Marine and Petroleum Geology最新文献

{"title":"Integrated seismic stratigraphic, sedimentological and petrophysical approaches for characterizing the Cenomanian reservoirs in transitional highs of north Western Desert intra-cratonic rift basins, Egypt","authors":"Ahmed Awadalla ,&nbsp;Ali Farag ,&nbsp;Andrea Moscariello ,&nbsp;Mahmoud Leila","doi":"10.1016/j.marpetgeo.2025.107581","DOIUrl":"10.1016/j.marpetgeo.2025.107581","url":null,"abstract":"<div><div>The Cenomanian Bahariya Formation is the most prolific hydrocarbon reservoir within the Mesozoic intra-cratonic rift basins of the Egyptian Western Desert. However, it remains under-explored in the transitional structural highs bordering these basins. These transitional regions host thin hydrocarbon pay zones in the sandstones of the Bahariya Formation. These sandstones exhibit pronounced petrophysical heterogeneity, which poses significant challenges to reservoir characterization and prediction, and their depositional characteristics and controls on the reservoir facies distribution have never been investigated. This study employs an integrated approach utilizing seismic stratigraphy, sedimentary facies analysis and petrophysics to establish the relationship between the Bahariya depositional patterns, reservoir rock types, and hydraulic flow units. Understanding these relationships is essential for assessing reservoir performance and identifying high-quality reservoir intervals for future exploration and production in these transitional regions. The studied core intervals comprise the Upper Bahriya reservoirs in two wells (Wadi El-Rayan-3X “WR-3X″ and Rayan-3X “R-3X”). The cored intervals consist mainly of sixteen sandstone, mudstone and siltstone lithofacies that were grouped into nine facies associations (FA) deposited in a muddy tide-dominated estuarine environment. Sandstone lithofacies were preferentially accumulated in narrow (&lt;1 km width) tidal channels (FA2) and sub-tidal bars (FA3). The sandstones of FA2, FA3 were classified as reservoir rock types (RRTs) 1 and 2 (RRT1, RRT2) with best reservoir characteristics and contribute to more than 90 % of the flow capacity of the Upper Bahariya reservoir. Conversely, mixed tidal flats (FA1) and intertidal sand bars (FA4) exhibit the poorest reservoir quality with pore system dominated by micropores and mesopores and act as effective fluid flow barriers. Petrophysical heterogeneity analysis indicates that sandstone lithofacies deposited within the outer estuarine tidal channels and subtidal bar environments exhibit the lowest degree of pore system heterogeneity. These facies are characterized by the dominance of well-connected macropores. The present results underscore the inherent heterogeneity of tide-dominated estuarine systems, where rapid lateral and vertical facies transitions, driven by fluctuating tidal energy and sediment supply, create complex reservoir architectures. Despite this complexity, the study demonstrates that higher-quality reservoir facies tend to preferentially accumulate in zones subjected to stronger tidal currents—specifically in the outer estuarine domain.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"182 ","pages":"Article 107581"},"PeriodicalIF":3.6,"publicationDate":"2025-08-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144842653","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Multi-scale characterization and control factors of bedding-parallel fractures in continental shale reservoirs: Insights from the Qingshankou Formation, Songliao Basin, China","authors":"Xiaocen Su ,&nbsp;Rukai Zhu ,&nbsp;Jingya Zhang ,&nbsp;Chang Liu ,&nbsp;Lei Gong ,&nbsp;Xiaohua Jiang ,&nbsp;Xiaofei Fu ,&nbsp;Mehdi Ostadhassan","doi":"10.1016/j.marpetgeo.2025.107580","DOIUrl":"10.1016/j.marpetgeo.2025.107580","url":null,"abstract":"<div><div>Bedding-parallel fractures play a critical role in enhancing storage capacity and horizontal permeability in tight shale reservoirs, significantly influencing the enrichment and productivity of shale oil. This study focuses on the continental shale of the Qingshankou Formation in the Songliao Basin, China, and systematically investigates the development characteristics and controlling factors of bedding-parallel fractures using a multi-scale dataset including core observations, image logs, scanning electron microscopy (SEM), and optical microscopy. Results show that bedding-parallel fractures are extensively developed across nano-to macro-scales, with nano-scale