15 Energy Sources- Fossil Fuels

Balen Bhagbaty

Module 20: Energy Sources- Fossil Fuels

Fossil fuel is a general term for buried geologic deposits of organic materials, formed from decayed plants and animals that have been converted to crude oil, coal, natural gas or heavy oils by exposure to heat and pressure in the earth’s crust over millions of years. There are mainly two types of fossil fuel, namely coal and petroleum.

COAL

Humans have been using coal since ancient time as fuel. In the ninth century A.D. coal had been used as domestic fuel in England. It found utilization in industrial fields since thirteenth century only. The principal use of coal is mainly seen in production of heat and electricity along with making of coke for blast furnace. Few years back 75% of India’s total coal production was consumed as fuel for locomotive engines, ships and factories, Iron and Steel industry takes 20% while remaining 5% was consumed by gasification of coal.

1.1 Characteristics of Coal:

Coal contains complex organic compounds along with little amount of inorganic matter and water. The main constituents of coal are carbon, hydrogen and oxygen besides small amount of nitrogen and sulphur. The transformation of plant material to coal in peat forming swamps involves a process which increases the proportion of carbon and decreases the proportion of oxygen and hydrogen, while the proportions of nitrogen remain more or less same.

The chemical analyses of coal are determined by two methods, namely proximate analysis and ultimate analysis. The proximate analysis of coal determines the combustible and noncombustible fractions of coal. The combustible fractions are volatile matter and fixed carbon while the non-combustible fractions are represented by moisture and ash contents. The proximate analysis reflects the quality of coal as fuel. The ‘fuel ratio’ is another one parameter that can be determined by the proximate analysis. The proportion of fixed carbon to volatiles is called the ‘fuel ratio’. The fuel ratio is an important factor to consider for classifying and grading coals. The heating power of coal is expressed as the ‘calorific value’. The calorific value is the amount of heat generated when a unit amount of coal is burnt under atmospheric pressure and temperature.

Ultimate analysis is more comprehensive and dependent on quantitative analysis of various elements present in the coal such as carbon, hydrogen, nitrogen, sulphur, and oxygen.

Macroscopic component of coal: Stopes and Wheeler (1918) defined four megascopically distinguishable ingredients of humic coal as Vitrain, Clarain, Durain and Fusain. These are also known as ‘lithotypes’. The lithotypes can be usually be observed in banded bituminous coals.

Vitrain: It occurs in narrow (< 0.5 cm) bands. These bands are bright glossy with a massive texture. Vitrain bands are very brittle and show conchoidal fracture.

Clarain: It has bands of variable thickness with a pronounced glossy and silky lustre, but less brighter than vitrain. It breaks with a smooth surface when fractured at right angles to bedding plane.

Durain: It forms band of variable thickness. Durains are compact, granular, hard and lusterless.

Generally it is dark grey to black in colour and breaks with an irregular fracture.

Fusain: It occurs as lenses or lenticular bands of dull, soft and friable material. It is greyish black in colour. It has a fibrous structure similar to that of charcoal and break down to powder form. Fusains mostly represent oxidized woody materials.

Microscopic component of coal:

Coals are generally observed in polished sections under reflected light microscopes. The microscopic constituents that can be identified under the reflected light microscopes are known as macerals (Stopes, 1935). There are three groups of macerals in coals, viz., vitrinite, liptinite and inertinite. The macerals are classified on the basis of morphology and optical characters. All the maceral groups have the suffix ‘inite’ and three maceral groups have been recognized in coals, namely, vitrinite, liptinite and inertinite.

Vitrinite: The Vitrinites are the most dominant type of macerals in coal. They are composed of lingo-cellulosic tissues of roots, stem, leaves etc. Vitrinites are gray in colour and sometimes display cell structures of woody tissues. The reflectance of vitrinite in low and medium rank coals is intermediate between highly reflecting internites and dark liptinites. The individual vitrinite macerals are identified based on degree of degradation and morphology. Vitrinite macerals originate when the parent plant materials get deposited in an anaerobic environment.

