put as small
differently- shaped spots in different corners of specimen so as to get back the original
position of the two during exposure, thus facilitating easy matching. After exposure,
the film is developed and dried, when black spots appear. These are formed due to
bombardment of alpha particles from radioactive minerals in the specimen. By
matching these spots with the help of indicator, the exact location of radioactive
minerals in the specimen is noted. As the yield of alpha radiation is directly
dependent on the contents of U and Th that produce the black spots on the film, the
intensity of blackness of spots is a measure of amount of radioactivity of RM. In the
SSNTD technique, instead of photographic film an alpha–sensitive cellulose nitrate
film (Kodak CA 850) or coating on a plastic film (Kodak LR 115 Film) is used and
exposed in a laboratory without the necessity of a dark room. After exposure, the
film is etched in 10% Na-/ or K- hydroxide solution at about 30 – 40oC on a hot plate
for about 30 minutes, when tracks (formed due to bombardment of alphas from RM)
are recorded. The density of the alpha tracks in unit area is directly proportional to
the contents of U and Th, or intensity of radioactivity. These tracks help in both
location of the RM with its shape and indication, at least qualitatively, of the intensity
of radioactivity in them. After locating the RMs, their identification is carried out
under a microscope, based on their optical properties, like colour, relief, pleochroism,
internal reflections, reflectivity and micro-hardness. Generally, the above methods are
used for identification of primary minerals. For secondary and metamict (crystal-structure
damaged due to bombardment of radiation from RM) minerals as well as primary minerals,
the technique of X-ray diffraction (XRD) is used; for this, RMs are pre-concentrated, using
heavy liquids and magnetic method.
1.3. EXPLORATION FOR ATOMIC (RADIOACTIVE) MINERALS
1.3.1. Nature of Exploration
Exploration for atomic (radioactive minerals, RM) encompasses diverse techniques in the
disciplines of geology, geophysics, geochemistry, geostatistics, remote sensing, aerial
surveys, instrumentation physics, analytical chemistry, ore petrology, mineral technology,
survey, drilling and exploratory mining. These are carried out as field- and laboratory-based
investigations. They are simultaneously undertaken, starting from regional level and
ending with establishment of an economically workable mineral deposit.
1.3.2. Uranium: Compared to the exploration for other metals, like Fe, Mn and Al with grade
of ~30-70%, exploration for uranium is unique in that even very low concentrations of ~0.1%
U3O8 are economical to work. Based on geological setting and multi-disciplinary evaluation,
sites selected. These are integrated with their radioactivity. Such radioactive sites are
12
explored for RM. The investigative methodology adopted in exploration for RM is given in
Figure 6.
Fig. 6. - Multi-disciplinary Exploration-sequence for Atomic (Radioactive) Minerals.
1.3.3. Thorium : For establishing Th-mineralisation in the form of monazite as well as
its associated placer minerals, like ilmenite, rutile, zircon, garnet, sillimanite etc.,
drilling is carried out on sand deposits; these are mainly coastal, like on the east and west
coasts of India, and minor inland, like in Tamil Nadu.. Such deposits are drilled in both the
dry zone (i.e., above water table) and wet zone (below water table), and even in a
lake-bed. Following a methodology for field-based exploration of placer heavy minerals,
sand
samples
are
collected
at
regular intervals for subsequent estimation of heavy mineral resources. For this,
representative sand samples are subjected to mechanical analysis by sieving into different sizefractions. This is followed by (i) magnetic and heavy media (bromoform) separation of
13
each sieved fraction and (ii) estimation of the wt.% of different heavy minerals,
including Th-bearing monazite, in such sieved fractions by microscopic- or XRF-analysis.
Using the bulk density of the ore and the sub-surface data on the areal extent and grade
of mineral content, the ore reserves in different blocks of a deposit are estimated,.
They are expressed under different categories of proved (or measured, with confidence level
of 90%), indicated (75%) and inferred (50%) reserves. A suitable flow-sheet is established
by repetitive ore dressing operations on the Run-Of-the Mine (ROM) ore. These
operations are undertaken from laboratory- to industrial-scale, through the intermediate scale
of pilot–plant.
1.3.4. Rare Metals-Rare Earths: In prospecting for RMRE deposits, mobile ore dressing
plants are operated in the field to pre-concentrate rare metals like Nb-Ta, and Y, and
heavy REE-bearing xenotime and light REE-bearing monazite in the gravel; this preconcentration is carried out before final industrial-scale recovery.
1.3.5. Mining: After establishing a deposit, it is to be mined. The mining is carried out first
on an exploratory scale and then on industrial scale, either by open-cast or
underground methods. Selection of these methods depends upon various factors, like
depth of mineralisation, its grade and tonnage, ore-characteristics, available infrastruc-ture in
the area and environmental-ecological considerations. The ore obtained, thus, is treated on
an industrial scale in a mill for recovery of metals like U. The mill can be located
either close to the mining area as in the case of the underground uranium deposits at
Jaduguda and nearby locales in the State of Jharkhand, and open-cast mining of
monazite (Th)-bearing coastal sands as at Chhatrapur in Orissa, or at a farther distance. The
decision depends upon the environmental, ecological, infrastructural, socioeconomic and
related factors of the area of mining.
1.4. MAJOR DEPOSIT-TYPES OF ATOMIC (RADIOACTIVE) MINERALS, WITH
INDIAN EXAMPLES AND RESOURCES
1.4.1. Occurrence of Atomic (Radioactive) Minerals in diverse Rock types
Radioactive minerals occur in very low abundance (usually <1%) in different rock types,
viz., in (i) magmatic or igneous rocks (rocks formed from a silicate melt, called
magma, like that flowing out from a volcano); (ii) sedimentary rocks (rocks formed by
consolidation
of
detrital
material
like
sands,
silt,
clay
or
chemical/biological precipitation like lime, iron, sulphate etc.; and (iii) metamorphic rocks
(formed by transformation of magmatic and sedimentary rocks) of low- to mediumgrade (due to varying temperature and pressure) like phyllites and schists (Figs. 7 a to
h). In the magmatic rocks, they usually concentrate in acidic (SiO2 ~ >62%) plutonic
(deep – seated) rocks, which include granitoids – pegmatites, and volcanic rocks, like
rhyolites and acid tuffs. Radioactive minerals like monazite and zircon also occur in placers,
derived from such magmatic rocks. Amongst the sedimentary rocks, sandstones, pyritebearing quartz–pebble conglomerates and phosphatic and carbonaceous rocks are good
hosts for uranium minerals. Low–and medium-grade (low-medium temperature, ~
<350oC) metamorphic rocks like phyllites and schists, subjected to metasomatic
alterations involving addition of volatiles (H2O, OH, F, Cl, CO2 etc.) within
14
structurally weak zones, are the loci for uranium minerals. Accordingly, terrains with
these rocks are usually explored for uranium minerals. Thorium minerals occur
generally in acidic igneous rocks and high-grade (granulite facies) metamorphic rocks, and
placers derived from these rocks.
15
Fig. 7. - Some important atomic (radioactive) minerals in different magmatic, sedimentary and metamorphic rocks. (a
bearing uraninite (U), rimmed by pyrite (P) in the biotite granite from Binda-Nagnaha, Bihar; (b): Th-poor uraninite (me
grey with fractures) associated with pyrite (white) in the basement granite at Lambapur, Andhra Pradesh; (c): Pitchblend
associated coffinite (C), pyrite (Py) and galena (G), in the biotite granite from Gogi, Karnataka; (d): Coffinite (C) as v
associated with pyrite (P) in the fluorite-bearing biotite granitoid from Jajawal, Chhattisgarh; (e): Thucholite [Th-be
uraninite (U) with fractures and borders occupied by carbonaceous matter (C)] in mica-quartz schist from Arbail- Dab
Karnataka; (f): Uraninite (U) and sulphides [pyrite (P) and chalcopyrite (Cp)] as veins in the biotite-chlorite-quartz schist
Bagjatha, Jharkhand; (g): Pitchblende (P) with pyrite (Py) in sandstone from Domiasiat, Meghalaya: and (h): Xenotime gr
separated from the riverine placers along the Siri river, Chhattisgarh. (all in reflected light with 1 Nicol) (Source: ‘Radioa
Minerals’, by R. Dhana Raju; published by Geol. Soc. India, Aug. 2005, 65p.).
16
1.4.2. Major Types of Uranium Deposits in the World
Based upon the geological setting and economic significance, the International Atomic
Energy Agency (IAEA) has classified the following fifteen types of uranium deposits, in
decreasing order of importance:
1. Unconformity-related; 2.Sandstone; 3. Quartz-pebble conglomerate (QPC);
4. Veins (Hydrothermal); 5. Breccia Complex; 6. Intrusive; 7. Phosphorite;
8. Collapse Breccia Pipe; 9. Volcanic; 10. Surfacial; 11. Metasomatite;
12. Metamorphite; 13. Lignite; 14. Black Shale; and 15. Other types.
1.4.3. Indian Uranium deposits: Of the above 15 types, the types of U-deposits established
so far by AMD in India are: (i) hydrothermal (vein and disseminated), (ii) sandstone, (iii)
unconformity-proximal, (iv) stratabound, carbonate-hosted (rare) and (v) albitite, while QPC
and phosphorite types occur at prospect level. These different types of U-deposits, with
variable tonnage and usually of low grade (<0.1% U3O8), occur in different states of India
(Fig. 8). Their notable features are given in the following.
Fig. 8. - Geological map of India showing Atomic (Radioactive) Mineral Deposits* and important occurrences,
legend of Geology (I) and Deposits/occurrences of U (II), Th (III) and Rare Metal-Rare Earths (IV).
17
1.4.3.1. Hydrothermal (Vein and Disseminated) type: This type accounts for much of the
uranium resources in the country. It mainly occurs in the Singhbhum shear zone (SSZ) in the
State of Jharkhand and to a limited extent at Gogi in the State of Karnataka. The
hydrothermal type in SSZ is both of vein and disseminated type. It is hosted mostly by lowgrade metamorphic (schistose) rocks containing major rock-forming silicates of
chlorite, sericite, biotite, quartz and occasionally tourmaline.
