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A project report on petroleum. This project report will help you to learn about: 1. Origin of Petroleum 2. Meaning of Petroleum 3. Types of Petroleum 4. Nature and Source Material 5. Transformation of Organic Matter into Petroleum Hydrocarbons 6. Migration and Accumulation of Petroleum and Gas 7. Petroliferous Basins in India.
Contents:
- Project Report on the Origin of Petroleum
- Project Report on the Meaning of Petroleum
- Project Report on the Types of Petroleum
- Project Report on Nature and Source Material
- Project Report on Transformation of Organic Matter into Petroleum Hydrocarbons
- Project Report on Migration and Accumulation of Petroleum and Gas
- Project Report on Petroliferous Basins in India
Project Report # 1. Origin of Petroleum:
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Nearly all petroleum occurs in sediments, and these sediments are chiefly of marine origin. Further no two petroleum are alike in composition which is chiefly due to variations in the primary source material or may be the result of subsequent environments and such factors like migration, catalysis, polymerization, pressure and temperature changes and metamorphism.
Their origin is within an anaerobic and reducing environment. The presence of porphyrins in some petroleum means that anaerobic condition developed early in the life of such petroleums, as porphyrins are rapidly oxidized and decomposed under aerobic conditions. The low oxygen content of petroleums generally fewer than two percent by weight also indicates that they were formed in a reducing environment.
The time required for forming petroleum and their deposition into pools is probably less than one million years. The highest ratio of oil pool occurrence to volume of sediments occurs in the Pliocene series, which ended about one million years ago. Late Pliocene sandstones and rocks such as the Plio-Pleistocene rocks in the Quirequire field of eastern Venezuela contain commercial oil.
There are two theories of petroleum origin, viz., Organic or Biogenic origin and Inorganic origin. The later has only historical significance and most of them have been abandoned.
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Biogenic Origin:
The organic theory became the accepted theory about the turn of the century, as the carbon and hydrogen necessary for the formation of oil and gas were derived from early marine life forms living on the Earth.
The different reasons in favour of the organic origin are:
a) First and foremost, is the carbon-hydrogen- organic matter connection. Carbon and hydrogen are the primary constituents of organic material, both plant and animal. Moreover, the life processes of plants and animals continually produce carbon, hydrogen, and hydrocarbons.
A major breakthrough occurred when it was discovered that hydrocarbons and related compounds occur in many living organisms and are deposited in the sediments with little or no change.
b) Many crude oils have been found to contain porphyrins and nitrogen. The porphyrins are found in the blood and chlorophylls and in the petroleum it occurs in the form of complex hydrocarbon compounds.
This explains that anaerobic conditions must have developed early in the formation process because porphyrins are easily and rapidly oxidized and decomposes under aerobic conditions. Additionally, low oxygen content also implies a reducing environment. Thus there is a high probability that petroleum originates within an anaerobic and reducing environment.
Nitrogen is present in practically all petroleum’s, chiefly as constituent of complex hydrocarbon compounds. The continuous chain of occurrence of nitrogen from living matter through organic matter in sediments of petroleum seems to offer a reasonable indication of the organic nature of the source material.
c) Optical activity is a property of most petroleum, and is not known to occur in oils of inorganic origin. It is believed that the optical activity in most petroleum is due to the presence of cholesterol (C26H45OH), which is found in both plants and animal matters.
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d) A wide variety of petroleum hydrocarbons, and even crude oil, have been found included in the organic material that is found in nearly all non-reservoir rocks, like shales and carbonates. The same types of hydrocarbons occur in both the fine grained sediments and in crude oil. The intimate relation of the organic material and the petroleum in the sediments leaves no doubt that organic matter was the original source of the petroleum.
Nearly all petroleum occurs in sediments that are primarily of marine origin. Petroleum contained in non-marine sediments probably migrated into these areas from marine source materials located nearby.
