Marine and Petroleum Geology最新文献

{"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":"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":"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}

{"title":"The Guajira contourite depositional system along the northern Colombian Caribbean convergent margin","authors":"J. Naranjo-Vesga ,&nbsp;O. Mantilla ,&nbsp;D. Rincón-Martínez ,&nbsp;E. Rodriguez-Rubio ,&nbsp;A. Ortiz-Karpf ,&nbsp;C. Winter ,&nbsp;Y. Rojas-Agramonte","doi":"10.1016/j.marpetgeo.2025.107556","DOIUrl":"10.1016/j.marpetgeo.2025.107556","url":null,"abstract":"<div><div>Bottom currents have a significant role in the transport, erosion and deposition of sediments. They also have the power to modify the seabed morphology. Contourite depositional systems have been reported worldwide, mainly in passive margins; with few examples reported at convergent margins. This study uses regional multibeam bathymetry and seismic data, to document for the first time a∼20,000 km² slope contourite depositional system along the upper continental slope of the northern Colombian Caribbean convergent margin. We compare the characteristics of the slope geomorphology with hydrodynamic modeling of the bottom currents. We identified on the upper slope, close to the shelf edge, the presence of erosional terraces and moats over an area of∼2,700 km². Near this sector, the modelled ocean currents can reach speeds of up to∼10 cm/s. However, the bottom currents have a high degree of variability, and low values of∼1 cm/s are also identified over the terraces; this may suggest that erosion can occur when the currents reach their highest speeds of circulation. Therefore, the erosion is neither homogeneous nor continuous along the slope. On the other hand, the plastered drift and sediment wave fields related to sediment accumulation have low current velocities between∼1 - 5 cm/s, and they cover a large area of the upper slope (∼17,600 km²), suggesting that sediment accumulation may occur in areas where bottom currents have low velocities. The plastered drift thickness also shows high variability in the study area. The major thicknesses of∼785 ms (or ± 800 m) are related to a gentle slope topography (&lt;2°). In contrast, the lowest thicknesses of∼300 ms (or ± 300 m) are identified in areas with steep slope topography (&gt;2–5°), indicating that in gently slope topography (&lt;2°) plastered drift deposits have a greater thickness. This work allows us to characterize for the first time a regional slope contourite depositional system along the northern Colombian Caribbean margin and highlights the influence of bottom current strength and slope gradient topography in controlling the erosion and preferential accumulation of sediments in an active margin with low sediment supply. This mode of occurrence may be characteristic of contourite depositional system development on convergent margins with low fluvial sediment discharge worldwide.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"182 ","pages":"Article 107556"},"PeriodicalIF":3.7,"publicationDate":"2025-07-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144654850","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 sedimentary provenance of Upper Miocene Dongfang submarine fan, Yinggehai Basin: source-to-sink system unravelled through new detrital zircon U-Pb ages and heavy mineral analysis","authors":"Xingzong Yao ,&nbsp;Congjun Feng ,&nbsp;Wei Zhou ,&nbsp;Pengfei Wu ,&nbsp;Hongjun Qu ,&nbsp;Jiahao Lei ,&nbsp;Zhiqiang Chen ,&nbsp;Yanlong Ge ,&nbsp;Mengsi Sun","doi":"10.1016/j.marpetgeo.2025.107557","DOIUrl":"10.1016/j.marpetgeo.2025.107557","url":null,"abstract":"<div><div>The Upper Miocene Dongfang submarine fan, developed in the Yinggehai Basin, is considered one of the most valuable reservoirs in the northern South China Sea. However, the provenance of the fan remains a controversy between the Red River drainage area and Central Vietnam, hindering hydrocarbon exploration in the basin. In this study, heavy mineral analysis and detrital zircon geochronology of samples from the Upper Miocene intervals in four boreholes were conducted for provenance analysis of the fan. The occurrence of Cr-spinel and high leucoxene contents (34.3 %–85.9 %) in heavy mineral assemblages from these wells suggest sediment contributions from the Red River drainage area and Central Vietnam. Detrital zircon grains from the fan exhibit a wide U-Pb age range, including