Other host rocks include
apatite-magnetite rock and quartzite. The major uranium mineral is uraninite with minor
pitchblende and brannerite; these are associated mainly with sulphides like pyrite,
18
chalcopyrite, bornite, molybdenite etc., and Fe-Ti oxides like magnetite and ilmenite. The
mineralisation is accompanied by wall-rock alterations, represented by chloritisation,
sericitisation and epidotisation. It is controlled mainly by structure (shear zone, cross-folds
etc.), lithology and metamorphism-metasomatism. The average grade of U varies from
~0.035 to 0.065% U3O8 in various deposits within SSZ. These include the deposits at
Jaduguda, Narwapahar, Turamdih, Bhatin, Mohuldih and Bagjatha, with each containing a
few hundreds to thousands of tonnes of U. Besides, U is recovered as a by-product of copper
from the tailings of the copper deposits at Ghatsila and Rakha in the southeastern part of SSZ,
while Ni and Mo are recovered as by-products during extraction of U at Jaduguda.
At Gogi, the hydrothermal vein type deposit is of low-tonnage (~3000 t) but of the highest
grade (~0.2% U3O8) so far identified in India. It occurs in both the basement biotite granite
and its overlying limestone, respectively, ~50 m both below and above the unconformity, in
the late Proterozoic (~1000-570 Million years or aeons, My or Ma) intracratonic Bhima basin
in Karnataka. The major U-minerals are pitchblende and coffinite. These are intimately
associated with organic matter and sulphides like pyrite, chalcopyrite, galena and
arsenopyrite. It is controlled mainly by structure (fault zone). In this deposit, there is a
possibility of recovery of Ag as a by-product of U. Similar hydrothermal vein type uranium
mineralisation along the fractures of Gulcheru quartzite in the Cuddapah basin of Andhra
Pradesh is under exploration; in this, gold, in association with U, is reported.
1.4.3.2. Sandstone type: The sandstone type uranium mineralisation occurs in (i) the Upper
Cretaceous (~100 Ma) Mahadek sandstone in the Domiasiat-Wahkyn area in the State of
Meghalaya and (ii) the Neogene ((~<35 Ma) Siwalik sandstones along the foothills of
Himalaya in the States of Himachal Pradesh, Uttar Pradesh, Uttaranchal and Jammu &
Kashmir. The former is established as a medium-tonnage deposit with an average grade of
~0.1% U3O8. Its major primary uranium minerals are coffinite and pitchblende, associated
with organic matter and sulphides, like pyrite and chalcopyrite.
1.4.3.3. Unconformity-proximal type: This occurs in the Lambapur-Peddagattu-Chitrial
area in Andhra Pradesh. It occurs in the northeastern part of the intra-cratonic middle
Proterozoic (~1700-1100 Ma) Cuddapah basin, on either side of the unconformity between
the basement biotite granite and its overlying Srisailam/Banganapalle quartzite. The uranium
mineralisation is hosted by both the granite (~80%) and quartzite (~20), along their
structurally weak zones. It is in the form of uraninite and lesser coffinite, associated with
sulphides. This deposit is of medium-tonnage with grade in between 0.05 and 0.1% U3O8.
1.4.3.4. Stratabound, Carbonate-hosted type: This deposit is hosted by phosphatic
siliceous dolostone of the Vempalle Formation, along the southwestern margin of the
intracratonic Cuddapah basin in the State of Andhra Pradesh. It is rather a rare deposit since
carbonate rocks are considered as unfavorable hosts for U. This is because of the soluble
nature of uranyl bi-/tri-carbonate complex, and in this form, U is normally transported. This
deposit extends for ~160 km in length with a width of ~100-150 m. It is a low-grade
(~0.045% U3O8) but large-tonnage (>15,000 t in ~6 km strike-length) deposit. The major
uranium minerals are pitchblende and coffinite; these are associated with cellophane
(phosphate) and silicate minerals, like quartz and feldspars. Molybdenum and vanadium, each
of ~200 ppm, can be taken as by-products during extraction of U from this deposit.
1.4.3.5. Albitite type: This appears to be a potential type. It occurs in the Rohil-GhateswarKhandela area in the State of Rajasthan. The uranium mineralisation occurs in diverse rock
19
types that are albitised along structurally weak zones. The primary uranium minerals like
uraninite are intimately associated with notable content of a host of sulphides of copper and
molybdenum. There is a possibility of recovering Ag as a by-product of U from this deposit
that is still under detailed exploration.
1.4.3.6. Other types: These include: (i) The pyriteferous quartz-pebble conglomerate (QPC)
type at the base of the Dharwar Supergroup and overlying the Archaean basement at
Walkunji and Chickmagalur, and similar type but hosted by meta-arenite at Arbail and
Dabguli, all in the State of Karnataka. U-mineralisation in these is in the form of mainly
detrital Th-bearing uraninite, thucolite, brannerite and thorite. These U-Th minerals are
associated with sulphide and oxide ore minerals. (ii) The phosphorite type in the Mussorie
area in the State of Uttaranchal and Mardeora in the State of Uttar Pradesh; from these, U can
possibly be recovered as a by-product.
Since the Proterozoic intra-cratonic basins like the Cuddapah and Bhima host diverse types of
U-deposits with notable tonnage and grade, detailed exploration by AMD is being carried out
in other similar basins like the Chhattisgarh, Gwalior, Vindhyan, Kaladgi-Badami, Pranhita
Godavari and Abujhmar.
1.4.4. Thorium deposits
Thorium deposits, containing the Th-bearing mineral, monazite (associated with other placer
minerals like ilmenite, rutile, zircon, garnet and sillimanite), occur at many places along the
East and West Coasts of India (Fig. 8). Notable ones of these coastal heavy mineralsand deposits are at Chhatrapur - Gopalpur in Orissa, Bhavanapadu –Kalingapatnam Srikurmam - Bhimunipatnam in Andhra Pradesh, Manvalakurichi (besides Teri inland
placers) in Tamil Nadu, Chavara in Kerala and Ratnagiri in Maharashtra.
1.4.5. Rare Metal - Rare Earth deposits
Deposits of rare metal minerals, viz., columbite-tantalite (for Nb-Ta), cassiterite (Sn),
spodumene-lepidolite (Li) and beryl (Be), occur mainly in the pegmatite belts of Bastar
(Chhattisgarh)-Malkangiri (Orissa), Marlagalla (Karnataka) and in parts of Bihar, Jharkhand
and Rajasthan (Fig. 8). Besides, Nb-Ta prospects, in the form of pyrochlore-microlite, occur
in the carbonatites of the Sung Valley (Meghalaya) and Sevattur (Tamil Nadu).
Deposits of Rare Earths, in the form of the minerals, xenotime and monazite, occur in the
riverine placers of the Siri River in the Jashpur district (Chhattis-garh) and Deo River
in the Gumla district (Jharkhand), besides in the apatite (RE-bearing)-magnetite veins at
Kanyaluka, Singhbhum district (Jharkhand) (Fig. 7).
1.4.6. Atomic (Radioactive) Mineral Resources in India
AMD, by its multi-disciplinary, -faceted and -dimensional exploration activities spread
over all parts of our country, has established during the last 57 years the following
resourcesof radioactive, rare metal and rare earth minerals and placer heavy minerals.
20
.Atomic Mineral Resources of India (Sources: Chaki, 2007; Chandrasekharan, 2007; Dhana Raju, 2007) Uranium Reserves,
proved by AMD in India (up to the Field Season, 2006-2007): 1,07,268 t U3O8, with the following break-up:
1.
Vein-type:
60,811 t
2.
Sandston-type:
18,172 t
3.
Unconformity-proximal type:
13,490 t
4.
Stratabound, dolostone-hosted type: 14,795 t
Total
1,07,268 t
Resources of Thorium, Thorium-bearing Monazite and Other Heavy Minerals in Mineral-Sands:
1.
Thorium:
0.9 to 1.0 Million tonnes (Mt)
2.
Th-bearing Monazite: 10.21 Mt (~36% world resources)
3.
Ilmenite:
4.
461 Mt ( ~16%
-do-
)
Rutile:
27 Mt (~15%
-do-
)
5.
Zircon:
28 Mt (~5%
-do-
)
6.
Garnet:
150 Mt (meets ~30% world requirement)
7.
Sillimanite:
190 Mt
________________________________________________________________________________________________
Uranium: As noted earlier, almost all the uranium deposits, barring possibly the Gogi
deposit, established so far are of low-grade [(<0.1% U3O8), as per the International
standard]. U-reserves of 1,07,268 t U3O8 under measured (proved, with ~90% confidence
level), indicated (~70%) and inferred (~50%) categories are identified so far by AMD. Of
these, the major chunk of 60,811 t is from vein-type, 18,172 t from the sandstone-type,
13,490 t from the unconformity-proximal type and 14,795 t from the stratabound, carbonatehosted type (Chaki, 2007). Uranium mineralisataion in these deposits is mostly in the form of
uraninite, pitchblende, coffinite and brannerite/U-Ti oxide. It is associated primarily with
many sulphides, organic matter and Fe-Ti oxides. There is a possibility of recovering some
high-value metals like silver, gold, molybdenum and vanadium as by-products during
processing of these ores for extraction of uranium.
Thorium: About 0.9-1.0 Million tonnes (Mt) of ThO2 contained in 10.21 Mt of
monazite (light REE and Th phosphate) are established so far, mainly in the coastal and to
a lesser degree in the inland placer mineral sands. This resource constitutes nearly 36% of the
world resource. Along with monazite, notable resources of the following placer minerals,
having many hi-tech industrial applications, are established in the coastal and inland mineral
sand deposits:
Ilmenite (FeO.TiO2): 461 Mt (~16 % of the world resource)
Rutile (TiO2): 27 Mt (~15 % of the world resource)
Zircon (ZrO2.SiO2): 28 Mt (~5% of the world resource)
Garnet (Fe-Mg-Ca-Mn, Al Silicate): 150 Mt (meets ~30% world-requirement)
Sillimanite (Al2O3.SiO2): 190 Mt
Of the above total resources of heavy minerals identified in India, the State of AndhraPradesh
hosts 35%, Orissa 25%, Tamil Nadu 21% and Kerala 18% (Chandrasekharan, 2007).
21
1.5. HIGH-TECH INDUSTRIAL APPLICATIONS, SUPPORTED BY U, Th, RARE
METALS AND RARE EARTHS
1.5.1. Uranium and Thorium: The most important use of radio-elements, U and Th, is
for production of nuclear energy (power). These two are considered as natural resources
of primary energy. The others are wood, coal, oil, natural gas, wind, hydro(water) and
solar; all these may be converted into secondary energy such as electricity and petrol,
which have direct applications in meeting the requirements of World Energy Family (Fig.