Liptinite: Liptinite macerals are considered to be produced from non-woody plant materials like resin, cutine, spore, pollen, suberine and also algal debris. They are usually dark in colour and show lowest reflectance among all macerals of coal. Litptinites are hydrogen rich and show very strong fluorescence.

Inertinite: These derived mainly from oxidized woody materials. The same kind of material give rise to vitrinite in anaerobic condition. The interninites are the brightest macerals of coal. They show brilliant preservations of cell structures. As they are composed mainly of oxidized woody materials, they are not as reactive as vitrinite and litptinite and so the name inertinite was coined after the word ‘inert’. Presence of inertinites in high amount usually degrades quality of coal as fuel.

Rank of a Coal:

Rank of coal depends on the degree of coalification with the passage of time. The chief agent of coalification is the geothermal heat. The rank of coal starts at lignite and it ends at anthracite. Rank is a maturity parameter. However, a high rank coal may not essentially be a high quality coal as a fuel. The general progression of coal ranks with increasing temperature is shown below: Peat-> lignite-> sub-bituminous-> bituminous-> anthracite-> graphite.

Peat: Peat is not considered as coal. However, it is precursor of all type of coals. It is an accumulation of partly decomposed vegetal matter that represents the first stage in the formation of all coals. Peats are usually soft and compressible. The vegetal structures in coal could be identified easily with naked eyes. Peats are mostly used as fertilizer.

Lignite: Lignite represents the second stage in coalification process. It is more solid than peat, but less compact than ordinary coal. It is a low-rank coal which is brown, brownish black, but rarely black in colour. It is composed of woody matters embedded in decomposed vegetal matters. The vegetal structures are still visible with naked eyes. Because of high moisture content, it slacks or disintegrates easily after drying in air.

Sub-bituminous: It is more compact than lignite. The carbon content is relatively higher than that of lignite. When it burns, it emits smoky yellow flames, although this is devoid of any real bitumen. It is glossy in lustre and usually unbanded. The vegetal structures are no longer seen with naked eyes.

Bituminous: Bituminous coal is a medium to high rank coal. It contains a high percentage of carbon and less amount of intrinsic moisture. It is usually banded in nature. It gives highest calorific value, so it is the best fuel coal. This coal is ideal for steam-raising, heating purpose, gasification and coking. Worldwide it is used for heating and power generation activities. Bituminous coals are mostly found in the rock formations of Carboniferous and Permian age.

Anthracite: Anthracite is a dense, hard and black coal that has brilliant sub-metallic luster. It breaks with conchoidal fracture. It represents the highest attainment rank of the coal. It is the richest in carbon and poorest in O and H of all coals. it is not as good as bituminous coal as a fuel since it burns slowly, owing to its very high carbon content and very low hydrogen content. Anthracite coals are usually the oldest of coals. As it burns with a smokeless flame and thus it is better than bituminous coal as domestic fuel.

1.2 Origin of Coal:

Coal is primarily composed of carbon, along with various quantities of other elements. Coal forms when dead plant matters deposited in peat lands is converted to peat, which in turn converts to lignite, and finally to anthracite through the stages of sub bituminous and bituminous rank. This involves a brief biological process which is followed by a geological process encompassing millions of year under a thick pile of sedimentary rocks in sedimentary basins. The ideal condition for the transformation of plant materials into coal exists in temperate or moist tropical climate with slowly rising groundwater in slowly subsiding sedimentary environment. The deposited plant materials in peat forming swamps are first converted to peat by a biochemical process, dominated by anaerobic bacteria. The peats progress through various ranks of coal because of geothermal heat during further subsidence of the sedimentary basin under a thick pile of sedimentary rocks. This stage of transformation is also known as the geo-chemical stage which is analogous to metamorphism of sediments. The chief agent transformation of peat to various ranks of coal is heat.

