Marine and Petroleum Geology最新文献

{"title":"Extreme sulfur isotope heterogeneity in individual Ediacaran pyrite grains revealed by NanoSIMS analysis","authors":"Yongliang Hu ,&nbsp;Wei Wang ,&nbsp;Xianye Zhao ,&nbsp;Chengguo Guan ,&nbsp;Chuanming Zhou ,&nbsp;Chenran Song ,&nbsp;Hongyi Shi ,&nbsp;Yunpeng Sun ,&nbsp;Zhe Chen ,&nbsp;Xunlai Yuan","doi":"10.1016/j.marpetgeo.2024.107201","DOIUrl":"10.1016/j.marpetgeo.2024.107201","url":null,"abstract":"<div><div>Pyrite sulfur isotopic composition (δ³⁴S_py) is a crucial proxy for reconstructing ancient Ediacaran marine environments. However, recent <em>in situ</em> isotopic analyses of sedimentary pyrite have revealed distinct δ³⁴S_py signatures among different pyrite morphologies, indicating that secular changes in bulk δ³⁴S_py may reflect variations in proportions of different pyrite morphologies rather than environmental signals. Up to now, intragrain isotopic patterns within individual pyrite grains have not yet been extensively investigated for Ediacaran samples. The absence of this specific data set has hindered our ability to understand current complexities of bulk δ³⁴S_py in reconstruction paleoenvironment. This study aims to elucidate δ³⁴S_py patterns by conducting <em>in situ</em> isotopic analysis on pyrite grains from Ediacaran drill-core samples. We employed scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), Raman spectroscopy, and nanoscale secondary ion mass spectrometry (NanoSIMS) to examine the crystal texture, element atomic ratios (S/Fe), mineral composition, and <em>in situ</em> isotopic composition within single pyrite grains. SEM-EDS observations reveal that the euhedral/subhedral pyrite crystals generally exhibit uniform mineral texture, although some grains show varying degrees of dissolution edges and surface cavities. Raman spectroscopy demonstrates the possible presence of pyrrhotite mineral within pyrite grains at some specific sites and points. <em>In situ</em> isotopic analysis reveals significant intragrain δ³⁴S heterogeneity, with difference reaching up to 69.3‰ on a micrometer scale. Distinct deposition depths and burial rates may contribute to the varying value ranges and degrees of isotopic heterogeneity amongst pyrite grains. A model suggesting rapid precipitation from numerous nucleation sites simultaneously could account for the observed intragrain heterogeneity of <em>in situ</em> δ³⁴S values. Pyrite grains exhibit general atomic S/Fe ratios of &gt; 2, potentially due to the presence of trace elements incorporated into the pyrite structure. The occurrence of pyrrhotite leads to a slightly positive correlation between <em>in situ</em> δ³⁴S_py values and S/Fe ratios, yet the ³²S-enriched pyrrhotite plays less substantial in generating intragrain δ³⁴S heterogeneity of pyrite grains. Our findings reveal clear isotopic heterogeneities within individual pyrite grains, in addition to the notable δ³⁴S_py differences among pyrite of various morphologies. These results highlight significant microenvironmental heterogeneity and dynamic sulfur pool mixing on rapid short-term timescale during pyrite growth.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"171 ","pages":"Article 107201"},"PeriodicalIF":3.7,"publicationDate":"2024-11-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142656659","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":"Methane leakage from abandoned wells in the Dutch North Sea","authors":"G. de Bruin ,&nbsp;H. de Stigter ,&nbsp;M. Diaz ,&nbsp;A. Delre ,&nbsp;I. Velzeboer ,&nbsp;N. Versteijlen ,&nbsp;H. Niemann ,&nbsp;M. Wilpshaar ,&nbsp;G.J. Reichart","doi":"10.1016/j.marpetgeo.2024.107184","DOIUrl":"10.1016/j.marpetgeo.2024.107184","url":null,"abstract":"<div><div>Methane is a powerful greenhouse gas and the second most important when considering global warming due to anthropogenic added gasses. Global inventories of greenhouse gasses currently do not take into consideration methane emitted from the ocean and seas. The North Sea is an intensely exploited seas for oil and gas and it was recently suggested to be a major source for manmade methane emissions. All wells drilled through shallow gas (methane) were found to be leaking and one-third of all abandoned wells was found to be drilled through shallow gas. Here we present the results from a research expedition to investigate methane leakage at abandoned wells drilled through shallow gas in the Dutch North Sea. We surveyed 57 