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Hydrocarbon Exploration & Development Notes 1

Petroleum Properties

  • Typical well stream contains hydrocarbon liquid and gas phases as well as water, sulfurous compounds, acid gases, solids and other non hydrocarbon products.
  • This multi-components must be conditioned prior to processing to produce stabilized products
  • The processing of these stabilized products entail many chemical and physical changes before going into the market
  • Boyle’s Law and Charles’ Law applied in determining pressure, temperature and volume parameters of hydrocarbon gases.
  • MSDS /CDS needed before the hydrocarbon can be processed satisfactorily which include properties such as specific gravity, density, boiling and freezing points.
  • There are 5 series of hydrocarbons that are of interest to us
    1. Alkanes or paraffin: hydrocarbon molecule in which all the carbons are linked with single bond (saturated). The paraffin series is composed of one or more carbon atoms link to form a long chain-like molecules. Example, Methane CH4, Ethane C2H6, …
    2. Alkenes or Olefins: Unsaturated hydrocarbons use a straight chain of double and single bonds to combine carbon and hydrogen atoms.
      • General formula of alkenes CnH2n, where n is the number of carbon atoms in the chain
      • Alkene is more reactive than Alkanes and are produced by downstream processing of oil and gas.
    3. Acetylenes or Alkynes:
      • triple carbon bonds between adjacent carbon atoms
      • Alkynes are unsaturated hydrocarbons of the straight chain series, using the suffix ‘yne’.
    4. Napthenes or Cycloparaffins:
      • single bond, saturated hydrocarbons having a ring shaped molecule.
      • General formula CnH2n where n equals the number of carbons.
    5. Arenes or Aromatics
      • this group of unsaturated hydrocarbons is composed of a closed chain of six carbon atoms arranged in alternate single and double bonds to form a benzene ring.
      • benzene ring is represented by a hexagonal shape having a carbon atom bonded to a hydrogen atom at each other.
      • general molecular formula CnH2n-6, where n=3,4 . . . Alkene groups can attach to a carbon atom in place of the Hydrogen atom of the aromatic such as in the case of Toluene, C6H5CH3.



Classification of Crude Oil and Natural Gas

Crude oil

  1. Crude oil is mixture of hydrocarbons with non-hydrocarbons
  2. The character of the crude oil is determined by the proportion of paraffinic components relative to cyclo paraffinic components.
    • Light crude – large proportion of C5-C8 hydrocarbons
    • Heavy crude – napthenic hydrocarbons
    • Waxy crude – very long chain paraffins
  3. Different crudes have different proportions of each of the hydrocarbons and therefore different cuts or products can be expected when different specification when the crude is processed.
  4. Paraffinic crude are normally low specific gravity crude and are often light in color
    • easily and quickly be refined
  5. Naphthenic crude generally have a higher specific gravity than paraffinic crudes and are darker (tar like color, brown to black).
    • not easily fractionated as paraffinic crudes and as such give greater percentage of residues.
  6. Initial product range from a crude distillation unit is based on the difference in boiling points of the products.
  7. Impurities in the crude are also an important factor.
    • most crude contain some sulphur and acid gases which are toxic and corrosive, making refining more difficult and expensive.

Natural Gas

  1. Mixture of gases taken from a reservoir or gas which is removed from produced crude (solution gas)
  2. The main constituent of natural gas is methane with various lesser proportions of ethane, propane, butane, pentane, hexane and heptane.
  3. Traces: alkenes, bencenes and napthenes
  4. Methane and ethane cannot be condensed at the pressure and temperature which are experienced at the wellhead and will always appears as gases.
  5. Impurities: hydrogen sulphide, carbon dioxide, nitrogen and helium.
  6. Water is associated with the production of both crude oil and natural gas.
  7. Aliphatic hydrocarbons are acyclic and alicyclic hydrocarbon compounds found naturally in or derived from crude oil and natural gas.
    • acyclic compounds form open chain and the most common forms found in natural gas are
      • methane
      • ethane
      • propane
      • butane
      • pentane
      • hexane
    • Alicyclic compounds are whose atoms are arranged in a single ring without double or triple bonds.
      • these are heavier components and are not normally associated with natural gas.

Condensate

  1. very light hydrocarbon fraction in liquid form
  2. associated with natural gas production
  3. not necessarily produced from all gas reservoirs
  4. not to be confused with water that has condensed , which is also known as condensate.

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Categories: Oil & Gas Notes

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