Chemical Composition of Oil & Gas

8/3/2019 Chemical Composition of Oil & Gas

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CHEMICAL COMPOSITIONCHEMICAL COMPOSITIONOFOF

OIL & GASOIL & GAS

BY

Mrinmay Mishra, Durgaprasad Komali,

Parmod Nain, Satya Manoj,

Navaratan Singh Chouhan


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PetroleumPetroleum -- DefinitionDefinition

Petroleum: Petra = Rock; Oleum = Oil

Petroleum is a form of bitumen composedprimarily of hydrocarbons and exists ingaseous or liquid state in its natural reservoir.

(Hunt, 1979)


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Principal forms of PetroleumPrincipal forms of Petroleum

Based on the physical state of the mixture ofHC, Petroleum can be classified into:

Natural Gas

Condensate

Crude Oil


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Natural GasNatural Gas

Mixture of hydrocarbons that does notcondensate at standard temperature andpressure. It mainly consists of Methane with

decreasing amounts of heavier hydrocarbons.


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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 C2H2 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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CondensateCondensate

Gaseous in the sub surface and condensesat the surface.

The condensate generally has an API gravityhigher than 55 and are composed ofsaturated hydrocarbons in the light gasolinerange.


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Crude Oil

It is a mixture of hydrocarbons that existed inthe liquid phase in natural undergroundreservoir and remains liquid at atmospheric

pressure.

In appearance, crude oils vary from strawyellow, green and brown to dark brown or

black in color.


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Elemental Composition of

Crude 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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CompositionComposition of Petroleumof Petroleum


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Molecular Type Variations inMolecular Type Variations in

HydrocarbonsHydrocarbonsHydrocarbon 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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ParaffinsParaffins /Saturated/Saturated HCsHCs

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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ParaffinsParaffins /Saturated HCs/Saturated HCs


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NaphthenesNaphthenes oror CycloCyclo ParaffinsParaffins

General formula CnH2n for one ringcompounds.

Most abundant hydrocarbon.

The naphthenes and paraffins are alsoreferred to as saturated hydrocarbons

because all the available carbon bonds aresaturated with hydrogen.


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NaphthenesNaphthenes oror CycloCyclo ParaffinsParaffins


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Alkenes or OlefinsAlkenes or Olefins

General formula is CnH2n-2 Olefin hydrocarbons contains double bonds

between two or more carbons atoms. This

cause them to be very reactive, comparedwith other hydrocarbon types.

Very small amounts in crude oil, because it

easily gets saturated produced duringrefining.


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AromaticsAromatics HydrocarbonHydrocarbon ((ArenesArenes))

General formula is (CnH2n-6)

Rarely exceeds 15% in crude.

Tend to be concentrated in heavy fractionsof petroleum (gas oil, lubricating oil,residuum)

The heavy gas oil, lubricating oil, and

residuum of petroleum contain increasingamounts of polycyclic hydrocarbons.


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AromaticsAromatics HydrocarbonHydrocarbon ((ArenesArenes))


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NSO CompoundsNSO 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 PetroleumDistillation of Petroleum


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Petroleum CompositionPetroleum Composition

Molecular GroupsMolecular 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 GravityAPI Gravity


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BiomarkersBiomarkers

The organic compounds in sediments, rocksand crude oils whose carbon structure can betraced back to a living organism, are calledbiomarkers. (Hunt)

These are micro-microfossils, less than 30 nm indiameter.

They are found in rocks and sediments and

undergo minor or no change in structure fromtheir parent organic molecules in livingorganisms.


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AApplications ofBiomarkerspplications ofBiomarkers

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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ConclusionsConclusions

Knowing the chemical composition ofpetroleum helps in ascertaining the marketvalue of the crude oils.

Biomarkers and other related studies carriedout on oils and source rocks provide vitallink between oils discovered and potential

source rock which helps in identifying thepetroleum systems in a basin.


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Thank You

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Chemical Composition of Oil & Gas