Changes

  | part    = Predicting the occurrence of oil and gas traps

  | part    = Predicting the occurrence of oil and gas traps

  | chapter = Applied paleontology

  | chapter = Applied paleontology

  | frompg  = 17-1

  | frompg  = 17-40

  | topg    = 17-65

  | topg    = 17-41

  | author  = Robert L. Fleisher, H. Richard Lane

  | author  = Robert L. Fleisher, H. Richard Lane

  | link    = http://archives.datapages.com/data/specpubs/beaumont/ch17/ch17.htm

  | link    = http://archives.datapages.com/data/specpubs/beaumont/ch17/ch17.htm

  | isbn    = 0-89181-602-X

  | isbn    = 0-89181-602-X

}}

}}

Many of the elements of basin modeling programs—maturation of source rocks, reservoir diagenesis, and [[porosity]] evolution—are affected by thermal and burial history.<ref name=ch17r91>van Gizjel, P., 1980, Characterization and identification of kerogen and bitumen and determination of thermal maturation by means of qualitative and quantitative microscopical techniques, in How to Assess Maturation and Paleotemperatures: SEPM Short Course Notes, p. 1–56.</ref><ref name=ch17r70>Pradier, B., Bertrand, P., Martinez, L., Laggoun-Defarge, F., 1991, Fluorescence of organic matter and thermal maturity assessment: Organic Geochemistry, vol. 17, no. 4, p. 511–524., 10., 1016/0146-6380(91)90115-Z</ref> Thermal maturation data used to model these parameters are usually derived from fossils.

 

Many of the elements of basin modeling programs—maturation of source rocks, reservoir [[diagenesis]], and [[porosity]] evolution—are affected by thermal and burial history.<ref name=ch17r91>van Gizjel, P., 1980, Characterization and identification of kerogen and bitumen and determination of thermal maturation by means of qualitative and quantitative microscopical techniques, in How to Assess Maturation and Paleotemperatures: SEPM Short Course Notes, p. 1–56.</ref><ref name=ch17r70>Pradier, B., Bertrand, P., Martinez, L., Laggoun-Defarge, F., 1991, Fluorescence of organic matter and thermal maturity assessment: Organic Geochemistry, vol. 17, no. 4, p. 511–524, DOI: 10.1016/0146-6380(91)90115-Z.</ref> Thermal maturation data used to model these parameters are usually derived from fossils.

The following table shows which fossil material changes appearance due to thermal stress and therefore can be used as organic geothermometers.

The following table shows which fossil material changes appearance due to thermal stress and therefore can be used as organic geothermometers.

| Thermal Alteration Index (TAI)

| Thermal Alteration Index (TAI)

|-

|-

| Ostracodes

| Ostracods

| Ostracode Alteration Index (OAI)

| Ostracod Alteration Index (OAI)

|-

|-

| Conodonts

| Conodonts

==Vitrinite==

==Vitrinite==

Vitrinite is a coaly organic maceral derived from the connective tissue of vascular plants. The reflectance of vitrinite changes with heat. Vitrinite reflectance (V_r or R_o), the most commonly used thermal indicator, is the benchmark for maturation studies in the petroleum and coal industries.<ref name=ch17r36>Dow, W., G., O'Connor, D., I., 1982, Kerogen maturity and type by reflected light microscopy applied to petroleum generation, in How To Assess Maturation and Paleotem-peratures: SEPM Short Course Notes, p. 79–99.</ref> This technique is primarily useful for Devonian and younger clastic sediments and coals.

Vitrinite is a coaly organic [[maceral]] derived from the connective tissue of vascular plants. The reflectance of vitrinite changes with heat. [[Vitrinite reflectance]] (V_r or R_o), the most commonly used thermal indicator, is the benchmark for maturation studies in the petroleum and coal industries.<ref name=ch17r36>Dow, W., G., O'Connor, D., I., 1982, Kerogen maturity and type by reflected light microscopy applied to petroleum generation, in How To Assess Maturation and Paleotemperatures: SEPM Short Course Notes, p. 79–99.</ref> This technique is primarily useful for Devonian and younger clastic sediments and [[coal]]s.

