Biomarkers maturity

Simoneit B. R. T., Kawka O. E., and Wang G.-M. (1992) Biomarker maturation in contemporary hydrothermal systems, alteration of immature organic matter in zero geological time. In Biomarkers in Sediments and Petroleum (eds. J. M. Moldowan, P. Albrecht, and R. P. Philp). Prentice Hall, Englewood Cliffs, NJ, pp. 124-141. 

Few biomarkers will become surrogate endpoints. However, characteristics supporting a biomarker maturing into a surrogate endpoint are (a) biologic plausibility, (b) successful application in prior clinical trials, and (c) presence of significant risk-benefit considerations. Table 17.1 presents a summary of these considerations... 

Farrimond P., Taylor A., Telnres N. (1998) Biomarker maturity parameters the role of generation and thermal degradation. Org. Geochem. 29, 1181—97. 

Fig. 7. Cross plots of calculated vitrinite reflectance equivalent biomarker maturity (Ro Ts) and light hydrocarbon maturity (Schaefer Ro) effectively indicates that almost all oils are mixtures in the true sense with a range of maturities of charge being present together in the trap. Only the flagged oils (red dots) may represent single maturity point charges, but even here that is doubtful. A mass fraction maturity concept better describes the maturity of an oil.

Fig. 8. The distribution of fraction-specific maturity for the oils and condensates in the data set. Mean maturities for the data set based on representative biomarker, aromatic hydrocarbon and light hydrocarbon parameters are indicated, based on parameters proposed by Radke (1988) and Schaefer Littke (1988). Biomarker maturities are based on proprietary source rock correlations. The cyclic biomarkers are generated earlier than the aromatic hydrocarbons with the quantitatively most abundant light hydrocarbons being generated, on average at higher maturity than the more structurally exotic molecules.

Oil biomarker compositions were measured in samples from three wells in the central part of the Ross Field (Fig. 11). Wells 13/28-2 and 13/28a-5 had similar compositions, but the oil in 13/29a-3 has a different composition, related to a higher thermal maturity. If diffusion was the only mechanism leading to fluid mixing, then in 40 Ma the oil would be able to mix over a distance of about 520 m, illustrated by dashed circles around the wells in Figure 11. It is thus possible that the biomarker differences were inherited from the reservoir filling history, and subsequently have not had time to mix completely. This would indicate that the oil chemistry could not be interpreted to indicate compartmentalization. However, it is possible that the biomarker maturity parameters reflect oils of different density (unfortunately, density was not measured in oils from the crucial location). Indeed, there are density differences between the oils in wells 13/29a-l and 13.29a-3. The density-mixing model (equation (10)) would indicate that density overturn would mix oil densities over the whole central part of the field... 

Figure 7 shows a crossplot of an aromatic sterane cracking parameter (A3) and a hopane biomarker maturity parameter (H14). The A3... 

Maturity. Conventional biomarker maturity indicators suggest that source rock maturity has... 

Fig. 10. Saturate (Ts/Ts-f Tm) and aromatic (MPI-1) biomarker maturity indicators for Magnolia oil and condensate samples. The shallowest saturated gas-condensate sample is omitted due to low yields. For ratio definitions see Table 2.

Suzuki N., Sakata S. and Kaneko N. (1987) Biomarker maturation levels and primary migration stage of Neogene Tertiary erude oils and condensates in the Niigata sedimentary basin, Japan. J. Jpn. Assoc. Petrol. Technol. 52(6), 499 510 (in Japanese). 

Determining the thermal maturity of light oils and condensates can be difficult. Biomarker concentrations in crude oils are low and biomarker maturity parameters have limited applicability at high levels of thermal maturity (Peters and Moldowan, 1993). Light hydrocarbons (C6-C7) are volatile, susceptible to biodegradation and maturity parameters derived from these compounds may be unreliable. In this chapter, we report on the correlation of C4-benzene and C4-naphthalene compounds with thermal maturity in oil cracking pyrolysis products of a Western Canada Sedimentary Basin (WCSB) oil. The use of C4-benzene and C4-naphthalene compound ratios as thermal maturity indicators in natural systems was evaluated using crude oils from the Fort Worth Basin, Texas, USA. 

Calculating an equivalent %Rq value for pyrolysis experiments based on experimental conditions is a convenient way to compare the level of thermal stress achieved in experiments performed at various temperatures and times and eliminates uncertainty in biomarker maturity indicators that arise during pyrolysis. In this way, the level of thermal stress achieved for an experiment performed at 360°C and 12 days can be easily compared with an experiment performed at 400°C and 1 day, for instance. The positive correlation between various C4-naphthalene and C4-benzene ratios with increased thermal stress (calculated %/ o) in the oil pyrolysis experiments motivated the evaluation of these ratios as maturity parameters in oils from the Fort Worth Basin. The Fort Worth Basin oils were analyzed as part of this study because the Barnett Shale is the only petroleum system in the basin and also because samples were readily available from various stratigraphic horizons. The TAS ratio is an accepted thermal maturity indicator for low API gravity oils (Mackenzie et al, 1981) and was used in this study to evaluate C4-naphthalene and C4-benzene as potential maturity indicators for high API gravity oils. Thus, correlation of C4-naphthalene or C4-benzene ratios with the TAS maturity ratio is viewed as a confirmation of the effectiveness of these parameters to estimate the thermal maturity of a light crude oil. 

Biomarkers form a small percentage of bitumen and cmde oils, but relative distributions and complex stmctures are modified by the various processes involved during petroleum generation and accumulation. These biomarkers are widely used for correlation studies, and for recognition and documentation of the progress of generation and maturation (52,53). 

Radke J, Bechtel A, Gaupp R, Piittmann W, Schwark L, Sachse D, Gleixner D (2005) Correlation between hydrogen isotope ratios of lipid biomarkers and sediment maturity. Geochim Cosmochim Acta 69 5517-5530... 

The hopane series are the natural product biomarkers elucidated initially as attributable to bacteria.The 17a(H),2ip(H)-hopanes ranging from C27 to C35 (no C28) were encountered in numerous ancient sediments and petroleums, and diagenesis and maturation of the microbial precursors (e.g. bacteriohopanepolyol and diploptene, Fig. 4) were elucidated. The diagenesis of diploptene in contemporary sediments proceeds by double bond migration from via to... 

The characterization of a novel series of biomarkers is illustrated with the g 7 2-dialkylalkanes in bitumen from a hydrothermal system on the Mid-Atlantic Ridge. The total bitumen consists of hydrocarbons, a major UCM (unresolved complex mixture of branched and cyclic compounds) and mature biomarkers (e.g. hopanes) (Fig. 13a). The bitumen contains a series of cyclopentylalkanes Cfi 2n) that range from n = 14 to 34, with only even-chained pseudohomologs and a concentration maximum (Cmax) at n = 18. Their source is biogenic, based on the presence of only even-carbon number homologs, but the precursors are unknown. 

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