10). Solar-, geothermal-, wind- and wave-energy, energy from biomass (wood, sugar) and
hydro-power are renewable. Fossil fuels, viz., coal, oil and natural gas, which provide over
80% of our energy today plus U and Th are non-renewable. Electricity generated in the
world (Fig. 11) is mostly from non-renewable energy resources plus hydro-power amongst
renewable ones, with the rest accounting for very little amount. The conversion of
energy into heat values [in Mega (106) Joules (MJ); joul is a unit of energy] of various
common fuels is as follows:
Firewood: 16MJ/kg; Coal of different qualities: 9-30MJ/kg; Natural gas: 39MJ/m3
Crude Oil: 45-46 MJ/kg
Natural Uranium (in light water reactor): 500,000 MJ/kg
Fig. 10. - World Energy Family (Source: ‘Energy for the World – Why Uranium?’, W
Nuclear Association).
22
Fig. 11. - World Electricity Generation, with % contribution from
major resources (Source: ‘Nuclear Power in the World Today’,
Dec. 2001, World Nuclear Association).
As (a) fossil fuels of coal, oil and natural gas are fast depleting, (b) generation of
hydro-power being localized and depends much on good monsoon and (c) the
renewable energy resources, like solar, tidal, bio-mass and geothermal are being
diffuse and intermittent with limited potentiality, the generation of nuclear power
(presently from U) in India (like in many developed countries in the world) is an absolute
necessity to meet the ever increasing demands for power. Other highly appealing
aspects of nuclear power are: (i) its very high heat value, as compared to other fuels;
hence, the volume of fuel required is much less, the cost of which is usually comparable or
even less than for an equivalent coal-fired power station, (ii) clean nature of power
with no emission of greenhouse gases, like carbon dioxide, methane and halocarbon
(CFCs), (iii) no site-restriction and (iv) dependability. For example, a one million
kilowatt (1,000 MWe) power station operating at 80% capacity consumes about 3.1
million tonnes of coal each year or only about 24 tonnes of UO2 (enriched to about
4% of 235U). This U is obtained by mining of over 200 tonnes of natural U, recovered
from, say, 25 -100,000 tonnes of typical uranium ore. As per the economics, though
the construction of a nuclear power reactor requires higher capital cost, in the long run
of 25-40 years of its operation, the cost per unit of electricity generated (even after
including expenditure for treatment of radioactive waste) is comparable to that from a
coal–based plant. It may even be less, if the site of production of coal is far away
from the power generation plant. In view of these, there is increasing preference for
generation of nuclear power in many parts of the world. Thus, over 440 commercial
reactors with an installed capacity of 350,000 MWe are presently operating in 31
countries (besides 284 research reactors in 56 countries). These commercial reactors
supply 16% of the world’s electricity (Fig. 12). In countries like France and Lithuania, the
contribution of nuclear power to the country’s total power is >75%. In rest of the
developed countries, it ranges from 20 to 60%. In India, it is presently at about 3%. India is
one of the few countries in the world, which operates the complex `nuclear fuel cycle’
with indigenous technology. This nuclear fuel cycle encompasses from the `first end’ to
`back end’, through the most important stage of production of electricity in a nuclear
power reactor (Fig. 13). The ‘first end’ includes exploration – mining – milling – conversion
- fabrication of fuel (U). The ‘back end’ covers the treatment of spent fuel and radioactive
waste, by storage – recovery – recycling – disposal, .
23
Fig. 12. - Nuclear Electricity Generation (in %) in different
countries (Source: ‘Nuclear Power in World Today’, Dec. 2001,
World Nuclear Association).
Fig. 13. - Nuclear Fuel Cycle (Source: ‘The Nuclear Age’ by Jacques Leclercq;
Publisher: Le Chene, p. 284, 1986).
Following is the summary of sequential steps of the `Nuclear Fuel Cycle’ with
respective operating units of the Dept. of Atomic Energy:
1. Exploration and cost-effective establishment of U/Th deposits:
Directorate for Exploration and Research (AMD)
24
Atomic Minerals
2. Mining and Milling:
(a) U-mining at Jaduguda, Narwapahar, Bhatin, Turmadih etc., in SSZ and milling of
U-ore up to the production of ‘yellow cake’ (Ammonium /Sodium diuranate) Uranium Corporation of India Ltd. (UCIL);
(b) Th-mining (as the mineral monazite) in the coastal placer sand deposits at
Chavara, Manvalakurichi and Chhatrapur, and separation of the placer heavy
minerals, with a little value-addition, like preparation of (a) synthetic rutile from
ilmenite and (b) RE-compounds from monazite - Indian Rare Earths Ltd. (IREL)
3. Conversion of Yellow Cake to UF6 and Fuel fabrication: Fuel is fabricated as pellets,
packed in zircalloy tubes and transported as bundles to different nuclear power reactors Nuclear Fuel Corporation (NFC); NFC makes two types of fuel bundles, viz. (i) 19-element
bundle, each containing 15kg of high-density UO2 pellets for 220 MWe PHWR, capable of
generating 0.64 million units of electricity; and (ii) 37-element bundle, each containing 22 kg
UO2 pellets for 540 MWe PHWR, with a capacity to generate 0.926 million units of power,
besides enriched UO2 fuel assemblies for two Boiling water Reactors at Tarapur. So far, it
has manufactured over 3 lakh Zircaloy clad Natural UO2 fuel bundles for PHWR.
4. Generation of Electricity: In the Nuclear Power Reactors located at Kalpakkam, Kota,
Narora, Kaiga, Tarapur etc., in the Pressurised Heavy Water Reactors (PHWR) with heavy
water (from the plants of Heavy Water Corporation as at Manuguru, Tuticorin etc.) as
moderator and natural U as fuel (Candu type); and at Tarapur with enriched fuel in the
Boiling Water Reactor(BWR) - Nuclear Power Corporation of India Ltd. (NPCIL)
5. Spent fuel storage, reprocessing and vitrification: Bhabha Atomic Reasearch Centre
(BARC), Indira Gandhi Centre for Atomic Research (IGCAR)
Indian Nuclear Power Programme, as envisaged by late Dr. Homi J. Bhabha (Fig. 14), the
father of Indian Nuclear Industry, comprises the following three stages (Fig. 15):
Fig. 14. - Homi J. Bhabha, the Father of Indian Nuclear Programme.
25
First Stage: Setting up of PHWR of the Candu-type and associated fuel cycle facilities. This
is already in the industrial domain. Twelve PHWRs are operating and two more 220 MWe
PHWRs and two PHWRs of 500 MWe rating are under construction. On March 6, 2005, the
540 MWe PHWR Tarapur-4 nuclear power plant went into criticality making the total
number of operating nuclear power plants as 15 with an installed generating capacity of 3310
Mwe. Average capacity utilisation factor of nuclear power plants is about 83%.
Second Stage: Setting of Fast Breeder Reactors (FBRs), backed by reprocessing plants and
plutonium-based fuel fabrication plants. A 40 MWe Fast Breeder Test Reactor (FBTR) is
operating at IGCAR. This is providing valuable experience for the construction of a 500
MWe Prototype FBR.
Third Stage: This will be based on Th-U-233 cycle, with U-233 obtained by irradiation of
Thorium in PHWRs and FBRs. An advanced Heavy Water Reactor (AHWR) is being
developed at BARC to expedite transition to Th-based systems.
Fig. 15. - Three Stages of the Indian Nuclear Power Programme (Source: ‘Nuclear India’, p. 6, v. 38, nos.
3-4, Sept.-Oct. 2004, Dept. of Atomic Energy, Govt. of India, Mumbai-1).
In parallel to the above indigenous, self-reliant, 3-stage programme, two light water reactors,
each of 1000 MWe capacity, are planned to set up at Kudankulam in Tamil Nadu in a deal
with the Russian Federation. This is similar to the setting up of two BWRs at Tarapur in late
1960s. The overall plan is to have nuclear installed generating capacity of 20,000 MWe by
the year, 2020.
26
Other Applications: These include production of radiation sources and radio-isotopes for
health care, agriculture, food preservation, industry and water resources, besides basic
research.
1.5.2. Rare Metals and Rare Earths: Apart from uranium and thorium, the nuclear industry
requires rare metals and rare earths (RMRE) for many of its operations. The nuclear and
other hi-tech industrial applications of RMRE are listed below, element-wise.
Niobium (Nb): Zr-2.5% Nb alloy for pressure tubes in heavy water reactor; Zr-Nb-Cu for
garter springs, Stainless Steel super-alloys, super-conductors, micro-alloyed steel industry.
Tantalum (Ta): Capacitors; transmitting and vacuum tubes; heating elements and heat
shield; carbides for tools; magnetic films of Fe-Ta or Fe-Nb nitride used in corrosion
resistance.
Beryllium (Be): (a) as metal – canning material in nuclear reactors; in aerospace and
defence; X-ray window; high-speed computer and audio components; (b) as oxide – electrical
insulator; microwave communications; alloys (Be-Cu in electrical and electronic industries;
Be-Al as hardner in Al-Mg alloy melting).
Lithium (Li): Nuclear fusion; ceramics; glass; battery technology; and many chemical
compounds.
REE: Phosphars (Eu, Y in crt; Tb, Gd, La in X-ray; Eu-Sc in lamps); lasers (Nd, Pr, Ho, Er,
Tm); superconductors(Y); ceramics (Sc, Y, Ce, La, Pr); additive (Nd, Yb, Er in fiber optics;
Ce for decolouring; Nd, Pr, Er for colouring); metallurgy (ferrous steels and non-ferrous
alloys/super-alloys).
Light REE (from monazite): nuclear fuel; control rods; reactor components; alloys, superalloys; super-conductors, permanent magnets; petroleum industry, misch metal; ceramics;
chemicals; illumination; electronics; polishing and colouring-glass.
Zirconium (Zr) and Hafnium (Hf) (from zircon): Hf-free Zr as cladding material in nuclear
reactors; Zr as alloys, in chemical industry, photo-flash bulbs, pigment, ceramics, chemical
and compounds, refractories (steel and glass works), toiletries, medicine, tanning and oil; Hf,
as control-rods in reactors.
Suggested Bibliography
1. Boyle, R.W. (1982). Geochemical Prospecting for Thorium and Uranium. Elsevier, 1982.
2. Chaki, A. (2007). Exploration strategy for atomic minerals in India. Indian Nuclear Society
Annual Conference (INSAC)-2007, Nov. 21-24, Nuclear Fuel Complex (NFC), Hyderabad,
Abst.-I-1.
3. Chandrasekharan, S. (2007). Mineral sand resources in India – Some constrains in
exploitation. INSAC-2007, Nov. 21-24, NFC, Hyderabad, Abst.- E-5.
4. Dhana Raju, R. (2005). Radioactive Minerals. Geological Society of India, P.B. No. 1922,
Gavipuram P.O., Bangalore – 560 019.
