Changes

==Effects of maturation and migration==

==Effects of maturation and migration==

[[Sterane]] and [[triterpane]] concentrations decrease greatly during oil [[cracking]]. Therefore, thermal condensates (light oils) do not normally contain large amounts of steranes and triterpanes. Consequently, steranes and triterpanes are usually of little value in high-maturity oils and condensates. Furthermore, some condensates that do contain steranes and triterpanes may have picked up all or most of them during [[migration]] by extraction from the rocks through which they passed (see Waples and Machihara<ref name=ch08r59>Waples, D. W., and T. Machihara, 1991, Biomarkers for geologists: Tulsa, AAPG, 91 p.</ref> for examples and references). Finally, because triterpane and particularly sterane distributions change greatly during maturation, correlations of those biomarkers between an immature [[source rock]] and an oil can be very difficult. In such cases a strictly numerical approach, working with peak ratios and relative proportions, can be better than a visual one, since the eye can be unduly influenced by maturity-related differences instead of genetic characteristics.

[[Sterane]] and [[triterpane]] concentrations decrease greatly during oil [[cracking]]. Therefore, thermal condensates (light oils) do not normally contain large amounts of steranes and triterpanes. Consequently, steranes and triterpanes are usually of little value in high-[[maturity]] oils and condensates. Furthermore, some condensates that do contain steranes and triterpanes may have picked up all or most of them during [[migration]] by extraction from the rocks through which they passed (see Waples and Machihara<ref name=ch08r59>Waples, D. W., and T. Machihara, 1991, Biomarkers for geologists: Tulsa, AAPG, 91 p.</ref> for examples and references). Finally, because triterpane and particularly sterane distributions change greatly during [[maturation]], correlations of those biomarkers between an immature [[source rock]] and an oil can be very difficult. In such cases a strictly numerical approach, working with peak ratios and relative proportions, can be better than a visual one, since the eye can be unduly influenced by maturity-related differences instead of genetic characteristics.

==Biodegradation and sterane distributions==

==Biodegradation and sterane distributions==

[[Category:Critical elements of the petroleum system]]  

[[Category:Critical elements of the petroleum system]]  

[[Category:Oil–oil and oil–source rock correlations]]

[[Category:Oil–oil and oil–source rock correlations]]