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Methane-oxidizing bacteria (MOB) have long been considered as a microbial indicator for oil and gas prospecting. However, due to the phylogenetically narrow breath of ecophysiologically distinct MOB, classic culture-dependent approaches could not discriminate MOB population at fine resolution, and accurately reflect the abundance of active MOB in the soil above oil and gas reservoirs. Here, we presented a novel microbial anomaly detection (MAD) strategy to quantitatively identify specific indicator methylotrophs in the surface soils for bioprospecting oil and gas reservoirs by using a combination of 13 C-DNA stable isotope probing (SIP), high-throughput sequencing (HTS), quantitative PCR (qPCR) and geostatistical analysis. The Chunguang oilfield of the Junggar Basin was selected as a model system in western China, and type I methanotrophic Methylobacter was most active in the topsoil above the productive oil wells, while type II methanotrophic Methylosinus predominated in the dry well soils, exhibiting clear differences between non- and oil reservoir soils. Similar results were observed by quantification of Methylobacter pmoA genes as a specific bioindicator for the prediction of unknown reservoirs by grid sampling. A microbial anomaly distribution map based on geostatistical analysis further showed that the anomalous zones were highly consistent with petroleum, geological and seismic data, and validated by subsequent drilling. Over seven years, a total of 24 wells have been designed and drilled into the targeted anomaly, and the success rate via the MAD prospecting strategy was 83 %. Our results suggested that molecular techniques are powerful tools for oil and gas prospecting. This study indicates that the exploration efficiency could be significantly improved by integrating multi-disciplinary information in geophysics and geomicrobiology while reducing the drilling risk to a greater extent., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Cyanobacteria are important primary producers on the surface of oceans and are susceptible to oil spills. However, their tolerance to oil and their roles in the bioremediation of crude oil remain elusive. We analysed the response of microbial communities to a simulated oil spill in estuarine sediment microcosms under a series of oil concentrations (0, 25, 125, and 250 g kg -1 dry wt.). Cyanobacterial blooms only occurred on the sediment surface in the low oil (LO, 25 g kg -1 dry wt.) group, and cyanobacteria grew from very small amounts to enriched levels according to an internal mechanism. The dominant phylotypes enriched in the oil-contaminated sediments on day 35 were Leptolyngbya, Oscillatoria, Arthrospira (Spirulina), Geitlerinema and Cyanothece, and the majority were capable of fixing nitrogen. Gammaproteobacterial blooms occurred during the early stage, and Oceanospirillales dominated the sediment surface. The annotation of unassembled metatranscriptomic data revealed an increase in nitrogen metabolism, particularly photosynthesis (antenna proteins) during the later stage, together with depletion of fatty acid metabolism. In summary, high concentrations of crude oil are toxic to cyanobacteria but can facilitate the emergence of cyanobacterial aggregation at low concentrations (crude oil concentration < 25 g kg -1 dry wt.)., (© 2018 Society for Applied Microbiology and John Wiley & Sons Ltd.)

With the increasing demand for and consumption of crude oils, oil spill accidents happen frequently during the transportation of crude oils and oil products, and the environmental hazard they pose has become increasingly serious in China. The exact identification of the source of spilled oil can act as forensic evidence in the investigation and handling of oil spill accidents. In this study, a weathering simulation experiment demonstrates that the mass loss of crude oils caused by short-term weathering mainly occurs within the first 24h after a spill, and is dominated by the depletion of low-molecular weight hydrocarbons (

• Biodegradation can affect the distribution of aromatic carotenoids in crude oils. • Significant influence occurs after moderate biodegradation. • Caution must be taken when using crude oils and outcrop rocks. In this study, we use a previously confirmed group of progressively biodegraded oils to investigate the biodegradation effects on the distribution of aromatic carotenoids. The results clearly show that compared to the saturated C 40 β-carotane, all aromatic carotenoids detected in crude oils were affected by biodegradation. Significant changes mainly occur after moderate biodegradation and trace or undetectable levels of aromatic carotenoids and carotane would be expected in severely degraded oils. These results suggest that caution must be taken during evaluations on the degree of anoxia/euxinia in the depositional system by concentrations of aromatic carotenoids and/or related ratios when potentially biodegraded crude oils and outcrop rocks are used. [ABSTRACT FROM AUTHOR]