5. Dhana Raju, R. (2007). Nuclear fuel resources in India. Proceedings of the ‘Foundation
Day Lecture’ of Prof. C. Mahadevan’s Students and Admirers Association, Dec. 29, 2007,
Belson Tajmahal hotel, Secunderabad, pp. 3-18.
27
6. Frondel, C. (1958). Systematic Mineralogy of Uranium and Thorium. US Geological
Survey Bulletin 1064, Washington D.C., 400p.
7. Frondel, J.W., Fleischer, M. and Jones, R.S. (1967). Glossary of Uranium- and Thoriumbearing Minerals. US Geological Survey Bulleting1250, Washington D.C.
8. George D’Arcy, R. (1950). Mineralogy of Uranium and Thorium Bearing Minerals. RMO563, USAEC Technical Information Service, Oak Ridge, Tennessee.
9. Heinrich, E.W. (1958). Mineralogy and Geology of Radioactive Raw Materials. McGrawHill, New York, 654p.
10. Nininger, R.D. (1954). Minerals for Atomic Energy. D. Van Nostrand Co. Inc., New York,
367p.
28
Part II - FOSSIL FUELS
Fossil fuels are the natural fuels formed from the remains of plants and animals. These
include mainly (i) coal-lignite (plus coal bed methane) and (ii) oil-natural gas (plus gas
hydrates). Salient aspects of these fossil fuels, viz., (a) introduction, (b) classification and
constitution, (c) origin, source materials, conditions of accumulation-formation, reservoir and
cap rocks, (d) uses, (e) occurrence, distribution, reserves and estimates in India and (f) future
strategy, are presented in the following sections.
2. COAL – LIGNITE
2.1. Introduction
Coal, being a primary source of energy, has been the backbone of industrialisation since long.
It was known in ancient times and has entered household use in England in 9th century. Trade
on it was active by 13th century. The invention of the steam engine stimulated active coalmining. Further development in the coal industry had taken place, when cities began
producing artificial gas from coal for domestic and industrial use. In India, the earliest known
reference to coal dates back to 1774, when coal was mined on a minor scale near Sitarampur
in the Raniganj area. The East India Company was on the search for coal to meet the internal
fuel demand. The first scientific attempt to examine the Indian coal deposits and assess their
potential was made by D.H. Williams of the British Geological Survey. In 1846, he came to
India as a geologist of the East India Co., to examine the ‘coal districts of India’. He
discovered many potential coal deposits in the Damodar valley region. To expand the
exploration for coal-bearing belts of this country, the Geological Survey of India (GSI) was
set up in 1851, under the leadership of late Sir Thomas Oldham. Since then, GSI had been
taking the lead role in regional exploration for coal and lignite in various parts of the country.
Detailed exploration for and exploitation of coal in different areas are looked after by the
organizations like the Coal India Ltd., Eastern Coalfields Co., Singareni Colleries Ltd. and
Neyveli Lignite Corporation. After the independence of India on August 15, 1947, coal has
become the most important energy resource. In the Country, coal mines were nationalised in
1973. With continued oil crisis, especially after its recent phenomenal increase in global
price, the importance of coal, as the prime indigenous energy resource, became evident. This
led to more attention for its exploration and proving more of its reserves to meet the ever
increasing energy demands in the Country (Acharyya, S.K., Coal and Lignite Resources of
India: An Overview, Geological Society of India, Bangalore - 560 019, 2000, 50p.)
2.2 Classification and Constitution
Coal is broadly divided into 4 main groups. These are anthracite or hard coal, bituminous or
soft coal, lignite and cannel coal. Canned coal is a special type and the others are divided into
ranks. Chemically, coals are made up of various proportions of carbon (C), hydrogen (H),
oxygen (O), nitrogen (N) and impurities. From lignite to anthracite, there is a progressive
elimination of water, O and H, and an increase in C. The general classification and
constituents of different classes of coals are given in Table 5.
Table 5. Classification and Constituents of different classes/ranks of coal*
Classs
I. Anthracite
Group
1. Meta anthracite
2. Anthracite
3. Semi-anthracite
FC
98+
98-92
92-86
O
]
]0
]
H
3-6
29
VM
22-8
8-14
M
]
]3-6
]
Btu
14,400
to
14,880
PP
NA
&
NW
86-78 ]
]
14-22 ]
14,000
NA
4II. Bituminous 1. Low volatile
2. Medium volatile 78-69 ] 0-5 ] 4-6 22-31 ] 5-6
to
&
3. High volatile A
69]
]
31]
14,400
NW
4. High volatile B
]
]
14,000-13,000
5. High volatile C
]
]
13,000-11,000 A/NW
III. Sub-bitu1. Sub-bituminous A
]
]
]
13,000-11,000 ] NA
minous
2. Sub-bituminous B
]5-15 ] 4-6
]6-23 11,000- 9,500 ] &
3. Sub-bituminous C
]
]
]
9,500- 8,300 ] W
IV. Lignitic
1. Lignite
15 – 4 –
23 to 8,300 Consolidated
2. Brown coal
20
6.5
43
8,300 Unconsolidated
*Compiled from data given in Bateman, A.M., Economic Mineral Deposits, 3rd Indian Ed.,
Asia Publishing House, New York, pp. 636-639.
FC: Fixed Carbon; VM: Volatile Matter; A: Agglomerating; NA: Non-Agglomerating;
W: Weathering; NW: Non-Weathering. O: Oxygen; H: Hydrogen; M: Moisture; Btu: British thermal unit (heat);
PP: Physical Properties.
N.B.: Peat lies below lignite and graphite above anthracite.
Peat is not coal, even though it is a fuel. It is an accumulation of partly decomposed
vegetable matter and represents the first stage in the formation of all coals.
Lignite (and brown coal) represents the second stage. It is brownish black. It is composed of
woody matter, embedded in macerated and decomposed vegetable matter. It is banded and
jointed. Due to its high moisture content, it slacks or disintegrates, after drying in the air. It is
used for local fuels and to make producer gas. In powdered form, it is used for heating and
steam-generation.
Sub-bituminous coal is intermediate and often difficult to distinguish from bituminous coal.
It is dull black, waxy and banded. It splits parallel to the bedding, but lacks the columnar
cleavage of bituminous coal. It shows little woody material. Upon exposure, some varieties
disintegrate. It is a good clean fuel but of relatively low heating value.
Bituminous coal is dense, dark, brittle, banded and well jointed. It breaks into cubic or
prismatic blocks. Upon exposure to air, it does not disintegrate. Vegetable matter in it is not
usually visible to the eye. It has dull and bright bands, and smooth and hackly layers. It
ignites readily and burns with smoky yellow flame. Its (i) moisture is low, (ii) volatile matter
is medium and (iii) fixed carbon and heating-value are high. In the world, it is the most used
and most desired coal. It is utilised for steam, heating, gas and coking. Of all coals, the higher
ranks of bituminous coal have the maximum heating power. Cannel coal is a special variety
of bituminous coal. It (i) breaks with splintery or conchoidal fracture, (ii) is not banded, (iii)
does not soil the fingers and (iv) is lusterless. It is made up of windblown spores and pollen.
It is clean, burns with a long flame and is preferred as fireplace coal.
Anathracite is a jet-black and hard coal. It (i) has high luster, (ii) is brittle and (iii) breaks
with a conchoidal fracture. It (i) ignites slowly, (ii) is smokeless, (iii) burns with a short blue
flame and (iv) has high heating value. It is restricted in distribution, and is used almost
exclusively for domestic heating.
In coals, carbon is present as fixed carbon and in volatile matter. The ratio of these, i.e., fixed
carbon/volatile matter, is termed as fuel ratio. It is an important characteristic of coal and
determines the rank of coal. It is high in anthracite and low in lignite.
30
Grade of coals is determined by the relative abundance of organic and inorganic constituents.
It can be determined by microscopic methods and by proximate analysis to find out the ash
content, Ash content of coals represents the mineral matter. Lesser the quantity of mineral
matter better is the grade of coal. Generally, mineral matter does not contribute to the
generation and adsorption of gases; it acts only as diluents.
2.3. Origin, source materials and conditions of accumulation-formation
2.3.1. Origin and Source: That coal is of vegetable origin has been accepted since 1825.
However, there have been other views. These are accumulation in a Sargasso sea, transported
vegetable debris, fresh- or salt-water deposition, lacustrian deposition and growth of
vegetation in situ. It is mostly agreed upon that all ordinary coals are of vegetable origin, with
the banded ones formed in situ. It may be argued whether the different kinds of coal
originated because of different kinds of vegetation or by different degrees of alteration. The
general concept is that all coal originated in swamps and went through the stage of peat. Raw
material of banded coals was vascular swamp vegetation like that growing in present-day,
peat-forming swamps. Numerous plant species were identified from coal beds. Roots and
stumps found in clays below beds attest that the vegetation grew and accumulated in situ.
Luxuriant vegetation flourished. It consists mainly of ferns, lycopods and flowering plants,
with conifers and other varieties. Ferns are treelike, rushes grew 30 m high and lycopods
(small shrubs) attain 33 m in height. Bulbous and arched roots attest to trees that lived in
water. Same kinds of plant remains are usually found in coals of all ranks (Bateman, op. cit.,
p. 640).
2.3.2. Places and Conditions of Accumulation: Distribution of many individual coal seams
implies swamp accumulation on (i) broad delta and coastal plain areas,
(ii) subsiding
base-level continental regions and (iii) broad interior basin low-lands that have been nearly
leveled and where shallow waters persist throughout the year. Many coals are underlain by
carbonaceous shales of lake-bottom deposition. Low-lying surrounding lands are necessary,
else there would be too much inflow of silt. The fresh-water swamps necessary for the growth
of plant species found in coal may be separated from the sea by only a sand bar or barrier of
vegetation, since marine beds commonly alternate with or rest unconformably upon coal. A
subsiding shoreline offers the best conditions of accumulation. The rate of accumulation
depends upon the vegetation and climate. It may take 125-150 years to accumulate enough
material for ~0.3 m of bituminous coal and 175-200 years for same amount of anthracite. The
climatic conditions that favored coal accumulation were mild temperate to subtropical, with
moderate to heavy rainfall, well distributed through the year. The change from plant debris to
coal involves (i) biochemical action producing partial decay, (ii) preserving this material
from further decay, and (iii) later dynamo-chemical processes that affect. Environment, kind
of plants and nature and duration of bacterial action, all control the type of coal produced,
whereas the degree of metamorphism controls its rank. The biochemical changes liberate
oxygen and hydrogen, and concentrate carbon. Accumulation of detrital material in the
swamp gives peat (initial stage of coal). The progressive change from peat to anthracite
involves chemical, physical and optical changes. After the stage of peat, most of the changes
are chemical that are induced by pressure and slight increase of temperature, which result
from deposition of overlying sediments. In peat, about 10% oxygen is reduced. Further
progressive elimination of it is probably caused by its combining with carbon to form CO and
CO2, which escape. As per David White (cited in Bateman op.cit., p. 642), the main changes,
affected by progressive metamorphismm are as follows:
31
Physical: Compaction, drying, induration and lithification; jointing, cleavage and schistosity;
reconstruction; optical changes; dehydration up to anthracite; colour change from brown to
black; increase of density; change of luster; and changes in fracture from bedding to cleavage
to conchoidal.
