Hydrocarbon and seismology 307

Hafezahmad,4th
batch Oceanography:hydrocarbonExplorationandSeismology,OCEAN 307
1
Minerals, classification, prospect and status of mineral of Bay of Bengal, Bangladesh
Minerals are the building blocks of rocks. Geologists define a mineral as: A naturally occurring, inorganic,
solid, crystalline substance which has a fixed structure and a chemical composition which is either fixed or
which may vary within certain defined limits. There are also minerals which form both by inorganic and
organic processes.For example, calcite (CaCO3).Importantmineral deposits of Bangladesh are natural gas,
coal, limestone, hard rock, gravel, boulder, glass sand, construction sand, white clay, brick clay, peat, and
beach sand heavy minerals.
Present status and prospect of minerals deposits of Bay of Bengal, Bangladesh
The recent two verdicts of maritime boundary of Bangladesh with Myanmar and India, allowed
the country to exercise sovereign right to 118,813 sq. Km of waters extending up to 12 nautical
miles of territorial sea and a further Exclusive Economic Zone (EEZ) of 200 nautical miles into
the sea and Continental Shelf extending up to 354 nm from the Chittagong coast (MoFA, 2014b).
Oil and gas There are 23 discovered gas fields in Bangladesh of various sizes. Bangladesh has now
26 offshore blocks, of which 11 are shallow sea blocks and 15 are deep sea blocks. until 2014
Bangladesh drilled 20 wells in the offshore locations of the BoB but only two gas reserves were
discovered (Hossain et al. 2014). So far, a total of 26 Trillion Cubic Feet (Tcf) gas reserve has
been discovered in Bangladesh. Among those, the Sangu reserves having 0.8 Tcf discovered and
already depleted. On the other hand, Kutubdia reserves having 0.04 Tcf are yet be developed.
Drilling at two other offshore places viz. Magnama (3.5 Tcf) and Hatiya (1.0 Tcf) yet be developed
and completed (Alam 2014).
In the country, Bangladesh Petroleum Exploration & Production Company Limited (BAPEX) is
the only authorized company to carry out oil and gas exploration and exploitation. In view of
harnessing and identifying more potential oil and gas reserves a logical plan and framework need
be established by the concerned ministry of the Govt.
On the basis of that a thorough survey with the present boundary of BoB to be conducted and
afterwards the qualified international companies should be appointed to accelerate offshore
exploration and drilling activities to ensure the country's future energy security. Public and private
partnerships are to be encouraged and allowed to share data and information, monitoring, and best
practices, as well as monitoring and assessment protocols and results.
Besides oil and gas, potential mineral resources yet to be explored within the maritime
boundaries of BoB , there might be promising potentials of deposits of marine
minerals from deep sea mining at the seabed areas to explore the elements belonging to the
categories like i) polymetallic sulphides; ii) ferromanganese crusts; iii) ferromanganese
nodules and iv) rate earth elements e.g. Yttrium etc.
Main mineral resources in the ocean include elements and compounds dissolved in sea water,
mineral sands, manganese and prosperitie nodules deposited on the sea bed. One of the important
compounds extracted from sea water is salt (NaCl). A major component of the county’s salt
demand is from the salt produced in coastal area such as cox’s bazar.
Mineral sands which could be deposited in offshore areas. Deposits of mineral sand have been
identified in the coastal belt and in the coastal islands of Bangladesh. Different heavy minerals and
their reserves (in metric ton) are Zircon (158117), rutile (70274), ilmenite (1025558), leucoxene
(96709), kyanite (90745), garnet (222761), magnetite (80599) and monazite (17352).

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Characteristics of minerals:
1: Hardness:A measure of the ease with which a smooth surface of a mineral can be scratched,or of its
resistance to abrasion.
2: Specific gravity: A mineral's specific gravity is the ratio of its mass to the mass of an equal volume of
water. For example, magnetite has a specific gravity value of 5.2, meaning 1cm3 of magnetite will be 5.2
times as heavy as 1cm3 of water.
3: Transparency: refers to the degree to which light can pass through a mineral.
4: Colour: Colour is best described by using primary or simple colours, with descriptors and subsidiary
colours added as necessary,e.g. dull reddish-brown, pale greenish-blue.
5 :Streak: The colour of a mineral when powdered and observed against an unglazed white porcelain plate
6 ;Lustre: The quality and intensity of light reflected from the surface of a mineral.
7: Cleavage/fracture
8: Crystal habit/ mode of occurrence: Crystal habit - is the most commonly found shape or form that a
mineral adopts. Mode of occurrence - reflects the environment of a mineral's formation.
A basic classification for minerals is:
 Native elements. eg. Gold, Silver, Mercury, graphite, diamond.
 Oxides. eg corundum (incl. sapphire), hematite, spinel.
 Hydroxides. eg. Goethite, brucite.
 Sulfides. eg. Pyrite, galena, sphalerite.
 Sulfates. eg. Baryte, gypsum.

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 Carbonates. eg. Calcite, magnesite, dolomite.
 Phosphates. eg. Apatite, monazite.
 Halides. eg. Fluorite, halite (rock salt).
 Silicates (most common)
 Orthosilicates. eg. Garnet, olivine.
 Ring silicates. eg. Tourmaline, beryl.
 Chain silicates. eg. Pyroxenes, amphiboles.
 Sheet silicates. eg. Muscovite mica, biotite mica, clay minerals
 Framework silicates. eg. Quartz, feldspars, zeolites
Gas and petroleum of Bangladesh in EEZ of Bangladesh
The Bayof Bengal(BoB) is the north-easternextension of the Indian Oceanwhich lies north of 6°Nlatitude
and west of about 95°E longitude, the Andaman Sea and Andaman Islands excluded (IHO 1953). At the
end of the final settlement of maritime border disputes with neighboring states Myanmar and India in 2012
and 2014 respectively, Bangladesh has received entitlement to 118,813 sq. km in the BoB comprising her
territorial sea and Exclusive Economic Zone (EEZ) (MoFA, 2014).Bangladesh has a huge amount of gas
reserve in the Bangladesh’s maritime area of the Bayof Bengal.Bangladesh is yet to assessthe true potential
of its offshore oil and gas prospects. Bangladesh has so far discovered 26 gas fields by which we had 27.12
trillion cubic feet (Tcf) gas. But we have already exhausted well over 14 Tcf. According to Petrobangla ,
the remaining reserve of gas in the country is estimated around at 13 Tcf. Some 26 Tcf (trillion cubic feet)
gas reserve has so far been discovered in Bangladesh, of which only about 1 Tcf is located in the offshore
areas. Until 2014, 19 exploratory wells were drilled in the Bay of Bengal, resulting in only two gas
discoveries, i.e. the Sangu and the Kutubdia, with small reserves. The Sangu reserves of 0.8 Tcf have
already depleted, whereas the Kutubdia reserves 0.04 Tcf are yet to be developed. Moreover, the drilling
of the Magnama (3.5 Tcf) and Hatia (1.0 Tcf) yet to produce any commercial volumes of hydrocarbons.
Limitations / obstacle ofExploration and exploitation ofoil and gas in EEZ of Bangladesh.
Bangladesh has vast maritime area with huge different types of resources but there are many obstacle .
1: lack of skilled man power
2: lack of technological instruments and advancements
3: don’t have any exact idea, research or survey how many oil gas reserved in bay of Bengal, what it’s
profitability?
4: lack of strong management of ocean resources like oil and gas.
5: lack of big investment in ocean oil and gas exploration.
6: there is no cooperation among others organizations. sectoral cooperation is needed to develop .
7: there are not true survey data.
8: lack of experienced institution that works on offshore projects.

