Changes

===Original total organic carbon and hydrogen index determinations===

===Original total organic carbon and hydrogen index determinations===

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M97FG3.jpg|{{figure number|3}}Modified Espitalie et al. (1984) kerogen type and thermal maturity plot. A worldwide collection of immature marine shales shows a range of original hydrogen index (HI_o) values from approximately 250 to 800 mg HC/g TOC, with the majority plotting in the 300 to 700 mg HC/g TOC range. The key points are the range of values, and that all generate more oil than gas from primary cracking of kerogen. TOC = total organic carbon.

M97FG3.jpg|{{figure number|3}}Modified Espitalie et al.<ref name=Espit>Espitalie, J., M. Madec, and B. Tissot, 1984, Geochemical logging, in K. J. Voorhees, ed., Analytical pyrolysis: Techniques and applications: Boston, Massachusetts, Butterworth, p. 276–304.</ref> kerogen type and thermal maturity plot. A worldwide collection of immature marine shales shows a range of original hydrogen index (HI_o) values from approximately 250 to 800 mg HC/g TOC, with the majority plotting in the 300 to 700 mg HC/g TOC range. The key points are the range of values, and that all generate more oil than gas from primary cracking of kerogen. TOC = total organic carbon.

M97FG4.jpg|{{figure number|4}}Organofacies plot of original total organic carbon (TOCo) and original generation potential (S2o). These data show the high degree of correlation of the worldwide collection of marine shale source rocks. The slope of the correlation line is inferred to indicate the initial original hydrogen index (HI_o) value (533 mg HC/g TOC) for the entire group of source rocks with a y-intercept forced through the origin (Langford and Blanc-Valleron, 1990). R2 = linear correlation coefficient.

M97FG4.jpg|{{figure number|4}}Organofacies plot of original total organic carbon (TOCo) and original generation potential (S2o). These data show the high degree of correlation of the worldwide collection of marine shale source rocks. The slope of the correlation line is inferred to indicate the initial original hydrogen index (HI_o) value (533 mg HC/g TOC) for the entire group of source rocks with a y-intercept forced through the origin (Langford and Blanc-Valleron, 1990). R2 = linear correlation coefficient.

M97FG5.jpg|{{figure number|5}}Distribution of original hydrogen index (HI_o) values for a marine shale database containing immature samples. The highest percentage of HI_o values are in the 400 to 499 mg HC/g TOC range. Delimiting P90, P50, and P10 values from this distribution yields a P90 of 340, a P50 of 475, and a P10 of 645 mg HC/g TOC. TOC = total organic carbon.

M97FG5.jpg|{{figure number|5}}Distribution of original hydrogen index (HI_o) values for a marine shale database containing immature samples. The highest percentage of HI_o values are in the 400 to 499 mg HC/g TOC range. Delimiting P90, P50, and P10 values from this distribution yields a P90 of 340, a P50 of 475, and a P10 of 645 mg HC/g TOC. TOC = total organic carbon.

^{HI_o = original hydrogen index; TOC = total organic carbon; GOC = generative organic carbon; NGOC = nongenerative organic carbon.}

^{HI_o = original hydrogen index; TOC = total organic carbon; GOC = generative organic carbon; NGOC = nongenerative organic carbon.}

If HI_o is known or taken as an average value or P50 value, the percent GOC in TOCo can readily be determined. Assuming that a source rock generates hydrocarbons that are approximately 85% carbon, the maximum HI_o can be estimated by its reciprocal, that is, 1/0.085 or 1177 mg HC/g TOC. The values for organic carbon content in hydrocarbons can certainly vary depending on the class of hydrocarbons and can range from about 82 to 88% (which would yield maximum HI_o values of 1220 and 1136 mg/g, respectively; the most commonly reported value in publications is 1200 mg HC/g TOC; Espitalie et al., 1984). However, from rock extract and oil fractionation data of marine shales or their sourced oils, the value of 85% appears sound with a plusmn3% variance.

If HI_o is known or taken as an average value or P50 value, the percent GOC in TOCo can readily be determined. Assuming that a source rock generates hydrocarbons that are approximately 85% carbon, the maximum HI_o can be estimated by its reciprocal, that is, 1/0.085 or 1177 mg HC/g TOC. The values for organic carbon content in hydrocarbons can certainly vary depending on the class of hydrocarbons and can range from about 82 to 88% (which would yield maximum HI_o values of 1220 and 1136 mg/g, respectively; the most commonly reported value in publications is 1200 mg HC/g TOC).<ref name=Espit /> However, from rock extract and oil fractionation data of marine shales or their sourced oils, the value of 85% appears sound with a plusmn3% variance.

Using 1177 mg HC/g TOC as the maximum HI_o, the percentage of GOC can be calculated from any HI_o, that is,

Using 1177 mg HC/g TOC as the maximum HI_o, the percentage of GOC can be calculated from any HI_o, that is,

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* Emme, J. J., and R. Stancil, 2002, Anadarko's Bossier gas play: A sleeping giant in a mature basin (abs.): AAPG National Convention, March 10–13, 2002: http://www.searchanddiscovery.net/abstracts/pdf/2002/annual/SHORT/ndx_46627.pdf (accessed November 11, 2010).

* Emme, J. J., and R. Stancil, 2002, Anadarko's Bossier gas play: A sleeping giant in a mature basin (abs.): AAPG National Convention, March 10–13, 2002: http://www.searchanddiscovery.net/abstracts/pdf/2002/annual/SHORT/ndx_46627.pdf (accessed November 11, 2010).

* Espitalie, J., M. Madec, and B. Tissot, 1984, Geochemical logging, in K. J. Voorhees, ed., Analytical pyrolysis: Techniques and applications: Boston, Massachusetts, Butterworth, p. 276–304.

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* Faqira, M., A. Bhullar, and A. Ahmed, 2010, Silurian Qusaiba Shale Play: Distribution and characteristics (abs.): Hedberg Research Conference on Shale Resource Plays, December 5–9, 2010, Austin, Texas, Book of Abstracts, p. 133–134.

* Faqira, M., A. Bhullar, and A. Ahmed, 2010, Silurian Qusaiba Shale Play: Distribution and characteristics (abs.): Hedberg Research Conference on Shale Resource Plays, December 5–9, 2010, Austin, Texas, Book of Abstracts, p. 133–134.

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