Geochemical application of tricyclic and tetracyclic terpanes biomarkers in crude oils of NW China

Abstract

a b s t r a c tComposition and distribution of tricyclic terpanes, tetracyclic terpanes and hopane in crude oils from Tarim, Turpan, Ordos and Qaidam basins, NW China, were investigated, and some new source dependent parameters were developed and evaluated. C 19 and C 20 tricyclic terpanes are more abundant in terrigenous oils, with C 24 tetracyclic terpane dominant. Relatively higher carbon number tricyclic terpanes, especially C 23 tricyclic terpane, are often the dominant homologues in crude oils from saline lacustrine and marine sources. On the whole, the relative content of C 23 tricyclic terpane of crude oils follow the order of saline lacustrine oils > marine oils > freshwater lacustrine oils > terrigenous oils for C 19e23 tricyclic terpane. Some new parameters based on the tricyclic/hopane and tetracyclic/tricyclic terpane as well as tetracyclic/hopane ratios, could be used to distinguish the oils and source rocks with similar maturity deposited in different sedimentary environments.

Biomarker distributions and depositional environments of continental source rocks in Sichuan Basin, SW China

“…In the organic matter of the marine or saline lacustrine facies, the dominant peak is 23TT, and compounds with 26TT are dominant (Peters and Moldowan, 1992; Zhu et al., 2015). In freshwater lacustrine source rocks and crude oils, the compounds with 21TT are dominant, indicating that the origins of the source rocks are aquatic and continental (Tao et al., 2015; Zhu et al., 2015). The 23TT is dominant in the Upper Triassic, and the 21TT is dominant in J 1 dn, with the characteristics of aquatic organism of saltwater lacustrine and freshwater lacustrine.…”

Oil retention and intrasource migration in the organic-rich lacustrine Chang 7 shale of the Upper Triassic Yanchang Formation, Ordos Basin, central China

“…Although some researchers have recognized the geochemical differences between crude oils and source rock extracts in the petroliferous Yanchang Formation (Hanson et al, 2007;Tao et al, 2015;Ji et al, 2016;Yang et al, 2016c), few of them have quantitatively examined the compositional and molecular differences, utilizing compositional mass balance calculations. Furthermore, elucidating the controlling factors on the bulk gas-to-oil (GOR) of shale oil, the effects of intraformational retention and fractionation on chemical composition are significant, because with the pressure drawdown during production even subtle changes in bulk fluid composition would bring about large difference in phase envelope geometry (Han et al, 2015), and these issues have yet to be addressed for the Ordos Basin.…”

Organic geochemical characteristics and comparison of the source rocks and the severely biodegradable oil sands around Karamay, China

“…Among them, the samples with the relative contents of C 20 TT greater than C 21 TT (such as Samples 68 and 78) are classified into Type 2 (Figure 5); the samples with the relative contents of C 20 TT less than C 21 TT and the relative contents of C 24 TT greater than C 21 TT (such as Samples 70 and YS-2) are classified into Type 3 (Figure 5); the samples with the relative contents of C 20 TT less than C 21 TT and the relative contents of C 24 TT less than C 21 TT (such as Sample 80) are classified into Type 4 (Figure 5). The (C 19 + C 20 )/C 23 TT ratio can reflect the OM’s source and the depositional paleo-environment (Bohacs et al., 2000; Peters et al., 2008; Tao et al., 2015). The ratios from P 2 w and P 1 f samples are the most similar, 0.96–1.93 (average = 1.34, SD = 0.45) and 0.29–2.36 (average = 1.33, SD = 1.04), respectively; the ratios from P 1 j samples are the largest, ranging from 1.07 to 4.15 (average = 2.35, SD = 1.31); the ratios from C samples are the smallest, ranging from 0.52 to 2.92 (average = 1.26, SD = 0.96) (Table 2).…”