fractures reaching densities of up to 10⁵ fractures/m. Fracture density is negatively correlated with both fracture scale and aperture. These fractures are generally sub-parallel to bedding or exhibit low-angle orientations (mostly &lt;10°), and are typically discontinuous with limited lateral connectivity. Quantitative analyses indicate that fracture density is positively correlated with the contents of clay minerals, pyrite, and carbonate minerals, while showing weak or negative correlations with brittle minerals such as quartz and feldspar. Higher fracture densities are also observed in shales with elevated TOC content and higher thermal maturity. Furthermore, the type, thickness, and density of lamination significantly influence fracture development. At micro- and nano-scales, bedding-parallel fractures primarily act as hydrocarbon storage spaces and micro-flow conduits, whereas at the macro-scale, they mainly serve as horizontal flow pathways. These findings elucidate the multi-scale development mechanisms of bedding-parallel fractures in continental shale and underscore their dominant role in improving reservoir performance.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"182 ","pages":"Article 107580"},"PeriodicalIF":3.6,"publicationDate":"2025-08-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144826897","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Pseudomorphic changes after iron sulfide concretions in Jurassic limestones, Ionian Basin, Greece: tracking changes in basinal fluids","authors":"Nikolaos Dimopoulos ,&nbsp;Georgia Pe-Piper ,&nbsp;David J.W. Piper ,&nbsp;Nicolina Bourli ,&nbsp;Elena Zoumpouli ,&nbsp;George Iliopoulos ,&nbsp;Avraam Zelilidis","doi":"10.1016/j.marpetgeo.2025.107579","DOIUrl":"10.1016/j.marpetgeo.2025.107579","url":null,"abstract":"<div><div>Middle Jurassic limestones, deposited on deep-water highs in the Ionian Basin, include Fe-rich concretions. Mineralogical and textural studies by SEM show the concretions now consist of goethite with minor lepidocrocite, hematite and quartz. The cm-scale concretions include radiating spheres and pseudomorphs after ammonites, with cubic and pyritohedral pseudomorphs after pyrite. Smaller mm-scale concretions occur at limestone hardgrounds. Concretions have REE signatures and high Mo and V suggesting formation in hypoxic water overlying a local euxinic basin. Textures suggest the following sequence of events: (1) Sea floor diagenetic iron monosulphide and pyrite concretions and veins. (2) With burial, recrystallisation to cubes or pyritohedrons of pyrite. (3) Pseudomorphous alteration of pyrite to hematite, with the 5 % volume reduction resulting in sub-micron pores that filled with silica (now quartz). (4) Widespread alteration of hematite to goethite with texturally complex, coupled dissolution-reprecipitation reactions. (5) Widespread secondary porosity, with precipitation of fibrous goethite and minor lepidocrocite. (6) Late cross-cutting fractures have Mn-rich minerals, with exotic trace elements such as asbolane (Co, Ni) and romanechite (Ba). The original pyrite concretions persisted during burial diagenesis until Paleogene uplift of the basin margins allowed ingress of oxidising meteoric water, circulated by thermal anomalies related to salt domes. Pyrite was oxidized to hematite and micropores were filled by silica. Oligocene thrusting created a new fracture set, increased loading of basinal sediments and allowed ingress of abundant meteoric water creating supergene alteration. Both chert and Fe-rich concretions provide important insights into diagenetic and hydrothermal evolution of thick limestone successions. [249 words]</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"182 ","pages":"Article 107579"},"PeriodicalIF":3.6,"publicationDate":"2025-08-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144852019","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Hydrothermal structures in alkaline lake shales, the Permian Fengcheng Formation of the Junggar Basin, NW China","authors":"Kai Zhong ,&nbsp;Pei Guo ,&nbsp;Zhiming Li ,&nbsp;Jian Wang ,&nbsp;Wangwei Liu ,&nbsp;Baozhen Zhang ,&nbsp;Meiyuan Song ,&nbsp;Changzhi Li ,&nbsp;Jinghong Xu","doi":"10.1016/j.marpetgeo.2025.107578","DOIUrl":"10.1016/j.marpetgeo.2025.107578","url":null,"abstract":"<div><div>This study investigates how hydrothermal activity since early diagenetic stage can alter continental shale properties by focusing on the alkaline lake shales of the Late Paleozoic