Chemical: Progressive elimination of water up to anthracite; progressive loss of oxygen;
conservation of hydrogen up to graphite stage; progressive increase of ulmins and progressive
loss of bitumens; development of heavy hydrocarbons; large loss of hydrogen in anthracite;
and increased resistance to solvents, oxidation and heat. All these changes result in the
successively higher-rank coals.
2.4. Uses: As already mentioned, coal is a primary source of heat and power. Of the coal
produced, predominant part (>75%) is used for fuel like in generation of electricity (thermal
power), steam raising, railway-transportation, domestic purposes and as bunker coal. Its other
uses include production of pig iron, steel and gas. The coal used to make coke for
metallurgical and other purposes yields important by-products like gas, tar, light oils and
ammonia. Different coals find specific uses. Thus, there are coking coals (compact, minimum
porosity, volatile range of 25-35%, presence of solid residual particles and cementing
material that is formed from resinous constituents and decides the coking property), gas coals
and steam coals.
2.5. Major producers in the world: Germany, United States, Canada, Great Britain,
Australia, Russia, France, Japan, People’s Republic (PR) of China, Poland, Slovakia,
Belgium and India are the major producers of coal.
2.6. Indian scenario
India is blessed with large reserves of coal (~211 billion tonnes). Coal and lignite constitute
the primary indigenous energy source of the Country as they meet nearly 60% of its current
energy requirement. The rest is met by oil, natural gas, hydropower, nuclear, solar, wind and
geothermal. With the limited established reserves of oil and uranium, the increasing oil-price
in the world market and restricted cost-effective exploitation of non-conventional energy
resources like solar, wind, geothermal and tidal, coal continues to be the prime indigenous
energy source for sustenance of the Country’s development. This will be so until costeffective exploitation of the Country’s abundant thorium reserves for Th-based nuclear power
is established. Furthermore, it is necessary to recognize and address the environmental issues
connected with (i) coal mining and (ii) thermal power generation, releasing increased
proportion of greenhouse gases resulting in global warming.
2.6.1. Occurrence and Distribution: The coal resource of the country belongs to the
following 2 different stratigraphic levels and basinal set-up: (i) Permian sediments, deposited
in the intracratonic Lower Gondwana basins; and (ii) early Tertiary coal and lignite, formed
in near-shore basins and shelf, having mainly pericratonic set-up. Most of coal resources are
confined to (i) and these are located in the eastern and southeastern parts of the Country (Fig.
16). The major Gondwana coalfields are distributed in the States of Jharkhand, Bihar, Orissa,
Madhya Pradesh, West Bengal, Andhra Pradesh and partly in Uttar Pradesh. The minor
Tertiary coalfields are mostly in the northeastern states of Assam, Meghalaya, Arunachal
Pradesh and Nagaland, with a part being in the Jammu area of the State of Jammu and
32
Kashmir. Lignite occurs mainly in the States of Tamil Nadu, Puducherry, Gujarat and
Rajasthan, with minor deposits in the Kashmir valley and Kerala. Although resource-wise,
small, Tertiary coal and lignite constitute important energy resource in the coal-starved
southern, western and northern parts of the Country (Acharyya op. cit, pp. 5-7).
Fig. 16. - Coal fields of India (Source: Coal Wing, GSI, Kolkata; cited from Pareek, 2004, p.
33).
2.6.2. Coal Reserves: Due to continued exploration for and assessment of coal by the
organizations like GSI, Coal India, Eastern Coalfields Ltd. and Singareni Collieries Ltd., the
Country’s total reserves have increased from 86 billion tonnes in 1976 to over 211.6 billion
tonnes by Jan. 01, 2000. Of these, the Gondwana coal accounts for 210.7 billion tones and the
Tertiary coal of NE-states accounts for 0.89 billion tones (Table 6). Nearly 2/3 of these, occur
within 300m depth and the rest down to 1200m depth.
Table 6. Coal Resources in different States of India (Source: Acharyaa, op.cit., p. 27)
Stratigraphic Level
of Coal
State
Reserves
(Million tonnes, Mt)
33
A. Gondwana
Jharkhand – Bihar
Orissa
Madhya Pradesh – Chhattisgarh
West Bengal
Andhra Pradesh
Maharashtra
Uttar Pradesh
Assam
B. Tertiary
Meghalaya
Assam
Arunachal Pradesh
Nagaland
69,128.19 ]
50,448.65 ]
43,492.71 ] Total of
25,908.54 ] Gondwana
13,586.80 ] Coal
7,077.11 ] 210,706.59
1,961.80 ]
2.79 ]
459.43 ] Total of
317.42 ] Tertiary
90.23 ] Coal
19.94 ] 887.02
2.6.3. Coal Production: After the nationalization of coal-mining in 1973, there is a
substantial increase in the production of coal with time, viz., from 2 Million tonnes (Mt) in
1890 to 298 Mt in 1998. Most of the coal comes from opencast mines, with their phenomenal
rise from 20 Mt in 1975 to 226 Mt in 1998 (76% of the total coal production in the Country).
Over the last 25 years, the rate of production from underground mines remained more or less
constant, with 60 Mt in 1975 to 72 Mt in 1998. Presently, India stands as the third largest
producer of coal, next only to Peoples Republic of China and USA (Acharyya op. cit., pp. 2630).
2.6.4. Coking and Non-coking Coals: Gondwana coals of India are broadly of two types,
viz., 15% coking and the rest non-coking. Based on the coking propensities, coking coals are
grouped into the following 3 categories; their distribution and general uses are as follows
(Acharyya op. cit., pp. 30-34):
Prime coking coal (for metallurgical purposes) (5.3 billion tonnes): Jharia coal field
Medium and Semi-coking coals (used as blends) (25.1 billion tonnes): Raniganj, Jharia,
Bokaro, Ramgarh, Karanpura, Sohagpur, Penkanhan and Sonhat.
The Country’s present scenario of coking-coal resource is of concern. Although the Jharia
coal is of high-rank, its ash content is generally high for which beneficiation is necessary.
Part of our requirement for metallurgical coal is already met by imports. This may have to be
increased with the projected growth in the iron and steel industry, especially for more import
of low-ash prime coking coal.
Non-coking coals account for 180.3 billion tonnes. The superior non-coking coals, with sum
of ash and moisture content being <29%, are generally used in fertilizer, cement, sponge, iron
and other coal-based chemical industries. These are mostly available from Raniganj, while
some minor contributors are the coal-fields of Godavari, Sohagpur, South Karanpura,
Singrauli, Birbhum, Hasdo-Arand, etc.
Inferior non-coking coal is a major contributor to the power sector. This is contained in
almost all the Indian coalfields. Some leaders of this group are Talchir, Ib-River, Rajmahal,
Korba, North Karanpura, Mand-Raigarh and Singareni.
34
2.6.5. Lignite: This ‘brown coal’ is a potential solid fuel resource. Its deposits are distributed
in the states of Tamil Nadu, Puducherry (Fig. 17), Gujarat, Rajasthan and the Kashmir valley
of Jammu and Kashmir (Fig. 18), with minor occurrences in Kerala (Table 7). Though its
resources, compared to that of the vast Gondwana coal, are limited, they are important for
areas starved of the latter. Thus, lignite constitutes an important solid fuel resource in the
southern and western parts of the Country. It is being utilized in power generation and other
sectors, like carbonization, briquette-making, fertilizer and chemical industries.
Fig. 17. - Lignite occurrences in southern India (Source: Acharyya, 2001, p. 11).
35
Fig. 18. - Lignite and coal occurrences in western and northern parts of India
(Source: Acharyya, 2001, p. 12).
Table 7. Lignite Occurrences and Reserves (Source: Acharyya op. cit., p. 35-37)
State
Tamil Nadu &
Puducherry
Gujarat
Rajasthan
Jammu &
Kashmir
Kerala
Occurrence (Formation)
Reserves (Mt)
Neyveli, Shrimushnam, Lalpettai, Jayamkondam,
26,154
Mannargudi & Bahur (Eocene and Oligo-Miocene)
Many in the Iachcha, Bhavnagar, Surat & Bharuch
1,505
districts (early Eocene over Deccan Traps)
In the Barmer, Bikaner & Nagaur districts (early
1,467
Eocene)
Small deposits in the Nichahom – Shaliganga &
128
adjacent areas of the Kupuwara district
(Pleistocene)
Isolated small occurrences in the Varkala,
108
Alleppey, Quilon, Cannanore &
Thiruvananthapuram districts (early Miocene)
Total
29,362
36
2.7. Coal Bed Methane (CBM): This is rather unique in that unlike conventional
hydrocarbon, coal acts both as source and reservoir. Coal contains methane gas as an inherent
component in large variable proportion, depending on the rank of coal and depth of
occurrence. The presence of methane in coal was earlier considered as a hazard, due to its
inflammable and explosive nature. Because of these, there were many fire accidents in coal
mines throughout the world. However in recent years, CBM has become a clean and ecofriendly source of clean thermal energy, due to its easy inflammability. It has become as an
additional energy resource from the coal basins, especially in countries like USA, Australia
and China, and recently in India. Comparatively high-rank (vitrinite reflectance of order of
0.7% and more) coals at notable depth (>300m) contain considerable volume of methane,
adsorbed on coal surfaces. With the release of pressure, this is liberated and is emitted out of
the coal-mass, through fracture-network. Methane is a saturated hydrocarbon and its
generation begins with the very commencement of coalification of vegetal deposits in the
swamps. During the early stage of coalification, vegetable deposits undergo slow biodegradation by bacterial action. Due to this, the complex organic structure of vegetal matter
gradually breaks down under limited supply of oxygen and at low temperature. Concomitant
with this change, methane starts forming in small quantity, and is partly trapped within the
pore space and partly released through permeable paths. This pattern continues from
peatification to the stage of lignite-formation. The factors that control the methane content in
coal are its quality, rank, porosity, permeability, reservoir pressure and depth of occurrence.