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9: It contributes to environmental pollution.
Extracting and burning petroleum generates greenhouse gases that contribute to environmental pollution
and, consequently, global warming.
10. It is a non-renewable form of energy.
Terrigenous, Biogenous, chemogenous minerals , placer mineral
Placer deposits are natural accumulations of heavy minerals in sediments such as stream or beach sand
and river gravel. Placer deposits form by a combination of processes that (1) separate heavy minerals
from their source rocks, (2) transport them as sediment, and (3) concentrate them as they are deposited.
Types of placer deposits include alluvium, eluvium, beach placers, and paleoplacers.
Cobalt rich crust: Cobalt crusts are rock-hard, metallic layers that form on the flanks of submarine
volcanoes, called seamounts. Cobalt crusts are a promising resource on the sea floor because they contain
large amounts of cobalt, nickel, manganese and other metals that could exceed the content in land deposits.
They form on the rocky surfaces of undersea rises.
Similar to manganese nodules, these crusts form over millions of years as metal compounds in the water
are precipitated. As with manganese nodules, deposition occurs very slowly. Crusts grow 1 to 5 millimetres
per million years, which is even slower than nodules.
Formation: Even though Fe-Mn crusts form by hydrogenetic precipitation, the exact mechanism of metal
enrichment in the water column and at crust surface are poorly understood. The ultimate sources of metals
to the oceans are river and Aeolian input, hydrothermal input, weathering of basalts, release of metals from
sediments, and extraterrestrial input. Scientific models show that most hydrogenetic elements in crusts
occur as inorganic complexes in sea water. Hydrated cations (Co, Ni, Zn, Pb, Cd, Tl, etc.) are attracted to
the negatively charged surface of Mn oxyhydroxides, whereas anions and elements that form large
complexes with low charge-density (V,As,P,Zr,Hf, etc.) are attracted to the slightly positive charge of Fe
Hydroxide surfaces. Mixed Fe and Mn colloids with adsorbed metals precipitate onto hard-rock surfaces as
poorly crystalline or amorphous oxyhydroxides, probably through bacterially mediated catalytic processes.
The metals are adsorbed because of the crusts’ very slow growth rates (1 to 5millimetres per million years)
and the enormous specific surface area(average 325 square metres per cubic centimetre of crust) (Hein et
al. 2000)

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distribution : Oxidized deposits of cobalt-rich ferromanganese crust are found throughout the global
oceans on the flanks and summits of seamounts (submarine mountains), ridges and plateaux. Cobalt crusts
are especially abundant in the western Pacific within a region the size of Europe, called the Prime Crust
Zone (PCZ).According to one estimate, about 6.35 million square kilometres, or 1.7 per cent of the ocean
floor, is covered by cobalt-rich crusts.
Carbonate rock
Carbonate rocks are a class of sedimentary rocks composed primarily of carbonate minerals. The two
major types are limestone, which is composed of calcite or aragonite (different crystal forms of CaCO3)
and dolostone, which is composed of the mineral dolomite (CaMg(CO3)2).
Difference between marine and non-marine reservoir rock
Marine reservoir rock Non marine reservoir rock
Polymetallic nodules, also called manganese nodules,are rock concretions on the sea bottom formed of
concentric layers of iron and manganese hydroxides around a core.
Occurrence: Mn nodules are concretions that occur on or near the surface of the sediment that covers
abyssal plains throughout the global ocean,where sedimentation rates are low, less than 10 centimeters
(cm) per thousand years. They vary greatly in abundance, covering more than 70% of the sea floor. The
total amount of polymetallic nodules on the sea floor was estimated at 500 billion tons [by Alan A.
Archer of the London Geological Museum in 1981]. Most Mn nodules form at water depths of about
3,500–6,500 meters (m). The location of nodule growth relative to the calcite compensation depth (CCD),
controlled by productivity in surface waters.
Formation : The formation of manganese nodules is conceivably simple
• The growth process can take place in two ways:

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I. The hydrogenous process
II. The diagenetic process
The metal compounds sinking through the water are precipitated
1: Up to 10mm per million year
2: formed due to slow deposition of metals out of sea water and characterized by a high concentration of
base metals and varying Mn/Fe ratios (from 0.5 -5)
THE DIAGENETIC PROCESS
1:Does not occur in the water column but within the sediments
2 :Between 10 and 100mm
3: characterized by high Mn/Fe ratios and relatively low concentration of base metals
Mn nodules grow by precipitation of Mn and Fe oxides around a nucleus that is commonly composed of a
fragment of an older nodule. Unlike Mn crusts,the Mn
and Fe minerals in nodules precipitate from two sources, cold seawater (hydrogenetic) and sediment pore
waters(diagenetic). Hydrogenetic nodules grow remarkably slowly, at a rate of about 1 to 5 mm per
million years,like Mn crusts, whereas diagenetic nodules grow at rates up to 250 mm per million years.
Because most nodules form by both hydrogenetic and diagenetic precipitation. Sediment pore fluids are
the predominant source of Ni,Cu, and Mn, and seawater is the dominant source of cobalt (Co). Metals in
the pore fluid are derived from early diagenetic oxidation-reduction (redox) reactions in upper sediment
layers and are incorporated into the Mn-oxide minerals forming at the seabed.
Polymetallic nodules are found in both shallow (e.g. the Baltic Sea) and deeper waters (e.g. the central
Pacific), even in lakes and are thought to have been a feature of the seas and oceans at least since the deep
oceans oxidised over 540 million years ago.
Polymetallic nodules were discovered in 1868 in the Kara Sea,in the Arctic Ocean of Siberia. During the
scientific expeditions of the HMS Challenger (1872–1876), they were found to occur in most oceans of
the world.

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Composition They are composed mainly of manganese, iron, silicates and hydroxides, and they grow
around a crystalline nucleus at a rate of only about one to 3 millimetres per million years. The chemical
elements are precipitated from seawater or originate in the pore waters of the underlying sediments the
chemical composition of nodules varies according to the kind of manganese minerals and the size and
characteristics of the core.
Elements Percentage Elements percentage Elements Percentage
Mn 29 Si 5 H 1.5
Fe 6 Al 3 Ni 1.4
Ca 1.5 Mg o.5 Co 0.25
Small amount of Sodium, potassium, barium, Titanium also found.
The prerequisite conditions to form the nodules are:
1. Low sedimentation rate
2. Availability of nucleus around which accretion of oxides takes place
3. Oxidising environment
4. Bottom currents of low velocity
Formation : Several theories have been proposed to explain the formation of different types of nodules.
Two of the more popular are:
1. A hydrogenous process in which concretions are formed by slow precipitation of the metallic
components from seawater. This is thought to produce nodules with similar iron and manganese content
and a relatively high grade of nickel, copper and cobalt.
2. A diagenetic process in which the manganese is remobilized in the sediment column and precipitates at
the
sediment/water interface. Such nodules are rich in manganese but poor in iron and in nickel, copper and
cobalt.
Other proposed mechanisms
- A hydrothermal process,in which the metals derive from hot springs associated with volcanic activity;
- A halmyrolitic process, in which the metallic components come from the decomposition of basaltic
debris by seawater;
- A biogenic process,in which the activity of microorganisms catalyzes the precipitation of metal

