Correlation between hydrogen isotope ratios of lipid biomarkers and sediment maturity

The effect of oil expulsion or retention on further thermal degradation of kerogen at the high maturity stage: A pyrolysis study of type II kerogen from Pingliang shale, China

“…D enrichments in n-alkanes, by 30-40‰, have also been reported for natural oil samples at various maturity stages (Li et al, 2001;Jia et al, 2013). However, n-alkanes in extracts from natural sediments and rocks might display more complicated variations in hydrogen isotopes during maturation, although a general trend of D enrichment for n-alkanes has been observed (Dawson et al, 2005(Dawson et al, , 2007Radke et al, 2005;Pedentchouk et al, 2006;Schimmelmann et al, 2006;Kikuchi et al, 2010). This is due to the diversity of sources of n-alkanes in sediments and rocks, and in some cases hydrogen exchange with inorganic hydrogen either in water or minerals has taken place.…”

Isotopic compositions and biomarkers in crude oils from the Tarim Basin: Oil maturity and oil mixing

“…Generally, n-alkanes are more hydrogen isotopically conservative than total oils because they are mostly bound to macromolecular structures by nonpolar and strong covalent bonds, therefore, a relatively high activation energy for H exchange is required (Schimmelmann et al, 2006). Hence, D/H ratios of n-alkanes could be less influenced by hydrogen exchange with environmental water or minerals than other compound classes as suggested in several reports on D/H ratios for various organic molecules with progressive maturation (Schimmelmann et al, 2004;Dawson et al, 2005Dawson et al, , 2007Radke et al, 2005;Pedentchouk et al, 2006;Kikuchi et al, 2010). Therefore, the change of relationship between the oil and n-alkanes may mainly be caused by oil not n-alkanes.…”

“…Compared with the correlation shown by carbon isotopes, the correlation of dD values of n-alkanes with oil maturity is relatively weak, which indicates that the hydrogen isotopic compositions of n-alkanes could also be affected by other factors. Generally, the n-alkanes in the oils and sediments could be progressively enriched in D by $40‰ during maturation (Li et al, 2001;Dawson et al, 2005Dawson et al, , 2007; however, n-alkanes extracted from the sediments might exhibit more complicated variations (Radke et al, 2005;Pedentchouk et al, 2006;Kikuchi et al, 2010). Radke et al (2005) reported that nalkanes were much more depleted in D in the sediments, with Ro values of 1.30%, relative to those in less mature sediments (Ro = 1.14%).…”

“…Generally, the n-alkanes in the oils and sediments could be progressively enriched in D by $40‰ during maturation (Li et al, 2001;Dawson et al, 2005Dawson et al, , 2007; however, n-alkanes extracted from the sediments might exhibit more complicated variations (Radke et al, 2005;Pedentchouk et al, 2006;Kikuchi et al, 2010). Radke et al (2005) reported that nalkanes were much more depleted in D in the sediments, with Ro values of 1.30%, relative to those in less mature sediments (Ro = 1.14%). Pedentchouk et al (2006) and Kikuchi et al (2010) also show that there were relatively large variations in dD values of n-alkanes from the low maturity sediments, and n-alkanes might not be always enriched in D with increasing maturity.…”

“…dD values of total oils and their fractions were used in characterizing the oil source and mixing (Yeh and Epstein, 1981;Peters et al, 1986;Santos Neto and Hayes, 1999;Fekete et al, 2009). During the past decade, compound specific hydrogen isotopic analysis, which is the same as the carbon isotopic approach, achieved its great potential for use in various fields of petroleum geochemistry, including tracing oil source (Li et al, 2001;Schimmelmann et al, 2004;Dawson et al, 2007;Aboglila et al, 2010), elucidating the depositional environment of source rocks (Li et al, 2001;Schimmelmann et al, 2004;Dawson et al, 2005), determining maturity (Radke et al, 2005;Dawson et al, 2007), and evaluating the impact of biodegradation on oils Asif et al, 2009). It has been well known that hydrogen isotopic compositions have unique values for the characterization of the oil source and related geological processes due to its large variations compared to carbon isotopic compositions.…”