Project Report # 2. Meaning of Petroleum:
Petroleum (Gr. petra, rock, L. oleum, oil) is the general term for all the natural hydrocarbons whether gaseous (natural gas), liquid or solid (bitumen). Technically speaking it is an inflammable mixture of oily hydrocarbons with very complex chemical properties.
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Petroleum end product = ([Raw Material + Accumulation + Transformation + Migration] + Geologic Time). The occurrence of petroleum from Ordovician to Pleistocene show that once formed they may have been preserved against the force of destruction and decay over long periods of geologic time.
Project Report # 3. Types of Petroleum:
There are three general types of petroleum:
i) Crude oil.
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ii) Natural gas, and
iii) Semi-solid and solid forms.
i) Crude oil:
It refers to liquid petroleum as opposed to refined oil. These are liquid hydrocarbons that contain varying amount of dissolved gases, bitumens, and other impurities. In raw state crude oil resembles ordinary lubricating oil that is immiscible with water and has a density less than that of sea water. It is however, soluble in naptha, carbon disulphide, ether and benzene. It varies in colour from amber- green to brownish black. The lighter grades are greenish.
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The modern petroleum industry recognizes three principal grades of crude oil:
a) Paraffin-base oil:
It contains a high percentage of the lighter hydrocarbons such as methane and yields the commercially more valued products, e.g., petrol, paraffin, and high grade lubricating oils.
b) Asphalt-base oil:
It consists mainly of the heavier hydrocarbons with a viscous, asphaltic base. It is of less commercial significance because it yields little motor oil during distillation. Much of its residue is in the form of asphalt or bitumen.
c) Mixed-base oil:
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This is an intermediate group with mixed properties of the lighter and heavier oils. It carries a high percentage of naphthalene and is graded 20 on a Baume Scale (In commercial circles, oil is gauged by hydrometers, whose readings are given in the Baume Scale). It is used as lubricants and fuel oils.
ii) Natural gas:
It is petroleum gas consisting of lighter paraffin hydrocarbons (hydrocarbons of methane series), the most abundant being methane gas.
There are three distinct types of natural gas based upon their origin:
a) Petroleum gas:
It is formed as a natural by- product during the generation of petroleum. It is often dissolved within the liquid hydrocarbon or in a free gas phase associated with the oil pool.
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b) Coal gas:
It is formed by the modification of the coal through the introduction of heat, pressure or other natural processes. It is the source of most of world’s supply of commercial natural gas.
c) Bacterial gas:
It is formed during the low temperature alteration of organic matter at or near earth’s surface.
iii) Semi-solid and solid forms:
These are called heavy hydrocarbons and bitumens. They comprise materials such as asphalt, tar, pitch, albertite, etc.
Project Report # 4. Nature and Source Material of Petroleum:
Nature:
Petroleum consists of an extremely complex mixture of hundreds of different hydrocarbons, generally accompanied by small quantities of related compounds containing nitrogen, sulphur or oxygen. The hydrocarbons fall into several natural series of which the alkane series is the most familiar and all its members can be expressed by the formula CnH2n+2.
The components of the crude oil can be classified into two hydrocarbon series, viz., methane series and naphthene series. Crude oil belonging to the methane series is also referred to as paraffin. Paraffins are straight- chain hydrocarbons having a general formula of CnH2n+1. The four principal types of paraffins are methane, ethane (C2H6), propane (C3H8), and butane (C4H10).
The crude oil belonging to the napthane series have the general formula CnH2n. These are called cycloparaffins with the most common being cyclopropane (C3H6) and cyclobutane (C4H8). However, this group of hydrocarbons may contain long, branched chains with complex rings, such as C30H50OH.
Natural Gas consists of hydrocarbons not condensable at atmospheric temperatures (20°C) and atmospheric pressure. They comprise the first four series members of the paraffin series. If the natural gas is comprised almost entirely of methane, it is referred to as dry gas. However, if the ethane content in methane exceeds 5%, it is referred to as a wet gas.