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hydroxides.
Common Factors
Several of these processes may operate concurrently or may follow one another during the formation of a
nodule.
Whichever of them is operative in particular cases,a number of common factors have been established:
1. Nodule formation requires a low rate of sedimentation or some process for removing sediment before it
accumulates. This enables concretions to grow before they are buried, when they would be cut off from
the conditions that allow them to develop.
2. Plankton concentrates trace elements such as copper and nickel. The organic matter that falls to the sea
bottom when these organisms die is a probable source of the metals incorporated into the nodules.
3. Manganese in seawater comes mainly from hydrothermal vents (hot springs), where it is leached out of
the underlying basalt as the superheated fluids percolate upwards through the oceanic crust.
4. Concretion is furthered by the activity of microorganisms.
Mn nodules Commercial utilization and exploration in the world
Together with cobalt crusts,manganese nodules are considered to be the most important deposits of
metals and other mineral resources in the sea today. These nodules contain mainly manganese,as their
name suggests, but also iron, nickel, copper, titanium and cobalt.
4: Manganese is used also as an alloy with metals such as aluminum and copper
5: non metallurgical uses include battery cathodes, soft ferrites used in electronics, micronutrients in
fertilizers, micronutrients in animal feed, water treatment chemicals, colorant for automobile
undercoating, bricks, frits, glass, textiles, and tiles.
6: used for the coloration of plastics, powder coatings, artist glazes, and cosmetics.
7:
8: A hydrocarbon is an organic compound made of nothing more than carbons and hydrogens.

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1: Aliphatic hydrocarbons are compounds of hydrogen and carbon that do not contain benzene rings.
Aliphatic hydrocarbons tend to be flammable. There are two types of aliphatic hydrocarbon and they are–
open chain hydrocarbon and other is closed chain hydrocarbon : alkanes, alkenes, alkynes and alkenynes.
Characteristics :
1: quite flammable
2: react with oxygen in atmosphere and produce carbon di oxide
3: boiling points and meting points increase as the size of the molecule increases
 Nonpolar molecules
 Main attractive forces as dispersion forces
4: less dense than water
5: insoluble in water
2: Aromatic hydrocarbons are those which contain one or more benzene rings. Examples of aromatic
hydrocarbons include benzene, toluene, purines and pyrimidines.
Characteristics: a compound must have To be classified as aromatic, a compound must have
1) Cyclic structure.
2) Coplanar structure.
3) Each atom of the ring must have a p orbital to form a delocalized π system i.e. no atoms in the ring can
be sp3 hybridized instead all atoms must be sp2 hybridized (N.B. carbocation and carbanions are sp 2
hybridized or an unshared pair electrons).

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4) Fulfill Huckel rule i.e. the system must have 4n + 2 pi electrons : thus by calculating n value it will be
an integral number i.e. n=0, 1, 2, 3
Theories of their origin
Migration of oil and gas and processes
Any Movement of oil and gas in the crust is called petroleum migration, including primary and secondary
migration.
Primary migration of petroleum from source to reservoir is caused by the movement of water,which
carries oil out of the compacting sediments. When the source mud is deposited it contains 70 to 80
percent water the remainder is solids, such as clay materials, carbonate particles or fine-grained silica.
Primary migration mechanisms
1. Migration by diffusion. Because of differing concentrations of the fluids in the source rock and the
surrounding rock there is a tendency to diffuse. A widely accepted theory.
2. Migration by molecular solution in water. While aromatics are most soluble in aqueous solutions, they
are rare in oil accumulations, therefore discrediting the generalimportance of this mechanism, although it
may be locally important.
3. Migration along micro fractures in the source rock. During compaction the fluid pressures in the source
rock may become so large that spontaneous “hydro-fracing” occurs. A useful if underestimated
hypothesis.

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4. Oil-phase migration. OM in the source rock provides a continuous oil-wet migration path along which
the hydrocarbons diffuse along pressure and concentration gradient. This is a reasonable but unproved
hypothesis, good for high TOCs.
Secondary Migration: The process in which hydrocarbons move along a porous and permeable layer
to its final accumulation is called secondary migration.
Tertiary migration: the migration of petroleum accumulation which trapped in the reservoir to the
surface.
Accumulation
Accumulation: The phase in the development of a petroleum system during which hydrocarbons migrate
into and remain trapped in a reservoir.

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Reservoir:A subsurface body of rock having sufficient porosity and permeability to store and transmit
fluids.
 Sedimentary rocks are the most common reservoir rocks because they have more porosity than
most igneous and metamorphic rocks and
 they form under temperature conditions at which hydrocarbons can be preserved.
 A reservoir is a critical component of a complete petroleum system.
Seal (cap rock):An impermeable rock that acts asa barrierto further migration of hydrocarbon liquids.
Rocks that forms a barrier or cap above and around reservoir rock forming a trap such that fluids cannot
migrate beyond the reservoir. The permeability of a sealcapable of retaining fluids through geologic time
is ~ 10-6
to 10-8
darcies. commonly
 shale, mudstone
 anhydrite
 salt,
 A seal is a critical component of a complete petroleum system.
Trap: A configuration of rocks suitable for containing hydrocarbons and sealed by a relatively
impermeable formation through which hydrocarbons will not migrate.
Traps are described as
 structural traps
 Hydrocarbon traps that form in geologic structures such as folds and faults
 stratigraphic traps
 Hydrocarbon traps that result from changes in rock type or pinch-outs, unconformities, or
other sedimentary features such as reefs or buildups

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Characteristics of petroleum forming environment
1. Oil and gas were found in both the Pleistocene and Holocene within a homogeneous to layered, clayey
mud. The oil has undergone a high degree of microbial degradation.
2. The oil in the cores occurred in four modes: (i) in large amounts as an interconnecting network of veins
with gemlike texture; (ii) in smaller amounts as disseminated tiny droplets; iii) disseminated as linings of
gas vugs; or (iv) lining high-angle fractures.
Basic criteria for the formation of fossil fuel in environment
1. An abundant supply of organic matter
2. A relatively rapid rate of accumulation of inorganic material particularly fine grained
3. A small supply of oxygen the water
Petroleum major sources and transformation process,accumulation and composition ofpetroleum
Petroleum (L. petroleum, from Greek: (petra (rock) + Latin: oleum (oil)) is a Petroleum is a naturally
occurring substance consisting of organic compounds in the form of gas, liquid, or semisolid. Organic
compounds are carbon molecules that are bound to hydrogen (e.g., hydrocarbons) and to a lesser extent
sulfur, oxygen, or nitrogen that are found in geologic formations under the Earth's surface.
Petroleum pool : Petroleum pool means a naturally occurring discrete accumulation of petroleum.
Petroleum pools are also known as oil pools... and are also known as oil fields which is "a subsurface oil
accumulation. An oil field consists of one or more oil pools or distinct reservoir in a shape that will trap
hydrocarbons and that is covered by an impermeable or sealing rock.
Transformation process of petroleum
Hydrocarbon series
Major sources of petroleum hydrocarbon in ocean:
1: point sources
a. Spills (vessels, platforms , pipeline
b. Rivers
c. Produced water
d. Coastal refinery wastewater
2: diffuse sources
a. Natural seeps
b. Atmosphere on open seas
c. Coastal urban runoff
d. Marine transport operation
e. Recreational boating
There are two different theories for the origin of petroleum; Organic and Inorganic origin.

