Marine and Petroleum Geology最新文献

{"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}

{"title":"Turbidite sands filling accommodation associated with supra-mass transport deposit topography: Outcrop examples from Western Argentina","authors":"Victoria Valdez Buso ,&nbsp;Luke Fairweather ,&nbsp;Ben Kneller ,&nbsp;Juan Pablo Milana ,&nbsp;Fernando Farias Vesely","doi":"10.1016/j.marpetgeo.2025.107567","DOIUrl":"10.1016/j.marpetgeo.2025.107567","url":null,"abstract":"<div><div>Mass transport deposits (MTDs) generate topographic relief on their upper surfaces. The scale and geometry of the topographic features, and the interconnectivity of their sediment fill plays a crucial role in defining the characteristics of associated turbidite reservoirs. Turbidite sands may be ponded in isolated depocenters created by supra-MTD topography. The spacing and maximum thickness of ponded and isolated or tortuously interconnected sands are controlled by the dominant topographic wavelength and amplitude on the surface topography. Once the topography is filled to the saddles (the lowest point between adjacent topographic lows), the sand body forms a continuous sheet peppered with lacunae (‘holes’) marking the emergent heights (‘nunataks’). This is illustrated by confined turbidites over a 200-m thick MTD at Cerro Bola, Western Argentina. Field data differentiate ponded turbidites into a) Underfilled section; an isolated and laterally variable sand interval, confined by short-wavelength (tens to hundreds of meters) topography. Correlation of thicker beds suggests that larger flows were able to over-run at least the saddles in the topography, with only a small portion of the flow being captured in each low. b) Overfilled section; consists of a laterally continuous sand interval that covers the short-wavelength topography while progressively onlapping longer-wavelength (km-scale) features. Depositional facies may help to differentiate the confined/ponded stages, where local topography is still emergent, and thus to indicate the overall connectivity.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"182 ","pages":"Article 107567"},"PeriodicalIF":3.7,"publicationDate":"2025-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144704831","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":"Temporal and spatial variations of redox conditions in the middle Triassic Chang 7 member of the Yanchang formation, Ordos Basin, North China","authors":"Hanlin Liu ,&nbsp;Yuangeng Huang ,&nbsp;Xiangdong Zhao ,&nbsp;Wei Wang ,&nbsp;Xincheng Qiu ,&nbsp;Zhen Qiu ,&nbsp;Juan Han ,&nbsp;Zhen Shen ,&nbsp;Yujie Li ,&nbsp;Ganlin Hua ,&nbsp;Zhong-Qiang Chen ,&nbsp;Caineng Zou","doi":"10.1016/j.marpetgeo.2025.107565","DOIUrl":"10.1016/j.marpetgeo.2025.107565","url":null,"abstract":"<div><div>The Chang 7 member of the lower Yanchang Formation, situated within the Ordos Basin, dates back to the Ladinian stage of the late Middle Triassic. These strata, notable for their organic-rich black shales, serve as a key lacustrine hydrocarbon-bearing unit in China. The Chang 7 shales encompass a wide array of vertebrate, invertebrate, and plant fossils, offering valuable perspectives on the ecological recovery of lacustrine systems following the end-Permian mass extinction (EPME). Redox conditions within the water column play a critical role in influencing organic matter deposition and shaping lacustrine biodiversity. Nonetheless, prior investigations into redox dynamics during the formation of the Chang 7 shales have predominantly relied on single redox proxies or isolated sampling locations, which restrict a comprehensive understanding of the redox evolution across the entire Ordos Basin. For these reasons, this study employs framboidal pyrite size statistics, pyrite sulfur isotopes, major and trace element concentrations, and lipid biomarkers of five Ladinian-age wells from both deep and shallow sedimentary facies to rebuilt up evolutional patterns of redox conditions in the Basin. Our results reveal remarkable difference of redox conditions amongst deposition periods of three submembers. Notably during the formation of the Chang 7₃ submember (lower Chang 7 member), the Ordos paleo-lake exhibited progressively declining oxygen levels, transitioning from dysoxic to anoxic conditions in deeper facies. Dysoxic conditions prevailed in the deep facies, with transient anoxic conditions emerged. By contrast, evidence indicates that the Chang 7₂ submember (middle Chang 7 member) was primarily deposited under fluctuating dysoxic-oxic conditions, while the Chang 7₁ submember (upper Chang 7 member) was formed in predominantly oxic environments. Collectively, the Chang 7 member shows remarkable organic matter preservation, with an average total organic carbon (TOC) content of 11.02 wt%, and peak TOC levels reaching 35.8 wt% in the Chang 7₃ submember. These findings indicate that by the Ladinian, the Ordos paleo-lake had already achieved a high level of productivity, capable of sustaining a fully developed, trophically complex lacustrine ecosystem in the aftermath of the EPME. The relatively oxygen-depleted bottom waters during deposition of the Chang 7₃ submember provided favorable conditions for the preservation of the abundant and diverse biota. This comprehensive analysis offers valuable insights into the lacustrine paleoenvironmental conditions and biotic recovery following the EPME, and provides important clues for the formation environment of source rocks.