On the changes of polycyclic aromatic compounds in waterflooded oil and their implications for geochemical interpretation

Chang, Xiangchun; Wang, Yue; Xu, Ying; Cui, Jing; Wang, Tao

doi:10.1016/j.orggeochem.2018.03.011

Cited by 22 publications

(8 citation statements)

References 59 publications

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“…Although their origin is controversial, 25-norhopanes have always been considered indicators of severe biodegradation (>PM6). The presence of 25-norhopanes in degraded petroleum has been mainly attributed to the degradation of their hopane counterparts and is well-documented. ,,,− However, the opinion that 25-norhopanes were originally present in oils and source rock extracts before biodegradation and were unmasked only when hopanes were removed , challenges the interrelationship between hopanes and 25-norhopanes . Non-hopanoid teriterpanes, such as gammacerane and diahopanes, are highly bioresistant and can be used as internal standards to measure and evaluate the relative quantities of individual isomers in the saturated fraction .…”

Section: Resultsmentioning

confidence: 99%

Improved Understanding of the Alteration of Molecular Compositions by Severe to Extreme Biodegradation: A Case Study from the Carboniferous Oils in the Eastern Chepaizi Uplift, Junggar Basin, Northwest China

Chang

Zhao

et al. 2018

Energy Fuels

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Biodegraded oils have been widely discovered throughout the world, whereas the alteration of the molecular composition of oils at extreme levels (>PM8) has been insufficiently documented. A suite of crude oils from Carboniferous volcanic reservoirs in the eastern Chepaizi Uplift, Junggar Basin, experienced severe to extreme biodegradation (from PM6+ to PM9+), which provided an ideal case for the present study. This investigation showed that the variations in molecular composition were not strictly consistent with their stepwise fashion in established schemes. The idea that 25-norhopanes are derived from hopanes was confirmed by the sharp decreases in the C29 hopane/gammacerane (C29H/G) and C30 hopane/gammacerane (C30H/G) values at the level of extreme biodegradation, which were associated with the increases in their counterparts of C28 25-norhopane/gammacerane (C28 25-NH/G) and C29 25-norhopane/gammacerane (C29 25-NH/G). 25-Norhopanes were also biodegraded at an extreme level, with C29 25-NH being more susceptible than C28 25-NH. The preferential biodegradation of individual homohopanes by carbon number occurred at an extreme level, whereas C29H featured more bioresistance than C30H and shared a similar susceptibility to biodegradation as 18α-30-norneohopane (C29Ts). The formation of 22R isomers for 25-norhopanes seemed to be favored over that of 22S isomers, although the 22S isomer was degraded faster that the 22R epimer for the C31, C32, and C33 homohopanes. However, the constant values of 22S/(22S + 22R) for the C34 homohopane implied no preferential biodegradation of 22S or 22R isomers for this extended hopane. Lower molecular weight tricyclic terpanes (TTs) were preferentially removed at extreme biodegradation levels, and the late eluting stereoisomers were degraded faster than the early eluting stereoisomers for C26TT, C28TT, and C29TT. C24 tetracyclic terpane (C24Tet) is much more resistant to biodegradation than TTs. Pregnanes have a similar susceptibility to biodegradation as gammacerane, but they are more resistant than C23TT. The biodegradation of regular steranes was characterized by their faster depletion than diasteranes and the preferential depletion of C27 regular sterane to the C29 homologue and the 20R isomers to the 20S isomers. At the extreme level, even C20 and C21 triaromatic steroids (TAS) were distinctively reduced, coexisting with the relatively highly degraded steranes and terpanes, although water washing can also be responsible for the decreases in (C20 + C21)-TAS/C26–28-TAS values.

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Section: Resultsmentioning

confidence: 99%

Improved Understanding of the Alteration of Molecular Compositions by Severe to Extreme Biodegradation: A Case Study from the Carboniferous Oils in the Eastern Chepaizi Uplift, Junggar Basin, Northwest China

Chang

Zhao

et al. 2018

Energy Fuels

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“…Organic geochemistry analysis is an important approach to evaluate the petroliferous basin. − The C 27 , C 28 , and C 29 RS contents of rock extracts can be used to analyze the depositional environment of OM. − C 27 RS originates from plankton, whereas C 29 RS typically originates from higher terrestrial plants. , The ternary plot in this study shows that all of the samples are characterized by planktonic and/or bacterial sources (Figure ).…”

