Difference between revisions of "Pyrolysis gas chromatography"

From AAPG Wiki
Jump to navigation Jump to search
(merging article from chapter 8)
 
(20 intermediate revisions by 4 users not shown)
Line 6: Line 6:
 
  | 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  = 6-20
−
  | topg    = 6-41
+
  | topg    = 6-20
 
  | 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
Line 14: Line 14:
 
  | isbn    = 0-89181-602-X
 
  | isbn    = 0-89181-602-X
 
}}
 
}}
−
'''Pyrolysis gas chromatography''' (Py-GC) is anhydrous thermal decomposition of a material that leads to the conversion of kerogen to hydrocarbon compounds. Py-GC can be conducted on whole rock or isolated kerogen samples to obtain a visual signature or “fingerprint” of the organic material present.
+
'''Pyrolysis [[gas chromatography]]''' (Py-GC) is anhydrous thermal decomposition of a material that leads to the conversion of [[kerogen]] to hydrocarbon compounds. Py-GC can be conducted on whole rock or isolated kerogen samples to obtain a visual signature or “fingerprint” of the organic material present.
  
−
When kerogen is pyrolyzed and the products are analyzed by [[gas chromatography]], those products can be similar to those present in oils. One can compare the pyrolysis products either with the products of natural generation (oil) or with the products of laboratory pyrolysis of the asphaltenes from oils. Both comparisons are useful for oil–[[source rock]] correlations. Oil–oil correlations can also be carried out by comparing products of asphaltene pyrolysis from the various oils.
+
When kerogen is pyrolyzed and the products are analyzed by gas [[chromatography]], those products can be similar to those present in oils. One can compare the pyrolysis products either with the products of natural [[Petroleum generation|generation]] (oil) or with the products of laboratory pyrolysis of the [[asphaltenes]] from oils. Both comparisons are useful for oil–[[source rock]] correlations. Oil–oil correlations can also be carried out by comparing products of asphaltene pyrolysis from the various oils.
  
 
==Dry vs hydrous pyrolysis==
 
==Dry vs hydrous pyrolysis==
Line 24: Line 24:
  
 
==How to read gas chromatograms==
 
==How to read gas chromatograms==
−
[[file:evaluating-source-rocks_fig6-5.png|thumb|{{figure number|1}}See text for explanation.]]
+
[[file:evaluating-source-rocks_fig6-5.png|300px|thumb|{{figure number|1}}Typical gas chromatogram examples for types I, II, and III kerogen.]]
  
 
[[Gas chromatography]] generally is a qualitative tool. It is not typically used as a quantitative measurement of hydrocarbon molecules. However, the patterns generated in the chromatograms can help us determine if a source rock will be oil or gas prone.
 
[[Gas chromatography]] generally is a qualitative tool. It is not typically used as a quantitative measurement of hydrocarbon molecules. However, the patterns generated in the chromatograms can help us determine if a source rock will be oil or gas prone.
Line 31: Line 31:
  
 
==Interpreting gas chromatograms==
 
==Interpreting gas chromatograms==
 +
 +
[[file:oiloil-and-oilsource-rock-correlations_fig8-44.png|300px|thumb|{{figure number|2}}Sterane m/z 217 mass fragmentograms of an immature rock extract (bottom left), a hydrous pyrolyzate (top right), and the correlatable oil (bottom right). Modified from Moldowan et al.;<ref name=Moldowan1992>Moldowan, J. M., C. Y. Lee, P. Sundararaman, T. Salvatori, A. Alajbeg, B. Gjukic, G. J. Demaison, N. E. Slougue, and D. S. Watt, 1992, Source correlation and maturity assessment of select oils and rocks from the central Adriatic Basin (Italy and Yugoslavia), in J. M. Moldowan, P. Albrecht, and R. P. Philp, eds., Biological markers in sediments and petroleum: Englewood Cliffs, New Jersey, Prentice-Hall, 411 p.</ref> courtesy AAPG.]]
 +
 
A gas chromatogram is evaluated qualitatively to determine the potential of a rock to generate oil vs. gas. The table below shows how chromatograms for oil- vs. gas-prone rocks are evaluated.
 