Fengcheng Formation in the Junggar Basin, NW China. By utilizing core and thin section observations, cathode luminescence investigations, and in-situ carbon, oxygen, and strontium isotopic analyses, the formation mechanisms of the abundant white carbonate mineral-filled structures have been studied. Four distinct types of white structures are recognized: Type-1 calcite-filled (sub)horizontal bands, Type-2 calcite-filled speckles, Type-3 dolomite-filled speckles and Type-4 dolomite-filled root-like structures. The blocky calcite in Type-1 and Type-2 structures shows dark luminescence, slightly positive carbon isotopes (+0.2 ‰ to +2.38 ‰), moderately negative oxygen isotopes (−10.53 ‰ to −7.59 ‰) and very low ⁸⁷Sr/⁸⁶Sr ratios (0.705136 to 0.705740). The dolomite in Type-3 and Type-4 structures shows dark red to green luminescence, moderately positive oxygen isotopes (+3.04 ‰ to +3.98 ‰), negative carbon isotopes (−13.64 ‰ to −8.42 ‰) and very low strontium isotopes (0.705453 to 0.705903). We interpret that the Type-1 and Type-2 structures were related to hydrothermal activity that introduced recycled meteoric waters into shallow buried sediments, induced horizontal vein formation, and led to the dilution and calcification of sodium-carbonate evaporite minerals. The Type-3 and Type-4 structures were also induced by hydrothermal activity that introduced deep-sourced hydrothermal fluids into shallow to deep burial sediments, leading to the dilution and dolomitization of sodium-carbonate evaporite minerals and molar tooth structures in shales. These hydrothermally-influenced structures can increase carbonate mineral contents, reservoir space and fluid transport pathways, significantly impacting the reservoir properties of shales.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"182 ","pages":"Article 107578"},"PeriodicalIF":3.6,"publicationDate":"2025-08-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144826646","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"‘Resurrected’ concretions – their resumed cementation after exhumation, transport, re-deposition and exploitation by producers of the trace fossil Chondrites when still being soft","authors":"Andreas Wetzel ,&nbsp;Maciej Bojanowski","doi":"10.1016/j.marpetgeo.2025.107576","DOIUrl":"10.1016/j.marpetgeo.2025.107576","url":null,"abstract":"<div><div>Incipient concretions having argillaceous matrix and methane-derived cement were exhumed from a low-oxygenated muddy setting, transported and embedded in a fine-sandy tempestite. They were still soft after deposition of the tempestite because subsequently they were preferentially exploited by producers of the trace fossil <em>Chondrites</em>; its tubes are wide-spaced and rare in the tempestite but abundant and narrow-spaced in the concretions. The tubes are filled with fine sand taken from the tempestite. The stable isotope signature of the concretions (δ¹³C −39 to −22 ‰) markedly differs from that of the tempestite (δ¹³C −3 to −2‰). Organoclastic sulfate reduction (OSR) and anaerobic oxidation of methane (AOM) dominated the initial cementation of the concretions. During OSR and AOM, sulfate was reduced to sulfidic phases, including H₂S being toxic to animals. Nonetheless, <em>Chondrites</em> producers exploited the incipient concretions. Because around their tubes are no haloes that would indicate flushing with oxygenated water, the <em>Chondrites</em> producers likely lived in symbiosis with microbes utilizing and detoxicating sulfides and hence, followed a chemichnial behavior. After burrowing ceased, resumed precipitation of early diagenetic micrite filled the remaining porosity of concretions, whereas the tempestite sand was cemented by late diagenetic carbonate.</div><div>Burrowing of the displaced incipient concretions documents their still soft-to-stiff consistency, since they were only partly cemented but resistant to compaction although still in a plastic state, so that they could be burrowed. This fact explains why early diagenetic concretions are rarely found in modern muddy sediments because they are hardly recognized and easily overlooked in modern sediment cores.</div><div>Since coarse near-shore components are lacking, sediment reworking occurred distant from shore on a local swell. There, waves and currents enriched sand while concretions formed in mud underneath/nearby from where they became eroded and displaced by a stronger-than-average storm depositing them in a somewhat deeper area of restricted spatial extent.