Source Material:
The existence of oilfields in pre- Carboniferous sediments (as far back as the Ordovician) suggests that land plants were not essential to oil formation. The main production of organic carbon seems to have started some 3 billion years ago when photosynthesis is thought to have commenced on a worldwide scale.
Photosynthesis in the oceans has been estimated to produce 12 million tons of hydrocarbons (80,000,000 barrels) material annually. A minute fraction of this amount, preserved in the sedimentary rocks, would supply all the known petroleum deposits, plus those we can expect to discover in the future.
Studies in the organic content of sedimentary rocks indicate that the primary source materials are fish and microscopic marine life. Some species of fish contain greater than 50% oil and there have been enough fish since Ordovician time to account for all known oil deposits in the world. Moreover, fossilized fishes are common in sedimentary strata believed to be source rocks.
Among the microscopic marine life, plankton, are considered to be the primary source of all hydrocarbons. There are two types of planktons, phytoplankton and zooplanktons. Phyto- plankton is the most important and comprises the bulk of the marine plankton. The most abundant, are the siliceous unicellular diatoms.
They contain minute droplets of oil that accumulate in their cellular structure late in the vegetative period. It has been estimated that from 5 to 50 percent of the volume of diatom consists of oil globules. The colonial diatom Elaeaphyton contains oil or oily substances in their cell walls. The Rhizoslenia is known to form extensive oily patches along the western coast of Japan during the months of August and September.
These phytoplanktons are shallow water creatures and are restricted to the photic zones in oceans because growth is totally dependent upon photosynthesis and also upon mineral nutrients with the greatest supply coming from land. Therefore, phytoplanktons are restricted to continental shelf areas, bordering and overlapping the continents.
Such shelf areas experience periodic water blooms, which are voluminous concentrations of phytoplankton. The periodic blooms observed in these areas are the result of the upwelling of cold, stratified, nutrient-rich bottom water into the shallow photic zone (Fig 14.7).
The upwelling conditions that coincide with spring weather create even more massive volumes of plankton because of the result of an increase in solar activity. This hypertrophy increases the BOD (Biological Oxygen Demand) as a result there is mass mortality of living organisms including fish and benthoic invertebrates.
Further there is stratification within the water, which prevents the mixing of surface and deeper oceanic waters. This means that not only is the oxygen not renewed to the deeper water, but also the deeper water becomes colder, denser, and more saline.
A narrow zone called a thermocline separates the surface from the deeper water. This massive volume of dead plankton sink to the bottom of the ocean, they fall through the surface water zone, through the thermocline and into an oxygen deficient floor of the ocean.
Among the zooplankton, foraminifera and radiolaria are the most widely represented fossils in young oil bearing strata with Copepods being the most numerous. Modern zooplankton also contains minute oil droplets. Plankton creates the oil by synthesizing fatty acids. Fatty acids are the essential constituents of animal fats and plant oils, and form the largest source of long-chain molecules. Further the molecular structure of the fatty acid is similar to the molecular structure in crude oil.
Non-marine organic matter, the humus substances, is another potential source material for hydrocarbons. The humus substances are carried into the oceans by the rivers, and include humic acid (C20H10O6), geic acid (C20H12O7), and ulmic acid (C20H14O6). These humus substances are formed by the slow decomposition of the lignin in peats and are found in soils highly charged with decaying vegetation.
Vast quantities of humic acids are forming constantly in swampy regions and, especially in the tropics, are carried into the oceans, either in solution or in colloidal dispersion. Mingling of salt and fresh water might cause the precipitation of the organic material.
In addition to the soluble petroleum hydrocarbons, the organic matter contains numerous insoluble hydrocarbon compounds, soluble asphalts (complex compounds derived from cellulose, purines and pyrimidines), and complex organic substances (kerogen), some of which through bacterial action, heat, pressure, or catalytic action, or combination of these, may be transformed into petroleum hydrocarbons. Kerogen is an important component because it is pyrobituminous organic matter that comprises the bulk (85-95%) of the organic matter of most non-reservoir sediments.