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Inorganic or Abiotic origin
States that hydrogen and carbon came together under great temperature and pressure,far below the earth’s
surface and formed oil and gas where chemical reactions have occurred. )oil and gas then seeped through
porous rock to deposit in various natural underground traps.It has also excluded the hypothesis that
petroleum is a finite substance. There are some different theories that describe the inorganic origin of
petroleum which include:
1. Metal carbide theory
Developed by a Russian chemist and states that the deposition of petroleum is controlled by tectonic
activities that occurred during the life of sedimentary rock. To explain his observations, he has put forth
"metal carbide theory". Metal carbides deep in Earth reacted with water at high pressure and temperature
to form acetylene which condenses to heavier hydrocarbons.
Reaction equation is: CaC2+H2O= C2H2+Ca(OH)2
2. Volcanic theory
Involves outgassing of the mantle via volcanic activity or eruption.
3. Earthquake theory
Involves outgassing deep Earth's mantle via tectonic activities such as faults, and this is still happening till
now.
4. Serpentinization theory
States that hydrocarbon is a by-product that came from a metamorphic transformation of the green dark
Olivine mineral, which was found in Earth's mantle.
Organic theory :Modified from Tissot and Welte, 1984. Petroleum formation and occurrence,Springer –
Verlag, 699 pp.
Step 1: Diagenesis forms Kerogen
Diagenesis is a process of compaction under mild conditions of temperature and pressure. When organic
aquatic sediments (proteins, lipids, carbohydrates) are deposited, they are very saturated with water and
rich in minerals. Through chemical reaction, compaction, and microbial action during burial, water is
forced out and proteins and carbohydrates break down to form new structures that comprise a waxy
material known as “kerogen” and a black tar like substance called “bitumen”. All of this occurs within
the first severalhundred meters of burial.
The bitumen comprises the heaviest components of petroleum, but the kerogen will undergo further
change to make hydrocarbons
Step 2: Catagenesis (or “cracking”) turns kerogen into petroleum and natural gas
As temperatures and pressures increase (deeper burial) the process of catagenesis begins, which is the
thermal degradation of kerogen to form hydrocarbon chains. Importantly, the process of catagenesis is
catalyzed by the minerals that are deposited and persist through marine diagenesis. The conditions of
catagenesis determine the product, such that higher temperature and pressure lead to more complete
“cracking” of the kerogen and progressively lighter and smaller hydrocarbons. Petroleum formation, then,

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requires a specific window of conditions; too hot and the product will favor natural gas (small
hydrocarbons), but too cold and the plankton will remain trapped as kerogen.
This behavior is contrary to what is associated with coal formation. In the case of terrestrial burial, the
organic sediment is dominated by cellulose and lignin and the fraction of minerals is much smaller. Here,
decomposition of the organic matter is restricted in a different way. The organic matter is condensed to
form peat and, if enough temperature (geothermal energy) and pressure is supplied, it will condense and
undergo catagenesis to form coal. Higher temperatures and pressures,in general, lead to higher ranks of
coal
Fossil fuel
Fossil fuels are hydrocarbons, primarily coal, fuel oil or natural gas, formed from the remains of dead
plants and animals. Fossils are the remains of creatures that lived long ago. So, fossils include organic
matter buried beneath layers of rocks. A fuel is a source of energy.The energy in fossil fuels originally

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came from the Sun. Plants use the energy in sunlight to make their own food. The energy in plants passes
to the animals that eat the plants. Some energy remains in plants and animals that die and become fossil
fuels
Basic processes of formation of fossil fuel
A fossil fuel is a fuel formed by natural processes,such as anaerobic decomposition of buried dead
organisms, containing energy originating in ancient photosynthesis. Fossil fuels contain high percentages
of carbon and include petroleum, coal, and natural gas. There are three major forms of fossil fuels: coal,
oil and natural gas. All three were formed many hundreds of millions of years ago.
1: Coal is a hard, black colored rock-like substance. It is made up of carbon, hydrogen, oxygen, nitrogen
and varying amounts of sulphur. There are three main types of coal - anthracite, bituminous and lignite.
Coal is created by the decomposed plants. The story of how coal is created is very similar to that for oil.
There are four stages in coal formation: peat, lignite, bituminous and anthracite.
2: Natural gas is formed by marine microorganisms. Petroleum, also known as crude oil, is used for
generating electricity and for manufacturing.
3: Petroleum is formed from the remains of biodegraded organic marine microorganisms. When the
microorganisms compressed they became oil.

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Crude petroleum , different refined products , characteristics , commercial application of these products
Crude oil is a mixture of hydrocarbons that exists as a liquid in underground geologic formations and
remains a liquid when brought to the surface. Petroleum products are produced from the processing of
crude oil and other liquids at petroleum refineries, from the extraction of liquid hydrocarbons at natural
gas processing plants, and from the production of finished petroleum products at blending facilities.
Petroleum is a broad category that includes both crude oil and petroleum products.
Composition of crude petroleum: The relative percentage of each varies from oil to oil.
elements % Elements %
Carbon 83-87 sulphur 06-8
Hydrogen 10-14 Oxygen 0-1.5
Nitrogen 0-0.1 metals 0-03
Others =salts , water and sediments . Reference : Arun Bahl & B.S Bahl ,inorganic chemistry
Petroleum products are materials derived from crude oil (petroleum) as it is processed in oil refineries.
Characteristics of petroleum products :
Petroleum fuels should ignite and burn easily and release their energy completely.
1: Hydrocarbons : Gasoline contains hydrocarbons in the range of (C4-C10), kerosene (C4-C19)diesel
(C8-C21)
2: Volatility : Lighter fuels as gasoline are more volatile than JET or diesel fuels at the same
temperature and pressure
3: Impurities : Refined fuels contain a number of impurities like gums, metals, microbial growth,
sediment, sulfur and water
4: Fuel Microbes : As fuel is sterilized when it leaves the refinery, microbial growth occurs after fuel

