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Rock Eval analysis using hydrogen index (HI) and oxygen index (OI) (view source)
Revision as of 19:42, 28 January 2014
, 19:42, 28 January 2014no edit summary
==Oxygen index==
==Oxygen index==
The oxygen index (OI) represents the amount of oxygen relative to the amount of organic carbon present in a sample. The S<sub>3</sub> curve of a Rock-Eval analysis can help us determine the total amount of oxygen present in a sample according to the following formula:
The oxygen index (OI) represents the amount of oxygen relative to the amount of organic carbon present in a sample. The S<sub>3</sub> curve of a Rock-Eval analysis can help us determine the total amount of oxygen present in a sample according to the following formula:
[[file:evaluating-source-rocks_fig6-4.png|thumb|{{figure number|1}}. Copyright: Tissot and Weite, 1984; courtesy Springer-Verlag.]]
:<math>\mbox{OI} = \mbox{S}_{3} \mbox{ (mg/g)}/\%\mbox{TOC} \times 100</math>
:<math>\mbox{OI} = \mbox{S}_{3} \mbox{ (mg/g)}/\%\mbox{TOC} \times 100</math>
==Determining kerogen quality==
==Determining kerogen quality==
The type of kerogen present in a rock determines its quality. Type I kerogen is the highest quality; type III is the lowest. Type I has the highest hydrogen content; type III, the lowest. To determine the kerogen type present in a source rock, plot the hydrogen and oxygen indices on a modified Van Krevlen diagram (at right).
The type of kerogen present in a rock determines its quality. Type I kerogen is the highest quality; type III is the lowest. Type I has the highest hydrogen content; type III, the lowest. To determine the kerogen type present in a source rock, plot the hydrogen and oxygen indices on a modified Van Krevlen diagram ([[:file:evaluating-source-rocks_fig6-4.png|Figure 1]]).
[[file:evaluating-source-rocks_fig6-4.png|thumb|{{figure number|6-4}}. Copyright: Tissot and Weite, 1984; courtesy Springer-Verlag.]]
==Caveat==
==Caveat==