Coals are product of terrestrial plants. Therefore, true coals first appear in the sedimentary column of the earth in the Devonian Period, as true land plants appeared on the surface of the earth during this time only. Most of the bituminous coals in the world are found in Carboniferous (Europe and North America) and Permian (Gondwanaland continents). These coals formed mainly from gymnosperms and pteridophytes that profusely covered the surface of the earth during this

1.2 Origin of Coal:

1.3 Distribution of coal in India:

In India, coals are found mainly in two geological periods, viz., Lower Gondwana (Permian) and Paleogene (Eocene to Miocene). A little amount of coal are also found in the Upper Gondwana rocks, but economic significance of the Upper Gondwana coal is little. More than 90% of total coal deposits of India are represented by the Lower Gondwanat coals.

Gondwana Coal:

The significant coal seams have been found in the rocks of the Damuda Group of Lower Gondwana age. Coal seams are found within the rocks of two formations, viz., the Lower or Barakar Coal Measures and the Upper or Raniganj Coal Measures. Geographically the rocks of the Barakar Formation are more extensive and the coal is superior in quality and more in quantity than the coals of the Raniganj Formation. Generally the Gondwana coals are represented by bituminous and sub-bituminous coals. The ash content in Gondwana coal is usually high, normally ranging between 15 to 30 % of ash. The lower Gondwana coalfields are scattered in the province of Andhra Pradesh, Odisha, West-Bengal, Jharkhand, Madhya Pradesh, Sattishgarh, Uttar Pradesh, Maharashtra and Sikkim.

Upper Gondwana coalfields are distributed in Gujarat (Ghuneru coalfield of Kachchh), Madhya Pradesh (Hiran river valley coalfield of Jabalpur district) and Maharashtra (Kota and Chikiala coalfields). However, in terms of deposit and production the Upper Gondwana coalfields are in no match with their Lower Gondwana counterparts. About 98 per cent of India’s total coal production comes from the Lower Gondwana coalfields. The Jharia and Raniganj coalfields are the most important Lower Gondwana coalfields in India.. Other important coal fields are East Bokaro and West Bokaro, Pench-Kanhan-Tawa valley, Singrauli, Talchir, Ramgarh, Chanda-Wardha, Godavari valley etc

Paleogene coal:

Paleogene coals account for only 2% of India’s total coal production. But even then, these coals are very useful in those areas where they are produced, since those areas are devoid of Gondwana coals.

Paleogene coals are mostly lignite to subbituminous in rank. However, the Paleogene coals of Kashmir have reached the stage of the sub-bituminous to bituminous rank presumably due effect of Himalayan orogeny.

Paleogene coals contain a significant amount of sulphur. However, the ash content is low (2 to 8 %). Usually with low amount of moisture, the Paleogene coals contain volatiles up to 45%. These medium-grade coking coals have a calorific value of around 8000 calories per gram.

The Paleogene coalfields are located in Assam, Meghalaya, Jammu and Kashmir, Kerala, Gujarat, Rajasthan and Tamil Nadu. Recently small lenses of coal have been reported from Andaman and Nicobar Islands.

Assam accounts for 63% of the Paleocene coal reserves. Major coal fields in Assam are the Makum (235 million tons), and Dilli-Jeypore (54 million tons). The Makum coalfield is the largest and most developed field in the entire Northeast India. Among the other fields of Northeast India West Darrangiri (127 million tons), Langrin and Bapung in Meghalaya, Namchik (90 million tons) in Arunachal Pradesh and Borjan in Nagaland are important.

Lignite is mainly produced in two states – Tamil Nadu and Gujarat. Small lignite coal fields are also found in Rajasthan and Jammu and Kashmir. Neyveli is the lignite field in Tamil Nadu which is located in South Arcot district. Neyveli is the largest lignite mine of India. This field supplies fuel for thermal power generation in Tamil Nadu.