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comes into contact with air and water.
5 : Octane:Gasoline fuels are rated with a octane number and this is an indication of their resistance
against detonation (knocking). The higher the rating the more resistant.
6: Volatility: Relates to a liquids boiling point and its tendency to evaporate at normal ambient
temperatures and pressures.
7: Flammability: Indicates how readily a fuel will start to burn, very helpful in an engine combustion
chamber after the spark plug creates a spark.
Petroleum is used extensively in Modern day life. Petroleum provides fuel to run vehicles, cook food,
heat homes and generate electricity. Apart from being used as a fuel petroleum has its applications in products
that we utilize daily. Detergents used to clean dishes and wash clothes contain petrochemical glycerin a
derivative of Petroleum. Plastics are made of Petrochemicals unless it is bioplastic. Wax used to make candles
is a raw petroleum product. Cosmetics that contain oils, perfumes are petroleum derivatives. Petrochemical
ethylene is used in photographic film. Gasoline is a common fuelused for transportation needs. Oil based paints
and paint additives are produces from petrochemicals. Ammonia based fertilizers that are used in agriculture to
make the land fertile is derived from natural gas. Rubber is derived from plant resins apart from that synthetic
rubber is produced from petrochemicals which are used to make car tires, rubber soles on shoes. Petrochemical
uses are in making synthetic fibers, Polyester, nylon, and acrylic are petrochemical derivatives. Oil used to fuel
furnaces or boilers is a petroleum product called Heating oil. Heavy Oil is used to power ships. To prevent
sparking, gumming, corrosion, and icing a petroleum product called jet fuel are used. Diesel, fuel used to run
cars is extracted from crude oil upon distillation.
Organic source of hydrocarbon Inorganic source of hydrocarbon
Plankton (phytoplankton , zooplankton) , plants,
animals, insects, bacteria ,brachiopda ,
crustaceans, bryozoan , mollusks, worms ,coral,
hydrogen and carbon came together ,
extraterrestrial , rain , nebula

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sponge , radiolarians, foraminifera, ,
dinoflagellates , vertebrates
9: Seismology is the study of earthquakes and seismic waves that move through and around the earth. A
seismologist is a scientist who studies earthquakes and seismic waves.
The seismic survey is one form of geophysical survey that aims at measuring the earth’s (geo-) properties
by means of physical (-physics) principles such as magnetic, electric, gravitational, thermal, and elastic
theories. It is based on the theory of elasticity and therefore tries to deduce elastic properties of materials
by measuring their response to elastic disturbances called seismic (or elastic) waves.
Seismic survey is used to develop an image of the underground geology. Seismic surveys use reflected
sound waves to produce a scanning of the Earth’s subsurface. Seismic surveys can help locate ground
water,are used to investigate locations for landfills, and characterize how an area will shake during an a
earthquake, but they are primarily used for oil and gas exploration (Seismic acquisition)
2d and 3D seismic survey ,seismic resolution
Difference between 2D and 3D seismic data
2D seismic data 3D seismic data
Difference between 2D and 3D seismic survey
2D seismic survey 3D seismic survey
Uses one sound source and one set of receivers Uses multiple synchronized sound sources
and hydrophones
Offshore mining, importance
Oil extraction from platforms situated a short distance from the coast.
Exploration of offshore petroleum prospects involves various technologies. Seismic surveying uses
seismic waves propagated in the crust of the Earth to identify and map rock structures that are likely to
contain petroleum reservoirs , such as basins and traps. When likely structures are found. Procedures may
include core sampling of the rocks with geological and laboratory analysis; data logging and interpretation
of formation characteristics; geochemical sampling and analysis of reservoir rocks and fluids; and reservoir
modeling to evaluate the potential for economic development and exploitation.
Offshore Drilling.
If the prospects for reservoir and field development are economically feasible, based on estimates of
recoverable reserves, current market prices, and possible environmental impact, exploratory drilling can
begin. The drilling program is designed according to the characteristics of rocks and formations that have
been identified during the exploration stage.Offshore drilling involves the use of various technologies and

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20
types of equipments such as Drilling ships, semi-submersible drilling barges, or other mobile drilling units
are preferentially used for offshore drilling.
Economic value:
The value of energy-rich petroleum in all of its forms lies in the many products that can be made from it
and the importance of their uses. Crude oil, natural gas, and other hydrocarbon compounds are the bases of
the fuel products that are essentialfor modern modes of transportation, which are predominantly fueled by
motor gasoline, jet fuel, and diesel fuel. Petroleum also provides fuels for heating, industrial-manufacturing
processes, and generation of electricity. Petroleum can be converted into petrochemicals and derivative
products, such as pharmaceutical ingredients, plastics, and building materials, which represent other
portions of the petroleum-source market.
Ecoshouning and scanned sonar methods for offshore oil gas exploration
Impact of offshore drilling /mining on ecology and biodiversity
Offshore drilling operations create various forms of pollution that have considerable negative effects on
marine and other wildlife.
These include drilling muds, brine wastes,deck runoff water and flowline and pipeline leaks.
Catastrophic spills and blowouts are also a threat from offshore drilling operations. These operations also
pose a threat to human health, especially to oil platform workers themselves.
Drilling muds and produced water are disposed of daily by offshore rigs. Offshore rigs can dump tons of
drilling fluid, metal cuttings, including toxic metals, such as lead chromium and mercury, as well as
carcinogens, such as benzene, into the ocean.
Effects ofDrilling Muds
Drilling muds are used for the lubrication and cooling of the drill bit and pipe. The muds also remove the
cuttings that come from the bottom of the oil well and help prevent blowouts by acting as a sealant. There
are different types of drilling muds used in oil drilling operations, but all release toxic chemicals that can
affect marine life. One drilling platform normally drills between seventy and one hundred wells and
discharges more than 90,000 metric tons of drilling fluids and metal cuttings into the ocean.
Effects ofProduced Water
Produced water is fluid trapped underground and brought up with oil and gas. It makes up about 20
percent of the waste associated with offshore drilling. Produced waters usually have an oil content of 30
to 40 parts per million. As a result, the nearly 2 billion gallons of produced water released into the Cook
Inlet in Alaska each year contain about 70,000 gallons of oil.
Effects ofExploration
Factors other than pollutants can affect marine wildlife as well. Exploration for offshore oil involves
firing air guns which send a strong shock across the seabed that can decrease fish catch, damage the
hearing capacity of various marine species and may lead to marine mammal strandings.
More drilling muds and fluids are discharged into the ocean during exploratory drilling than in
developmental drilling because exploratory wells are generally deeper,drilled slower and are larger in

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diameter. The drilling waste,including metal cuttings, from exploratory drilling are generally dumped in
the ocean,rather than being brought back up to the platform.
Effects ofOffshore Oil Rigs
Offshore oil rigs may also attract seabirds at night due to their lighting and flaring and because fish
aggregate near them. Bird mortality has been associated with physical collisions with the rigs, as well as
incineration by the flare and oil from leaks. This process of flaring involves the burning off of fossil fuels
which produces black carbon.
Black carbon contributes to climate change as it is a potent warmer both in the atmosphere and when
deposited on snow and ice. Drilling activity around oil rigs is suspected of contributing to elevated levels
of mercury in Gulf of Mexico fish.
Hydrothermal vent and the gas produces at hydrothermal vent
A hydrothermal vent is a fissure in a planet's surface from which geothermally heated water issues.
Hydrothermal vents are commonly found near volcanically active places, areas where tectonic plates are
moving apart at spreading centers,ocean basins, and hotspots.[1] Hydrothermal vents exist because the
earth is both geologically active and has large amounts of water on its surface and within its crust.
Gas produced from hydrothermal vent : hydrogen sulfide, hydrogen gas, ferrous iron and ammonia,
H2S , CH4 ,
Common techniques for quantitative seismic interpretation
Oil field water ,classification
Produced water is a term used in the oil industry to describe water that is produced as a byproduct along
with the oil and gas. Oil and gas reservoirs often have water as well as hydrocarbons, sometimes in a zone