It is a challenge to determine the source and genetic relationship of condensate, waxy and heavy oils in one given complicated petroliferous area, where developed multiple sets of source rocks with different maturity and various chemical features. The central part of southern margin of Junggar Basin, NW China is such an example where there are condensates, light oils, normal density oils, heavy crude oils and natural gases. The formation mechanism of condensates has been seriously debated for long time; however, no study has integrated it with genetic types of waxy and heavy oils. Taking the central part of southern margin of Junggar Basin as a case, this study employs geological and geochemical methods to determine the formation mechanism of condensates, waxy and heavy oils in a complicated petroliferous area, and reveals the causes and geochemical processes of the co-occurrence of different types of crude oils in this region. Based on detailed geochemical analyses of more than 40 normal crude oils, light oils, condensates and heavy oils, it is found that the condensates are dominated by low carbon number n-alkanes and enriched in light naphthenics and aromatic hydrocarbons. Heptane values of these condensates range from 19% to 21%, isoheptane values from 1.9 to 2.1, and toluene/ n-heptane ratios from 1.5 to 2.0. The distribution of n-alkanes in the condensates presents a mirror image with high density waxy crude oils and heavy oils. Combined with the oil and gas-source correlations of the crude oils, condensates and natural gas, it is found that the condensates are product of evaporative fractionation and/or phase-controlled fractionation of reservoir crude oils which were derived from mature Cretaceous lacustrine source rocks in the relatively early stage. The waxy oils are the intermediate products of evaporative fractionation and/or phase-controlled fractionation of reservoir crude oils, while the heavy oils are in-situ residuals. Therefore, evaporative fractionation and/or phase-controlled fractionation would account for the formation of the condensate, light oil, waxy oil and heavy oil in the central part of southern margin of Junggar Basin, resulting in a great change of the content in terms of light alkanes, naphthenics and aromatics in condensates, followed by great uncertainties of toluene/ n-heptane ratios due to migration and re-accumulation. The results suggest that the origin of the condensate cannot be simply concluded by its ratios of toluene/ n-heptane and n-heptane/methylcyclohexane on the Thompson's cross-plot, it should be comprehensively determined by the aspects of geological background, thermal history of source rocks and petroleum generation, physical and chemical features of various crude oils and natural gas, vertical and lateral distribution of various crude oils in the study area. [ABSTRACT FROM AUTHOR]

By using fluorescence lifetime image microscope (FLIM) and time-correlated single photon counting (TCSPC) technique, we measured fluorescence lifetime of crude oils with density of 0.9521-0.7606 g/cm and multiple petroleum inclusions from Tazhong uplift of Tarim Basin. As indicated by the test results, crude oil density is closely correlated with average fluorescence lifetime following the regression equation Y=-0.0319 X+0.9411, which can thus be used to calculate density of oil inclusions in relation to fluorescence lifetime and density of corresponding surface crude. For type A oil inclusions showing brown-yellow fluorescence from Tazhong 1 well in Tarim Basin, their average fluorescence lifetime was found to be 2.144-2.765 ns, so the density of surface crude corresponding to crude trapping these oil inclusions is 0.852-0.873 g/cm, indicating that they are matured oil inclusions trapped at earlier stage of oil formation. For type B oil inclusions with light yellow-white fluorescence, their average fluorescence lifetime was found to be 4.029-4.919 ns, so the density of surface crude corresponding to crude trapping these oil inclusions is 0.784-0.812 g/cm, indicating that they are higher matured oil inclusions trapped at the second stage of oil formation. For type C oil inclusions showing light blue-green fluorescence, their average fluorescence lifetime was found to be 5.063-6.168 ns, so the density of surface crude corresponding to crude trapping these oil inclusions is 0.743-0.779 g/cm, indicating that they are highly-matured light oil inclusions trapped at the third stage of oil formation. [ABSTRACT FROM AUTHOR]