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"182 ","pages":"Article 107565"},"PeriodicalIF":3.6,"publicationDate":"2025-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144721568","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 dissolution mechanism of calcite and its impact on CO2 sequestration in deep-water sandstone during CO2 flooding: A case study in the Chang 7 member, Ordos Basin, China","authors":"Wei Wang ,&nbsp;Xiaolei Zhang ,&nbsp;ChaoJie Mao ,&nbsp;Zhilei Hao ,&nbsp;Zhengzhong Liang ,&nbsp;Dao Wei Wang ,&nbsp;Yushuang Zhu","doi":"10.1016/j.marpetgeo.2025.107566","DOIUrl":"10.1016/j.marpetgeo.2025.107566","url":null,"abstract":"<div><div>Robust and innovative strategies to reduce carbon emissions to address the growing threat of global climate change. Deep-water tight sandstone, with calcite as its primary cementing material, can be an essential reservoir for CO₂ sequestration. However, the microscopic dissolution mechanism of calcite is still poorly understood and can significantly impact the effectiveness of geological CO₂ storage. We investigated the dissolution behaviours of calcite in deep-water tight sandstone and its volume changes on CO₂ during CO₂ flooding. We used a novel 3D, micrometric-scale reactive-transport model, where the distribution and geometric characteristics of calcite were informed by section casting and cathode luminescence images. We found that the calcite particles adjacent to each other in deep-water tight sandstone form numerous micrometer-scale calcite aggregates. During CO₂ flooding, the dissolution rates of calcite particles vary since solute migration limits the overall dissolution rate. Calcite aggregates react as single particles, with the external surface continuously dissolving and the internal surface maintaining balance. The dissolution products of the calcite aggregates accumulate in the formation water, inhibiting the dissolution of the surrounding calcite and thereby reducing the overall dissolution rate of the deep-water tight sandstone calcite. Large volumes of calcite initially dissolve rapidly, then gradually slow down. This affects the CO₂ sequestration efficiency and migration patterns. These findings provide vital insights into the physical properties and geomechanical integrity during CO₂ storage in deep-water tight sandstone and have long-term storage security and environmental protection implications.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"182 ","pages":"Article 107566"},"PeriodicalIF":3.7,"publicationDate":"2025-07-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144704893","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":"Investigating key pressure loss factors in the Wufeng-Longmaxi formation shale gas reservoirs, Southern Sichuan: A quantitative approach","authors":"Nengwu Zhou ,&nbsp;Guangshun Xiao ,&nbsp;Shuangfang Lu ,&nbsp;Bo Song ,&nbsp;Jun Wang ,&nbsp;Zhong Chu ,&nbsp;Xinyu Jiang ,&nbsp;Yang Liu ,&nbsp;Wenbiao Li ,&nbsp;Pengfei Zhang ,&nbsp;Guohui Chen ,&nbsp;Min Wang","doi":"10.1016/j.marpetgeo.2025.107560","DOIUrl":"10.1016/j.marpetgeo.2025.107560","url":null,"abstract":"<div><div>Pressure loss in the Wufeng-Longmaxi Formation shale gas reservoirs of the southern Sichuan Basin is a complex issue. This occurrence is influenced by several critical factors: faults, stratigraphic properties, fold structures, and the timing and magnitude of uplift events. While we know these factors are significant, their quantitative impact and individual contributions to pressure loss remain poorly understood. In this study, we integrate the burial and thermal history of the basin to reconstruct the evolution of key reservoir parameters, including formation temperature, hydrostatic pressure, overburden pressure, total porosity, water-filled porosity, and gas adsorption porosity. Using this framework, we simulate the effects of different preservation conditions on pressure loss within shale gas reservoirs and evaluate the relative contributions of these controlling factors. Simulation results revealed that the location of fault development, particularly its penetration through the caprock, is the predominant factor governing pressure loss in local shale gas reservoirs. In contrast, the scale of fault development has a relatively minor impact. Additionally, the thickness and vertical diffusion coefficient of the caprock, along with the time, emerged as secondary controlling factors that substantially influence the rate of pressure loss across the shale gas reservoirs. Furthermore, the dip angle of synclinal folds and the lateral diffusion coefficient act as accelerators of pressure loss, potentially leading to rapid depletion of reservoir pressure. Conversely, the properties of anticlines exhibit minimal influence on pressure loss. These findings provide valuable insights for the management and optimization of shale gas reservoirs in the Wufeng-Longmaxi Formation.