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Properties of Natural Gases in Classical and High Pressure-High Temperature Conditions

Typical HP-HT conditions may be defined by fluid pressures in excess of 50 MPa or temperatures above 150°C, as encountered in deep reservoirs below the North Sea, the Caspian Sea, the Gulf of Mexico and offshore Brazil, among others. Under these conditions natural gas may contain hydrocarbons with chain length of as much as 30 carbon atoms and a methane content higher than 60% (molar concentration). Because of the high temperature, water content may be significant, and further, H2S or CO2 contents may be elevated in some HP-HT reservoirs.

Properties of Natural Gases in Classical and High Pressure-High Temperature Conditions

Under these conditions, the use of standard equations of state to compute volumetric properties becomes questionable. Nevertheless precise knowledge of volumetric properties is desirable for the following reasons:

  • The amount of gases and liquids that can be produced by primary recovery directly depends on the volumetric properties
  • During production, these fluids are known to heat up in an adiabatic expansion; this should be considered when selecting well equipment