A gas chromatogram is evaluated qualitatively to determine the potential of a rock to generate oil vs. gas. The table below shows how chromatograms for oil- vs. gas-prone rocks are evaluated.
  
 
{| class = "wikitable"
 
{| class = "wikitable"
 
|-
 
|-
−
! Chromatograms of oil-prone rock
+
! Chromatograms of oil-prone rock || Chromatograms of gas-prone rock
−
! Chromatograms of gas-prone rock
 
 
|-
 
|-
−
| Dominated by long-chain carbon compounds (greater than C<sub>10</sub> )
+
| Dominated by long-chain carbon compounds (greater than C<sub>10</sub>) || Dominated by short-chain carbon compounds from C<sub>1</sub> –C<sub>4</sub>
−
| Dominated by short-chain carbon compounds from C<sub>1</sub> –C<sub>4</sub>
 
 
|-
 
|-
−
| Contain carbon compounds up to C<sub>25</sub> or greater
+
| Contain carbon compounds up to C<sub>25</sub> or greater || Contain very few carbon compounds above C<sub>10</sub>
−
| Contain very few carbon compounds above C<sub>10</sub>
 
 
|}
 
|}
  
 
==Example==
 
==Example==
−
The figure below shows sterane m/z 217 mass fragmentograms of an immature rock extract (bottom left), a hydrous pyrolyzate (top right), and the correlatable oil (bottom right). The carbon-number distribution changes during pyrolysis, indicating a fundamental difference in composition between the immature extract and the kerogen. The pyrolyzate, however, is molecularly very similar to the oil.
+
[[:file:oiloil-and-oilsource-rock-correlations_fig8-44.png|Figure 2]] shows sterane m/z 217 mass fragmentograms of an immature rock extract (bottom left), a hydrous pyrolyzate (top right), and the correlatable oil (bottom right). The carbon-number distribution changes during pyrolysis, indicating a fundamental difference in composition between the immature extract and the kerogen. The pyrolyzate, however, is molecularly very similar to the oil.
−
 
 
−
[[file:oiloil-and-oilsource-rock-correlations_fig8-44.png|thumb|{{figure number|8-44}}Modified.]]
 
  
 
==See also==
 
==See also==
 
* [[Gas chromatography]]
 
* [[Gas chromatography]]
−
* [[Data obtained by gas chromatography]]
+
* [[Gas chromatography: data obtained]]
−
* [[How is GC/MS done?]]
+
* [[Gas chromatography/mass spectrometry (GC/MS): procedures]]
−
* [[Examples of correlations using GC/MS]]
+
* [[Gas chromatography/mass spectrometry (GC/MS): examples of correlations]]
−
* [[Limitations of GC/MS]]
+
* [[Gas chromatography/mass spectrometry (GC/MS): limitations]]
−
* [[Data obtained by high-performance liquid chromatography]]
+
* [[High-performance liquid chromatography]]
−
* [[Evaluating source rock quality]]
 
 
* [[Kerogen types]]
 
* [[Kerogen types]]
−
* [[Evaluating quality using rock-eval HI/OI]]
+
* [[Rock Eval analysis using hydrogen index (HI) and oxygen index (OI)]]
 +
 
 +
==References==
 +
{{reflist}}
  
 
==External links==
 
==External links==
Line 67: Line 67:
  
 
[[Category:Critical elements of the petroleum system]] [[Category:Evaluating source rocks]] [[Category:Oil–oil and oil–source rock correlations]] [[Category:Geochemistry]]
 
[[Category:Critical elements of the petroleum system]] [[Category:Evaluating source rocks]] [[Category:Oil–oil and oil–source rock correlations]] [[Category:Geochemistry]]
 +
[[Category:Treatise Handbook 3]]

Latest revision as of 18:19, 9 February 2022

Exploring for Oil and Gas Traps
Series Treatise in Petroleum Geology
Part Critical elements of the petroleum system
Chapter Evaluating source rocks
Author Carol A. Law
Link Web page
Store AAPG Store

Pyrolysis gas chromatography (Py-GC) is anhydrous thermal decomposition of a material that leads to the conversion of kerogen to hydrocarbon compounds. Py-GC can be conducted on whole rock or isolated kerogen samples to obtain a visual signature or “fingerprint” of the organic material present.

