Changes

==Biodegradation limitations==

==Biodegradation limitations==

[[file:oiloil-and-oilsource-rock-correlations_fig8-20.png|400px|thumb|{{figure number|16}}(left) Gas chromatograms of three oils from a common source in central Myanmar. A waxy oil (top) is sequentially converted into an extremely biodegraded remnant oil (bottom). (right) Whole-oil gas chromatograms of three oils from the offshore Mackenzie Delta, northwestern Canada, showing a modest decrease in the pristane–phytane ratio, apparently as the result of minor biodegradation. From Curiale et al.;<ref name=ch08r12>Curiale, J. A., 1994, [http://archives.datapages.com/data/specpubs/methodo2/data/a077/a077/0001/0250/0251.htm Correlation of oils and source rocks—a conceptual and historical perspective], in L. B. Magoon, and W. G. Dow, eds., The [[Petroleum system]]—From Source to Trap: [http://store.aapg.org/detail.aspx?id=1022 AAPG Memoir 60], p. 251–260.</ref> and Curiale<ref name=ch08r9>Curiale, J., A., 1991, The petroleum geochemistry of Canadian Beaufort Tertiary “non-marine” oils: Chemical Geology, vol. 93, p. 21–45., 10., 1016/0009-2541(91)90062-V</ref> reprinted with permission from Elsevier.]]

[[file:oiloil-and-oilsource-rock-correlations_fig8-20.png|400px|thumb|{{figure number|16}}(left) Gas chromatograms of three oils from a common source in central Myanmar. A waxy oil (top) is sequentially converted into an extremely biodegraded remnant oil (bottom). (right) Whole-oil gas chromatograms of three oils from the offshore Mackenzie Delta, northwestern Canada, showing a modest decrease in the pristane–phytane ratio, apparently as the result of minor biodegradation. From Curiale et al.;<ref name=ch08r12>Curiale, J. A., 1994, [http://archives.datapages.com/data/specpubs/methodo2/data/a077/a077/0001/0250/0251.htm Correlation of oils and source rocks—a conceptual and historical perspective], in L. B. Magoon, and W. G. Dow, eds., The [[Petroleum system]]—From Source to Trap: [http://store.aapg.org/detail.aspx?id=1022 AAPG Memoir 60], p. 251–260.</ref> and Curiale<ref name=ch08r9>Curiale, J. A., 1991, The petroleum geochemistry of Canadian Beaufort Tertiary “non-marine” oils: Chemical Geology, vol. 93, p. 21–45., 10., 1016/0009-2541(91)90062-V</ref> reprinted with permission from Elsevier.]]

[http://www.oiltracers.com/services/exploration-geochemistry/oil-biodegradation.aspx Biodegradation] can severely alter gas chromatograms. In the earliest stages of biodegradation, [[Wikipedia:Alkane#Linear_alkanes|''n''-alkanes]] are removed selectively, leading to significant loss of information.

[http://www.oiltracers.com/services/exploration-geochemistry/oil-biodegradation.aspx Biodegradation] can severely alter gas chromatograms. In the earliest stages of biodegradation, [[Wikipedia:Alkane#Linear_alkanes|''n''-alkanes]] are removed selectively, leading to significant loss of information.

===Examples of biodegradation===

===Examples of biodegradation===

[[:file:oiloil-and-oilsource-rock-correlations_fig8-20.png|Figure 16]] (left) shows gas chromatograms of three oils from a common source in central Myanmar. A waxy oil (top) is sequentially converted into an extremely biodegraded remnant oil (bottom). The [[http://wiki.aapg.org/Petroleum_reservoir_fluid_properties#API_specific_gravity|API gravity]] of the oil decreases and sulfur content increases substantially with increasing biodegradation.

[[:file:oiloil-and-oilsource-rock-correlations_fig8-20.png|Figure 16]] (left) shows gas chromatograms of three oils from a common source in central Myanmar. A waxy oil (top) is sequentially converted into an extremely biodegraded remnant oil (bottom). The [http://wiki.aapg.org/Petroleum_reservoir_fluid_properties#API_specific_gravity API gravity] of the oil decreases and sulfur content increases substantially with increasing biodegradation.

[[Pristane-phytane ratio]]s may also be affected slightly at low stages of biodegradation. At moderate levels these compounds are removed completely (left figure). The right figure below shows whole-oil gas chromatograms of three oils from the offshore [[Mackenzie Delta]], northwestern Canada, showing a modest decrease in the pristane-phytane ratio, apparently as the result of minor biodegradation.

[[Pristane-phytane ratio]]s may also be affected slightly at low stages of biodegradation. At moderate levels these compounds are removed completely (left figure). The right figure below shows whole-oil gas chromatograms of three oils from the offshore [[Mackenzie Delta]], northwestern Canada, showing a modest decrease in the pristane-phytane ratio, apparently as the result of minor biodegradation.