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"182 ","pages":"Article 107560"},"PeriodicalIF":3.7,"publicationDate":"2025-07-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144670281","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 and geological significance of dolomite in shales of the first member of the cretaceous Qingshankou Formation, central depression, Songliao Basin, China","authors":"Min Yan ,&nbsp;Jinglan Luo ,&nbsp;Zihui Feng ,&nbsp;Hongmei Shao ,&nbsp;Danting Luo ,&nbsp;Bo Gao ,&nbsp;Jiping Wang ,&nbsp;Yongchao Wang","doi":"10.1016/j.marpetgeo.2025.107564","DOIUrl":"10.1016/j.marpetgeo.2025.107564","url":null,"abstract":"<div><div>This study presents the first nano-, micro-, and macro-scale analyses of dolomite minerals of varying maturity (all references to maturity in this study pertain to the maturity of organic matter) sampled from the first member of the Cretaceous Qingshankou Formation in the central depression of the Songliao Basin, China. Mineralogical, petrological, isotope and elemental analyses were combined to elucidate the pore fluid evolution and dolomite diagenesis, as well as their implications for the shale organic matter and reservoir space. Three types of authigenic dolomites are identified. The precipitation of authigenic dolomite during the early diagenesis to the mesodiagenesis followed the sequence of anhedral dolomite in low-maturity dolomitic shale (Ro: 0.58–0.70 %) → rhombic ankerite formed overgrowths on anhedral dolomite in medium-maturity dolomitic shale (Ro: 0.78–1.29 %) → saddle-shaped ankerite in crack in high-maturity dolomitic shale (Ro: 1.34–1.70 %); this was accompanied by the transition of pore fluid from seawater to organic fluid, and subsequently to high-temperature hydrothermal fluid. During the early diagenesis to the A₁ stage of mesodiagenesis, the methanogenic archaea in seawater induced the precipitation of anhedral dolomite, which prevented interparticle pore destruction during compaction and preserved the micropores in low-maturity dolomitic shales. During the A₂ stage of mesodiagenesis, the cementation of rhombic ankerite decreased the effective porosity, and consumed organic carbon as the carbon framework in the medium-maturity dolomitic shales. In the hydrocarbon expulsion environment, the dissolution of rhombic ankerite by organic acids promoted the development of micro-nano-scale dissolution pores and increased the effective porosity, which facilitated the expulsion of hydrocarbons from the medium-maturity dolomitic shales. During the B stage of mesodiagenesis, although the high-temperature hydrothermal fluid led to the occlusion of cracks by the cementation of saddle-shaped ankerite, the heat source provided by hydrothermal fluids and/or burial promotes the pyrolysis of organic matter and the development of organic pores, which increased the effective porosity and the expulsion of hydrocarbons in the high-maturity dolomitic shales. Therefore, the low-maturity dolomitic shales exhibit higher effective porosity and higher total organic carbon (TOC) content compared to medium- and high-maturity dolomitic shales. This study expands the high-quality shale from the traditionally organic pore region in higher-maturity conditions to the inorganic pore region with the enrichment of organic matter in lower maturity conditions, which is crucial for developing the hydrocarbon exploration field of shale.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"182 ","pages":"Article 107564"},"PeriodicalIF":3.7,"publicationDate":"2025-07-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144654701","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":"Can compaction modeling and pore pressure prediction be simplified by the definition of effective stress?","authors":"Matt R. Hauser,&nbsp;Brent A. Couzens-Schultz","doi":"10.1016/j.marpetgeo.2025.107563","DOIUrl":"10.1016/j.marpetgeo.2025.107563","url":null,"abstract":"<div><div>Disequilibrium compaction is a significant source of overpressures in sedimentary basins, and for decades relationships between effective stress and compaction state have been used in such settings to model compaction and to predict pore pressure. These relationships have proved to be robust when calibrated and applied in formations with similar geologic history, lithologies, and pressure controls. However, they are also found to break down in many cases and these failures often lead workers to invoke a variety of complicating processes which may or may not be supported by geologic