chemical composition of oil & gasold

8/6/2019 Chemical Composition of Oil & Gasold

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Chemical CompositionOf Petroleum & FractionalCharacterization


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Petroleum - Definition

}Petroleum: Petra = Rock; Oleum = Oil

}Petroleum is a form of bitumencomposed primarily of hydrocarbonsand exists in gaseous or liquid state in

its natural reservoir.(Hunt, 1979)


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Principal forms of Petroleum

Based on the physical state of the

mixture of HC, Petroleum can beclassified into:

}Natural Gas

}Condensate

}Crude Oil


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Composition of Natural Gas

Name Formula Molecular

weight

Boiling

point(rc)

Solubility

(g10rg water)

Methane CH4 16.04 - 162 24.4

Ethane C2H6 30.07 -89 60.4

Propane C3H8 44.07 -42 62.4

Isobutene C4H10 58.12 -12 48.9

n-Butane C4H10 58.12 -1 61.4

Isopentane C5H12 72.15 30 47.8

n-Pentane C5H12 72.15 36 38.5

n-Hexane C6H14 86.17 69 9.5


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Condensate

}Gaseous in the sub surface and

condenses at the surface.

}The condensate generally has anAPI gravity higher than 55 and arecomposed of saturatedhydrocarbons in the light gasolinerange.


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Crude Oil

} It is a mixture of hydrocarbons that

existed in the liquid phase in naturalunderground reservoir and remainsliquid at atmospheric pressure.

} In appearance, crude oils vary fromstraw yellow, green and brown todark brown or black in color.


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Elemental Composition ofCrude Oil

Element Minimum Maximum

Carbon 82.2 87.1

Hydrogen 11.8 14.7

Sulfur 0.1 5.5

Oxygen 0.1 4.5

Nitrogen 0.1 1.5

Other trace 0.1


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Composition of Petroleum


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Molecular Type Variations in

HydrocarbonsHydrocarbon molecules occur in following

structural types

Paraffins (CnH2n+2)/Saturated HCs

Naphthenes or Cyclo Paraffins (CnH2n)

Olefin Hydrocarbons (CnH2n-2)

Aromatic Hydrocarbon (CnH2n-6)


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Paraffins /Saturated HCs

}General formula is CnH2n+2}Boiling point and density increase with

increasing number of C atoms.

}Branched alkanes (iso-alkanes) is very smallin quantity.

}Boiling point of straight chains > iso-alkanes

with the same number of C.}Second most common constituent of crude

oil, next to naphthenes.


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Paraffins /Saturated HCs


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Naphthenes or Cyclo Paraffins

}General formula CnH2n for one ringcompounds.

}Most abundant hydrocarbon.

} The naphthenes and paraffins are also

referred to as saturated hydrocarbonsbecause all the available carbonbonds are saturated with hydrogen.


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Naphthenes or Cyclo Paraffins


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Alkenes or Olefins

}General formula is CnH2n-2}

Olefin hydrocarbons contains doublebonds between two or more carbonsatoms. This cause them to be veryreactive, compared with otherhydrocarbon types.

}Very small amounts in crude oil,because it easily gets saturated produced during refining.


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Aromatics Hydrocarbon (Arenes)

}General formula is (CnH2n-6)}Rarely exceeds 15% in crude.} Tend to be concentrated in heavy

fractions of petroleum (gas oil,lubricating oil, residuum)

} The heavy gas oil, lubricating oil, and

residuum of petroleum containincreasing amounts of polycyclichydrocarbons.


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Aromatics Hydrocarbon(Arenes)


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NSO Compounds

} The crude oil contains S, O and N in small

amount.

} The sulfur content may vary from 0.1% to nearly10%.

} The oxygen content up to 3% and oxygencompounds are available in fatty acids,naphthanic acids and nahtheno-aromaticacids.

} The nitrogen content is rarely higher than 1%.}As metal compounds, oil sometimes contains

traces of V, Ni and other elements as well.


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Distillation of Petroleum


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Petroleum CompositionMolecular Groups

C1 to C4: Gas

C5 to C10: Petrol (Gasoline)

C11 to C13: Kerosene

C14 to C18: Diesel oil(Light gas oil)

C19 to C25: Heavy gas oil

C26 to C40: Lubricating oilMore than C40: Residuum


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API Gravity


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Biomarkers

} The organic compounds in sediments,rocks and crude oils whose carbon

structure can be traced back to a livingorganism, are called biomarkers. (Hunt)

} These are micro-microfossils, less than 30nm in diameter.

}

They are found in rocks and sedimentsand undergo minor or no change instructure from their parent organicmolecules in living organisms.


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Applications of Biomarkers

Biomarker can provide information on:

} Type of organic matter

} Environment of deposition

}

Type of lithology}Age of source rock

}Maturity

}Unraveling the filling history

}Oil-oil and oil-source correlations leadingto identification petroleum system in a basin


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Conclusions

}Knowing the chemical composition ofpetroleum helps in ascertaining the

market value of the crude oils.}Biomarkers and other related studies

carried out on oils and source rocksprovide vital link between oilsdiscovered and potential source rockwhich helps in identifying thepetroleum systems in a basin.


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Thank You

chemical composition of oil & gasold

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