==Pollen and spores==

==Pollen and spores==

Pollen and spores are the organic-walled microfossils most commonly used for gauging paleotemperature. Fossil color, which changes with heating, is used to estimate a Thermal Alteration Index, or TAI.<ref name=ch17r82>Staplin, F., L., 1969, Sedimentary organic matter, organic metamorphism, and oil and gas occurrence: Bulletin of Canadian Petroleum Geology, vol. 17, no. 1, p. 47–66.</ref><ref name=ch17r56>Lerche, I., McKenna, T., C., 1991, Pollen translucency as a thermal maturation indicator: Journal of Petroleum Geology, vol. 14, no. 1, p. 19–36., 10., 1111/jpg., 1991., 14., issue-1</ref><ref name=ch17r62>Marshall, J., E., A., 1991, Quantitative spore colour: Journal of the Geological Society of London, vol. 148, p. 223–233., 10., 1144/gsjgs., 148., 2., 0223</ref> The use of pollen and spores lets us examine in situ fossils rather than evaluate an aggregate “kerogen soup.” Other organic-walled fossils [acritarchs, chitinozoans, graptolites, scolecodonts (annelid worm jaws), and dinoflagellates] have been examined for their visual and reflected values, but these fossil groups have not been rigorously calibrated to the standard vitrinite reflectance scale.<ref name=ch17r16>Bertrand, R., Heroux, Y., 1987, Chitinozoan, graptolite and scolecodont reflectance as an alternative to vitrinite and pyrobitumen reflectance in Ordovician and Silurian strata, Anticosti Island, Quebec, Canada: AAPG Bulletin, vol. 41, p. 951–957.</ref>

Pollen and spores are the organic-walled microfossils most commonly used for gauging paleotemperature. Fossil color, which changes with heating, is used to estimate a [[thermal alteration index]], or TAI.<ref name=ch17r82>Staplin, F., L., 1969, Sedimentary organic matter, organic metamorphism, and oil and gas occurrence: Bulletin of Canadian Petroleum Geology, vol. 17, no. 1, p. 47–66.</ref><ref name=ch17r56>Lerche, I., McKenna, T., C., 1991, Pollen translucency as a thermal maturation indicator: Journal of Petroleum Geology, vol. 14, no. 1, p. 19–36, DOI: 10.1111/jpg.1991.14.issue-1</ref><ref name=ch17r62>Marshall, J., E., A., 1991, Quantitative spore colour: Journal of the Geological Society of London, vol. 148, p. 223–233, DOI: 10.1144/gsjgs.148.2.0223</ref> The use of pollen and spores lets us examine in situ fossils rather than evaluate an aggregate “[[kerogen]] soup.” Other organic-walled fossils—acritarchs, chitinozoans, graptolites, scolecodonts (annelid worm jaws), and dinoflagellates—have been examined for their visual and reflected values, but these fossil groups have not been rigorously calibrated to the standard vitrinite reflectance scale.<ref name=ch17r16>Bertrand, R., Heroux, Y., 1987, [http://archives.datapages.com/data/bulletns/1986-87/data/pg/0071/0008/0950/0951.htm Chitinozoan, graptolite and scolecodont reflectance as an alternative to vitrinite and pyrobitumen reflectance in Ordovician and Silurian strata, Anticosti Island, Quebec, Canada]: AAPG Bulletin, vol. 41, p. 951–957.</ref>

==Other microfossils==

==Other microfossils==

Fossils composed of phosphate (conodonts), carbonate (ostracodes), and agglutinated grains (agglutinated foraminifera) are also used for geothermometry. The organic framework of these fossils responds to thermal stress with color change. Of these, conodonts (Conodont Alteration Index, or CAI) are the most widely used<ref name=ch17r37>Epstein, A. G., Epstein, J. B., Harris, L. D., 1977, Conodont color alteration—an index to organic metamorphism: U., S. Geological Survey Professional Paper 995, p. 1–27.</ref> and conodont alteration values are calibrated to the vitrinite reflectance scale. The use of ostracodes<ref name=ch17r1>Ainsworth, N., R., Burnett, R., D., Kontrovitz, M., 1990, Ostracod colour change by thermal alteration, offshore Ireland and Western UK: Marine and Petroleum Geology, vol. 7, p. 288–297., 10., 1016/0264-8172(90)90006-3</ref> and foraminifera<ref name=ch17r64>McNeil, D., H., Issler, D., R., 1992, Correlation of foraminiferal coloration (FCI) and time-temperature (TTI) indices from Beaufort Sea exploration data: AAPG Annual Convention Abstracts, p. 87.</ref> is a newly emerging approach and is not yet calibrated to vitrinite reflectance standards. The potential of these fossils is important because they commonly occur in lithologies devoid of organic-walled fossil remains (e.g., limestones, dolomites, fine-grained sands).