PETROLEUM AND NATURAL GAS

Petroleum is the most important fossil fuel. The word petroleum comes from Latin word petros means rock or stone and oleum means oil, i.e. rock oil. Humans knew the use of petroleum from ancient times. In the Neolithic and Paleolithic ages, humans used bitumen for constructing houses. Ancient Egyptians knew how to use rock oil for the preservation of mummy. Petroleum consists of hydrocarbons of various molecular weights and other organic compounds. The name petroleum covers both naturally occurring unprocessed crude oil and petroleum products that are made up of refined crude oil. A fossil fuel, petroleum is formed when large quantities of dead organisms, usually zooplankton and algae, are buried underneath sedimentary rock formations and subjected to both intense heat and pressure.

2.1 Composition:

Petroleum includes liquid, gaseous and solid hydrocarbons. In normal pressure and temperature

conditions, lighter hydrocarbons methane, ethane, propane and butane occur as gases, while pentane and heavier hydrocarbons are in the form of liquids or solids. An oil well produces predominantly crude oil, with some natural gas dissolved in it. A gas well produces predominantly natural gas. The hydrocarbons in crude oil are mostly alkanes, cycloalkanes and various aromatic hydrocarbons, while the other organic compounds contain nitrogen, oxygen and sulfur, and trace amounts of metals such as iron, nickel, copper and vanadium. Many oil reservoirs contain live bacteria.

The alkanes (paraffins) have the general formula CnH2n+2 are saturated hydrocarbons with straight or branched chains which contain only carbon and hydrogen. These are generally having 5 to 40 carbon atoms per molecule, along with trace amounts of shorter or longer molecules.

The alkanes from pentane (C5H12) to octane (C8H18) are refined into gasoline, the ones from nonane (C9H20) to hexadecane (C16H34) into diesel fuel, kerosene and jet fuel. The alkanes with more than 16 carbon atoms can be refined into fuel oil and lubricating oil. The paraffin wax is an alkane with approximately 25 carbon atoms, while asphalt has 35 and more, these are usually processed by modern refineries into more valuable products

2.2 Origin of petroleum

Theories on the origin of petroleum can be divided into two groups on the basis of the primary source material, as organic or inorganic. Early ideas leaned towards the inorganic sources, whereas the modern theories, with few exceptions, assume that the primary source material was organic. The change was brought about by an increasing number of objections to the inorganic ideas. But since these objections have not completely eliminated the possibility that inorganic substances especially hydrogen playing some part in the origin of petroleum.. The intimate relation of the organic material and the petroleum in the sediments leaves no doubt that organic matter is the original source of the petroleum.

Theories on the accumulation of oil have a direct bearing on origin. Some geologists hold that all petroleum was formed in place, either at or adjacent to the position of present pool. Others hold that petroleum was migrated from the source areas to the trap areas, and that the source area does not necessarily coincide with the accumulation area.

Origin of petroleum formation: Petroleum is derived from the remains of living organisms which which upon deposition in sedimentary basins convert to an inert solid organic material known as ‘Kerogen’. Kerogens are considered precursor to petroleum.

Before dead organic matters become petroleum with time, the kerogen matures into an assortment of hydrocarbon molecules of all sizes and weights. The lightest (small) hydrocarbon molecules waft away (escape) as natural gas, as the heavier ones make up an oily liquid. Petroleum source rocks are of terrestrial and marine origin. Terrestrial source rocks are deposited in lakes, delta and river basins having woody plant matter, algae etc. Marine source rocks contained dead planktons, algae organic remains etc. In both the cases, they were buried under conditions of free oxygen.

Under the anaerobic conditions, kerogen is transformed into flammable substances called bitumen by the action of heat and anaerobic microbes in the sediments and natural catalyst. Most of the bitumen is eventually cooked into tarry asphalt releasing hydrocarbon molecule (H₂O and CO₂) out of the source rocks as it heats. Heavy oils form first then light oils. As temperature rise to an above 100⁰C, source rocks produce more gas. Being lighter than rocks, petroleum tends to rise upward through fractures and the pores of coarse sandstone beds. A small fracture of that leakage perhaps 2 % is preserved in large pools having an impermeable cap/silt over it.

