CHAPTER 2- Physical and Chemical Properties of Hydrocarbons
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CHAPTER 2- Physical and Chemical Properties of Hydrocarbons. Gas Dry Gas Methane Wet Gas Ethane, Butane… Condensate *gaseous in subsurface liquid at surface Liquid H/C- oil, crude oil, crude Plastic H/C- asphalt & related… Solid H/C- Coal and Kerogen

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CHAPTER 2- Physical and Chemical Properties of Hydrocarbons

  • Gas

  • Dry Gas

    • Methane

  • Wet Gas

    • Ethane, Butane…

  • Condensate

  • *gaseous in subsurface

  • liquid at surface

  • Liquid H/C- oil, crude oil, crude

  • Plastic H/C- asphalt & related…

  • Solid H/C- Coal and Kerogen

  • Gas Hydrates- ice crystals containing H/C

  • Natural Gas- mixture of H/C and non H/C in gaseous phase

  • or in solution with crude oil


Dissolved- in solution with other liquids in reservoir

Associated- gas cap gas- in gas phase above liquid

Non associated- little or no crude in reservoir

Organic vs inorganic

Wet vs Dry Gas- dry <0.1 g/mcf

Sweet vs Sour- H2S in sour gas

H/C gases- major constituent

- H/C paraffin series

CH4 most common, C2, C3, …

Ethane, butane (the inferior gas),

propane all common

All others uncommon

Methane- swamp gas,

fire damp- Coal mine

shale gas- drillers term



*biogenic gas

*thermogenic gas

20% of natural gas produced is

Biogenic (methane only)

Inert Gases

He, Ar, Ra

He- 5 ppm in atmosphere

up to 8% in reservoirs

He-rich deposits derived from

U, Th, Ra- i.e. granites and shales- basement rock

Natural production rate from parent low, expulsion and

transport rate high

Panhandle Hugoton Field, gas processing plant since 1929, contains

1.86% He


*inorganic- volcanic in origin

*organic- degradaton of ammonia and nitrates

shallow diagenesis

Fig. 2.2

97% N

2% He

1% CO2

Atmospheric N also

Trapped in connate gas


H- rare – highly reactive and mobile

1.36 TCF found in Mississippian Age sediments in Kansas

40% H, 60% N, CO2, Ar, CH4- thermogenically mature, never


CO2- Biogenic and Volcanic

major constituent of volcanic gas

3CH4 + 6O2 = 3CO2 + 6H2O

CaCO3 + H2 = Ca+ + H2O + CO2-

Acids flowing through limestones


Free gas and highly soluble

Major concern when drilling- kills people on rigs in the USA several

times a year

Highly corrosive to steel- sour gas and oil

Low H2S- bad, drives production costs up- have to scrub out

High H2S- good, produce S

Volcanic and biogenic origin

CaSO4 + 2CH2O = CaCO3 + H2O + CO2 + H2S

2CH2O = organic matter

Also associated with carbonates and Pb-Zn deposits and

deep basin brines

Anydrite  calcite- exothermic- hot enough to mobilize

Pb-Zn sulfide brines

Crude Oil

Mixture of H/C in a liquid

phase which remains a liquid

at the surface

Yellow, green, brown, black

Wide variety of viscosities

Most lighter than water

Vary in Specific Gravity

Chemistry- C, H, V, Ni,…

no two oils the same.

Ponca Crude, 234 compounds

Hydrocarbons- cont.

Paraffins- alkanes- straight

chain carbon with branching

n < 5 gas at surface

5 < n 1< 5 liquid at surface

n> 15 grade into solid wax

for given molecular wt.

Straight chain higher boiling

point than isomers



Cyclo alkanes- single


All liquids at surface


Benzene ring structure

Liquid at surface



Hetero compounds

Organic compounds containing O, N, S & metals, acids, esters,

Ketones, phenols, alcohols

In younger oils- fatty acids, isoprenoids, naphthenic and

carboxylic acids

Sulfur also common, both as H2S and other phases

Nearly any ions found in sedimentary minerals can be found

in crude

Va & N occur as organometallics generally in porphyrin-

derived from chlorophyll and hemoglobin

Metals most often associated with resins

Sulfur and asphaltene fraction most common in shallow, younger,

degraded crude.

Classification of Crude Oil

Many classification schemes

*engineering based- refineries

Physical properties:


boiling pt

refractive index

molecular wt


Classification of Crude Oil

*geochemical based- maturation,

genesis, and history and

other geoparameters of


Molecular structure:

key to source and

geological history


of Crude Oil

Paraffins, Naphthenic and intermediates

based on distillation factors

time and temperature

Tissot and Welte (1978) used ratio between para & naph & aromatics

Oils vary not only w/ age, but w/ variatin in source and degree of

Degradation- degradatin causes wide variations , esp. w/shallow oils