Changes

* Gas chromatography-mass spectroscopy (GCMS)

* Gas chromatography-mass spectroscopy (GCMS)

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 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]]).