Fossils composed of phosphate ([[conodont]]s), carbonate ([[ostracod]]s), and agglutinated grains (agglutinated [[foraminifera]]) are also used for geothermometry. The organic framework of these fossils responds to thermal stress with color change. Of these, conodonts ([[conodont alteration index]], or CAI) are the most widely used<ref name=ch17r37>Epstein, A. G., Epstein, J. B., Harris, L. D., 1977, Conodont color alteration—an index to organic metamorphism: U., S. Geological Survey Professional Paper 995, p. 1–27.</ref> and conodont alteration values are calibrated to the vitrinite reflectance scale. The use of ostracods<ref name=ch17r1>Ainsworth, N., R., Burnett, R., D., Kontrovitz, M., 1990, Ostracod colour change by thermal alteration, offshore Ireland and Western UK: Marine and Petroleum Geology, vol. 7, p. 288–297, DOI: 10.1016/0264-8172(90)90006-3</ref> and foraminifera<ref name=ch17r64>McNeil, D., H., Issler, D., R., 1992, Correlation of foraminiferal coloration (FCI) and time-temperature (TTI) indices from Beaufort Sea exploration data: AAPG Annual Convention Abstracts, p. 87.</ref> is a newly emerging approach and is not yet calibrated to vitrinite reflectance standards. The potential of these fossils is important because they commonly occur in lithologies devoid of organic-walled fossil remains (e.g., limestones, dolomites, fine-grained sands).

==Whole kerogen analysis==

==Whole kerogen analysis==

Geochemists use a wide variety of organic compounds, derived from both terrestrial (land and aquatic) and marine organisms, to determine depositional environments and thermal maturation. These analyses assay whole kerogen assemblages and include elemental analyses (gas chromatography–mass spectrometry, or GC-MS), Fourier transform infrared spectroscopy (FTIR), biomarkers, spectral fluorescence, and Rock-Eval pyrolysis.

Geochemists use a wide variety of organic compounds, derived from both terrestrial (land and aquatic) and marine organisms, to determine depositional environments and thermal maturation. These analyses assay whole kerogen assemblages and include elemental analyses ([[gas chromatography–mass spectrometry]], or GC-MS), [[Fourier transform infrared spectroscopy]] (FTIR), biomarkers, spectral fluorescence, and [[Rock-Eval pyrolysis]].

==Use of multiple techniques==

==Use of multiple techniques==

Since none of these techniques is infallible in quantifying thermal maturation history for all conditions, two or more should be used when possible as a cross-check of the maturation data.<ref name=ch17r66>Nuccio, V., F., 1991, Combining methods yields best source rock maturity: World Oil, vol. 212, no. 9, p. 63–72.</ref> Caution is necessary, however, when equating thermal values to petroleum generation windows because different organic materials generate at different times during thermal exposure (e.g., early generators vs. late generators). This affects transformation ratios used in hydrocarbon systems modeling.

Since none of these techniques is infallible in quantifying thermal maturation history for all conditions, two or more should be used when possible as a cross-check of the maturation data.<ref name=ch17r66>Nuccio, V., F., 1991, Combining methods yields best source rock maturity: World Oil, vol. 212, no. 9, p. 63–72.</ref> Caution is necessary, however, when equating thermal values to [[petroleum generation]] windows because different organic materials generate at different times during thermal exposure (e.g., early generators vs. late generators). This affects transformation ratios used in hydrocarbon systems modeling.

==See also==

==See also==

* [[Quantitative paleoenvironmental analysis]]

* [[Quantitative paleoenvironmental analysis]]

* [[Palynofacies and kerogen analysis]]

* [[Palynofacies and kerogen analysis]]

* [[Sequence stratigraphy]]

* [[Biostratigraphy in sequence stratigraphy]]

==References==

==References==

[[Category:Predicting the occurrence of oil and gas traps]]  

[[Category:Predicting the occurrence of oil and gas traps]]  

[[Category:Applied paleontology]]

[[Category:Applied paleontology]]