abandoned wells of which 33 were drilled through shallow gas. Nine locations showed bubble plumes (acoustic flares). We noted a distinct difference between gas leakage of abandoned wells and locations with natural gas seepage. Whereas well leakage consists of one or two bubble plumes at the wellhead itself and no bubble plumes in the surrounding area, natural plume fields are characterized by tens to hundreds of plumes and none at the wellhead. At six wells, we conclude that the plumes are caused by the well leaking shallow gas, whereas three observed plume fields classify as natural seepage. We found that 18% of wells drilled through shallow gas were leaking, with 11% of all abandoned wells being drilled through shallow gas. When we compensated for over-representation of shallow gas wells in our sample (58% of our sample is drilled through shallow gas), we find that less than 2% of all abandoned wells in the Dutch North Sea is likely leaking. Well leakage seems to occur when large quantities of shallow gas are present and the abandoned well apparently suffers from an integrity issue.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"171 ","pages":"Article 107184"},"PeriodicalIF":3.7,"publicationDate":"2024-11-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142656705","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Evaluation and modeling of velocity dispersion and frequency-dependent attenuation in gas hydrate-bearing sediments","authors":"Linsen Zhan ,&nbsp;Jun Matsushima ,&nbsp;Haotian Liu ,&nbsp;Hailong Lu","doi":"10.1016/j.marpetgeo.2024.107204","DOIUrl":"10.1016/j.marpetgeo.2024.107204","url":null,"abstract":"<div><div>Wave velocity and attenuation of gas hydrate-bearing samples are often extrapolated from ultrasonic to lower seismic/sonic frequencies, but the impact of measurement frequency on these properties is rarely studied. This study evaluates velocity dispersion and frequency-dependent attenuation in gas hydrate-bearing sediments (GHBS) by comparing vertical seismic profile (VSP) and sonic logging data from the Nankai Trough and Mallik field. We also employ rock physics modeling to simulate the velocity dispersion and frequency-dependent attenuation at both sites. The results show strong velocity dispersion and frequency-dependent attenuation in the Nankai Trough, attributed to thin, low-saturation hydrate intervals. In contrast, the Mallik field exhibits weak dispersion and frequency dependence, likely due to thick, highly saturated hydrate layers. A compilation of global hydrate reservoir attenuations indicates frequency dependence, with a peak in the sonic logging range, likely due to pore-scale hydrate effects. These findings emphasize the necessity of considering the effect of measurement frequency when performing time-to-depth conversion for seismic data based on the sonic velocity at higher frequencies, particularly for thin and lowly saturated hydrate layers, thereby improving the accuracy of hydrate reservoir characterization.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"171 ","pages":"Article 107204"},"PeriodicalIF":3.7,"publicationDate":"2024-11-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142656658","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":"Characterization of a deep-water turbiditic reservoir under an active hydrodynamic regime (Niger delta)","authors":"V. Spina ,&nbsp;S. Amoyedo ,&nbsp;C. Wibberley ,&nbsp;R. Tozer ,&nbsp;C. Ribes ,&nbsp;R. Maia ,&nbsp;H. Atoyebi ,&nbsp;E. Vincent","doi":"10.1016/j.marpetgeo.2024.107185","DOIUrl":"10.1016/j.marpetgeo.2024.107185","url":null,"abstract":"<div><div>The Egina Field, situated in the deep-water region of the eastern Niger Delta, is characterized by a NE-SW trending anticline that contains several Middle to Upper Miocene stacked reservoirs. Notably, one of the reservoirs in the field includes three sandy intervals, which have been identified as deep marine turbidite systems. The lowest level (Interval 1) comprises a lobe complex, while the uppermost Intervals 2 and 3 consist of erosive channel complexes. These three reservoir intervals exhibit both static and partial dynamic communication. The Egina Field is affected by a coherent network of extensional and oblique-slip faults, with current activity confined to the eastern sector of the structure. Large displacement faults (throw &gt;30m) offset individual reservoir intervals, creating lateral disconnection and acting as barriers