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The power of the transmitted light is continuously measured. At each equilibrium pressure, the sample volume is measured and the corresponding density is calculated. The sample oil is first charged into the PVT cell and the pressure of the cell is then lowered isothermally at programmable rates. (2000) performed experimental studies on the onset of asphaltene precipitation using a solids detection system (SDS), which consists of a visual PVT cell and fiber-optic light transmission probes.
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If sufficient quantities of normal alkane are added to the oil, the asphaltene molecules aggregate to such an extent that the particles would overcome the Brownian forces of suspension and begin to precipitate.
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Because of the desorption of resins, asphaltene micelles start to agglomerate to reduce overall surface free energy ( Hammami et al., 2000). On the other hand, if normal alkane (pentane or heptane) liquids are added to crude oil, the crude oil becomes lighter and resin molecules desorb from the surface of asphaltenes in an attempt to reestablish the thermodynamic equilibrium that existed in the oil before the addition of normal alkane liquids. Resins have a strong tendency to associate with asphaltenes, and they help reduce the asphaltene aggregation. Asphaltenes and resins are heterocompounds and form the most polar fraction of crude oil. Tian Ran Lin, in Offshore Pipelines (Second Edition), 2014 15.6.2 Onset of Asphaltene PrecipitationĪsphaltene solubility parameter can also be affected by other components in the oil, like resins ( Hirschberg et al., 1984).