− | Molecular compositions can be used to categorize oils (such as waxy or paraffinic and aromatic) and to determine the effects of geological processes (such as [ http://www.oiltracers.com/services/exploration-geochemistry/oil-biodegradation.aspx biodegraded], water washed, or immature). Bulk properties such as API gravity can sometimes be predicted from molecular composition data.<ref name=pt05r94>Kennicutt, M. C., Brooks, J. M., 1988, Surface geochemical exploration studies predict API gravity off California: Oil and Gas Journal: Sept. 12, p. 101–106.</ref> Chromatographic methods are typically used to determine these characteristics. | + | Molecular compositions can be used to categorize oils (such as waxy or paraffinic and aromatic) and to determine the effects of geological processes (such as [http://www.oiltracers.com/services/exploration-geochemistry/oil-biodegradation.aspx biodegraded], water washed, or immature). Bulk properties such as API gravity can sometimes be predicted from molecular composition data.<ref name=pt05r94>Kennicutt, M. C., Brooks, J. M., 1988, Surface geochemical exploration studies predict API gravity off California: Oil and Gas Journal: Sept. 12, p. 101–106.</ref> Chromatographic methods are typically used to determine these characteristics. |
| Gas chromatography (GC) data can indicate the geological mechanisms responsible for changes in composition of an oil. For example, during biodegradation, bacteria preferentially remove the ''n''-paraffins that are prominent features in most chromatograms ([[:file:oil-and-condensate-analysis_fig2.png|Figure 2]]). Therefore the decrease or absence of n-paraffins is a strong indication that an oil is biodegraded. Other geological processes recognizable from chromatograms are thermal immaturity (odd-even predominance of the ''n''-paraffins), water washing (depletion of light aromatics), leaky reservoir seals (loss of light ends), and source characteristics (biomarkers) ([[:file:oil-and-condensate-analysis_fig3.png|Figure 3]]). Drilling additives and contaminants can also be identified by chromatography ([[:file:oil-and-condensate-analysis_fig4.png|Figure 4]]). | | Gas chromatography (GC) data can indicate the geological mechanisms responsible for changes in composition of an oil. For example, during biodegradation, bacteria preferentially remove the ''n''-paraffins that are prominent features in most chromatograms ([[:file:oil-and-condensate-analysis_fig2.png|Figure 2]]). Therefore the decrease or absence of n-paraffins is a strong indication that an oil is biodegraded. Other geological processes recognizable from chromatograms are thermal immaturity (odd-even predominance of the ''n''-paraffins), water washing (depletion of light aromatics), leaky reservoir seals (loss of light ends), and source characteristics (biomarkers) ([[:file:oil-and-condensate-analysis_fig3.png|Figure 3]]). Drilling additives and contaminants can also be identified by chromatography ([[:file:oil-and-condensate-analysis_fig4.png|Figure 4]]). |