When kerogen is pyrolyzed and the products are analyzed by gas chromatography, those products can be similar to those present in oils. One can compare the pyrolysis products either with the products of natural generation (oil) or with the products of laboratory pyrolysis of the asphaltenes from oils. Both comparisons are useful for oil–source rock correlations. Oil–oil correlations can also be carried out by comparing products of asphaltene pyrolysis from the various oils.

Dry vs hydrous pyrolysis

Two different pyrolysis techniques can be employed. Dry Rock-Eval pyrolysis is technically simpler but yields products rather different from those in natural systems. It is therefore more difficult and risky to use as a detailed correlation tool.

In contrast, hydrous pyrolysis techniques, where source rock candidates are artificially matured at relatively high temperatures in the presence of liquid water, can be very helpful in correlating oils to source rocks since it yields products that are fairly similar to those obtained by natural maturation. Hydrous pyrolysis experiments are also particularly helpful when only immature source rock candidates are available. These source rocks can be “matured” experimentally, and the resulting expelled “oil” can be compared to other oils.

How to read gas chromatograms

Figure 1 Typical gas chromatogram examples for types I, II, and III kerogen.

Gas chromatography generally is a qualitative tool. It is not typically used as a quantitative measurement of hydrocarbon molecules. However, the patterns generated in the chromatograms can help us determine if a source rock will be oil or gas prone.

The X-axis of a gas chromatogram is retention time, and the Y-axis is the relative quantity of each compound. Each spike in the chromatogram represents a particular hydrocarbon compound, beginning with lowest number of carbon atoms in the compound on the left and going to higher chains of carbons to the right. The height of the spike represents the relative abundance of the compound pyrolized from the sample's kerogen. Typical gas chromatogram examples for types I, II, and III kerogen are shown in Figure 1.

Interpreting gas chromatograms

Figure 2 Sterane m/z 217 mass fragmentograms of an immature rock extract (bottom left), a hydrous pyrolyzate (top right), and the correlatable oil (bottom right). Modified from Moldowan et al.;[1] courtesy AAPG.

A gas chromatogram is evaluated qualitatively to determine the potential of a rock to generate oil vs. gas. The table below shows how chromatograms for oil- vs. gas-prone rocks are evaluated.

Chromatograms of oil-prone rock Chromatograms of gas-prone rock
Dominated by long-chain carbon compounds (greater than C10) Dominated by short-chain carbon compounds from C1 –C4
Contain carbon compounds up to C25 or greater Contain very few carbon compounds above C10

Example

Figure 2 shows sterane m/z 217 mass fragmentograms of an immature rock extract (bottom left), a hydrous pyrolyzate (top right), and the correlatable oil (bottom right). The carbon-number distribution changes during pyrolysis, indicating a fundamental difference in composition between the immature extract and the kerogen. The pyrolyzate, however, is molecularly very similar to the oil.

See also

References

  1. ↑ Moldowan, J. M., C. Y. Lee, P. Sundararaman, T. Salvatori, A. Alajbeg, B. Gjukic, G. J. Demaison, N. E. Slougue, and D. S. Watt, 1992, Source correlation and maturity assessment of select oils and rocks from the central Adriatic Basin (Italy and Yugoslavia), in J. M. Moldowan, P. Albrecht, and R. P. Philp, eds., Biological markers in sediments and petroleum: Englewood Cliffs, New Jersey, Prentice-Hall, 411 p.

External links

find literature about
Pyrolysis gas chromatography 		Datapages button.png GeoScienceWorld button.png OnePetro button.png Google button.png
Retrieved from "https://wiki.aapg.org/index.php?title=Pyrolysis_gas_chromatography&oldid=27422"