Inorganic Theory

Petroleum

Petroleum

Petroleum occurs either in

 Gaseous form called Natural gas

 Liquid form called Crude Oil

 Solid form called Bitumin or Pitch

Uses

Petroleum, as found in nature, cannot be directly used, it has to be refined

&/or separated into various fractions before it can be marketed.

The main uses of Petroleum Products are:

As a fuel (eg: Natural gas, gasoline, Diesel Fuels and Fuel Oil)

As a source of heat and power generation (eg: Kerosene and Fuel Oil) As a lubricant (eg: Lubricating Oils & greases)

As a raw material for the Petrochemical Industry (eg: Natural gas and Naphtha)

Origin & Theories

 The question of the origin of petroleum has been hotly debated for a long time.

 Many theories have been suggested to account for the origin of petroleum in nature, the most important of these are:

 The Inorganic Theory

 The Organic Theory

Inorganic Theory

 Hydrocarbons present in petroleum are formed by the action of water on inorganic carbides. They are formed by the reaction of metal and carbon under high temperature & pressure conditions inside the earth.

Reactions of metal carbides within the Earth

FeC2 + 2H2O = C2H2 [acetylene] + Fe(OH)2

CaC2 + 2H2O = C2H2+ Ca(OH)2

The Organic Theory (Universally Recommended)

 There are a number of compelling reasons that support an organic development hypothesis.

First and foremost, is the carbon-hydrogen-organic matter connection.

 Carbon and Hydrogen are the primary constituents of organic material, both plant and animal.

 Simply stated, the organic theory holds that the carbon and hydrogen necessary for the formation of oil and gas were derived from early marine life forms living on the Earth during the geologic past -- primarily marine plankton.

 Second were observations dealing with the chemical characteristics of petroleum reservoirs.

 Nitrogen and porphyrins (chlorophyll derivatives in plants, blood derivatives in animals) are found in all organic matter; they are also found in many petroleums.

 Third were observations dealing with the physical characteristics.

 Nearly all petroleum occurs in sediments are primarily of marine origin.

Petroleum contained in non-marine sediments probably migrated into these areas from marine source materials located nearby.

 Temperatures in the deeper petroleum reservoirs seldom exceed 300^oF (141^oC). But temperatures never exceeded 392^oF (200^oC) where porphyrins are present because they are destroyed above this

temperature. Therefore the origin of petroleum is most likely a low- temperature phenomenon.

Summary

Petroleum was produced when sea creatures died

and got covered with sand and clay. Under high

pressure, these dead organisms changed into

petroleum and natural gases.

Formation of Petroleum

95% of living matter in the ocean is plankton. The Sun's energy provides energy for all living things including plankton and other forms of marine life.

As these early life forms died, their remains were captured by the processes of erosion and sedimentation. Successive layers of organic-rich mud and silt covered preceding layers of organic rich sediments and over time created layers on the sea floor rich.

Once the organic material is buried within the sea floor completely including mud and sand, transformation begins. It is a slow process that occurs to the OM. The general process can be illustrated by the following formulas:

Organic matters + Time + Temperature + Pressure = KEROGEN + BITUMEN

Kerogen + Bitumen + more Transformation = Petroleum

Kerogen

It is a complex, disseminated organic matter in sediments and major starting material for most oil and gas generation, made up from altered remains of marine and lacustrine microorganisms, plants and animals.

There are three phases in the transformation of OM into hydrocarbons((Tissot, 1997):

Diagenesis (shallow to 1000m deep, < 60⁰ C = Kerogen formed here)

On increase in T & P, maturation of Kerogen start, which is divided into:

Catagenesis ( 1000-6000m, 60-150⁰ C, Oil & Gas formation)

Metagenesis (150-200⁰C, methane & other non-hydrocarbon gases)

Migration of Petroleum & Oil Traps

Source Rock: The fine grained muddy sediments in which petroleum originates. E.g. Shale, limestone and silt.

Reservoir Rock: The petroleum migrates from source rock into adjacent porous and permeable rocks and accumulates there to form a pool. These rocks are called reservoir rocks. E.g. Sandstone, conglomerates, porous limestone, fractured shale and jointed igneous and metamorphic rocks.

 There are two types of migration when discussing the movement of petroleum, primary and secondary.

 Primary migration refers to the movement of hydrocarbons from within the source rock and into reservoir rock.

 Secondary migration refers to the subsequent movement of hydrocarbons within reservoir rock.

Oil Traps

Petroleum trap, is subsurface reservoir of petroleum. The oil is always accompanied by water and often by natural gas; all are confined in porous rock, usually such sedimentary rocks as sandstones, arkoses and fissured limestones. The natural gas being lightest, occupies the top of the trap and is underlain by the oil and then the water. A layer of impervious rock, called the roof rock, prevents the upward or lateral escape of the petroleum.

Geologists classify reservoir shapes, or traps into the following types.

Structural traps: Structural traps are created when the seal or barrier is concave upward[looking from below]. This concave nature may be due to local deformation as a result of folding, faulting or both of the reservoir rock.