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22
that lies under the hydrocarbons, and sometimes in the same zone with the oil and gas. Oil wells
sometimes produce large volumes of water with the oil, while gas wells tend to produce water in smaller
proportion. To achieve maximum oil recovery, waterflooding is often implemented, in which water
is injected into the reservoirs to help force the oil to the production wells. The injected water eventually
reaches the production wells, and so in the later stages of waterflooding, the produced water proportion
("cut") of the total production increases.
The five special properties of water are:
(1)Primary salinity (alkali salinity); that is, salinity not t o exceed twice the sum of the reacting values of the
radicles of the alkalies.
(2)Secondary salinity (permanent hardness); that is, the excess (if any) of salinity over primary salinity, not t
o exceed twice the sum of the reacting values of the radicles of the alkaline earths group.
(3)Tertiary salinity (acidity); that is, the excess (if any) of salinity over primary and secondary salinity.
(4)Primary alkalinity (permanent alkalinity); that is, the excess (if any) of twice the sum of the reacting
values of the alkalies over salinity.
(5) Secondary alkalinity (temporary alkalinity);that is, the excess (if any) of twice the sum of the reacting
values of the radicles of the alkaline earths group over secondary salinity.
PALMER’S CLASSIFICATION :Waters are classified into five classes:
Class l: d < a
2d = primary salinity
2(a - d ) = primary alkalinity
2b = secondary alkalinity
Class 2: d = a
2u or 2d = primary salinity
2b = secondary alkalinity
Class 3: d > a ; d < (a + b )
2a = primary salinity
2(d - a ) = secondary salinity
2(a + b - d ) = secondary alkalinity256 CLASSIFICATION OF OILFIELD WATERS
Class 4: d = (a + b)
2a = primary salinity
2b = secondary salinity
Class 5: d > (a + b)
2u = primary salinity

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23
2b = secondary salinity
2(d - a - b ) = tertiary salinity (acidity)
Oil field water may be classified genetically into three groups meteoric , connatic and mixed
water
1. Meteoric water is a water that has fallen as rain and has filled up the porous shallow
rocks or percolated through them. Such waters contain combined oxygen chiefly as CO2 .
They are carried into the ground when the 0 reacts with sulfides to produce sulfates and
the CO2 reacts to produce carbonates and bicarbon- ates. Therefore, presence of CO3
-2
,HCO3
- , SO4
2- in an oil-field water suggests that at least some of the water had come
from the surface. Such meteoric water may be related to the present ground surface and
may reflect the mixing of ground water with oil-field waters or it may be related to a
buried surface which was once exposed to rains. Generally dilute nature of many rocky
mountain oil-field water is thought to be due to dilution by meteoric waters.
Waters are classified by numerical values of the relationships of anions to the cations, where a, b,
and d represent the percentage values of the alkali cations, alkaline earth cations, and strong acid
anions, respectively.
2 . Connate water was originally intended to mean the sea-water in which marine sediments were
deposited and it originally filled all" the-pores r~but-it is found that there is a change in most reservoir
waters and their chemical composition differs from seawater,indicating that they have circulated and
moved. Most oilfield waters are brines, characterised by the abundance of NaCl and they sometime have
concentration of dissolved solids much greater than modern sea-water.d
3: Mixed waters are characterised by both chloride and sulfate carbonate - bicarbonate content. This
suggests a multiple origin, presumably mixing up of meteoric water and connate water of rocks.
Caprock is a rock that prevents the ﬂow of a given ﬂuid at a certain temperature and pressure and
geochemical conditions. For a long time, the only force causing the movement of oil and gas in the
subsurface was believed to be buoyancy. If so, then to form oil and gas accumulation, their migration
paths must have been stopped by a roof, i.e., caprock (seal). Clays, shales, carbonates, evaporites, and
their combinations can form caprocks.
The caprocks can be categorized into three types.
Type I caprocks are typical for argillaceous
sequences in a state of continuing compaction; they
are developed in areas of young subsidence of
Earth’s crust, with abnormally high pore water
pressure.
Type II caprocks are associated with rocks
compacted beyond the plasticity limit and having
lost ability to swell on contact with water. Such
rocks do not contain swelling clay minerals, and interstitial water contains surfactants.
Type III caprocks are typical for rocks with a rigid matrix and intense fracturing. Such caprocks are
mainly developed over the old platforms in regions of low tectonic mobility, with no detectable

Hafezahmad,4th
24
hydrodynamic breakdown of the section. Formation water potential in such regions is practically equal
throughout the section and corresponds to the calculated hydrostatic potential.
Reservoir rocks
Reservoir Rocks are the rocks that have ability to store fluids inside its pores, so that the fluids (water,oil
and gas) can be accumulated. In petroleum geology, reservoir is one of the elements of petroleum system
that can accumulate hydrocarbons (oil or gas). Reservoir rock must be has good porosity and permeability
to accumulate and drain oil in economical quantities. All types of rock (igneous, sedimentary, metamorphic)
can act as reservoir rocks if it can accommodate and drain hydrocarbons. Reservoir rocks around the world
is dominated by sedimentary rocks because generally it has primary porosity. Igneous and metamorphic
rocks can be reservoir if there are in fracturing state (secondary porosity).
A source rock is a rock that is capable of generating or that has generated movable quantities of
hydrocarbons.

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25
Type Definition
Potential source
rock
Rock which contains organic matter in sufficient quantity to generate and expel hydrocarbons if
subjected to increased thermal maturation.
Effective source
rock
Rock which contains organic matter and is presently generating and/or expelling hydrocarbons
to form commercial accumulations.
Relic effective
source rock
An effective source rock which has ceased generating and expelling hydrocarbons due to a
thermal cooling event such as uplift or erosion before exhausting its organic matter supply.
Spent source
rock
An active source rock which has exhausted its ability to generate and expel hydrocarbons either
through lack of sufficient organic matter or due to reaching an overmature state.
Characterizing source rocks
To be a source rock, a rock must have three features:
 Quantity of organic matter
 Quality capable of yielding moveable hydrocarbons
 Thermal maturity
marine vs non marine reservoir rock
MARINE RESERVOIR ROCK NON MARINE SERVOIR ROCK
Carbonate rocks are a class of sedimentary rocks composed primarily of carbonate minerals. The two
major types are limestone, which is composed of calcite or aragonite (different crystal forms of CaCO3)
and dolostone, which is composed of the mineral dolomite (CaMg(CO3)2).