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"182 ","pages":"Article 107576"},"PeriodicalIF":3.6,"publicationDate":"2025-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144826637","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"On the limitations of spot permeability measurements to quantify bulk permeability of bioturbated reservoirs: Insights from digital rock physics modeling","authors":"Ahmed Refaat ,&nbsp;Hassan A. Eltom ,&nbsp;Ammar El-Husseiny","doi":"10.1016/j.marpetgeo.2025.107577","DOIUrl":"10.1016/j.marpetgeo.2025.107577","url":null,"abstract":"<div><div>Substantial permeability contrasts between the fine-grained host rock matrix (HRM) and the coarse-grained burrow fillings (BF) are observed in bioturbated reservoirs, which are characterized by burrows that create a dual-porosity system. Consequently, assessing bulk permeability becomes particularly challenging, as these reservoirs often exhibit permeability contrast between HRM and BF spanning several orders of magnitude. To address this issue, the present study utilizes insights from digital rock physics modeling to critically examine the limitations of spot permeability measurements in accurately estimating bulk permeability in bioturbated systems. Specifically, we applied an integrated workflow to examine samples from a bioturbated interval in the upper Hanifa Formation in Saudi Arabia, incorporating spot permeability measurements, petrographic analysis, micro-CT scanning, pore network modeling, and permeability simulations to evaluate the effectiveness of spot permeability data in capturing bulk flow behavior. Our findings revealed that although spot permeability data are valuable for identifying localized permeability trends, they can be misleading when used to infer true bulk permeability, as they may fail to account for isolated or poorly connected pore systems. In particular, our results showed a significant discrepancy emerged between the CT scan data and spot measurements: while the CT imaging showed isolated and poorly connected pores within the burrow fillings—resulting in negligible flow during simulations—the spot measurements indicated substantially higher permeability values, ranging from 2.65 mD to 796.30 mD. This contrast underscores the complexity of relying on localized measurements to characterize bulk reservoir properties. Therefore, achieving more accurate permeability estimations in bioturbated reservoirs necessitates a comprehensive approach that integrates spot permeability data with high-resolution imaging and digital simulation techniques.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"182 ","pages":"Article 107577"},"PeriodicalIF":3.6,"publicationDate":"2025-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144858215","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The impact of extensional and strike-slip composite tectonic activity on the development of fine-grained sedimentary rocks and the enrichment of organic matter in lacustrine rift basin: Insights from the Paleogene of the Shanan Sag, Bohai Offshore Basin","authors":"Yujie Ning ,&nbsp;Hao Liu ,&nbsp;Carlos Zavala ,&nbsp;Hehe Chen ,&nbsp;Wenlong Shi ,&nbsp;Xiaodong Lan ,&nbsp;Liang Zhou","doi":"10.1016/j.marpetgeo.2025.107574","DOIUrl":"10.1016/j.marpetgeo.2025.107574","url":null,"abstract":"<div><div>Fine-grained sedimentary rocks (FGSRs), are critical hydrocarbon source and reservoir units. In lacustrine rift basins, the development of FGSRs is constrained by factors such as paleoclimate, but predominantly governed by tectonics in terms of their spatio-temporal distribution. Although the paleoclimatic impacts are studied, the tectonic control mechanisms remain poorly understood, especially in extensional and strike-slip composite settings. By integrating 3D seismic data with well-logs, petrology, and geochemistry, we investigate how differential basin structural evolution influences fine-grained sedimentation and organic matter (OM) enrichment. In our study, three lithofacies associations (FA1, FA2, and FA3) were identified, corresponding to deep lake, semi-deep lake, and shallow lake environments, respectively. We suggest that, the sag's multi-phase, complex tectonics controlled the spatio-temporal evolution of FGSRs and their OM enrichment via architecture modification. (1) During the rifting stage (Es₃^L), the intense activity of the NW-trending faults formed a north-faulted south-onlapping half-graben, with thick OM-rich, semi-deep