to fluid flow across faults. Minor NNE-SSW oriented faults can locally baffle the flow of fluids, as evidenced by well tests and 4D seismic data. Nonetheless, well interference tests suggest good communication within the reservoir. Vertical communication between the stacked sand bodies is facilitated through erosional contacts between reservoir intervals, while lateral communication occurs around segmented faults, via relay ramps and fault tips, in a NE-SW direction. Across the field, ten oil-water contacts have been identified, with a general trend of deepening towards the south. This pattern has been interpreted as a tilted contact caused by an active hydrodynamic regime, where aquifer overpressures gradually decrease from north to south (31 m of difference), aligning with the regional trend. This paper describes how the geological (structural and sedimentological) heterogeneities are paramount in deep-water turbiditic reservoirs, for both static and dynamic conditions. The work presented here shows how the geological analysis can impact reservoir management, driving strategic decisions on field development, as such as the identification of infill wells opportunities or the optimizing the placement of injectors wells, to effectively support producers.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"172 ","pages":"Article 107185"},"PeriodicalIF":3.7,"publicationDate":"2024-11-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142722564","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":"Seismic geomorphology and evolution of Mid-Late Miocene deepwater channels offshore Taranaki basin, New Zealand","authors":"Marco Shaban Lutome","doi":"10.1016/j.marpetgeo.2024.107202","DOIUrl":"10.1016/j.marpetgeo.2024.107202","url":null,"abstract":"<div><div>Deepwater channels play a significant role in deep marine environments by transporting sediments to deep marine environments, but they are also hydrocarbon reservoirs. In contrast, traditional seismic interpretation techniques have provided insights into these features; intricate channel-fill heterogeneities present challenges in revealing small features or associated elements. This study integrates high-resolution 3D seismic data, relative time geologic models (RGT), spectral decomposition, and geobody to identify the Middle-late Miocene submarine channels, their evolution, and their associated deposition elements. The geomorphologic and stratigraphic analysis results have revealed four depositional elements in the study area. These include (1) channel complexes, (2) distributary channels, (3) frontal splay channel complexes, and (4) crevasse splays. However, the channels lack constructional levee development outside the channel banks, which is linked to the limited sediment supply to deep areas. The identified channels are characterized by a narrow to wide width (0.37 km–1.92 km), a low to high degree of sinuosity, medium incision depths, and lateral migration. The channel fill geometries are highly variable, displaying horizontal to sub-horizontal, lateral accretion, divergent, and inclined reflection packages. Most channels originate as large and wide channels from the northeast and prograde southwest direction of the Taranaki coastline, and they have evolved differently at different development stages. The channel fills exhibit a variable basal amplitude reflection, ranging from medium to high, indicating the presence of sand-prone and mixed facies, such as sand and mudstone. The spectral decomposition maps show variable color intensity, which implies different facies associations within the channels. The channel evolution is likely to be controlled by the interplay of sediment discharge, faults, sea level changes, variable gravity flow strength, and the type of materials supplied from the shelf edge.