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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]

Flash pyrolysis (Py) in combination with gas chromatography (GC) and mass spectrometry are often used to elucidate the structure of geomacromolecules such as kerogens, coals, asphaltenes and humic acids by analyzing their low molecular weight pyrolysis products. Most previous work restricts itself to C 6+ pyrolysis products with only a few reports on the quantitative measurement of individual C 1 –C 5 gaseous hydrocarbons. This is because of the difficulty in simultaneously separating C 1 –C 5 efficiently. By using a GasPro capillary column to separate C 1 –C 5 gaseous hydrocarbons and using polystyrene as external standard, we explore a quantitative Py-GC flame ionization detector (FID) method to study the C 1 –C 5 pyrolysis products released from kerogens (coals) by primary cracking. Our study indicates that there is a good linear relationship between peak area of C 1 –C 5 on Py-GC FID and kerogen sample weight. Based on the above methods, the yields of C 1 –C 5 gaseous hydrocarbons released from various kerogen types were quantitatively studied. The results indicate that kerogen type plays a key role in controlling the compositions of C 1 –C 5 gaseous hydrocarbons released by kerogen primary cracking under pyrolysis conditions. Type III kerogens (vitrinite rich coals) seem to have more abundant short alkyl chains linked to aromatic nuclei. Sequential flash pyrolysis at 800 °C, 1000 °C and 1200 °C suggests the generation mechanism of C 1 is different from that of C 2 –C 5 . C 2 –C 5 are mainly generated by the release of alkyl precursors while aromatization and condensation of the kerogen structure may also be an important source of C 1 at high maturity, especially for type III kerogens (vitrinite rich coals). It seems to be a reliable way to study the generation mechanisms of C 1 –C 5 by kerogen primary cracking and also the distribution of short alkyl chains within kerogen structure. [ABSTRACT FROM AUTHOR]

Methane-oxidizing bacteria (MOB) have long been used as an important biological indicator for oil and gas prospecting, but the ecological characteristics of MOB in hydrocarbon microseep systems are still poorly understood. In this study, the activity, distribution, and abundance of aerobic methanotrophic communities in the surface soils underlying an oil and gas field were investigated using biogeochemical and molecular ecological techniques. Measurements of potential methane oxidation rates and pmoA gene copy numbers showed that soils inside an oil and gas field are hot spots of methane oxidation and MOB abundance. Correspondingly, terminal restriction fragment length polymorphism analyses in combination with cloning and sequencing of pmoA genes also revealed considerable differences in the methanotrophic community composition between oil and gas fields and the surrounding soils. Principal component analysis ordination furthermore indicated a coincidence between elevated CH oxidation activity and the methanotrophic community structure with type I methanotrophic Methylococcus and Methylobacter, in particular, as indicator species of oil and gas fields. Collectively, our results show that trace methane migrated from oil and gas reservoirs can considerably influence not only the quantity but also the structure of the methanotrophic community. [ABSTRACT FROM AUTHOR]

• DOM chemistry was investigated in the Three Gorges Reservoir • Higher terrestrial input, molecular and isomeric complexity of DOM were detected in storage period • Hydrological management of reservoirs shifts the DOM chemistry • Hydrological management would affect DOM mineralization and CO 2 emission in young reservoirs Reservoirs are well known as a far-reaching human modification on the functions of natural river networks. However, changes in the chemistry and reactivity of dissolved organic matter (DOM) responding to hydrological management for water retention structures, and its influence on the river carbon cycle, remain poorly understood. Here we show that hydrological management does shape the molecular composition of DOM in the world's largest Three Gorges Reservoir, as revealed by optical spectroscopy and ultrahigh-resolution mass spectrometry. Relatively higher terrestrial input, molecular complexity, isomeric complexity, and environmental stability of DOM were observed during the storage period, whereas the inverse occurred during the drainage period. The results demonstrate that the hydrodynamic processes, which are mainly controlled by water intrusion from mainstream to tributaries, are likely the underlying mechanism controlling DOM chemistry. Integrated with observations from worldwide river reservoirs, the DOM degradation experiments suggest that reservoir hydrological management would enhance DOM mineralization, thereby increase CO 2 emission and change the river carbon cycle. Image, graphical abstract [ABSTRACT FROM AUTHOR]

The global dispersal of forests and soils has been proposed as a cause for the Late Devonian mass extinctions of marine organisms, but detailed spatiotemporal records of forests and soils at that time remain lacking. We present data from microscopic and geochemical analyses of the Upper Devonian Chattanooga Shale (Famennian Stage). Plant residues (microfossils, vitrinite and inertinite) and biomarkers derived from terrestrial plants and wildfire occur throughout the stratigraphic section, suggesting widespread forest in the southern Appalachian Basin, a region with no macro plant fossil record during the Famennian. Inorganic geochemical results, as shown by increasing values of SiO2/Al2O3, Ti/Al, Zr/Al, and the Chemical Index of Alteration (CIA) upon time sequence, suggest enhanced continental weathering that may be attributed to the invasion of barren lands by rooted land plants. Our geochemical data collectively provide the oldest evidence of the influences of land plants from the southernmost Appalachian Basin. Our synthesis of vascular plant fossil record shows a more rapid process of afforestation and pedogenesis across south-central Euramerica during the Frasnian and Famennian than previously documented. Together, these results lead us to propose a new hypothesis that global floral dispersal had progressed southward along the Acadian landmass rapidly during the Late Devonian. [ABSTRACT FROM AUTHOR]