Hafezahmad,4th
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Sediment is a naturally occurring material that is broken down by processes of weathering and erosion,
and is subsequently transported by the action of wind, water,or ice, and/or by the force of gravity acting
on the particle itself.
There are three kinds of sea floor sediment: terrigenous, pelagic, and hydrogenous.
Terrigenous sediment is derived from land and usually deposited on the continental shelf, continental
rise, and abyssal plain. It is further contoured by strong currents along the continental rise.
Terrigenous sediments are those derived from the erosion of rocks on land; that is, that are derived from
terrestrial environments. Consisting of sand, mud, and silt carried to sea by rivers, their composition is
usually related to their source rocks; deposition of these sediments is largely limited to the continental
shelf. Sources of Terrigenous sediments include volcanoes, weathering of rocks, wind-blown dust,
grinding by glaciers, and sediment carried by icebergs.
Pelagic sediment is composed of clay particles and microskeletons of marine organisms that settle slowly
to the ocean floor. Some of these organic sediments are called calcareous or siliceous “oozes” because
they are so thick and gooey. The clay component (or sometimes volcanic ash) is generally carried from
land by wind and falls on the surface of the ocean. Pelagic sediment is least abundant on the crest of
midoceanic ridges because of the active volcanism.
Hydrogenous sediments are rich with minerals, such as manganese nodules, that precipitate from
seawater on the ocean floor. An evaporite is a rock composed of salt minerals left behind by the
evaporation of salty water. Examples include rock salt (NaCl) and gypsum (CaSO4 • x H2O).
Biogenic minerals: Biogenous sediments are composed of the remains of living organisms, including
microscopic phytoplankton (plants) and microscopic zooplankton (animals), terrestrialand aquatic plants,
shells of invertebrates, and vertebrate material (teeth, bone), and associated organic residues. Coal, oil,
and gas are derived from biogenous sediments.
Dissolved weathering products constitute most of the salt in the sea. The major- and minor-element
chemistry of biogenically produced minerals, most importantly calcite, aragonite, and opal-A (amorphous
silica)
10: illustration
Geochemical map
Isopach map
Paleogeographic map
Structural map
Placer deposit
hydrothermal sulphide , their location in marine environment
subsurface geology: Subsurface geology is the study of the physical properties and location of rock and
soil found below the ground surface. One of the most valuable reasons for learning about the subsurface is
understanding the materials below man-made structures.

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subsurface mapping , types of subsurface maps
flood model
structural and stratigraphic interpretations of seismic data
Ecoshouning and scanned sonar method for off shore exploration
Some of the sound reflects off the seafloor but some of the sound penetrates the seafloor,
sometimes as much as 20-30 km below it depending on how the array is designed. The sound that
penetrates the seafloor may also reflect off layers of sediment or rock within the seafloor. The
reflected sounds travel back up to the surface. The ship also tows a number of hydrophones (called
a towed array or streamer)) which detects the reflected sound signal when it reaches the surface.
They use many hydrophones to hear weaker reflections from deeper in the Earth.
The time it takes the sound to return to the ship can be used to find the thickness of the layers in
the seafloor and their position (sloped, level, etc). It also gives some information about the
composition of the layers. By towing multiple hydrophone streamers separated by 50-200 m,
scientists can create three-dimensional images of the Earth’s sediment layers. This technique is
called multi-channel seismics.
Seismic refraction gives more information about the layers. Sound pulses that enter the seafloor
are both reflected and refracted (or bent) as they pass into different layers. The refracted sound
pulse follows a complex path. With seismic refraction, the density of the layers can be determined.

Hafezahmad,4th
28
A potential application of the side-scan images is the mapping of seafloor resources,such as the
manganese nodules (Scanlon and Masson, 1992,) and oil seep sites. The sidescan sonar (SOund
NAvigation and Ranging) system is designed to image the seafloor by transmitting sound energy and
analyzing the return signal or echo that bounces back from the seafloor or from submerged objects. A
towfish transmits energy in a fan shape to both sides of the track line. The fan width varies with the
frequency of the sonar system. Seabed features are characterized by mapping the intensity of reflected
returns from different materials. The shape and character of features on the bottom are displayed in gray-
scale images. More advanced sidescan units include a vertical 'pinger' that provides a simultaneous
estimation of depth directly below the unit.s ide-scan sonar imagery is also a commonly used tool to
detect debris items and other obstructions on the seafloor that may be hazardous to shipping or to seafloor
installations by the oil and gas industry.
Seismic resolution which are used to search the petroleum resources in marine environment
High-frequency seismic reflection profiling is a wellestablished and often used technique in marine
investigations. seismic data are viewed as two-dimensional time sections. Given closely spaced profile
lines, it is possible to produce posted two-way travel time maps of sub-surface reflectors which,
when plotted as isometric displays, clearly show the three-dimensional spatial morphology of the sub-
surface topography. With borehole control, such information can be used to provide a series
of images which indicate temporal as well as spatial relationships of sub-surface reflectors.
Common techniques for quantitative seismic interpretation
Conventional seismic interpretation implies picking and tracking laterally consistent seismic reflectors for
the purpose of mapping geologic structures, stratigraphy and reservoir architecture. The ultimate goal is to
detect hydrocarbon accumulations, delineate their extent, and calculate their volumes.
1. AVO Analysis
2. Seismic Inversion
3. Seismic Attributes
4. Forward Seismic Modeling

Hafezahmad,4th
29
Amplitude versus offset (AVO) is primarily the variation in seismic reflection amplitude with
change in distance between shot point and the receiver. Its another name is AVA (amplitude
variation with angle). AVO analysis is conducted on CMP data, where the offset rises with
the angle. Increase in AVO on the seismic section are the identifications of softer reservoir
rock with hydrocarbons (low acoustic impedance) than ambient shales and decrease in
amplitude with offset is because of geometrical spreading, attenuation, absorption, anisotropy
and several other aspects.
Draw backs of AVO Analysis:
Lithology, tuning & overburden effects create ambiguities.
The processing and aqusition effects may lead to false AVO anomalies.
The common reason for failure being lack of shear wave velocities information and
use of simple geologic models.
Also, the professionals must be expert and experienced for geologic input.
Processing techniques that affect the near offset traces (CDP Gathers) in different way from
far offset traces could also lead to false AVO anomalies.
2 : Seismic Inversion : It is defined as process of converting seismic reflection data into a
quantitative rock-properties of a reservoir. Seismic inversion may be pre-stack or post-stack,
deterministic, random or geostatistical. It includes other reservoir measurements like well logs and
cores. The process of moving rocks on the left to seismic on the right is labeled as “seismic
method”.
Benefits of Seismic Inversion
The concept of impedance and geology is better understood by most geologists than the seismic
trace. Thus working in the impedance domain is a great mechanism for coordinating with the
various disciplines in a multidisciplinary team.
It removes the effects of the wavelet within the seismic bandwidth.
Forces well ties to be made and understood.
Reservoir properties are separated from the overburden.
May provide quantitative predictions on reservoir properties.
Leads to improved Stratigraphic interpretation.
Interpretation in the impedance domain is frequently easier than in the seismic domain.
Also there is possibility of extending beyond the seismic bandwidth.
Inversion Limitations
Estimate the frequencies available within seismic by wavelet estimation or spectral analysis.
Take the well impedance data and band pass it to the same frequencies as the seismic data.
As a rule of thumb use 15 dB down point as limits.
If the target is still visible then using Seismic Colored Inversion should be adequate.
If not, then need to add frequencies by model assumption.
3 :Seismic Attribute
It is the quantity obtained or derived from seismic data that can be analyzed in order to improve
information that strength be finer in a traditional seismic image, leading to a