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"171 ","pages":"Article 107202"},"PeriodicalIF":3.7,"publicationDate":"2024-11-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142656657","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":"Integrated fracture analysis for improved oil recovery in the reefal limestones of Soğucak formation, Northwest Thrace Basin, Türkiye","authors":"Ergin Karaca ,&nbsp;İsmail Ömer Yılmaz ,&nbsp;Günay Çifci ,&nbsp;Bulut Tortopoğlu ,&nbsp;Serhat Akın","doi":"10.1016/j.marpetgeo.2024.107198","DOIUrl":"10.1016/j.marpetgeo.2024.107198","url":null,"abstract":"<div><div>Natural fractures play a crucial role in both exploration and development phases in oil and gas industry, as their network and orientation significantly affect flow and recovery strategies. This study highlights the importance of identifying opening-mode fracture systems within a mature Deveçatağı oil field that has been actively producing for nearly half a century. In order to investigate the most effective rock physics parameter to locate oil saturated zones in the field, this study applies detailed rock physics analysis and 2D forward modeling to pinpoint the principal factors affecting production in the Deveçatağı oil field, addressing the challenge posed by the limited shear wave wireline data acquired from only one well within this highly heterogeneous area. Analysis show that acoustic impedance is a crucial elastic property for detecting oil-saturated zones especially in areas with natural fractures. This study successfully integrates drilling-induced fracture (DIF) data, ant tracking maps, and seismic inversion outputs to understand on the issues leading to dry wells and advances in developing more effective exploration and recovery methods in fractured reservoirs. After almost 50 years of operational activities, well stimulation processes, and natural fractures that are present in this field, understanding oil drainage mechanisms in such environments is complex, emphasizing the need for comprehensive analysis to optimize production strategies.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"171 ","pages":"Article 107198"},"PeriodicalIF":3.7,"publicationDate":"2024-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142656718","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":"Genesis of Botryococcus-rich laminae of the Eocene Upper Xiaganchaigou Formation in the western Qaidam Basin, NW China","authors":"Guolong Liu ,&nbsp;Mingzhen Zhang ,&nbsp;Rongchang Zhao ,&nbsp;Dunzhu Jiaoba ,&nbsp;Xiangtong Lei ,&nbsp;Baoxia Du ,&nbsp;Jing Zhang ,&nbsp;Shaohua Lin ,&nbsp;Peihong Jin ,&nbsp;Aijing Li ,&nbsp;Jing Peng ,&nbsp;Yiqiao Fu ,&nbsp;Jianguo Hui","doi":"10.1016/j.marpetgeo.2024.107203","DOIUrl":"10.1016/j.marpetgeo.2024.107203","url":null,"abstract":"<div><div>Laminated source rocks exhibit high hydrocarbon potential and good reservoir characteristics. <em>Botryococcus</em> fossils with high hydrocarbon potential have been discovered in the laminated source rocks of the Upper Xiaganchaigou Formation in the Qaidam saline basin in earlier research. However, planktonic algae typically thrive in freshwater or slightly brackish water environments. Subsequently, the seemingly contradictory phenomenon of <em>Botryococcus</em> blooms in saline lakes may be the key to revealing the formation mechanism of these high-quality algae-rich laminated source rocks. This study investigates the rich <em>Botryococcus</em> laminated source rocks in saline lacustrine basins using petrology and elemental geochemistry. First, this study indicates that the detrital laminae are rich in <em>Botryococcus</em> and pyrite framboids and form a couplet with clay or carbonate laminae. Comparatively, the clay laminae in the couplet lack <em>Botryococcus</em> but are rich in halite and amorphous microcrystalline pyrite particles, whereas the carbonate laminae lack <em>Botryococcus</em> and contain very little pyrite. Second, the nutrient element phosphorus exhibits minor changes among these laminae, suggesting that the key factor controlling the <em>Botryococcus</em> bloom may not be the nutrient element but water salinity and temperature conditions related to growth habits. Finally, the particle size and formation characteristics of pyrite framboids indicate water column redox stratification, suggesting that in warm and humid summer, surface runoff resulting from heavy rainfall brings abundant terrigenous minerals and elements into the lake water, the lake deepens and stratifies under the joint influence of temperature, salinity, and algae; the detrital laminae contain debris, <em>Botryococcus,</em> and pyrite framboids. Conversely, in cold and dry winters, the shrinking salinized lake water inhibits <em>Botryococcus</em> growth and pyrite framboid formation. Clay laminae rich in halite or carbonate laminae are deposited. The regional distributions of these sediment types also exhibit obvious differences that the Yingxiongling sag is rich in clay–detrital couplet laminae, whereas the Zhahaquan sag exhibits a high abundance of carbonate–detrital couplet laminae. Overall, the investigation of the genesis of laminated source rocks in saline lake basins may be of great significance to hydrocarbon understanding and exploration.