Changes

Diasteranes are mainly associated with clastic environments, and they increase in relative abundance with increasing maturity. However, they are also known from nonclastic samples and can, in some cases, be abundant even in low-maturity samples.

Diasteranes are mainly associated with clastic environments, and they increase in relative abundance with increasing maturity. However, they are also known from nonclastic samples and can, in some cases, be abundant even in low-maturity samples.

Figure 1 shows two distinct distributions of diasteranes. The top oil has very few diasteranes, indicating a possible lack of clay in the source rock. The bottom oil, in contrast, has similar amounts of diasteranes and regular steranes and probably comes from a clastic source.

[[:file:oiloil-and-oilsource-rock-correlations_fig8-23.png|Figure 1]] shows two distinct distributions of diasteranes. The top oil has very few diasteranes, indicating a possible lack of clay in the source rock. The bottom oil, in contrast, has similar amounts of diasteranes and regular steranes and probably comes from a clastic source.

[[file:oiloil-and-oilsource-rock-correlations_fig8-26.png|thumb|{{figure number|4}}See text for explanation.]]

[[file:oiloil-and-oilsource-rock-correlations_fig8-26.png|thumb|{{figure number|4}}See text for explanation.]]

==Irregular homohopanes==

==Irregular homohopanes==

[[file:oiloil-and-oilsource-rock-correlations_fig8-27.png|thumb|{{figure number|5}}From Moldowan et al.;<ref name=ch08r33>Moldowan, J., M., Lee, C., Y., Sundararaman, P., Salvatori, T., Alajbeg, A., Gjukic, B., Demaison, G., J., Slougue, N.-E., Watt, D., S., 1992, Source correlation and maturity assessment of select oils and rocks from the central Adriatic Basin (Italy and Yugoslavia), in Moldowan, J., M., Albrecht, P., Philp, R., P., eds., Biological markers in sediments and petroleum: Englewood Cliffs, New Jersey, Prentice-Hall, 411 p.</ref> reprinted with permission from Prentice-Hall.]]

[[file:oiloil-and-oilsource-rock-correlations_fig8-27.png|thumb|{{figure number|5}}From Moldowan et al.;<ref name=ch08r33>Moldowan, J., M., Lee, C., Y., Sundararaman, P., Salvatori, T., Alajbeg, A., Gjukic, B., Demaison, G., J., Slougue, N.-E., Watt, D., S., 1992, Source correlation and maturity assessment of select oils and rocks from the central Adriatic Basin (Italy and Yugoslavia), in Moldowan, J., M., Albrecht, P., Philp, R., P., eds., Biological markers in sediments and petroleum: Englewood Cliffs, New Jersey, Prentice-Hall, 411 p.</ref> reprinted with permission from Prentice-Hall.]]

Irregular distributions of the C₃₂–C₃₅ homohopanes are associated with carbonates.<ref name=ch08r59 /> and/or more reducing conditions<ref name=ch08r39 /> Unusually large amounts of the C₃₁ homohopanes are sometimes associated with coals and coaly material.<ref name=ch08r59 />

Irregular distributions of the C₃₂–C₃₅ homohopanes are associated with carbonates<ref name=ch08r59 /> and/or more reducing conditions.<ref name=ch08r39 /> Unusually large amounts of the C₃₁ homohopanes are sometimes associated with coals and coaly material.<ref name=ch08r59 />

[[:file:oiloil-and-oilsource-rock-correlations_fig8-27.png|Figure 5]] shows m/z 191 mass chromatograms for two sediment extracts from the Brac-1 well (Croatia) showing irregular homohopane distributions [relative enhancement of the C₃₅ species (left) and C₃₄ species (right)]. We would expect the oils sourced from these sediments to show these same characteristics.

[[:file:oiloil-and-oilsource-rock-correlations_fig8-27.png|Figure 5]] shows m/z 191 mass chromatograms for two sediment extracts from the Brac-1 well (Croatia) showing irregular homohopane distributions [relative enhancement of the C₃₅ species (left) and C₃₄ species (right)]. We would expect the oils sourced from these sediments to show these same characteristics.