Thus there was massive accumulation of organic material over successive years, centuries, eons, that creates source beds- sedimentary layers containing source material needed to create oil and gas.
Project Report # 5. Transformation of Organic Matter into Petroleum Hydrocarbons:
The deposition of sediments rich in organic matter (>0.5 per cent by weight) depends on the environment of deposition Thus in oxidizing conditions little organic matter will be preserved, as they would be destroyed by both chemical and microbial action. If the sedimentation rate is too high then the percentage of organic matter will be lowered. The most ideal condition are found in quiet- water areas on the continental shelf and slope where there is an abundance of nutrients and a large contribution from both phytoplanktons and terrestrial material.
The only elements essential to the transformation of organic matter into petroleum are hydrogen and carbon. Thus the nitrogen and oxygen contained in the organic matter must somehow be removed while at the same time preserving the hydrogen rich organic residue.
The formation of petroleum at this stage must occur in an oxygen deficient environment, i.e. not to be subjected to prolonged exposure to the atmosphere or to the aerated surface or subsurface waters containing acids or bases or come into contact with elemental sulphur, or other igneous activity, and have a short transportation time from the time of the death to that of burial. All these conditions must be met in order to avoid decomposition of the organic matter.
All of this implies that as dead organic matter falls to the sea floor (organic rain), the hydrocarbon constituents needed for creating end product will be preserved only if the water column through which they are falling is anoxic- lacking living organisms, fall is rapid, the particle size must not be entirely microscopic, bottom dwelling predators are lacking, and there is a rapid sedimentation rate which buries the organic matter below the reach of mud feeding scavengers.
Once the organic matter is buried within the sea floor, transformation begins and it is a slow process involving the following steps:
Organic matter + Transformation = Kerogen + Bitumen (by product)
Kerogen + Bitumen + more transformation = Petroleum
One thing is to remember is that not all the organic carbon in sedimentary rocks is converted into petroleum hydrocarbons. The three phases in the transformation of organic matter into hydrocarbons are Diagenesis, Catagenesis, and Metagenesis.
i. Diagenesis:
It occurs at depths from shallow to as deep as 1,000 meters and at temperatures ranging from near normal to less than 60°C. Biogenic decay aided by bacteria like Thiobacillus, and non-biogenic reactions are the principal processes at work producing primarily methane, carbon dioxide, water, kerogen (precursor to petroleum), and bitumen. Temperature plays an important role in the process. Ambient temperature increases with depth of burial which decreases the role of bacteria in the biogenic reactions and this is simultaneously followed by the decline in the initial methane production.
Depending upon the nature of the original material three different types of kerogen is formed:
i) Type-I kerogen:
It contains an abundance of lipid material (e.g., waxes, vegetable oils and animal fats), which may either be due to a predominance of algal remains (similar to those found in present day lacustrine environments) or to the original biomass suffering severe biodegradation by microbial activity or to a combination of these effects. It has a high hydrogen/carbon (H/C > 1.5) atomic ratio, and is common in many oil shales.
ii) Type-II kerogen:
It is derived from a mixture of phytoplankton, zooplankton and microorganisms of the types now found in reducing marine environments. It has a relatively high H/C ratio and a medium to high sulphur content. This is the type that gives rise to important oil occurrence.
Crucial factors are the geothermal gradient and the length of time kerogen has been exposed to the appropriate heat. Larger hydrocarbon chains and cyclic compounds are broken down, with the maximum production of crude oil and so-called ‘wet gas’ taking place at about 100 °C.
iii) Type III kerogen:
It has relatively low H/C ratio (< 1.0) and is mainly derived from terrestrial plant materials. The oil potential is low though gas may be generated in some quantity at greater depths.
ii. Catagenesis:
It is a thermodynamic non-biogenic process that begins in the deeper subsurface (1,000- 6,000m) as burial, heating (60-175°C) and deposition continues. The transformation of kerogen into petroleum is brought about by a rapid controlled, thermo catalytic process where the dominant agents are temperature and pressure.