analyses; in other cases, to match data, workers may simply invoke <em>ad hoc</em> piecewise adjustments. A consistent thread through almost all such studies is the definition of effective stress as the difference between total stress and pore pressure, as defined by Terzaghi. Given persistent cases where typical models break down, though, it may be fair to ask if we have been using the best approach. An alternative definition of effective stress proposed by Biot is investigated here with a large field dataset and shown to give simpler compaction trends which are also much more consistent from region to region than those obtained with a Terzaghi definition. While the processes often invoked to explain departures from Terzaghi effective stress trends are likely present in many areas, this work suggests that their prevalence and significance may be less than often thought, and that a simple change of effective stress definition may provide substantially improved models with less need to invoke other geologic explanations.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"182 ","pages":"Article 107563"},"PeriodicalIF":3.6,"publicationDate":"2025-07-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144863177","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":"Impact of laminae characteristics on pore-fracture connectivity in the Wufeng-Longmaxi shale","authors":"Guanyu Xie ,&nbsp;Mengdi Sun ,&nbsp;Yiquan Ma ,&nbsp;Erfan Mohammadian ,&nbsp;Mehdi Ostadhassan ,&nbsp;Zhejun Pan ,&nbsp;Xianggang Duan","doi":"10.1016/j.marpetgeo.2025.107562","DOIUrl":"10.1016/j.marpetgeo.2025.107562","url":null,"abstract":"<div><div>The pore-fracture connectivity in unconventional shale systems is predominantly governed by laminae, necessitating comprehensive investigations through various perspectives. Thus, to quantitatively assess the influence of laminae and their characteristics on pore-fracture connectivity, optical microscopy and field emission scanning electron microscopy combined with Wood's metal impregnation are employed, integrated with mercury intrusion capillary pressure analysis, gas permeability testing, and nanoindentation experiments on Wufeng-Longmaxi marine shale samples from the southern Sichuan Basin, China. The results indicate that the level of pore-fracture connectivity (from good to poor) in three types of recognized lamina from petrographic observations of the samples follows: silty-organic rich laminae (η = 0.42–0.47) &gt; silty-clay rich laminae (η = 0.36) &gt; clay rich laminae (η = 0.20). Silty-organic rich laminae exhibit the best connectivity due to the higher abundance of organic matter, well-developed organic pores, and interlaminar fractures that facilitate their connectivity. In contrast, clay rich laminae demonstrate the poorest connectivity due to their low organic matter content and the predominance of isolated, elongated pores in clay minerals. Furthermore, permeability anisotropy of shale is primarily influenced by mineral composition and the degree of microfracture development where, silty-organic rich laminae exhibit the most extensive distribution of microfractures, supported by a rigid framework composed of brittle minerals. This results in the lowest pore-fracture compressibility coefficient, which helps maintain superior connectivity and fluid flow pathways. Nanoindentation experiments demonstrated that silty-organic rich laminae will have the highest elastic modulus (E &gt; 30 GPa) and hardness (H &gt; 2 GPa). With increasing clay content, these mechanical properties exhibit progressive reduction, promoting enhanced susceptibility to pore collapse and fracture closure, thereby significantly impairing pore-microfracture connectivity. Overall, the pore-fracture connectivity of different types of laminae controls the gas supply from matrix to the fractures, directly affecting the production and recovery rate of shale gas. During exploration, the silty-organic rich laminae in the middle-lower part of the TST of the Longmaxi Member 1 should be prioritized as the sweet spot. These findings have significant implications for evaluating favorable spots in shale reservoirs, for an optimized field development plans, specifically hydraulic fracturing, for higher gains and resource utilization.