Hafezahmad,4th
30
improved geological or geophysical interpretation of the data. Examples of seismic attributes can
include amplitude, measured time, frequency and attenuation and also the combinations of these.
Most of the seismic attributes are post-stack, but those that use CMP gathers (such as amplitude
versus offset) must be analyzed pre-stack.
Structural interpretation of seismic data Stratigraphic interpretation of seismic data
using a combination of seed detection and
line-based interpretation.
The stratigraphic interpretation involves
removal of opacity and seed detection.
on picking a set of depth horizons on amplitude manipulation.
Fourier transformation and advantages in data processing
Fourier transform defines a relationship between a signal in time domain and its representation in
frequency domain.
transform of a signal is a continuous complex valued signal capable of representing real valued
or complex valued continuous time signals.
Advantages • One of the important advantage is that Fourier transform can improve the signal-
to-noise ratio (SNR), e.g. one sinusoidal signal embedded in Gaussian noise.
Fellgette advantage- High speed. • Jacquinot advantage-High sensitivity. • Slitless system. • All
of the energy of the source is utilized in FTIR. • Rapid scan time with high sensitivity.
Source rock , classification and maturation
Source rock refers to rocks from which hydrocarbons have been generated or are capable of being
generated. They form one of the necessary elements of a working petroleum system. They are organic-rich
sediments that may have been deposited in a variety of environments including deep water marine,
lacustrine and deltaic. Oil shale can be regarded as an organic-rich but immature source rock from which
little or no oil has been generated and expelled.
Source rocks are classified from the types of kerogen that they contain, which in turn governs the type of
hydrocarbons that will be generated.
1: Type I source rocks are formed from algal remains deposited under anoxic conditions in deep lakes: they
tend to generate waxy crude oils when submitted to thermal stress during deep burial.
2 :Type II source rocks are formed from marine planktonic and bacterial remains preserved under anoxic
conditions in marine environments: they produce both oil and gas when thermally cracked during deep
burial.
3 : Type III source rocks are formed from terrestrial plant material that has been decomposed by bacteria
and fungi under oxic or sub-oxic conditions: they tend to generate mostly gas with associated light oils
when thermally cracked during deep burial. Most coals and coaly shales are generally Type 3 source rocks.
Source rock Maturation and expulsion

Hafezahmad,4th
31
With increasing burial by later sediments and increase in temperature,the kerogen within the rock begins
to break down. This thermal degradation or cracking releases shorter chain hydrocarbons from the
original large and complex molecules occurring in the kerogen.The hydrocarbons generated from
thermally mature source rock are first expelled, along with other pore fluids, due to the effects of internal
source rock over-pressuring caused by hydrocarbon generation as well as by compaction. Once released
into porous and permeable carrier beds or into faults planes, oil and gas then move upwards towards the
surface in an overall buoyancy-driven process known as secondary migration.
1: active and passive continental margin
Together, the continental shelf, continental slope, and continental rise are called the continental margin.
Continental margins constitute about 28% of the oceanic area.
A passive margin is the transition between oceanic and continental lithosphere that is not an active plate
margin. A passive margin forms by sedimentation above an ancient rift, now marked by transitional
lithosphere. The transition between the continental and oceanic crust that was originally created by rifting
is known as a passive margin. Passive margins are found at every ocean and continent boundary that is not
marked by a strike-slip fault or a subduction zone. Passive margins define the region around the Atlantic
Ocean, Arctic Ocean, and western Indian Ocean, and define the entire coasts of Africa.
Active continental margins are those that are tectonically active. An active continental margin is found on
the leading edge of the continent where subduction occurs. Active continental margins are typically narrow
from coast to shelf break, with steep descents into trenches. Active margins are commonly the sites of
tectonic activity: earthquakes, volcanoes, mountain building, and the formation of new igneous rock.
Sources of Marine Minerals
(a) Mineral deposits derived from land sources known prior to the advent of the theory of plate tectonics.
These constitute beach deposits and placer mineral deposits, as well as certain deposits precipitated from
seawater (lime and phosphorite).
(b) Mineral deposits derived from sources in ocean basins discovered at and after the advent of the theory
of plate tectonics. These comprise metalliferous sediments, polymetallic massive sulphides, and related
deposits.
(c) Mineral deposits derived from a combination of land and ocean basin sources. These comprise
polymetallic manganese nodules and cobalt-rich ferromanganese crusts.
2: minerals resources in continental shelf
The continental shelf is a gently sloping and relatively flat extension of a continent that is covered by the
oceans. The shelf occupies only 7% of the total ocean floor. Continental shelves contain valuable
resources,such as oil and gas and minerals. The estimated amount of oil in continental shelves around the
world is about 86 billion barrels. Similarly, 420 trillion cubic feet of recoverable natural gas lies beneath
the continental shelf. Oil and gas form from organic material that accumulates on the continental shelf.
Over time the material is buried and transformed to oil and gas by heat and pressure.
Principal minerals from continental shelf

Hafezahmad,4th
32
1: Phosphorite, phosphate rock or rock phosphate is a non-detrital sedimentary rock which contains high
amounts of phosphate minerals. The phosphate content of phosphorite varies from 4-20% phosphorus
pentoxide (P2O5)
2:placer:
The potential for the occurrence of placer deposits on and within then sedimentary accumulations of
entire continental margins (continental shelf, slope and rise) associated with land sources of minerals is
great.
When pebbles, sands, and silts become sorted through the action of moving water,minerals with higher
specific gravities and resistance to weathering may also become concentrated in beaches and drowned
river mouths.
Many mineral-bearing offshore and beach placers containing diamond, gold, platinum, tin, chromite, iron
sand, zircon, ilmenite, rutile, and monazite are currently being now mined 2:

Hafezahmad,4th
33
(i) Placers of Cassiterite (Tin, Sn): Primary cassiterite is found in high-temperature hydrothermal
veins and pegmatites (a course type of granite) associated with intrusive granites and
rhyolites ( a fine-grained type of granite).
(ii) Placers of Diamond: Diamonds were discovered on the shores of Namibia and South Africa
around 1928. The diamond content of the deposits varies from 0.15 carat per square metre
(ct/m2) to 2.45 ct/m2
(iii) Placers of Gold and Platinum
(iv) Placers of Ilmenite, Rutile and Zircon
(v) Placers of Chromite (Chromium, Cr)

Phosphorite
The MARMINdatabasecontains records of 56 occurrences of offshore phosphate deposits. They can be categorized in three
groups: (i) clastic deposits;(ii) coral deposits; and (iii) upwelling deposits.
(i) Clastic Deposits
Clastic deposits are detritic sands resulting from the erosion of on-land phosphate deposits. They can be concentrated in
paleobeaches or paleochannels owing to the high density of thegrains: 4 compared with the2.7 for quartz and carbonate.
(ii) Coral Deposits
Coral deposits were formed by the phosphatisation of coral limestones associated with volcanic
seamounts.
iii) Upwelling Deposits
The MARMIN database includes records of 33 occurrences of phosphate-bearing sediment apparently
linked with upwelling of deep ocean water along steep margins.
Deep sea mining is a relatively new mineral retrieval process that takes place on the ocean floor. Ocean
mining sites are usually around large areasofpolymetallic nodules or active and extinct hydrothermal vents
at 1,400 to 3,700 metres below the ocean’s surface. The vents create globular or massive sulfide deposits,
which contain valuable metals such as silver, gold, copper, manganese, cobalt, and zinc.The deposits are
mined using either hydraulic pumps or bucket systems that take ore to the surface to be processed.

Hydrocarbon and seismology 307

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