Abstract: The natural evaporation of a condensate from the Tarim Basin in northwest China was conducted at room temperature to investigate the stable carbon isotopic fractionation of individual light hydrocarbons (LHs) in the C6–C8 range. Our results show that individual LHs in this range in liquid residuals are progressively enriched in 13C, indicating the preferential evaporation of 12C containing compounds from the crude oil. When evaporative losses of individual LHs in the C6–C8 range are <70%, there is no significant carbon isotope fractionation (usually with δ 13Cfinal–initial <1‰). A δ 13Cfinal–initial of individual LHs in the C6–C8 range >1‰ mainly occurs when the evaporative losses are >70%, but the magnitudes of stable carbon isotopic fractionation strongly depend on compound classes. Compared to the straight chain and branched alkanes and the monoaromatic hydrocarbons, there is almost no stable carbon isotopic fractionation observed for cycloalkanes in the C6–C8 range. Using the Rayleigh model, stable carbon isotopic fractionation of individual LHs in the C6–C8 range during natural evaporation is described and the stable carbon isotope fractionation factors (α) are 0.998976 for n-hexane, 0.998991 for n-heptane, 0.999426 for n-octane, 0.999138 for 3-methylhexane, 0.999401 for methylcyclohexane and 0.998518 for toluene. Correspondingly, the stable carbon isotope enrichment factors (ε) are −1.024 for n-hexane, −1.009 for n-heptane, −0.574 for n-octane, −0.862 for 3-methylhexane, −0.599 for methylcyclohexane and −1.482 for toluene. Both α and ε values clearly show a progressive enrichment in 13C in the residual liquids during natural evaporation in a crude oil system (what is referred to as “normal isotope fractionation”), rather than an enrichment in 13C in the vapor phase as reported by previous studies (what is referred to as “inverse isotope fractionation”). The intermolecular binding energies due to the van der Waals attraction forces in crude oil likely plays an important role on the diffusion velocity and the escape of 13C containing LHs from the system, thereafter exerting a significant influence on stable carbon isotope fractionation, which is controlled by a kinetic isotopic effect. Since we cannot be certain of the exact amount of LHs that evaporated for one given crude oil from the subsurface to the laboratory, the results presented here strongly suggest that caution must be taken in the application of stable carbon isotopic composition of individual LHs in petroleum geochemistry and in environmental studies associated with oil pollution. However, δ 13C values of cycloalkanes in the C6–C8 range can still be used in confidence to decipher oil generation, migration, accumulation and secondary alteration in the subsurface of sedimentary basins and to address oil pollution issues. [Copyright &y& Elsevier]

Large amounts of data regarding the influence of temperature and pressure on the thermal stability of crude oil have been published; however, the role of reservoir mediums has received little attention. Experiments involving oil cracking in the presence of montmorillonite, illite, calcite, quartz and water were conducted in closed gold tubes to investigate the effects of these reservoir mediums on oil destruction. This was done by screening variations in the chemical and stable carbon isotopic components of nC10+ and gasoline-range hydrocarbons (nC8-) present in various systems. Results indicated that reservoir mediums have an active role in oil cracking under experimental conditions. The concentrations of nC10+ in the cracked residues progressively decreased in systems containing oil+water+illite, oil+water+montmorillonite, oil+water, oil+water+quartz and oil+water+calcite. In comparison with the system containing oil+water, our results indicated a retardation effect for oil cracking in systems in the presence of illite and montmorillonite, and an acceleration effect on oil destruction in systems in the presence of calcite and quartz. nC10+ became increasingly depleted in 13C in systems with oil+water+illite, oil+water+calcite, oil+water+montmorillonite, oil+water+ quartz and oil+water. No obvious correlation was observed between concentrations and stable carbon isotopic components of nC6-nC8 and nC10+ in the individual systems. The discrepancies in chemical and stable carbon isotopic components of nC6-nC8 and nC10+ in the pyrolyzed residues highlighted the important role of reservoir mediums to control carbon-carbon cleavage of nC10+ and then the isomerization, cyclolization and aromatization reactions; as well as governing the occurrence and thermal destruction of nC6-nC8 under experimental conditions. This research may have critical implications in reconstructing chemical kinetic models for natural oil cracking. [ABSTRACT FROM AUTHOR]

Using molecular geochemical data from infrared spectrometer and pyrolysis gas chromatography-mass spectrometry, this paper investigates the petroleum generation characteristics of Jurassic coal measures from Kuche depression, Tarim Basin, NW China. The results showed that the Jurassic coaly rocks with medium maturity (Ro%: 0.8– 1.1) were enriched in gas-prone functionalities (-CH3) and low molecular weight pyrolysates (

