ERSC 4P50 Lecture Notes - Lecture 5: American Association Of Petroleum Geologists, Clathrate Hydrate, Kerogen
20 Dec 2018
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Lecture 5 - Physical and Chemical Properties
Introduction
Oil and natural gas contain hydrocarbons (rings or chains of hydrogen and carbon atoms), e.g.
C3H8 (propane). Short-chain molecules are gaseous at room temp. (volatile), long-chain
molecules are viscous and of low volatility (oil and tar). Physically, hydrocarbons grade from gas
–> liquid–> solid.
• Gases:
o dry gas (methane)
o wet gases (ethane, propane, butane etc.)
• Condensates: gaseous below surface, but condense to liquid at cooler temps of surface.
• Liquid hydrocarbons: oil or crude oil (to distinguish from refined products)
• Plastic hydrocarbons: asphalt and related substances (tar, bitumen, pitch)
• Solid hydrocarbons: kerogen (insoluble organic matter in sedimentary rock) and coal.
• Gas hydrates: ice crystals with methane and other gases within crystal lattice.
Natural Gases – classification
Natural gas is “a mixture of hydrocarbons and varying quantities of nonhydrocarbons that exist
either in the gaseous phase or in solution with crude oil in natural underground reservoirs” API,
AAPG, SPE.
• Dissolved: in solution in crude oil in the reservoir.
• Associated: overlies and in contact with oil in the reservoir as “gas cap”.
• Nonassociated: in reservoirs not containing significant crude oil.
• Natural gas portions of natural gas that are liquefied by processing plants
• Liquids: at surface (e.g. ethane, propane, butane, pentane, natural gasoline, condensate).
• Dry/wet gases: Classified according to amount of contained liquid vapour. > 0.1 gal/1000 ft3
= wet gas.
o Methane typically a dry gas. Wet typically ethane, propane, butane.
• Sweet/sour: Absence/presence of H2S.
Document Summary
Oil and natural gas contain hydrocarbons (rings or chains of hydrogen and carbon atoms), e. g. c3h8 (propane). Short-chain molecules are gaseous at room temp. (volatile), long-chain molecules are viscous and of low volatility (oil and tar). Natural gas is a mixture of hydrocarbons and varying quantities of nonhydrocarbons that exist either in the gaseous phase or in solution with crude oil in natural underground reservoirs api, = wet gas: methane typically a dry gas. Wet typically ethane, propane, butane: sweet/sour: absence/presence of h2s. Hydrocarbon gases: major constituents of natural gas are hydrocarbons of paraffin series, abundance typically decreases with increasing molecular weight: Cnh2n+2 for values of n<5 the paraffins are gaseous at normal t and p. isopentane, n-pentane, n- Hexane liquid at surface but gaseous at subsurface temps (hence condensates). Methane (ch4, marsh gas at surface, fire damp below) is most abundant.