These, in turn, are inter-related to depositional environment and basin growth. As the coalforming basin subsides, the depth of burial increases, and the coaly materials are gradually
engulfed into higher geo-thermal energy. When this happens, the organogenic environment of
coalification process is taken over by thermogenic process that enhances the generation-rate
of methane. Such generation reaches its peak at the boundary of medium volatile to low
volatile bituminous coal. The gas is entrapped within the coal seam in different ways and
remains there, due to high pressure of overburden. Bulk of the gas is adsorbed on coal
surfaces as molecular layers, while parts of it accumulate within factures, cleat and other
surfaces as clusters of gas molecules. At this stage of geothermal heating, part of methane
may migrate into the surrounding sediments. However, during subsequent thermal cooling,
coal tends to re-adsorb this gas from surrounding clastic reservoir to the coal seam. Thus, a
deep-seated coal basin forms a potential gas resource. Advantages of CBM as an energy
source are as follows:
a) Below the zones of conventional mining, gas recovery does not affect the mine workings.
b) After recovery of gas, the host coal reserve remains undisturbed.
c) During later mining of coal, gas hazards due to methane are minimized.
d) Recovered gas can be utilized at the pit-head and power transmitted through national grid.
e) Both the concept and process are eco-friendly and environmentally clean.
Deep-seated, thick coal seams of the Gondwana basins, which do not have immediate mining
prospect, may be potential CBM-fields. Thick Tertiary coal of the Makum area in Assam and
thick lignite seams of Tamil Nadu and Gujarat may be positive areas for methane prospects
(Acharyya op. cit., pp. 41-43).
37
2.8. Future Strategy in the light of positive and negative aspects of Indian coal-lignite:
The positive aspects include (a) fairly large geological reserves of coal (~211 billion tones);
(b) occurrence of thick coal seams, amenable to opencast mining; and (c) lignite deposits,
with relatively softer overburden, making quarrying under an adverse seam-overburden ratio
possible.
The negative aspects are: (a) regional imbalance in distribution of resources; (b) high-ash
content of coals; (c) deficiency in high-rank coking coal and low-ash non-coking coal; (d)
less mineability of thick coal and lignite seams to depth, thereby locking up considerable
reserves; (e) over-dependence on opencast mining leading to depletion of shallow quarriable
reserves at a very fast rate; (f) low proven reserves of coal down to 600 m depth and
deficiency of sufficient knowledge on deep-seated deposits; and (g) unexplored areas remain
under the cover of Deccan Traps, younger Gondwana, Tertiary and Quaternary sediments,
including desert sands. In the light of these, the future strategy of exploration in this sector
should take into consideration the following:
(a) More emphasis should be given on production of coal from underground mines;
(b) By adopting better techniques, higher recovery should be achieved than the
present ~20%;
(c) Opening up new underground mines to exploit resources from depths of >300m;
(d) Assessing the potentiality of eco-friendly CBM in deeper coal and lignite mines; and
(e) Using geophysical methods of exploration, testing the areas under Deccan Traps, younger
Gondwana and Tertiary sediments for coal-bearing sediments.
Furthermore, it is interesting to note that the United States Air Force wants to build a coal-toliquid plant in Montana. In this, the process of converting coal to jet-fuel will be adopted. In
fact this is an old process, used by the Germans during the Second World War. In this
process, coal and steam are heated to produce carbon monoxide (CO), hydrogen (H) and
CO2. The CO2, as waste, is removed, while the gases of CO and H are passed through a
metallic catalyst, like iron or cobalt. Due to variations in heat and pressure, this leads to
production of diesel, gasoline, jet-fuel, waxes and plastics. (Source: Dr. Anthony Stranges,
Texas A & M University, Syntroleum; published on p. 14 of “The Hindu” of March 25, 2008,
Hyderabad edition).
Suggested Bibliography
1. Bateman, A.M. (1961). Economic Mineral Deposits - Coal. 3rd Indian Ed., Asia Publishing
House, New York, pp. 634-651.
2. Acharyya, S.K. (2000). Coal and Lignite Resources of India – An Overview. Geological
Society of India, Bangalore-560 019, 50p.
3. Pareek, H. S. (2004). Progress of Coal Petrology in India. Geological Society of India
Memoir 57, 161p.
3. OIL - NATURAL GAS
3.1. Introduction
38
Petroleum is the preferred fuel since the beginning of 20th century and has become a necessity
of modern civilization. The value of its products exceeds that of any other mineral used by
the society. Modern industry, transportation and warfare are much dependent upon it. Being a
fluid, it is quickly and cheaply extracted from the Earth (exclusively from sedimentary
terrains). Its mobility permits it and its products for easy handling and transportation.
Stupendous demand for it has been largely met by contribution of geology to oil-finding and extraction. It was known in antiquity. Both Neolithic and Paleolithic man used bitumen in
building. The Egyptians used it for mummy preservation and for making boats of woven bullrushes. The Japanese used ‘rock oil’ for light over two millenniums ago. The Chinese drilled
for it by 221 B.C. In 450 B.C., Herodotus referred to seeps in Persia and Greece. Pliny told
of how the Romans obtained it for light. The oil of Baku was exploited for over 300y. An
historic incident occurred in New Haven, Conn., USA. This really gave birth to the great
American oil industry. A sample of seepage oil from Pennsylvania was sent to Benjamin
Silliman, Jr., who obtained from it the desired kerosene and excellent lubricating stock.
Casual discussion of his discovery with 3 friends led to formation of a small company to drill
for oil. In 1859, the first well for oil was actually drilled in America. This historic Drake well
struck oil at a depth of ~21m, with a flow of 25 barrels. An exciting oil boom started. This
resulted in numerous discoveries throughout Pennsylvania, Ohio, West Virginia, Indiana,
Colorado, Kansas, Texas and other States in USA during 1970s-1980s (Bateman op. cit., p.
652-653). The Middle East or Gulf Countries, like Saudi Arabia, Kuwait, Iran, Iraq, United
Arab Emirates (UAE) and Oman have made remarkable oil development since last few
decades. They formed an organisation by name, ‘Organization of the Petroleum Exporting
Countries’ (OPEC). OPEC mainly controls the volatile international oil prices, which is
affecting the economies of many an oil-importing country, like India. Other countries
producing notable amounts of oil include Canada, United Kingdom, Russia, Venezuela,
Colombia, Peru, Argentina and Myanmar (Burma).
In India, the first commercial discovery of petroleum was made in 1889 in the Upper Assam
shelf area. This area and adjoining parts of Digboi in Assam are still being explored and
exploited by the Oil India Ltd. (OIL). The establishment of the Oil and Natural Gas
Commission (now Corporation, ONGC) in the mid 1950s boosted the much needed oil
exploration in the Country. Since last few years, the efforts of these two Public Sector
Undertakings are supplemented much by the entry of Private Sector Corporations, like the
Reliance, Gujarat Petroleum and Cranes. All these units are adopting state-of-the-art
geological, geophysical and geochemical techniques.
Their sustained and focused
exploration-exploitation is resulting in substantial addition to the proven reserves of oil and
natural gas, in both the onshore and offshore regions.
3.2. Constituents, Types and Properties of Oil
Petroleum is composed of many compounds of carbon (C) and hydrogen (H), with minor
oxygen (O), nitrogen (N) and a little sulphur (S). Each of the numerous members of its
different CH series has different properties. At normal temperatures, some are gases, some
are liquids and some are solid waxes; proportions of these vary in different oils. A crude oil
may contain CH members that give the oil high gasoline content, or certain members may be
absent and the oil will contain little or no lubricants. Thus, oils may be referred to as paraffinbase, or asphaltic- and naphtha-lene-, or mixed-base. Generally, paraffin-base oils are light
and yield good lubricants. Asphaltic-base oils are heavy, unsuited for good lubricants and
may be usable only for fuel oil. Contrasting crude oils may have the following range of yields
39
(%): benzenes (gasoline): 20-31; kerosene: 7-42; gas oil: 0-20; lubricants: 0-31; and
residuals: 4-27. The terms ‘light’ and ‘heavy’ refer to the gravity, measured in arbitrary units
called API (American Petroleum Institute), e.g., specific gravity of 1.00 equals 10 API; 0.9
equals 25.7 API (a medium oil) and 0.8 equals 45.4 (a light oil) (Bateman op. cit., p. 655656).
3.3. Origin of Oil and Gas
Oil and gas are of organic origin. Differences of opinion, however, exist as to the details of
the processes of conversion into petroleum-constituents. Briefly, organic materials buried in
marine muds underwent changes to produce natural hydrocarbons. These subsequently
moved into porous reservoir rocks and accumulated to form commercial oil pools. The slow,
oxygen-free decomposition of the remains of plant and animal organisms is considered as the
source of petroleum hydrocarbons; in this, plants play a more important part than animals.
Lower planktonic organisms, such as diatoms and algae that thrive abundantly near the
surface of the sea are considered the most probable and important source materials. The
organic remains accumulate in the bottom muds of lagoons or in depressions on the floor of
shallow seas, and become incorporated in accumulating sediments. The bacteria that thrive in
the upper mud of the sea floor are thought to change the organic matter into the mother
material of oil by removing oxygen and nitrogen, and producing other changes. The next step
is more elusive, i.e., whether bacterial processes on the sea floor yield oil droplets, prior to
burial, or the bacterial action presumably ceases, and then other chemical changes occur to
yield oil before consolidation. Further post-consolidation changes probably take place during
migration. Pressure probably exerts some influence, but not temperature, because certain
compounds could not exist at 140-300oC. Later changes to liquid hydrocarbons may have
been aided by polymerization or methylation. The liquid hydrocarbons that are formed are
capable of dissolving other organic substances, such as pigments, waxes and fatty acids.
During migration, other organic compounds might also be dissolved, thus, continually
changing the composition of the petroleum and giving rise to the differences in oils. During
the conversion of organic matter into petroleum, natural gas is formed. This is dominantly
methane. The same gas is formed in peat swamps and during the transformation of low-rank
to high-rank coals.
An oil pool is accumulation of petroleum in rock pores; dispersed droplets, generated in the
source muds, do not constitute an oil pool. The conditions necessary for formation of an oil
pool are: (i) migration and accumulation; (ii) suitable source (like shales), reservoir (usually
sands and sandstones, with high porosity and permeability) and cap rocks (shale, clay, dense
limestone-dolostone and gypsum); (iii) suitable stratigraphic (unconformities, ancient shore
lines, sandstone lenses, shoestring sands, up-dip wedging of sands, overlaps, reflected buried
hills and buried coral reefs) and structural (anticline, dome, monocline, faults and salt domes)
traps or structures; and (iv) retention (Bateman op. cit., pp. 657-669).