Hydrocarbons, include heavy oils, normal oils, waxy oils and light oils, condensate oils and gases were all found in Lunnan Oilfield, the occurrences of hydrocarbons with complicated physical properties indicates a complicated distribution of reservoirs. By the drilling data, the distribution pattern had been found that, in plan view, the density of crude oils in the western part is heavier than that of oils in the eastern part in Lunnan region, namely the crude oils were mainly found in the western part while the natural gases were mainly found in the eastern, which shows that an obvious differentiation in the east and west part was presented in the Lunnan region. Furthermore, in vertical view, the light hydrocarbons were mainly found in the Carboniferous reservoir while the heavier hydrocarbons were mainly found in the Ordovician and Triassic reservoirs. By analysis of the semi-logarithm distribution of n-alkanes, biomarker ratios and stable carbon isotopic compositions of crude oils, we have found that two oil families and discontinuous distribution were presented in hydrocarbons in Lunnan Oilfield. This kind of discontinuous distribution of geochemical parameters was not from continuous fractionation in migration process. The biodegraded heavy oil reservoirs in western part belong to the lower matured oil family, while the light or condensate oils reservoirs belong to higher matured oil family. Thus, a mixed filing of hydrocarbons was occurred in the middle part in Lunnan Oilfield and resulted in the occurrence of waxy oil. The mixed filling model may help to explain the distribution pattern of hydrocarbon reservoirs in Lunnan Oilfield, especially can lead to a relatively consistent explanation for all kinds of geochemical data, such as physical properties, pyrrolic nitrogen compounds, biomarker parameters and stable carbon isotopic compositions. [ABSTRACT FROM AUTHOR]

Molecular stable carbon isotope technique was employed to study well-sourced crude oils collected from a single drilling well and from the entire Lunnan oilfield, Tarim Basin, NW China. The stable carbon isotopic composition of n-alkanes from crude oils showed that Ordovician-derived oils are enriched in 13C and Triassic-derived oils are depleted in 13C. This is consistent with the distribution and evolution trend of stable carbon isotope ratios in crude oils/organic matter from all over the world in geological history (Stahl, 1977; Andrusevich et al., 1998). An extensive survey of literature indicates that, except for thermal maturity, organic matter input and depositional environment, paleoenvironmental background is another key factor that affects the stable carbon isotopic composition of Ordovician- and Triassic-derived crude oils. The results showed that gas chromatographic-isotope ratio mass spectrometry (GC-C-IRMS), combining with biogeochemical evolution of organic matter in geological history, may be a powerful tool in refining oil/oil, oil/source correlations in multi-age, multi-source petroliferous basins like Tarim. [ABSTRACT FROM AUTHOR]

Aryl isoprenoids have been detected for the first time in crude oils from Paleozoic petroleum systems in the Tabei uplift, Tarim Basin, northwestern China. The principal compounds possess the 1-alkyl-2,3,6-trimethyl substitution pattern characteristic of diaromatic carotenoids found in the Chlorobiaceae family of photosynthetic sulfur bacteria, with a predominance of C13 – C23 homologues in these samples. Flash pyrolysates of the asphaltene fractions isolated from crude oils show an unusual abundance of 1,2,3,4-tetramethylbenzene, an indicator for a significant contribution of diaromatic carotenoids to the source kerogen of these oils. The wide distribution of these compounds in crude oils reveals that penetration of the photic zone by sulfidic waters during deposition enabled prolific growth of photosynthetic green sulphur bacteria (Chlorobiaceae). This suggests that the source rocks for the Paleozoic petroleum systems in the Tabei uplift were likely deposited under euxinic conditions with sulfate and sulfide-rich water bodies, which doesn''t support previously published conclusions of a Middle-Upper Ordovician source that marks the slope facies at the margins of structural uplifts. [Copyright &y& Elsevier]

• A predominance of C 28 steranes was found in lacustrine source rocks. • δ 13C of the C 28 ααα 20R sterane was as low as −37‰, similar to that of a C 27 20R triaromatic steroid. • C 28 steranes were produced by algae blooming in a mixed water column. • Other steranes derived from algae growing in a stratified water column. C 27 –C 29 steranes are common constituents of crude oils and hydrocarbon source rocks and are usually dominated by either C 27 or C 29 compounds. In the current study, however, steranes dominated by C 28 components were detected in eight lacustrine source rock samples in the first member of the Shahejie Formation in the Qikou Sag, Bohai Bay Basin of Eastern China. Ratios of C 28 /(C 27 + C 28 + C 29) ααα 20R steranes in four samples can exceeded 50%. Furthermore, C 27 triaromatic steroids, presumably originating from C 28 steranes, were also observed at high levels, relative to C 26 and C 28 homologues. Stable carbon isotope compositions of a C 28 ααα 20R sterane and C 27 20R triaromatic steroid were found to be similar, with δ13C at −37‰ and −36‰ respectively, much lower than values for pristane (by ∼7‰) and total organic carbon (by ∼10‰). The abnormally low δ13C values of the steroids suggest that C 28 ααα 20R sterane was biosynthesized by algae blooming in the water column during phases of overturn and mixing, such as in autumn, during which recycled CO 2 and nutrients welling up from hypolimnion to the epilimnion are assimilated, contributing to a high algal productivity and low δ13C in algal organic matter. [ABSTRACT FROM AUTHOR]