2.3 Migration of Petroleum:

In order to explain the presence of petroleum in reservoir rocks, it becomes necessary to assume that there has been movement of fluid from the source rocks into the reservoir rocks, i.e. migration of petroleum must have occurred for formation of a commercial petroleum deposit (Fig.1).

Hydrocarbon migration is controlled by various processes like kerogen expansion, increase in pressure and hydrocarbon expulsion out of source rock. The expulsion of the oil out of the source rock is a dynamic process driven by the oil generation itself. Good source rocks have TOC (total organic content) ranging from 3 to 10%. At low TOC, the kerogen may occupy a position within the matrix porosity of the rock. At high TOC, the kerogen can form connected bands within the rock. In such situations the kerosene bears a part of the lithostatic load. As the organic matter transforms into oil, this load-bearing kerogen turns into liquid. The fluid pressure of the oil within the black shales can become high enough to produce microfractures in the rock. The oil is squeezed out through micro fractures and the source rock collapses. Therefore, primary migration can be viewed as a second episode of compaction. The microfractures of this type can be seen in the most productive source rocks and they are often filled with remnants of oil.

Migration of hydrocarbons can be thought of two distinct types, involving at least two distinct mechanisms, namely, primary and secondary migration. Primary is the process by which hydrocarbons are expelled from the source rock into an adjacent permeable carrier bed. Secondary migration is the process of movement of hydrocarbons along a “carrier bed” from the source area to the trap. Migration mostly takes place as one or more separate hydrocarbons phases (gas or liquid).

The term ‘Tertiary Migration’ has been applied to any subsequent movement of the accumulated hydrocarbons. Such movement could represents adjustments in response to changed geological conditions, such as changed in depth of burial, tilting of the strata, development of avenues by faulting or erosion escape to the surface to give seepages.

Fig.1. Primary and secondary migration of petroleum (after Tissot and Welte, 1984).

2.4 Accumulation of petroleum:

Migration of oil generally leads to accumulation, which is the collection of oil droplets into pools. Oil may migrate without accumulating or it will may accumulate in non-commercial bodies, as at the top of the horizontal beds, but concentrated accumulation is essential to produce commercial oil pools and this in turn is deepen upon requisite rocks of traps.

The process of generation and migration is a slow one, involving long periods of time. It is estimated that the whole process of generation and migration ending in entrapment takes at least a million of years, sometimes even more.

2.5 Distribution of petroleum in India:

In India, four categories of petroleum related sedimentary basins have been classed:

Category I: These are proved petroliferous basins with viable commercial production. For example, Assam-Arakan basin, Bombay basin, Cambay basin.

Category II: The occurrence of oil in these basins is known, but commercial production or viability is yet to be obtained. For example- Bengal basin, Andaman-Nicobar basin, Cauvery basin, Krishna-Godavari basin etc.

Category III: Although no significant oil or gas reserves have been discovered yet, geologically they are considered prospective. For example-Konkan basin, Saurastra basin etc.

Category IV: The prospects are uncertain. Some basic data are necessary for prognosis of these basins. For example-Arunachal foot hills, Ganga Valley.

Assam-Arakan Basin:

The Assam-Arakan basin covers vast areas of Assam, Arunachal Pradesh, Manipur, Nagaland, and Tripura. Arakan coast of Myanmar is its southeastward extension while westward plays over some parts of Bangladesh and touches the peripheral areas of Orissa, West Bengal and Bihar.

