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
• 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

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Gases 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 lt0.1 g/mcf Sweet vs Sour- H2S in
sour gas
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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
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Methane- swamp gas, fire damp- Coal mine
shale gas- drillers term Genesis- mantle b
iogenic gas thermogenic gas 20 of natural gas
produced is Biogenic (methane only)
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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
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Nitrogen 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
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Hydrogen 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 escaped CO2-
Biogenic and Volcanic major constituent of
volcanic gas 3CH4 6O2 3CO2 6H2O CaCO3
H2 Ca H2O CO2- Acids flowing through
limestones
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H2S 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
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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
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Hydrocarbons- cont. Paraffins- alkanes-
straight chain carbon with branching n lt 5 gas
at surface 5 lt n 1lt 5 liquid at surface ngt 15
grade into solid wax for given molecular
wt. Straight chain higher boiling point than
isomers Isomers-branching
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Naphthenes Cyclo alkanes- single bond All
liquids at surface Aromatics Benzene ring
structure Liquid at surface Occurrence Toluenegt
xylenegtbenzene
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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.
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Classification of Crude Oil Many classification
schemes engineering based- refineries Physical
properties viscosity boiling pt refractive
index molecular wt density
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Classification of Crude Oil geochemical based-
maturation, genesis, and history and other
geoparameters of occurrence. Molecular
structure key to source and geological history
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Classification 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
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Gas Hydrates