Changes

  | part    = Critical elements of the petroleum system

  | part    = Critical elements of the petroleum system

  | chapter = Evaluating source rocks

  | chapter = Evaluating source rocks

  | frompg  = 6-1

  | frompg  = 6-18

  | topg    = 6-41

  | topg    = 6-18

  | author  = Carol A. Law

  | author  = Carol A. Law

  | link    = http://archives.datapages.com/data/specpubs/beaumont/ch06/ch06.htm

  | link    = http://archives.datapages.com/data/specpubs/beaumont/ch06/ch06.htm

  | isbn    = 0-89181-602-X

  | isbn    = 0-89181-602-X

}}

}}

Obviously, the two main elements of hydrocarbons are hydrogen and carbon. Therefore, once we know the amount of [[total organic carbon (TOC)]] present in a rock, we then need to know the amount of hydrogen present in order to assess overall source rock quality. The amount of oxygen and hydrogen present in the kerogen defines the [[Kerogen types|kerogen]] as type I, II, or III and if the rock will be oil or gas prone.

Obviously, the two main elements of hydrocarbons are hydrogen and carbon. Therefore, once we know the amount of [[total organic carbon (TOC)]] present in a rock, we then need to know the amount of hydrogen present in order to assess overall source rock quality. The amount of oxygen and hydrogen present in the [[kerogen]] defines the kerogen as type [[Type I kerogen|I]], [[Type II kerogen|II]], or [[Type III kerogen|III]] and if the rock will be oil or gas prone.

==Hydrogen index==

==Hydrogen index==

The hydrogen index (HI) represents the amount of hydrogen relative to the amount of organic carbon present in a sample. The [[/Rock-Eval_pyrolysis#Rock-eval_pyrolysis|S2 curve]] of a Rock-Eval analysis can help us determine the total amount of hydrogen in milligrams of hydrogen to grams of sample according to the following formula:

The [[hydrogen index]] (HI) represents the amount of hydrogen relative to the amount of organic carbon present in a sample. The [[Rock-Eval_pyrolysis#Rock-eval_pyrolysis|S2 curve]] of a Rock-Eval analysis can help us determine the total amount of hydrogen in milligrams of hydrogen to grams of sample according to the following formula:

:<math>\mbox{HI} = \mbox{S2} \mbox{ (Mg/g)}/\%\mbox{TOC} \times 100</math>

:<math>\mbox{HI} = \mbox{S2} \mbox{ (Mg/g)}/\%\mbox{TOC} \times 100</math>

The oxygen index (OI) represents the amount of oxygen relative to the amount of organic carbon present in a sample. The [[Rock-Eval_pyrolysis#Pyrolysis_indices|S3 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 [[Rock-Eval_pyrolysis#Pyrolysis_indices|S3 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|300px|{{figure number|1}}. Copyright: Tissot and Weite, 1984; courtesy Springer-Verlag.]]

[[file:evaluating-source-rocks_fig6-4.png|thumb|300px|{{figure number|1}}Modified Van Krevlen diagram. Copyright: Tissot and Welte;<ref>Tissot, B. P., and D. H. Welte, 1984, Petroleum Formation and Occurrence, 2 ed.: New York, Springer-Verlag, 699 p.</ref> courtesy Springer-Verlag.]]

:<math>\mbox{OI} = \mbox{S3} \mbox{ (mg/g)}/\%\mbox{TOC} \times 100</math>

:<math>\mbox{OI} = \mbox{S3} \mbox{ (mg/g)}/\%\mbox{TOC} \times 100</math>

* [[Kerogen type and quality: visual assessment]]

* [[Kerogen type and quality: visual assessment]]

* [[Pyrolysis gas chromatography]]

* [[Pyrolysis gas chromatography]]

==External links==

==External links==

[[Category:Critical elements of the petroleum system]]  

[[Category:Critical elements of the petroleum system]]  

[[Category:Evaluating source rocks]]

[[Category:Evaluating source rocks]]