The Assam-Arakan basin is emplaced in a geologically disturbed zone. The eastern and the northeastern margin of it is flanked by the Eastern Himalayas. Across the Brahmaputra valley and facing the Eastern Himalayas is the zone of imbricate structures of the Naga Hills. These overthrusted sheets of rocks facing north-west constitute as the Belt of Schuppen of Assam-Arakan Basin. Emplaced between Eastern Himalaya and the Belt of Schuppen is the Upper Assam Shelf covered by the recent alluviums, which is the most promising petroliferous part of the basin. Exploratory advances have revealed that beneath the alluvium there are thousands of meters of Tertiary sediments cracked into a number of fault blocks which influence hydrocarbon accumlation. Seismic study across the upper Assam Shelf has shown inversion of tilt between older and younger sediments. Initially the basin slope was towards SE-SSE resulting in the increased thickness of Sylhet,Kopili, Barail and Tipam Formations (Tertiary) in the SE direction. However, there is reversal of slope towards NW after the deposition of the Tipam (Miocene). Owing to this inversion of slope, the post-Tipam the Girujan Clay Formation acts in general as a cap rock for the sandy Tipam reservoir rocks.

The Assam-Arakan Basin is mostly composed of Cenozoic sediments. The pre-Cenozoic rocks are mainly Precambrian rocks of Mikir Hills, Mishimi Hills, and the Shillong Plateau along with the limited occurrences of the lower Gondwanna rocks, Cretaceous rocks and Jurrassic Lava scattered along parts of Assam and Meghalaya. The Tertiaries were deposited in two environments of deposition viz. Shelf and Geosyncline. The dividing line between the two facies lies somewhere in the Belt of Schuppen.

Oil has been found to be confined within the marine and non-marine beds. The Oligocene and Miocene contain the principal production horizons of the basin. The basin presently contributes over half of India’s onshore oil production.

Bombay basin:

The Bombay basin is a part of the world’s largest continental shelf. The Bombay High oil field which was discovered in this basin is a giant oilfield situated 160 km off Bombay in the Arabian Sea at a water depth of about 75 m. The basin is bounded to the north and east by the Deccan Trap outcrops of Saurastra Peninsula and Western Ghats, respectively. The southern flank is marked by Pangann Arch and the Western side is marked by the shelf edge. The area occupied by the basin is approximately 120000 sq kms.

Deposition in the present tectonic framework of the Bombay basin area was initiated way back in the Cretaceous. The northern front of the basin is marked by the Saurastra-Arch, north of which lies the Kutch basin. The Bombay platform separates the Surat depression on the east from the shelf margin basin on the west. The Bombay platform and one Ratnagiri block to the south are separated by E-W trending faults. Tectonically, the basin is divided into Surat depression, Bombay platform; Ratnagiri block faulted zone, shelf margin basins and shelf edge basement arch.

Lithology: The basin consists mainly of Tertiary sediments which are more than 5000 m thick in some places. Sands and lignitic clays form the basal parts of the lithologic column which is overlain by limestones. Alterations of shales are found in the middle part. Finally shales and clays constitute the topmost part. In the west of the Bombay High and south of the Ratnagiri block, the shale sequence is replaced by the limestone.

With the help of seismic stratigraphic studies four seismic sequences have been identified from bottom to top. Sequence I, is entirely of basement section, and sequence II, is entirely of carbonate sections and Sequence III and IV are mainly shale sections. Each sequence is separated by unconformities.

This basin is the first oil discovery of a carbonate reservoir in the country. In the Miocene sequences four oil or gas-bearing reservoirs have been identified in limestones and sands. Although both primary and secondary porosities are present, the former acts as a main storehouse of hydrocarbon.

Cambay Basin:

The Cambay Basin is located in the north-western margin of the Indian Peninsular and occupies an area of approximately 56,000 sq km. The Ankleswar oil field was a major oilfield discovered in this basin in 1960.