3.4. Features of Occurrence of Oil and Gas
Oil occurs from the surface to great depths (~8,000m), with depth varying much from field to
field and even in the same field. Generally, the deeper horizons yield lighter oils. Oil and gas
in natural reservoirs are generally under sufficient pressure. This causes the oil to flow freely
from the well, often with great force, giving rise at times to huge gushers, with flows up to
40
300,000 barrels per day (1 barrel = 31.5 gallons; 1 gallon = 4.536 liters). Shallow wells,
lacking pressure, have to be pumped. Flowing wells ultimately have to be pumped, as the gas
pressure diminishes. Pressures in the oil sands range from a few pounds to 8,225 pounds per
square inch. Generally, the pressures within a given oil pool (reservoir pressure) increase
with depth. Apart from the hydrostatic head, other factors affecting pressure are: (i) weight of
the rock, overlying oil-bearing shales, (ii) diastrophism, (iii) expansive force of confined gas,
(iv) pressure, due to generation of oil and gas, (v) temperature gradient and (vi) mineralogical
alterations in the oil strata. The pressure is usually greatest at, or shortly after, the opening of
a well. It tends to diminish fairly rapidly with continued production, especially if gas is drawn
off excessively. High pressures are created by the introduction into the well of a column of
drilling mud containing finely ground heavy minerals, like barite or hematite. Temperaturegradient in oil wells may be of 10°C/m, and is generally higher than that recorded for deep
mines. Oil, like coal, is sensitive to metamorphism. If coal shows a high fixed-carbon content
on ash-free basis, any oil in the associated strata would have been volatilized or destroyed.
Thus, in regions where carbon ratios of more than 65-70 occur, no commercial oil pools may
be expected; between 50 and 65, medium to light oils and gas may be expected; and <50,
fields of heavy oils may be expected. Regions containing anthracite coals yield no oil, and
little or none is expected with high-rank coals. Salt waters underlie oil in most oil fields.
These are considered to be connate waters that have undergone subsequent chemical changes.
The waters of different oil sands may have different compositions and, thus, may serve as
means of correlation. As oil is withdrawn from a pool, the water rises to displace it, and
water encroachment into wells marks the decline of a pool. Too rapid oil withdrawal may
cause water to surge ahead of the oil with consequent loss. In some oil fields, water is
introduced into selected holes and flushes oil ahead of it to designated discharge wells,
thereby greatly increasing the oil-recovery. Oil filtered through bleaching clay loses certain
of its heavier ingredients. This feature suggests that some of the very light oils might have
been naturally fractionated by passage through clay; oils recovered from shale are generally
light. A pool normally accumulated may be destroyed or dissipated by subsequent geological
processes, such as faulting or long-continued erosion that bares the oil sand at the surface.
Diastrophism and resulting metamorphism may gasify or even carbonize the oil contained in
the strata (Bateman op. cit., 669-672).
3.5. Features of Oil-finding, Drilling and Production
When stratigraphy of a sedimentary basin indicates potential source, suitable reservoir and
appropriate cap-rocks, search for possible traps for oil is made. This search is carried out by
areal and structural contour mapping, subsurface geology and geophysical and geochemical
methods. Most geological work is subsurface, utilizing well logs, well samples, heavy
minerals, microfossils, sediment analyses and electric logging. Geophysical data are mainly
from 2D (dimensional)- and 3D-seismic. Geochemical data are on the contents of O, C and H
by Rock-Eval analysis, aliphatic and aromatic hydrocarbon characterization by gas
chromatography, and stable isotopic analyses of H, C, O, N and S by Mass Spectrometric
methods. Surface indications, like oil- or gas-seeps, paraffin dirt, or soil analyses, rarely give
a clue to the presence of oil. A test or ‘wildcat’ hole must be drilled to test the “structure”. If
a discovery is made, a scattered grid of holes is next drilled to the limits of the oil pool and its
productive acreage. After determining the thickness of the oil sand and its porosity and
permeability, an estimate of the oil can be made. Wells are commonly spaced with one well
in each 20-40 acres of land-area. Close spacing, unless carefully controlled, makes for rapid
decline and oil-loss. Completion of a producing well, close to a property line, requires the
41
drilling of an “offset” well to prevent oil drainage to the adjoining property. Directionaldrilling may be adopted by means of which a hole may be directed from an onshore location
to tap submarine oil, or several holes may be fanned out from a single location. Production
efficiency is increased by conservation of gas, proper well-spacing, re-pressuring and
controlled flow. Gas expansion is fundamental in causing wells to flow. Wells allowed to
flow wide open are wasteful of gas and induce rapid decline in pressure.
3.6. Natural Gas and Other Associated Products
Natural gas is a universal association of petroleum. It may be limited, abundant or constitute
the only valuable hydrocarbon present. Methane is the most important constituent of natural
gas; ethane increases its heating power, and other hydrocarbons, such as butane, pentane and
hexane, may be present. CO2 may also be present and rarely may be the main constituent.
Helium may also be present in some natural gas. Asphaltic-base oils at seepages yield natural
bitumens, like asphalt, maltha, rock asphalts, pyro-bitumens and related compounds. Paraffin
oils yield natural wax (desired for fine candles). Oil shale is shale containing bituminous
matter that yields petroleum by destructive distillation. A ton of rich oil shale may yield 1840 gallons of crude oil.
3.7. Uses of Oil and Gas
The primary use of oil and gas is to produce energy for power or heat, and for lubricants.
Petroleum is used mostly for motor fuel. Oil may be used in the crude state for fuel oil
[~19,000 Btu (British thermal units) per pound, as compared with ~13,000 for coal], but most
of it is refined into its constituent-parts. Refining essentially consists of heating crude oils in
stills and driving off as vapour, first the more volatile constituents, followed by the less
volatile. These are condensed to fluids, such as benzene, gasoline, distillate and kerosene.
The residuum is treated for lubricants and other constituents. In practice, the procedure is
complicated. Heavier hydrocarbons are ‘cracked under pressure’ to yield more gasoline. Raw
materials, their uses and refining-products, their average percentages and chief uses are
summarized in Table 8. Furthermore, hundreds of organic compounds, manufactured from
petroleum compounds, are used for chemicals, medicines, solvents, lacquers, textiles, resins,
dyes, explosives, saccharine, antiseptics, rubber and perfumes (Bateman op. cit., pp. 653654).
Table 8. Raw Materials and Refinery-Products of Oil-Gas and Their Uses*
Raw
Material
Crude
Oil
Natural
Gas
Natural
Gasoline
Bitumens
Uses
Fuel, road oil,
lubricants
Domestic &
commercial fuel,
natural gasoline,
carbon black
Blending with
gasoline (as motor
fuel), aviation fuel
Asphalt, roads, paints
Refinery
Products
Gasoline
%
of
Oil
40.9
Kerosene
4.7
Uses
Motor fuel, solvents
Range fuel, illuminant, motor fuel
Gas oil, distillate
14.5
Domestic fuel, diesel fuel
Residual fuel oils
27.3
Heavy fuel, diesel fuel, oils
42
6.0
2.4
2.3
0.6
0.2
0.2
1.1
0.4
Still gas
Lubricants
Asphalt
Coke
Road Oil
Wax
Others
Losses
Refinery fuel
Heavy & light oils, greases
Paving, roofing, paints, chemicals
Fuel, graphite, carbon products
Roads
Candles, sealing, water-proofing
*Source: Bateman op. cit., p. 653.
3.8. Indian Scenario
As mentioned earlier, the first commercial discovery of petroleum in India was made in 1889
in the Upper Assam basin. After the establishment of ONGC in the mid 1950s, efforts to
explore and exploit petroleum have remained unabated. Since over 115 years, dedicated
efforts of the petroleum-explorationists (using mainly geological and since a few decades, in
addition, both geophysical and geochemical techniques) have established the huge
hydrocarbon potential in the Country. Twenty-six sedimentary basins occur in India. They
cover an area of 3.14 million sq km, both on land and offshore. From the point of petroleumprospectivity, these basins are broadly classified into the following 5 categories: (i) categoryI basin of proven commercial productivity; (ii) category-II basin of identified prospectivity;
(iii) category-III basin of prospective ones; (iv) category-IV of potentially prospective; and
(v) category-V of Precambrian basement/tectonised sediments [Fig. 19, after the Directorate
General of Hydrocarbons (DGH), Govt. of India; cited in Babu, 2006, p. 571 of the paper,
‘On the Ancient Deltas of India’, J. Geol. Soc. India, v. 67 (5), pp. 569-574]. Tectonically,
these basins are broadly grouped into divergent margin (rift), convergent margin, passive
margin and interior sag basins. Within these, commercial quantities of hydrocarbons are
established in seven basins, viz., (i) Assam Shelf, (ii) Cambay, (iii) Mumbai Offshore, (iv)
Cauvery, (v) Krishna-Godavari (K-G), (vi) Assam-Arakan Fold Belt and (vii) Rajasthan. In
these basins, the effective source rocks that generated hydrocarbons are dominantly of type
III organic matter. It is deposited mainly in lacustrine-marginal marine environments and to
some extent shallow marine environment. Major source rocks in nearly all these basins are
multiple and formed mainly in the Tertiary period (<60 million years) in ages of late
Paleocene to Pliocene. In these seven basins, petroleum systems (defined as ‘a dynamic
petroleum generating and concentrating physico-chemical system, functioning in a geologic
space and time scale’) are well established in the first five (Table 9), with the generation of
hydrocarbons in the last two being not clearly understood due to insufficient data collected so
far. Hydrocarbons discovered in these basins, except the Mumbai Offshore basin, are
entrapped in clastic reservoirs that range in age from Precambrian (fractured basement) and
Triassic to Pliocene. In the Mumbai Offshore basin, the reservoir rock is mostly Lower
Miocene limestone. Most reservoirs are capped by regional transgressive shales, deposited in
inner to deep middle shelf environment. Critical moment, i.e., the timing of the entry of
hydrocarbons into the Cenozoic reservoirs, in these petroleum systems is very young. It
varies from Lower Miocene to Pliocene (18 to 2 million years). This is in conformity with the
world’s major oil and gas occurrences. However, in the K-G basin, the critical moment for
Cretaceous reservoirs is of Upper Cretaceous (92 million years). Of these commercially
proved petroliferous basins, some like the Cambay basin contain mostly oil, others like the KG basin mainly gas, while some like the Mumbai Offshore contain both oil and gas. Total
resources of these basins are around 28 billion tones of oil (O) and oil-equivalent gas (OEG),
with reserves being of the order of 7 billion tones of O + OEG. Globally, about 52% of the oil
43
is in the Mesozoic rocks, 27% in the Cenozoic, 20% in the Palaeozoic and balance in the PrePalaeozoic rocks. Contrasting this pattern, in the Indian basins over 97% of the discovered
hydrocarbon comes from Cenozoic and about 3% from the Mesozoic. However, with over 10
basins having a Mesozoic depositional history and at least half of them in the marginal
marine to marine realm, these and the geologically older basins like the Vindhyan and
Gondwana, merit more attention for exploration of oil-gas to augment hydrocarbon reserves
in the Indian sedimentary basins (Bhandari et al., 2007).