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"171 ","pages":"Article 107203"},"PeriodicalIF":3.7,"publicationDate":"2024-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142656717","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":"U-Pb ages of pre- to post-salt carbonates, Santos and Campos basins, SE Brazil: Implications for the evolution of the South Atlantic","authors":"Fernando F. Alkmim ,&nbsp;Cristiano C. Lana ,&nbsp;Marco A.L. Silva ,&nbsp;Dorval C. Dias-Filho ,&nbsp;Katia R.N. Mendonça ,&nbsp;Eveline E. Zambonato ,&nbsp;Bruno Raphael B.M. de Carvalho","doi":"10.1016/j.marpetgeo.2024.107192","DOIUrl":"10.1016/j.marpetgeo.2024.107192","url":null,"abstract":"<div><div>The exploration campaigns and independent studies conducted in the central South Atlantic basins after the discovery of giant oil accumulations in the Lower Cretaceous lacustrine carbonates sealed by the salt layer resulted in a new panorama of the tectonic framework, stratigraphic architecture, and petroleum systems of the investigated basins and passive margins in general. Despite these remarkable advances, the ages of the carbonate reservoirs and the sealing evaporites remain uncertain. Aiming to fill this gap, we present here the results of 30 U-Pb LA-ICP-MS calcite and dolomite age determinations representative of the depositional/eo-diagenetic processes and subsequent phases of carbonate cementation recorded by pre-to post-salt units of the Santos and Campos basins of southeastern Brazil. Microcrystalline calcite of a mudstone of the Itapema Formation (Santos Basin) yielded a minimum age of 126.8 ± 4.7 Ma. 19 depositional/eo-diagenetic ages obtained in mudstones, grainstones, shrubstones, spherulitestones, and travertines of the correlative Barra Velha and Macabu pre-salt lacustrine carbonates cluster around 124.1 ± 2.2 and 122.1 ± 2.3 Ma. Considering the errors, these results limit the deposition/eo-diagenesis of these units to the 126.2–120.0 Ma interval. Two determinations carried out in calcite laminae of a nodular anhydrite sample extracted from the lower portion of the Retiro Evaporite (Campos Basin) returned the ages of 119.2 ± 1.6 Ma and 119.18 ± 0.79 Ma, which we interpreted as the best approximation of the timing of the salt deposition. Analyses performed in 3 samples from the post-salt Quissamã carbonates (Campos Basin) provide a minimum age of 114.2 ± 2.8 Ma yielded by interparticle dolomite cement. Other phases of calcite and dolomite cements present in the investigated units were dated at ca. 119.4, 116.5, and 110.7 Ma. The stratigraphically coherent spectrum of ages obtained differs significantly from most available data, providing a new perspective for the ongoing discussions on the tectonic evolution of the South Atlantic and probably impacting the current views of the burial history and petroleum system of the Santos and Campos basins.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"171 ","pages":"Article 107192"},"PeriodicalIF":3.7,"publicationDate":"2024-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142656664","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":"Reconstruction of ancient sulfate‒methane transition depths using the concentrations and sulfur isotopic compositions of authigenic sulfide minerals in marine sediments","authors":"Chenhui Liu ,&nbsp;Shao-Yong Jiang ,&nbsp;Xin Su ,&nbsp;Tao Yang","doi":"10.1016/j.marpetgeo.2024.107199","DOIUrl":"10.1016/j.marpetgeo.2024.107199","url":null,"abstract":"<div><div>On the basis of a one-dimensional transport-reaction model, we propose a novel approach to identify the relationship between the depth of the sulfate‒methane transition (SMT) and the stratigraphic distribution of authigenic sulfide minerals in terms of both concentration and sulfur isotopic composition. We apply this approach to Ocean Drilling Program Sites 994 and 995 at the Blake Ridge, offshore southeastern North America. Within the present-day sulfate reduction zone, our numerical simulation suggests that sulfide mineralization is basically at a steady state, the concentrations of which depend largely on the reactivity of sedimentary organic carbon. The observed extreme ³⁴S-depletion of sulfide minerals (e.g., δ³⁴S values as low as −45‰ VCDT) can occur without