The Cambay Basin is an intracratonic rift graben in the form of a long and narrow depression extending north-south. Closely associated with the basin is East and West trending Kutch basin. The Cambay Basin is flanked on the NE by the Aravalli ridge, on the East and South by the Deccan Craton and on the west by the Saurastra Craton which is a residual horst. Tectonically, the basin is divided into seven blocks from north to south amongst which the important ones are:

Ø Ahmedabad-Mehsana Block
Ø Cmbay-Tarapur block
Ø Jambasar-Broach block
Ø Narmada Block

The basin is essentially filled up with a thick sequence of Cenozoic rocks unconformably overlying the Deccan Traps, which represents the Basement. In the Palaeogene section the volcanic conglomerates, sandstones, silts comprise the lower part, which is overlain by a thick sequence of dark grey to black shale, coaly shale and coal bands. The Neogene section is constituted mainly of sandstone, shale, claystone and sandy claystone.

The middle Eocene, Oligocene and Miocene are the payable horizons in this rich hydrocarbons basin. A few horizons in the Lower Eocene are also productive. All the hydrocarbon reservoirs are of sandstone or siltstone.

Cauvery Basin

Cauvery Basin, on the east coast of India, extends from Pondicherry in the north to Tuticorin in the South, stretching into offshore Bay of Bengal and spans over an area of 62,500 sq kms up to 200m isobaths. The predominant structural grain of the basin is parallel to the NE-SW trending Eastern

Ghats; a pull apart basin following rifting along the eastern continental margin of the Indian craton of the early Mesozoic. Down to basement faults define a series of horsts and grabens cascading down towards the ocean. The age of the basin is Late Jurassic to Recent. The basins rest unconformably over the Achaean gneisses.

The Early Cretaceous sediments deposited unconformably over the Gondwana sediments represent the first marine transgression in the basin. The entire Cretaceous sequence is dominated by fine clastic sediments. Carbonate sedimentation took place in the ridges and flanks. Prior to depositional of the Tertiary sediments, the rift tectonics in the basin ceased, and a homoclinal dip towards the coast was formed resulting in a N-S trend. The Tertiary and Quaternary sediments are mostly clastics with a few thick carbonate horizons in between. Palaeo-depth and oil generation potential studies have shown that bulk of the sediments reached oil generation conditions some 20-40 millions of years back.

2.6 Reserves and Production of Petroleum:

India has a crude oil reserve of 621.10 million tones as on 31st March, 2016.. The biggest reserve is found in Western Offshore (39.79%) followed by Assam (25.89%). The estimated reserve of natural gas in India as on 31st March, 2016 is 1227.23 billion cubic meters. The highest reserves of natural gas are located in the Eastern Offshore (36.79%) followed by Western Offshore (23.95%). The state wise crude oil and natural gas reserves are shown below:

The production of India’s crude petroleum in 2015-16 was 36.95 MTs while petroleum product production was 231.92 MTs. During this period India produced 25.46 billion cubic meters of natural gas.

Conclusion:

India has one of the biggest reserves of coal in the world. However, petroleum resources are meager in comparison to the major oil producing nations of the world. For securing the energy security in future India has no option but to venture in to nuclear energy as well as renewable energy resources.

Selected References:

Banerjee, D.K., 1998. Mineral resources of India. The world Press Private Limited, Calcutta. 474p.
Biswas, S.K., Dove, A., Garg, P., Pandey, J. Maithani, A. and Thomas (Ed). 1994. Proceedings Second Seminar on Petroliferous Basins of India. Vol.1, Vol.2, Vol.3. Indian Petroleum Publishers, Dehradun.
Levorsen, A.I., 1985. Geology of Petroleum. CBS Publishers & Distributors, New Delhi. 724p.
Moorie, E.S., 1950. Coal: Its Properties, Analysis, Classification, Geology, Extraction, Uses and Distribution. Jhon Wiley & Sons Inc., New York. 473p.
Pareek, H.S., 2004. Progress of Coal Petrology in India. Memoir 57, Geological Society of India, Bangalore. 159p.
Thomas, L., 2012. Coal Geology. Wiley India. 384p.