==Gammacerane==

==Gammacerane==

[[file:oiloil-and-oilsource-rock-correlations_fig8-28.png|left|thumb|{{figure number|6}}From Ocampo et al.;<ref name=ch08r35>Ocampo, R., Riva, A., Trendel, J., M., Riolo, J., Callot, H., J., Albrecht, P., 1993, Petroporphyrins as biomarkers in oil-oil and oil-source rock correlations: Energy & Fuels, vol. 7, p. 191–193., 10., 1021/ef00038a005</ref> reprinted with permission from American Chemical Society.]]

[[file:oiloil-and-oilsource-rock-correlations_fig8-28.png|left|thumb|{{figure number|6}}From Ocampo et al.;<ref name=ch08r35>Ocampo, R., Riva, A., Trendel, J., M., Riolo, J., Callot, H., J., Albrecht, P., 1993, Petroporphyrins as biomarkers in oil-oil and oil-source rock correlations: Energy & Fuels, vol. 7, p. 191–193, DOI: 10.1021/ef00038a005</ref> reprinted with permission from American Chemical Society.]]

In addition to the hopane family, several other types of triterpanes that are occasionally encountered can be very useful in correlations. Gammacerane is often found in sediments deposited under abnormal salinites, including lacustrine facies. Identification of gammacerane can be difficult, however, both because it is usually only a minor component and because it elutes at different places with different chromatographic columns.

In addition to the hopane family, several other types of triterpanes that are occasionally encountered can be very useful in correlations. Gammacerane is often found in sediments deposited under abnormal salinites, including lacustrine facies. Identification of gammacerane can be difficult, however, both because it is usually only a minor component and because it elutes at different places with different chromatographic columns.

[[file:oiloil-and-oilsource-rock-correlations_fig8-30.png|left|thumb|{{figure number|8}}From Curiale<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 Magoon, L., B., Dow, W., G., eds., The Petroleum system—From Source to Trap: [http://store.aapg.org/detail.aspx?id=1022 AAPG Memoir 60], p. 251–260.</ref> reprinted with permission from AAPG.]]

[[file:oiloil-and-oilsource-rock-correlations_fig8-30.png|left|thumb|{{figure number|8}}From Curiale<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 Magoon, L., B., Dow, W., G., eds., The Petroleum system—From Source to Trap: [http://store.aapg.org/detail.aspx?id=1022 AAPG Memoir 60], p. 251–260.</ref> reprinted with permission from AAPG.]]

Oleanane (two major isomers exist) originates from terrestrial flowering plants of Late Cretaceous or, more commonly, Tertiary age and as such is very valuable in correlation problems when deciding whether an oil comes from a source rock that is young or old.<ref name=ch08r45>Riva, A., Caccialanza, P., G., Quagliaroli, F., 1988, Recognition of 18β(H)-oleanane in several crudes and Cainozoic-Upper Cretaceous sediments. Definition of a new maturity parameter: Organic Geochemistry, vol. 13, p. 671–675., 10., 1016/0146-6380(88)90088-5</ref>

Oleanane (two major isomers exist) originates from terrestrial flowering plants of Late Cretaceous or, more commonly, Tertiary age and as such is very valuable in correlation problems when deciding whether an oil comes from a source rock that is young or old.<ref name=ch08r45>Riva, A., Caccialanza, P., G., Quagliaroli, F., 1988, Recognition of 18β(H)-oleanane in several crudes and Cainozoic-Upper Cretaceous sediments. Definition of a new maturity parameter: Organic Geochemistry, vol. 13, p. 671–675, DOI: 10.1016/0146-6380(88)90088-5.</ref>

[[:file:oiloil-and-oilsource-rock-correlations_fig8-30.png|Figure 8]] shows three mass chromatograms (m/z 191.18, 177.16, and 217.20, from top to bottom) for an oil from central Myanmar. The peak marked “o” is a combination of 18α(H) and 18β(H) oleanane. The tallest peak in the m/z 191 mass chromatogram is hopane, and the peaks indicated by solid dots are bicadinanes.

[[:file:oiloil-and-oilsource-rock-correlations_fig8-30.png|Figure 8]] shows three mass chromatograms (m/z 191.18, 177.16, and 217.20, from top to bottom) for an oil from central Myanmar. The peak marked “o” is a combination of 18α(H) and 18β(H) oleanane. The tallest peak in the m/z 191 mass chromatogram is hopane, and the peaks indicated by solid dots are bicadinanes.