1. 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

2. 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 <0.1 g/mcf
Sweet vs Sour- H2S in sour gas

3. 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

4. Methane- swamp gas,
fire damp- Coal mine
shale gas- drillers term
Genesis-
*mantle
*biogenic gas
*thermogenic gas
20% of natural gas produced is
Biogenic (methane only)

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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
Isomers-branching

12. Naphthenes Aromatics Cyclo alkanes- single bond All liquids at surface
Benzene ring structure
Liquid at surface
Occurrence:
Toluene>xylene>benzene

13. 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.

14. Classification of Crude Oil
Many classification schemes
*engineering based- refineries
Physical properties:
viscosity
boiling pt
refractive index
molecular wt
density

15. Classification of Crude Oil
*geochemical based- maturation,
genesis, and history and
other geoparameters of
occurrence.
Molecular structure:
key to source and
geological history

16. 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

17. Gas Hydrates