to deep lacustrine deposits. (2) During the strike-slip reversal stage (Es₃^m-u), NNE-trending faults underwent sinistral-to-dextral inversion, inducing local transpressional belts, uplifting early sedimentary areas, forming multi-sag patterns that altered the distribution of FGSRs and OM enrichment. (3) During the tectonic quiescence stage (Es_1-2), relatively mild extension favored the widespread deposition of shallow to semi-deep lacustrine sediments with enhanced OM preservation. (4) During the transtensional stage (Ed Formation), intense extension drove the deposition of thick-layers FGSRs in depocenters, while transcurrent motion controlled depocenter migration along the principal displacement zone. Our study provides insight into predicting characteristics of FGSRs in analogous lacustrine rift basins.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"182 ","pages":"Article 107574"},"PeriodicalIF":3.6,"publicationDate":"2025-08-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144863179","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"SynSection: Sedimentology-driven data generation for deep learning applications in carbonates petrography","authors":"Axel Ransinangue ,&nbsp;Richard Labourdette ,&nbsp;Erwann Houzay ,&nbsp;Sebastien Guillon ,&nbsp;Raphael Bourillot ,&nbsp;Emmanuel Dujoncquoy ,&nbsp;Nesrine Chehata","doi":"10.1016/j.marpetgeo.2025.107490","DOIUrl":"10.1016/j.marpetgeo.2025.107490","url":null,"abstract":"<div><div>The analysis of carbonate rocks through petrographic methods has long posed significant challenges in geological sciences, particularly regarding the systematic description and quantification of thin sections. Recent developments in artificial intelligence have suggested promising avenues for automation; however, the field remains constrained by limited training data availability, as manual annotation requires considerable time investment and can result in variable interpretations. This study addresses these challenges by introducing SynSection, a method for generating synthetic pairs of carbonate thin section images with corresponding labels for both classification and segmentation tasks. This approach has been carefully designed to incorporate sedimentological heuristics, ensuring the geological validity of generated samples through the integration of three primary components: 2D grain packing, groundmass generation using texture synthesis, and image blending for image composition. The advantage of this methodology lies in its ability to exponentially expand a limited set of manually labeled images, thereby reducing the resources required for dataset creation while maintaining consistency in annotation. The method was evaluated through the generation of 100,000 synthetic image-annotation pairs, implementing a transfer learning strategy in which models were initially trained on synthetic data before being fine-tuned on real thin section images. This approach demonstrated significant improvements in both classification and segmentation tasks compared to conventional training methods that rely solely on limited real data. In classification tasks, the transfer learning strategy enhanced performance metrics by 7.2%, achieving a top accuracy score of 94.9%. The impact of the method was particularly notable in segmentation tasks, where the binary grain segmentation model achieved an Intersection over Union (IoU) of 77.2% and a point counting determination score of 93.2%. The multiclass segmentation achieved a mean Intersection over Union (mIoU) of 55.3% and a point counting score of 89.6%, reflecting the inherent complexity of grain type differentiation. These results, which are consistent with medical imaging applications, demonstrate the method’s potential to optimize carbonate thin section analysis by reducing time allocated to descriptive tasks. The approach generates diverse training data that maintains geological validity, establishing a quantitative framework for automated petrographic analysis that aligns with standardized classification criteria and expert-defined features.