Luliangian, Jinningian, Caledonian, Indosinian, Yanshanian, and Himalayan populations. Multidimensional scaling (MDS) robustly supports a dual-provenance model consisting of the Red River drainage area and Central Vietnam. Furthermore, we propose that the Red, Ma, Lam, Gianh, and Ben Hai rivers served as sediment pathways owing to the similarities in zircon age distributions between the fan and modern drainage systems. Unmixing models employing the Kolmogorov-Smirnov (K-S) test D statistic quantify the relative source contributions, indicating a potential internal evolution of the fan. Among these, the Red River drainage area dominated the samples D132h and D1310h, accounting for 94.3 % and 86 % of detritus, respectively. Central Vietnam predominantly contributed 99.5 % of sediments to the sample D134h. For the sample D136h, 45.7 % of sediments were derived from the Red River drainage area and 54.3 % from Central Vietnam. The reconstruction of the source-to-sink system reveals that the global forcings (the uplift of the Tibetan Plateau, the expansion of Antarctic ice sheets) and regional adjustments (the intensification of East Asian monsoon, the reversal of Red River Shear Zone) collectively controlled the formation and development of Dongfang submarine fan. Specifically, the activity on the Red River Shear Zone destabilized the deltaic sediments along the western margin of Yinggehai Basin, generating sediment gravity flows that accumulated in the depocenter and formed the Dongfang submarine fan. The source-to-sink system model may provide valuable insights into the prediction of Upper Miocene reservoirs and guides the future hydrocarbon exploration in the basin.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"182 ","pages":"Article 107557"},"PeriodicalIF":3.7,"publicationDate":"2025-07-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144633923","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":"Isotopic equilibrium constraints on CO2 dissolution and carbon isotopic reversal in a thermogenic coalbed gas system associated with the Zhuzang syncline, Guizhou, China","authors":"Xiangrui Chen ,&nbsp;Yunpeng Wang ,&nbsp;Mingxin Tao ,&nbsp;Zheng Zhou ,&nbsp;Meng Wei","doi":"10.1016/j.marpetgeo.2025.107554","DOIUrl":"10.1016/j.marpetgeo.2025.107554","url":null,"abstract":"<div><div>Natural gas is a vital energy resource. The isotopic composition of natural gas plays a critical role in understanding its origin, thermal maturity, and secondary alteration. Both kinetic and equilibrium isotopic fractionations have been observed in various natural gas systems. However, the dominant mechanism (either equilibrium or kinetic) that controls the isotopic compositions of the primary natural gas is still unclear. Coalbed gas (CBG), formed and stored in situ coalbeds, is an ideal natural gas for studying this key issue. We collected CBG and coproduced water samples from the Zhuzang syncline in China. This study shows that the CBG is an over-mature thermogenic gas formed during the Yanshanian orogeny. The CH₄-C₂H₆-CO₂ system was likely near carbon isotope equilibrium during the CBG formation. However, later alterations, such as meteoric water recharge, CO₂ dissolution, and CBG recovery led to obvious isotopic disequilibrium of the CH₄-C₂H₆-CO₂-DIC (dissolved inorganic carbon) system. Carbon isotope reversals (δ¹³C_CH4 &gt; δ¹³C_C2H6) were observed in the CBG samples, resulting from decreasing δ¹³C_C2H6 values after CBG formation. Based on isotopic equilibrium, the δ¹³C values of the primary ethane were estimated. Some hypotheses often used to explain isotope reversals in natural gas cannot explain the isotope reversals of the CBG samples. We propose that the CBG recovery process led to more negative δ¹³C_C2H6 and thus δ¹³C_CH4 &gt; δ¹³C_C2H6. Model-estimated 53–99 % CO₂ generated during thermogenic or microbial CBG formation has dissolved into coalbed water to become DIC. Hence, dissolution trapping is an important mechanism for CO₂ storage in coalbeds over geological timescales. This study implies that isotopic equilibrium fractionation plays a vital role in understanding the primary geochemical composition and secondary alteration of CBG.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"182 ","pages":"Article 107554"},"PeriodicalIF":3.7,"publicationDate":"2025-07-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144614855","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}