The critical temperature is about 60°C which is called the critical jump temperature. This is the beginning of the oil formation which is referred as the liquid/oil window (Fig 14.8). The temperatures are of non-biological origin as it is derived from the burial process and the geothermal gradient that exists within the Earth’s crust. The catalysts are the various surfactant materials present in clays and sulphur.
At temperature above 200°C the catagenesis process is destructive and all hydrocarbons are converted to methane and graphite. At 300°C hydrocarbon molecules become unstable. Thus thermal energy is a critical factor, together with time as it provides stable conditions over long periods of time that allows the kerogen sufficient cooking time, i.e. exposure time of kerogen to catagenesis.
Thus the catagenesis phase involves the maturation of the kerogen. Petroleum is the first to be released from the kerogen followed by carbon dioxide and water. The relative amount of crude oil, wet gas, and dry gas that are produced at different thermal maturation stage and the range of number of carbon atoms in each of the maturation products are shown in Fig 14.9.
iii. Metagenesis:
This phase occurs at very high temperature and pressure which leads to low grade metamorphism. The last hydrocarbon released from the kerogen is generally only methane. The H:C ratio declines until the residue remaining is comprised mostly of carbon in the form of graphite.
Project Report # 6. Migration and Accumulation of Petroleum and Gas:
Most scientist agree that the vast majority of petroleum hydrocarbons are generated by thermal processes from organic material contained in certain types of sedimentary rocks referred to as source rocks. The movement of oil and gas out of the source rocks or within the reservoir is called migration.
The former is called the primary and the latter the secondary migration respectively. Both migrations occur through the water-saturated spaces with the relative porosities (source rocks have high porosities, i.e., clays and shales) and permeabilities (reservoir rocks have higher permeabilities) of the strata playing an important role.
There is considerable disagreement regarding why and how migration occurs. Squeezing of the oil out of the source rock cannot therefore account entirely for primary migration.
It appears that the continued formation of oil and gas during catagenesis produces such pressures that microfactures occur in the source rocks, thus allowing escape upwards into the reservoir rocks. Secondary migration thereafter takes place upwards and sideways due to the buoyant rise of the lighter oil and gas through the water-filled reservoir rocks and hydrodynamic conditions (movement of water through the reservoir rocks).
In general, oil migrates outwards and upwards from the source rocks, rises to the highest possible level, and collects into an oil pool wherever the structures provides a trap which impeded further migration. Gas, if present in excess of the amount that the oil can hold in solution, bubbles to the top and forms a gas cap over the oil pool.
Beneath the pool the pore spaces are occupied by water (usually salt) which is commonly under a very considerable head of pressure. If the pressure and the gas content are sufficiently high, the oil gushes out like an effervescent fountain when the pool is trapped by drilling. When the pressure is too low to drive the oil to the surface or becomes so as the initial pressure falls off and then a pumping is necessary.
Project Report # 7. Petroliferous Basins in India:
Petroliferous basins of India have been classified under four categories though these categories are undergoing continuous revision keeping in view the advancement in exploratory methods.
Category I:
It includes the basin with commercial production, viz., Assam Shelf, Bombay Offshore and Bombay Basin.
Category II:
It includes the following basins, viz., Andaman-Nicobar, Bengal, Cauvery, Himalayan foot hills, Jaisalmer, Krishna-Godavari, Mahnandi and Tripura-Cachar with known occurrence of oil and gas, however, commercial production is yet to be established (Fig 14.10).
Category III:
Basins at Bikaner, Nagpur, Kutch, Kerala-Lakshadeep and Saurashtra with no significant oil and gas but shows geological prospect.
Category IV:
It includes basins with uncertain prospects and requires basic data to be generated for further progress, viz., Arunachal Pradesh, Deccan syncline, Ganga Valley, Gondwana and Kerewa, Mizoram- Manipur, Narmada Basin and Vindhyan.