the process of sulfur disproportionation. We then derive a series of theoretical profiles by changing the SMT depth from 4 m to 30 m below the seafloor and construct a contour plot of the theoretical SMT depth as a function of the concentration and sulfur isotopic composition of solid-phase sulfides after complete mineralization under steady-state conditions. Below the present-day SMT, six stratigraphic locations of the ancient SMT are identified and their depths below each contemporaneous seafloor are interpolated. Theoretical estimates suggest that the SMT gradually subsided from 8.4 to ca. 24 m below the contemporaneous seafloor (mbcsf) over the past 643 to 6.6 ka. At present, the SMT has been occurring steadily at depths of ca. 21 to 22 mbcsf for at least 2.9 kyr. This is the first time that the evolution of the ancient SMT depth has been quantitatively reconstructed, by which the attainment of knowledge can be used to research the early diagenetic evolution history of the pore water sulfur species and will arouse much interest and concern from other researchers.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"171 ","pages":"Article 107199"},"PeriodicalIF":3.7,"publicationDate":"2024-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142656720","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":"Occurrence characteristics and factors that influence shale oil in the Jurassic Lianggaoshan Formation, northeastern Sichuan Basin","authors":"Xuefeng Bai ,&nbsp;Xin Wang ,&nbsp;Min Wang ,&nbsp;Junhui Li ,&nbsp;Shuangfang Lu ,&nbsp;Xinyi Yang ,&nbsp;Yidong Jia ,&nbsp;Rong Wu ,&nbsp;Tianyi Li ,&nbsp;Youzhi Wang","doi":"10.1016/j.marpetgeo.2024.107197","DOIUrl":"10.1016/j.marpetgeo.2024.107197","url":null,"abstract":"<div><div>Well Ping'an 1, located in the northeastern Sichuan Basin, tested 112.8 m³/d of oil from the Lianggaoshan Formation, marking an important breakthrough in shale oil production. However, due to the influence of complex lithofacies, high thermal maturity, and limited exploration, the occurrence and factors that influence shale oil across the different lithofacies of the Lianggaoshan Formation remain unclear, thereby severely impeding exploration and development. This study systematically examines the occurrence and factors that influence shale oil (adsorbed oil and free oil) in the Lianggaoshan Formation through an integrated approach involving petrology, geochemistry, scanning electron microscopy, nuclear magnetic resonance spectroscopy, multi-temperature pyrolysis, and gas chromatography. Results demonstrate the following: (1) Residual shale oil (adsorbed oil) in the study area predominantly exists as oil films, precipitated oil, and residues (asphalt). Oil films appear on the edges of organic matter (OM), clay minerals, pyrite, and felsic minerals. Crude oil adheres as thin layers to mineral edges, with part of the oil resulting from the lipophilic properties of OM. Precipitated oil tends to accumulate around organic pores, and at higher maturity stages, heavy oil components adhere to mineral surfaces as residues. The hydrocarbon loss of the sample is serious, and free oil is difficult to observe due to experimental processing. (2) Based on the experimental results of preserved cored samples, the shale oil in the study area is mainly free oil (0.86–4.46 mg/g, average 1.99 mg/g), followed by adsorbed oil (0.0007–1.36 mg/g, average 0.43 mg/g). The presence of higher concentrations of clay minerals and total organic carbon (TOC) correlates with increased quantities of free and adsorbed oil in the Lianggaoshan Formation. (3) The two-dimensional nuclear magnetic resonance method combined with the “e” index method was employed to quantify the free oil volumes in shale reservoirs of varying maturity within the study area. The recovery coefficient initially increases rapidly and then gradually with increasing R_o (vitrinite reflectance) values. Compared with other lithofacies types, OM-rich laminated argillaceous shale and OM-poor laminated siliceous shale have higher free oil content, which makes them easier to produce, in other words, these two lithofacies should be preferred as favorable exploration and development targets.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"171 ","pages":"Article 107197"},"PeriodicalIF":3.7,"publicationDate":"2024-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142656665","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}