Distribution and geochemical significance of trace elements in kerogens from Ediacaran–Lower Cambrian strata in South China

Some trace elements(TEs),both bio-essential and redox-sensitive,are promising tracers of Earth’s surface processes.As an essential sedimentary organic matter,kerogen may have inherited and retained the key TEs from organisms.In this study,the distribution of TEs in kerogens from two sections(Dongkanshang and Fengtan) in South China was analyzed to explore its biogeochemical significance during Ediacaran-Lower Cambrian.Compared with V and Zn,the relative concentrations of Co,Ni,Cu,and Mo were generally higher in kerogens than in the whole rocks.Enrichment of TEs in the kerogen was involved in the selective utilization of TEs by different organic precursors and the competition of sulfide in the depositional environment.The significant content of TEs in the kerogens from deep-water facies corresponded to a more negative δ^(13) Ckeras a result of the dominant taxa of chemo autotrophs with tremendous bioaccumulation potential for trace metals and the reduction conditions favorable for organic matter preservation.Furthermore,the content variations of trace elements in the kerogens coincided with the rise and fall of the Ediacaran biota,implying that the trace elements might have played an important role in early life evolution.

Comprehensive diag”nostic review of the (13)~C-enriched crude oils exemplified by TD2∈ and TZ62S in Tarim Basin, NW China

The crude oils typically from the CambrianLower Ordovician source rocks of Tarim Basin, NW"China, such as TD2 and TZ62S, are13C-enriched with the stable carbon isotopic ratios(VPDB) approaching-28 %.In this paper, the main research viewpoints on this issue are summarized, and combined with results from organic and inorganic carbon isotope stratum curves of the outcrop at the Ya'erdang Mountain in Tarim Basin. In addition, more alternative interpretations are discussed. On one hand, the inverse fractionation features of stable carbon and hydrogen isotopes of these crude oils may imply their protogenous nature. On the other hand, the anisotropy of source rocks and contribution from older stratum source rocks need verifying as well. For the sake of the final resolution of this issue, some further study topics are recommended.

Stable isotope(δ^(13)C_(ker),δ^(13)C_(carb),δ^(18)O_(carb)) distribution along a Cambrian outcrop section in the eastern Tarim Basin,NW China and its geochemical significance

This study investigated the geochemical features of the lower Paleozoic strata of Yaerdang Mountain outcrop along with the core samples from well TD2∈ in the eastern Tarim Basin,NW China.The total organic carbon abundance,hydrocarbon-generating precursor biospecies,and stable isotope ratios of organics and carbonate（δ13Cker,δ13Ccarb and δ18Ocarb） were comprehensively studied for their possible correlative constraints during sedimentary evolution.The results revealed that the δ13Cker（VPDB） of Cambrian kerogens along the outcrop section varied from-34.6‰ to-28.4‰,indicating an increasing tendency from the lower Cambrian to the upper Cambrian.This was on the whole accompanied by the variation in the δ13Ccarb and δ18Ocarb along the profile,which might be associated with the changes in the sea level and also in the compositional variation of benthic and planktonic biomass.The large variation in the stable carbon isotope ratios up to 6‰ along the outcrop section reflected the heterogeneity of the Cambrian source rocks from the eastern Tarim Basin.Hence,the 13C-enriched crude oils from well TD2∈might have been derived from a localized stratum of Cambrian source rocks.The results from this study showed the possibility of multiple source kitchens in the Cambrian-lower Ordovician portion of Tarim Basin.

Data modelling for crude oil migration studies using ranking method: a rapid geo-tracer technique for geochemists

The direction of oil charges within a field in the Niger Delta, Nigeria was determined by the sum of differences ranking method of carbazole concentrations after ascertaining other possible geological constraints on their compositional variations. The principle is that the smaller the sum, the closer the well to the source kitchen. The approach makes use of carbazoles' interaction with the matrix, which leads to a reduction in their concentration with increasing distance from the source kitchen, allowing prediction of the charging direction. A wide range of compositional variations was observed for C1(806.72–2152.90 lg/g) and C2(767–2469.72 lg/g) carbazoles within the field. Based on these results, we inferred a filling pathway orientation from west to east. This suggests that the source kitchen—the most promising region for oil exploration—is located in the western part of the oil field.

Asphaltenes in oil reservior recovery

Asphaltene is one of the important compositions in oil reservoirs, while it is also a major factor that causes difficulties in oil recovery and oil post-processings. Up to date, study on asphaltenes in oil recovery is stili a bottleneck problem, in this paper, the advances of studies on asphaltenes are reviewed, and some directions for further studying are suggested. What is reviewed in the paper includes the precipitation studies of asphaltenes, the degradation studies of asphaltenes and the applications of asphaltene’s studying in oil recovery; furthermore, it is regarded as a promising direction to study the possible applications of asphaltene’s selectively decomposing by chemical reagents in oil recovery.