Although oil and gas from coaly source rocks have been widely discovered worldwide, the role of oil generated from coal measures in marine-continental coaly deposits during the Carboniferous-Permian period in the Bohai Bay Basin has long been a subject of debate. The recent discovery of a condensate reservoir in the Wumaying buried hill within the Huanghua Depression of the Bohai Bay Basin offers new potential insights into this issue. In this study, we employed organic geochemical methods to explore the possibility of the Carboniferous-Permian coal deposit being a primary source of the condensate. The distribution of light hydrocarbons and the biomarker assemblage indicate that the condensate did not undergo significant secondary alterations such as thermal cracking, gas invasion fractionation, or biodegradation. The hydrocarbon generation potential of the Carboniferous-Permian coaly source rocks suggests that they could be an important contributor to the formation of condensate. High pristine/phytane ratios (1.0-7.5), an abundant presence of benzene series, and the dominance of C 29 steranes (>50%) within the condensate could be indicative of coaly organic matter. These features are comparable to those found in coaly source rocks. Moreover, the stable carbon isotopic compositions of n -alkanes in the condensate, ranging from -26.0 to -30.0‰, correlate well with those from coaly mudstone (-25.4 to -30.0‰). This suggests that the condensate of the Wumaying buried hill may predominantly originate from the Carboniferous-Permian coaly mudstone. When integrated with the geological background, the results distinctly demonstrate that the Carboniferous-Permian coaly source rocks have significantly contributed to the formation of the condensate reservoir in the Wumaying buried hill. This provides an essential reference for future exploration of oil and gas resources derived from the carboniferous-Permian coaly source rocks in the Bohai Bay Basin., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

Methane-oxidizing bacteria (MOB) have long been recognized as an important bioindicator for oil and gas exploration. However, due to their physiological and ecological diversity, the distribution of MOB in different habitats varies widely, making it challenging to authentically reflect the abundance of active MOB in the soil above oil and gas reservoirs using conventional methods. Here, we selected the Puguang gas field of the Sichuan Basin in Southwest China as a model system to study the ecological characteristics of methanotrophs using culture-independent molecular techniques. Initially, by comparing the abundance of the pmoA genes determined by quantitative PCR (qPCR), no significant difference was found between gas well and non-gas well soils, indicating that the abundance of total MOB may not necessarily reflect the distribution of the underlying gas reservoirs. 13 C-DNA stable isotope probing (DNA-SIP) in combination with high-throughput sequencing (HTS) furthermore revealed that type II methanotrophic Methylocystis was the absolutely predominant active MOB in the non-gas-field soils, whereas the niche vacated by Methylocystis was gradually filled with type I RPC-2 (rice paddy cluster-2) and Methylosarcina in the surface soils of gas reservoirs after geoscale acclimation to trace- and continuous-methane supply. The sum of the relative abundance of RPC-2 and Methylosarcina was then used as specific biotic index (BI) in the Puguang gas field. A microbial anomaly distribution map based on the BI values showed that the anomalous zones were highly consistent with geological and geophysical data, and known drilling results. Therefore, the active but not total methanotrophs successfully reflected the microseepage intensity of the underlying active hydrocarbon system, and can be used as an essential quantitative index to determine the existence and distribution of reservoirs. Our results suggest that molecular microbial techniques are powerful tools for oil and gas prospecting.

Studying the response and recovery of marine microbial communities during mass extinction events provides an evolutionary window through which to understand the adaptation and resilience of the marine ecosystem in the face of significant environmental disturbances. The goal of this study is to reconstruct changes in the marine microbial community structure through the Late Devonian Frasnian-Famennian (F-F) transition. We performed a multiproxy investigation on a drill core of the Upper Devonian New Albany Shale from the Illinois Basin (western Kentucky, USA). Aryl isoprenoids show green sulfur bacteria expansion and associated photic zone euxinia (PZE) enhancement during the F-F interval. These changes can be attributed to augmented terrigenous influxes, as recorded collectively by the long-chain/short-chain normal alkane ratio, carbon preference index, C 30 moretane/C 30 hopane, and diahopane index. Hopane/sterane ratios reveal a more pronounced dominance of eukaryotic over prokaryotic production during the mass extinction interval. Sterane distributions indicate that the microalgal community was primarily composed of green algae clades, and their dominance became more pronounced during the F-F interval and continued to rise in the subsequent periods. The 2α-methylhopane index values do not show an evident shift during the mass extinction interval, whereas the 3β-methylhopane index values record a greater abundance of methanotrophic bacteria during the extinction interval, suggesting enhanced methane cycling due to intensified oxygen depletion. Overall, the Illinois Basin during the F-F extinction experienced heightened algal productivity due to intensified terrigenous influxes, exhibiting similarities to contemporary coastal oceans that are currently undergoing globalized cultural eutrophication. The observed microbial community shifts associated with the F-F environmental disturbances were largely restricted to the extinction interval, which suggests a relatively stable, resilient marine microbial ecosystem during the Late Devonian., (© 2023 John Wiley & Sons Ltd.)

Objective: Hydrocarbon microseepage is a natural phenomenon that hydrocarbon gases of subsurface petroleum accumulations migrate upward by reservoir pressure. The detection of the activity and distribution of these highly specialized populations can be used to forecast the existence of oil and gas deposits. However, the hydrocarbon-oxidizing bacterial population are usually not predominant in soil samples above the typical onshore oil and gas reservoirs. It is hard to assess the abundance of hydrocarbon-oxidizing bacteria., Methods: In this study, changes of microbial abundance and functional genes were studied., Results: Under gaseous hydrocarbon condition, changes of methane and butane oxidizing bacteria were different. Furthermore, changes of functional genes indicated that genome analysis was more proper for microbial anomalies detection., Conclusion: The profiling data of this study provide a comprehensive insight into gene expression profiles and lay the foundation for optimizing the microbial prospecting technology.

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 (