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"182 ","pages":"Article 107562"},"PeriodicalIF":3.7,"publicationDate":"2025-07-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144654702","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":"Marine flooding induced basinal brine mixing and carbonate cementation: An example from Cretaceous ultra-deep clastic reservoirs in the Kuqa Depression, western China","authors":"Shunyu Wang ,&nbsp;Jian Wang ,&nbsp;Keyu Liu ,&nbsp;Yong Li ,&nbsp;Zhenkun Li ,&nbsp;Meiyi Chen ,&nbsp;Leilei Yang","doi":"10.1016/j.marpetgeo.2025.107561","DOIUrl":"10.1016/j.marpetgeo.2025.107561","url":null,"abstract":"<div><div>Marine flooding can significantly change hydrochemical features of pore water and provide needed ions for reservoir diagenesis. Present basinal brines and contemporaneous cements may record the participation of paleo-marine flooding. The ultra-deep (&gt;6000 m) sandstone reservoirs of the Cretaceous Bashijiqike Formation (K_1bs) in the Kelasu thrust-fold belt, Kuqa Depression of western China, are featured by a CaCl₂-type brine and widespread eodiagenetic carbonate cementation. Through a study integrating petrographic characterization, cathodoluminescence imaging, hydrochemical feature comparison, geochemical indicators, carbon and oxygen isotopes and reactive transport simulations, we have concluded that late Cretaceous marine flooding events provided the essential ion source required for carbonate cementation and controlled major-ion compositions of the K_1bs brine. There appears to be a complementary spatial distribution of calcite and dolomite cements in K_1bs. Calcite cement occurs mainly in the northern paleo-high terrains, which was precipitated from alternating redox conditions due to periodic infiltration of meteoric water. Dolomite cement occurs mainly in the southern paleo-lows, being formed under stable reducing conditions caused by submerged seawater. Calcite precipitation, dolomitization and dissolution of K-feldspar further modified major ionic compositions of the late Cretaceous seawater during burial, leading to the formation of the present CaCl₂-type brines in K_1bs. Reactive transport modeling showed that high-flux meteoric water can promote calcite deposition, while low-flux meteoric water is beneficial to dolomite deposition. The late Cretaceous marine flooding significantly enhanced the major-ion contents, altered the hydrochemistry of the initial pore fluid and induced carbonate cementation within the terrestrial sandstone reservoirs in the seawater-meteoric water mixing zone.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"182 ","pages":"Article 107561"},"PeriodicalIF":3.7,"publicationDate":"2025-07-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144665673","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":"Multidisciplinary characterization of migrated bitumen enrichment and pore network development in low-maturity Es4 shales of the Damintun Sag, East China","authors":"Yong Ma ,&nbsp;Qinhong Hu ,&nbsp;Jianbin Xu ,&nbsp;Binhao Feng ,&nbsp;Fujie Jiang ,&nbsp;Yanshan Wang ,&nbsp;Haiping Huang","doi":"10.1016/j.marpetgeo.2025.107559","DOIUrl":"10.1016/j.marpetgeo.2025.107559","url":null,"abstract":"<div><div>Low-maturity shale oil resources are widely developed in the Paleogene-aged Damintun Sag of the Bohai Bay Basin, yet the unclear pore architecture and reservoir space distribution have hindered its efficient exploitation. Focusing on the low-maturity Es₄ shale, this study integrates core observations, geochemical tests, X-ray diffraction, scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP) data from Well S352 to investigate lithofacies-controlled pore structures and residual oil characteristics. Three lithofacies reservoirs are identified: laminated felsic shale (LFS), mixed shale (MS), and massive dolomitic mudstone (MDM). LFS and MS are rich in Type I kerogen excellent hydrocarbon generation and retention. LFS acts as both source and reservoir rock, featuring abundant mesopores, strong pore connectivity, and bedding-parallel fractures, making it a favorable sweet spot for <em>in situ</em> generation and light oil expulsion. MS serves as a transitional facies with moderate generative and physical properties. In contrast, MDM, with low TOC and poor pore connectivity, lacks generative capacity and instead functions as a secondary reservoir that stores migrated oil from adjacent LFS. Thermal maturity assessments show high T_max values (up to 465 °C) indicative of peak oil generation, despite low measured R_o (∼0.6 %), likely suppressed by algal kerogen. Multiscale pore analyses reveal that LFS contains the highest cumulative pore volume and most developed pore–fracture networks, while MDM exhibits isolated, diagenetically altered pores. Geochemical zonation and gas chromatography fingerprinting distinguishes indigenous hydrocarbons in LFS/MS from migrated oils in MDM, confirming stratigraphically confined migration. Laminated shale—particularly those with interbedded MDM intervals—show optimal conditions for sweet spot development, as short-range migration enriches reservoir potential without requiring high maturity. This study underscores the viability of low-maturity shale oil systems and emphasizes the importance of integrating lithofacies, geochemistry, and pore network architecture to predict sweet spots for optimized exploration in lacustrine shale formations.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"182 ","pages":"Article 107559"},"PeriodicalIF":3.7,"publicationDate":"2025-07-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144633922","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}