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"182 ","pages":"Article 107490"},"PeriodicalIF":3.6,"publicationDate":"2025-08-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144828743","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Origin of hydrogen sulfide in produced gas of Upper Permian shales from western Hubei, southern China: A preliminary study","authors":"Yasheng Cui ,&nbsp;Le Li ,&nbsp;Huan Yang ,&nbsp;Keliang Pan ,&nbsp;Jie Xin ,&nbsp;Yuanqing Hu ,&nbsp;Xiaogui Peng ,&nbsp;Feng Yang","doi":"10.1016/j.marpetgeo.2025.107570","DOIUrl":"10.1016/j.marpetgeo.2025.107570","url":null,"abstract":"<div><div>An unexpected moderate concentration (0.3 %–2 %) of hydrogen sulfide (H₂S) was detected in the produced gas from upper Permian shales in western Hubei, southern China. This raised the hypothesis that H₂S could either be a primary component of the shale gas reservoir or a secondary product generated by fracturing. This study systematically acquired data on desorbed gas composition, produced gas composition, sulfur isotopes of H₂S in the produced gas, ion chemistry of flowback water, and compiled fracturing and production data, to preliminarily investigate the origin of H₂S in the produced gas. The unusually low sulfur isotope composition of H₂S in the produced gas (3.20 ‰–4.48 ‰, with an average of 3.66 ‰) rules out contamination from overlying (Changxing Formation) or underlying (Huanglong Formation) gas-bearing layers via natural fractures or fracturing-induced pathways. A two-order magnitude difference in H₂S content between desorbed and produced gas indicates that most of the H₂S in the produced gas is not supplied by the primary gas reservoir. The estimated volume of produced H₂S (62,025 m³) greatly exceeds the theoretical maximum H₂S yielded from acid-rock reactions (4243.5 m³), ruling out this reaction as the major source of H₂S. The reservoir temperature (average 89.39 °C), coupled with a positive correlation between H₂S content and sulfate and calcium ions, suggests that fracturing-induced bacterial sulfate reduction (BSR) is the main driver for secondary H₂S formation. Thermochemical sulfate reduction (TSR) is unlikely due to temperature constraints.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"182 ","pages":"Article 107570"},"PeriodicalIF":3.6,"publicationDate":"2025-08-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144781623","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Revisiting genetic affinities of Tertiary crude oils in the western Qaidam Basin: new insights from sulfurized biomarkers","authors":"Jian Ma ,&nbsp;Chaodong Wu ,&nbsp;Xingqian Cui","doi":"10.1016/j.marpetgeo.2025.107571","DOIUrl":"10.1016/j.marpetgeo.2025.107571","url":null,"abstract":"<div><div>Hydrocarbon biomarkers, diagnostic fossil molecules tied to specific organisms, are essential for classify crude oils and associated paleoenvironments. While previous studies on Tertiary crude oils and source rocks from the western Qaidam Basin emphasized uniform depositional environments, recent discoveries of Eocene marine incursions and H₂S-rich gas reservoirs complicate these interpretations. Organic sulfur compounds (OSCs) in Qaidam Tertiary crude oils, though unexplored, offer new insight into genetic affinities and depositional histories. However, the structural complexity of OSCs posts challenges for direct detection. Catalytic desulfurization, which release sulfurized biomarkers, provides an alternative approach to understanding OSCs and sulfurization mechanisms. Herein, sulfurized biomarkers from crude oils across the western Qaidam Basin were investigated using Raney nickel desulfurization. The new biomarker inventories after desulfurization exhibiting lower thermal maturity than their free hydrocarbon counterparts, indicating early sequestration of organic molecules via natural sulfurization. The exceptional abundance of desulfurized C₃₇ and C₃₈ alkanes likely originates from previously sulfurized C₃₇ and C₃₈ long-chain alkenones. Higher abundances of sulfurized homohopanes, gammacerane and carotenoids in the Qigequan and Gasikule Oilfields highlight distinctive anoxic and stratified environments in the westernmost Qaidam Basin. In contrast, anomalously over-matured signatures in the Yingzhong Oilfield reveal unusual thermal evolution. Overall, sulfurized biomarkers confirm compositional heterogeneities and genetic affinities among oilfields, providing primitive information that enhances oil-source rock correlations and paleoenvironment reconstruction. This study underscores the need to evaluate both free and sulfurized lipids to fully understand petroleum systems.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"182 ","pages":"Article 107571"},"PeriodicalIF":3.6,"publicationDate":"2025-07-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144770843","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}