Fig. 19. - Sedimentary basins of India and their potentiality for oil-natural gas (Source: Directorate General
of Hydrocarbons, 2003; cited from P.V.L.P. Babu, J. Geol. Soc. India, v. 67(5), 2006, p. 571).
Table 9. Salient Features of ‘Petroleum Systems’ in Commercially Hydrocarbon-
44
bearing Sedimentary Basins of India___________________
Sl.
no.
1.
Basin,
with location
Petroleum
System
Cambay
(intracratonic
rift basin on
WNW margin of Indian
platform
Mumbai
Offshore
(pericratonic
basin, on
continental
shelf off the
West Coast)
Cambay – Hazad (S.Cambay
basin);
Cambay– Kadi
(N. Cambay
basin)
PannaMumbai
3.
Cauvery (pericratonic basin)
on the East
Coast
4.
KrishnaGodavari
(interior basin,
super-imposed
by pericratonic
basin) on the
East Coast
Andimadam –
Bhuvanagiri in
Ariyalur Puducherry
sub-basin)
a) Krishna/
Gollapalli –
Kanukollu
(W. Godavari
sub-basin)
2.
Panna-Mukta
Source Rock
(SR)
Cambay
sh.
Panna F.
(Upper Palaeocene - L. Eocene)
Reservoir Rock (s)
(RR)
Cap Rock
(CR)
Depositional
Environment
Younger Cambay
sh. (L. Eocene),
Anklesvar (M.
Eocene),
Babaguru F.
(L. Miocene)
Panna, Bassein,
Mukta & L-III l.st.
(in Mumbai High,
within Mumbai F.
– L. Miocene)
U. Eocene
sh.
SR: Marginal
marine (brackish
hyposaline) to
fresh water;
CR: deep marine
Bandra F.,
Belapur F.
(M. Eocene)
Mahuva
F.
(L. Oligocene)
Andimadam,
Buhavanagiri F. (in
Ariyalur Puducherry
sub-basin)
Kanukollu s.st. &
Raghavapuram sh.
(Cretaceous)
Sattapadi
& Kudavasal sh.
SR: Non-marine to
shallow marginal
marine to shallow
inner shelf.
RR: Marginal
marine (hyposaline
to hypersaline) to
shallow marine;
CR: Marine
SR: marginal marine
RR: inner to middle shelf
CR: deep marine
SR: marginal marine – middle shelf;
RR: Lagoonal to
shallow inner shelf;
CR: middle shelf
SR: middle shelf;
RR: cyclical;
CR: fluctuating
inner shelf
Panna-Bassein
and
PannaPanna
b) Palakollu –
Pasarlapudi (E.
Godavari subbasin)
c) Vadaparru –
Ravva offshore sub-basin
Andimadam F.
(L. Cretaceous)
Krishna/
Gollapalli F. &
Gajulapadu
shale
Pasarlapudi F. –
alternate s.st. & sh.,
with a few l.st.
beds
Palakollu sh.
(U. Palaeocene)
Vadaparru sh.
& Ravva F.
Ravva sand (U/M
Miocene &
Pliocene
Raghavapuram sh.
Sh. & Brahmanapalli l.st.
Ravva F.
SR: shallow shelf
sh.; RR: shelf/
slope transition,
cyclical
SR: fluvial
Variegate
Kommugudem Mandapeta s.st.
d clays
(Triassic)
F. (Sand, sh.
(red bed)
with coal beds;
L. Permian)
5.
Upper Assam
Kopili
Kopili sh. (M- Kopili s.st., Sylhet
Sh. within SR: shallow inn-er
shelf
U Eocene)
l.st. & Tura F
Kopili &
shelf-marginal
(intermonta-ne Barail-Tippam Barail sh.
Barail & Tippam
Tura F.
marine
basin) in NE
(Oligocene)
sands
Girujan
RR: shallow
India
Eocene (Oil)
U. Langpar F. Same as SR
clay
marine-fluvial
&L. Lakadong
SR: marginal
of Sylhet F.
marine - fluvial
F.: Formation; L.: Lower; M: Middle and U.: Upper;
S.st.: Sandstone; Sh: shale; L.st.: limestone
*Source: Kuldip Chandra et al., 2001, Petroleum Systems in the Indian Sedimentary basins: Stratigraphic
and Geochemical Perspectives, Bulle. ONGC, v. 38(1), pp. 1-45.
d) Mandapeta
(E. Godavari
sub-basin)
Gas hydrate since last few years is getting prominence in the oil-natural gas exploration. The
Blake Ridge in the northwest Atlantic is the type-area for gas hydrate. Here, seismic
reflection profiles (Bottom Simulating Reflectors, BSR) and pore-water chlorine anomaly
45
have indicated that in between 185 and 450 mbsf (meters below sea floor), more precisely at
185-260 and 380-450 mbsf, gas-charged sediments are present. The requirements for the
formation of gas hydrate are: adequate amount of methane, interstitial pore water, high
porosity, high pressure and low temperature. Depleted total organic carbon at 185-260 mbsf
(0.8-1.3%) and 380-450 mbsf (0.9-2.1%) indicates transformation of organic carbon into
methane by methanogenesis. High bacterial population in the gas hydrate zone also supports
the formation of methane by bacterial decomposition of organic carbon. Presence of adequate
pressure, high organic carbon (0.2-2.6%), notable porosity in sediments and high bacterial
population make Blake Ridge an ideal place for in situ gas hydrate formation. In India, the
continental margin of the Bay of Bengal appears to be a promising zone for gas hydrate.
3.9. Future Strategy in Exploration and Exploitation of Oil-Natural Gas-Gas Hydrate
Demand for oil, the most important fossil fuel next only to coal, is ever increasing to meet the
energy requirements of the Country. The present indigenous production of oil is ~33 MMT,
against the demand of ~115 MMT. This means that only 30% of the demand is met by
indigenous production and the rest is presently met by imports. The huge import of oil is
draining a major chunk of the foreign exchange. In this scenario, the future strategy in
exploration of oil - natural gas - gas hydrate should aim at proving their resources and
establishing their reserves in the Country at an accelerated rate. For this to happen, all
appropriate methods and techniques should be employed so as to affect their exploitation
cost-effectively. Toward this end, some suggestions are given in the following:
(a) In both the onshore and offshore regions, integrated, multi-disciplinary (geological,
geophysical and geochemical) and in-depth state-of-the-art exploration techniques should be
adopted in the (i) categories II, III and IV basins (Fig. 19) as well as (ii) contiguous areas of
the basins that are already under commercial exploitation, like the K-G and Mumbai
Offshore.
(b) Enhanced Oil Recovery (EOR) processes, viz., thermal, chemical and miscible
displacement, should be developed to their full potential so as to (i) increase recovery from
depleted reservoirs and (ii) increase recovery from reservoirs that could not respond to
conventional water-flooding or gas-injection.
(c) Appropriate measures are to be taken to save in distribution as much as possible. For
example, supply of gas for domestic consumption can be economical with more safety by
supplying it through pipeline, instead of the present mode in gas cylinders.
(d)
Increased overseas exploration, like some of the present ones in Sudan and Vietnam by OVL (ONGC Videsh Ltd.) and other public and private sector oil
exploration
agencies, should be undertaken to get some part of proved reserves; these will supplement the
indigenous ones.
(e) Early clearance is to be accorded to the 3 proposed gas pipelines, viz., Iran-PakistanIndia (2720 km in length; estimated cost 4 billion US$), Turkmenistan-AfghanistanPakistan-India (1921; 3.5) and Myanmar-Bangladesh-India (897; 1) (Source: Vinish
Kathuria, Promise of Trans-border Gas Pipelines, The Hindu, p. 16 of May 8, 2006,
Hyderabad edition); these, however, have some geo-political problems.
46
Suggested Bibliography
1. Bateman, A.M. (1961). Economic Mineral Deposits – Petroleum and Associated
Products. 3rd Indian Ed., Asia Publishing House, New York, pp. 652-695.
2. Bhandari, A., Prasad, I.V.S.V. and Dwivedi, P. (2007). Stratigraphic distribution of
Hydrocarbons in the Sedimentary Basins of India. Jour. Appl. Geochem., v. 9 (1), pp.
48-73.
3. Chandra, K., Raju, D.S.N., Bhandari, A. and Mishra, C.S. (2001). Petroleum systems
in the Indian Sedimentary Basins: Stratigraphic and Geochemical Perspectives.
Bulletin of ONGC, v. 38(1), pp. 1-45.
Epilogue
Energy security to the Country is the major issue with wide ramifications. To have it in full
measure, we should prove the energy resources at a fast rate and utilize them judiciously.
Presently, the fossil fuels – coal-lignite and oil-natural gas – are producing to a predominant
extent, with nuclear fuel (presently uranium) from atomic minerals contributing ~3%, the
total energy generated in the Country. A major environmental problem with the excessive use
of fossil fuels for energy-generation is release of greenhouse gases. These are causing global
warming (expected to raise temperature by ~3-5oC in the next 4-5 decades). This has
disastrous consequences, like submergence of low-lying coastal areas due to melting of polar
ice and rise in sea-level. Hence, the non-renewable energy resources of fossil fuels should be
effectively supplemented by hydro and other renewable ones like solar, wind, tidal and
geothermal. Besides, non-conventional ones, like rice-husk (available in plenty in States like
Andhra Pradesh and West Bengal), bio-diesel from plants like jatropha and ethanol from
sugar-industry, should be utilized to the maximum extent. The lasting answer to energy
problems faced by the Country, however, appears to be cost-effective thorium-based nuclear
power. This is because that thorium-resources, in the form of mineral, monazite, are quite
abundant in India and constitute nearly 36% of the world resources. Th-based power is
expected to be commercially viable by the year, ~2020.
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