Some of the important structural traps are as follows.

a)

:

Salt Domes: Strata around the salt dome curve upward creating traps against the sealing salt layers.

b)Fault trap: fault can be a very effective trap, when a fault affects inclined strata, a reservoir rock may be blocked off by an impervious shale there by creating an oil trap.

Stratighraphic traps:

Stratigraphic traps are created by any variation in the lithology or stratigraphy, or both of the reservoir rock. The variation may be facies change, variable porosity and permeability or an up-structure termination of the reservoir rock.

Indian Occurrence

India, like many other countries, is oil deficient and imports huge quantities annually to meets its requirement. At present, oil is extracted mainly from oil reserves in Assam, Gujarat and Maharashtra.

Assam: Oil fields are Digboi, Nahorkatiya, Makum.

Gujarat: Oil fields are Ankleshwar, Kalol, Nawagam.

The Bombay high field lies in Arabian Sea about 160 km NW of Bombay.

Geology of Coal

 Coal is one of the world's leading fossil fuel.

 The term is generally applied to a sedimentary formation of highly carbonaceous character.

 It is Non-renewable fuel that formed long ago from the remains of plants and animals.

 The largest coal reserves are in the United States, Russia, China,

 Major use: electricity generation

Chemical Composition

 It is composed chiefly of carbon, oxygen, hydrogen, nitrogen, traces of sulphur and phosphorous. However, Carbon is a on major side.

 Besides these, it may contain varying proportion of mineral matter which may be residues of mineral constituent of the plant from which coals are derived.

 Carbon (60-90 %)

 Oxygen (2-20 %)

 Hydrogen (1-12 %)

 Nitrogen (1-3 %)

 Formation of Coal

Formation of Coal

There are four important steps in Coal formation.

→ Burial (Large accumulation of Vegetation in Swamps)

→ Compaction

→ Biochemical Change

→Transformation

The forests got buried under the surface of earth. Thus, the plants had no contact with oxygen. Successive layers of sediments sealed the buried plants. Over millions of year, these deposits were subjected to tremendous pressure and heat finally transformed them into coal.

Carbonization: The chemical process involved in the transformation of plant matter into coal is called the carbonization. These chemical changes brought about by the increase in Temperature and Pressure, which is caused due to deep burial.

Classification of Coal

Based on rank of coal, that defines degree of transformation plant matter in to coal, it is divided into four major classes.

 Peat: coal precursor made of partially decomposed organic material.

It is rich in moisture content. Not considered as coal. (First stage)

 Lignite: also called brown coal. Low calorific value. Youngest coal.

fixed carbon is around 50%. (Second stage- no oxygen)

 Bituminous: Common coal with high energy content, but higher sulfur concentrations. fixed carbon is around 63-75%. High calorific value. (Third stage - Increase T & P)

 Anthracite: Rare, but high quality coal with high energy content;

cleanest burning coal. fixed carbon is more or less 90 %. High calorific value. (Forth stage followed by more dense coal - Very high T & P).

Stages in formation of Coal

Chemical Properties

The quality and commercial value of coal depends on its chemical properties, which are as follows:

Moisture Content: It as measured as the amount of water released when a coal sample is heated at prescribed conditions. It can be driven up at 100⁰C.

Volatile Matter: The portion of a coal sample which, when heated in the absence of air at prescribed conditions, is released as gases.

It includes carbon dioxide, volatile organic and inorganic gases containing sulfur and nitrogen.

Fixed Carbon: The remaining organic matter after the volatile matter and moisture have been released. It is typically calculated by subtracting from 100 the percentages of volatile matter, moisture and ash.

Calorific Value: The energy released as heat on burning of coal. The most important parameter for assessment of the quality of coal because the use of coal is based on the available heat that is produced from it.

Distillation of Coal

The main products obtained by the destructive distillation of coal are as follows:

(1) Coke : It is derived from coal on burning in the absence of air. It contains 98 % carbon. It is porous, tough, black and the purest form of coal. Like

charcoal, it Is a good fuel and burns without smoke.

(2) Coal tar: Coal tar is a mixture of different carbon compounds. It thick, highly viscous black liquid with unpleasant smell like napthalenes and aromatic hydrocarbons.

Indian Occurrence

India is the 4th largest producer of coal in the world.

The country endowed with huge reserves of common or bituminous coal.

However good deposits of other rank have also mined at different places.

On the basis of occurrence and its relation to geological age, the deposits mainly classified into two groups are of great importance;

A. Lower Gondwana Coals: 98 % of Indian Coal belongs to this group. The

major coalfields are in states of Jharkhand (Jharia, Giridih, Bokaro etc.), West

Bengal (Raniganj), M.P. (Singrauli, Umaria etc.), Orissa (Talchir) and A.P.

(Singareni)

B. Tertiary Coals: The coals in this group found in the states of Assam, Arunachal Pradesh, Himachal Pradesh, Nagaland and J&K.

A third type called as lignite deposits mainly occur in Tamil Nadu, Kerala, Gujarat, Rajasthan and Uttar Pradesh.

1. North Antelope Rochelle, US (World largest Coal mine)

2. Jharia Coal field (India, biggest Coal mine)