Section: Resultsmentioning

confidence: 77%

Hydrocarbon Generation Evaluation, Burial History, and Thermal Maturity of the Lower Triassic–Silurian Organic-Rich Sedimentary Rocks in the Central Uplift of the South Yellow Sea Basin, East Asia

et al. 2020

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This study focuses on the organic-rich rocks in the Central Uplift of the South Yellow Sea Basin (SYSB) using the CSDP-2 borehole, which was drilled through the integrated Lower Triassic–Silurian sediments and yielded approximately 2736 m of cores. Geochemical analyses of core samples, including Rock-Eval pyrolysis, elemental analysis, maceral analysis, and gas chromatography–mass spectrometry, revealed multiple sets of effective source rocks developed from the Lower Triassic Qinglong Formation to the Lower Silurian Gaojiabian Formation. The organic matter is dominated by types II1–2–III kerogen, most of which are mature to post-mature. Comprehensive geochemical analysis shows that Permian and Lower Carboniferous mudstones are the most important source rocks and have strong hydrocarbon generation capacity. Most of the source rocks are dominated by planktonic/bacterial sources, deposited mainly in a low-salinity marine environment, and influenced by the input of terrigenous detrital materials. Basin modeling results show that most of the Paleozoic–Mesozoic source rocks in the Central Uplift generally entered the oil-generation window during the Triassic to Late Jurassic. The timing of hydrocarbon generation and expulsion was simultaneous or earlier than the collisional orogenic movement between the Sino–Korean Platform and the Lower Yangtze Craton, which may have some destructive impact on the oil and gas preservation. Therefore, it is preservation condition rather than source rocks that may be one of the most important elements for hydrocarbon accumulation in the Central Uplift of the SYSB.

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“…It suggests that they are mixtures of high-mature cracked und low-mature uncracked oils. Maturity indices calculated based on triaromatic steroids distribution are effective even for oils with extensive water washing (Chang et al 2018) and highly sensitive, especially for high maturity samples (Mackenzie et al 1981). Heating experiments of Beach et al (1989) indicate that the TA(I)/TA(I + II) ratio (Table 7, Fig.…”

Section: Maturitymentioning

confidence: 99%

Origin, migration and secondary processes of oil and natural gas in the western part of the Polish Outer Carpathians: geochemical and geological approach

Kotarba

Bilkiewicz

Jurek

et al. 2021

Int J Earth Sci (Geol Rundsch)

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The origin, migration pathways, as well as the influence of secondary processes of oil and natural gas accumulated in lower Cretaceous to lower Miocene strata of the western part of the Polish Outer Carpathians (between Kraków and Pilzno towns) based on results of organic geochemical analyses are investigated in this paper. Oil and thermogenic hydrocarbon gases were generated mainly from type II kerogen, and type II and III kerogen mixed in various proportions. These kerogens mainly occur in the Oligocene Menilite beds of the Silesian and Dukla nappes. Oils were generated from early to late “oil window”. Secondary cracking was recorded in oils from Dukla nappe, other secondary processes including biodegradation, water washing and evaporative fractionation were also developed to a various extent in many oils. The most biodegraded oils occur in seep S-Li, and the most extensive water washing is observed in the oil from seep S-Sa/1. The evaporative fractionation processes most significantly occur in the selected deepest parts of the multi-horizontal Biecz field. Hydrocarbon gases originated during both microbial and thermogenic processes of organic matter transformation. Natural gas has not been subjected to biodegradation processes. Carbon dioxide is derived from both microbial and thermogenic decomposition processes of organic matter and was generated together with hydrocarbon gases.

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On the changes of polycyclic aromatic compounds in waterflooded oil and their implications for geochemical interpretation

Cited by 22 publications

References 59 publications

Improved Understanding of the Alteration of Molecular Compositions by Severe to Extreme Biodegradation: A Case Study from the Carboniferous Oils in the Eastern Chepaizi Uplift, Junggar Basin, Northwest China

Improved Understanding of the Alteration of Molecular Compositions by Severe to Extreme Biodegradation: A Case Study from the Carboniferous Oils in the Eastern Chepaizi Uplift, Junggar Basin, Northwest China

Hydrocarbon Generation Evaluation, Burial History, and Thermal Maturity of the Lower Triassic–Silurian Organic-Rich Sedimentary Rocks in the Central Uplift of the South Yellow Sea Basin, East Asia

Origin, migration and secondary processes of oil and natural gas in the western part of the Polish Outer Carpathians: geochemical and geological approach

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