Many evidences for gas hydrate bearing sediments had been found in the continental slope of the East China Sea,such as bottom simulating reflections(BSRs),undersea gas springs,pyrite associated with methane leakage,mu...Many evidences for gas hydrate bearing sediments had been found in the continental slope of the East China Sea,such as bottom simulating reflections(BSRs),undersea gas springs,pyrite associated with methane leakage,mud diapirs/mud volcanos,bottom-water methane anomalies and so on.In this study,six key stratigraphic interfaces including T_0(seafloor),T_1(LGM,23 kyr B.P.),T_2(2.58 Myr),T_3(5.33 Myr),T_4(11.02 Myr)and T_5(16.12 Myr)were identified,and then five third-order sequences of SQIII1 to SQIII5 were divided.However,T5 in southern continental slope is not found,which shows that the middle-northern Okinawa Trough had begun to rift in the early Miocene,earlier than the southern segment.Four system tracts including lowstand systems tract(LST),transgressive systems tract(TST),highstand systems tract(HST)and falling stage systems tract(FSST)are further divided.The marine erosion interface of 11.02 Myr and regressive unconformity interface of 23 kyr B.P.indicate two large-scale sea level drop events in the research area.Seven typical seismic facies identified in the continental slope are continental shelf-edge deltas,littoral fluvial-delta plains,incised channels or submarine canyons,slope fans,submarine fans or coastal sandbars,littoral-neritic finegrained sediments,mud volcanos and some other geological bodies respectively.The minimum water depth for hydrate occurrence in the Okinawa Trough is 630 m,and the thickness of gas hydrate stability zone in continental slope is between 0 and 590 m.The calculated bottom boundary of hydrate stability zone is slightly deeper than BSRs on the seismic sections.The re-depositional turbidite sand bodies,such as canyon channels,slope fans and submarine fans developed in Quaternary strata,are the predominant hydrate reservoirs.According to developing process,the dynamic accumulation of hydrate systems can be divided into three evolutionary stages including canyon erosion and hydrate stability zone migration stage,sediments destabilizing and methane leakage stage,and channel filling and hydrate re-occurrence stage.展开更多
To address the discrepancies between well and seismic data in stratigraphic correlation of the Triassic Yanchang Formation in the Ordos Basin,NW China,traditional stratigraphic classification schemes,the latest 3D sei...To address the discrepancies between well and seismic data in stratigraphic correlation of the Triassic Yanchang Formation in the Ordos Basin,NW China,traditional stratigraphic classification schemes,the latest 3D seismic and drilling data,and reservoir sections are thoroughly investigated.Guided by the theory of sequence stratigraphy,the progradational sequence stratigraphic framework of the Yanchang Formation is systematically constructed to elucidate new deposition mechanisms in the depressed lacustrine basin,and it has been successfully applied to the exploration and development practices in the Qingcheng Oilfield.Key findings are obtained in three aspects.First,the seismic progradational reflections,marker tuff beds,and condensed sections of flooding surfaces in the Yanchang Formation are consistent and isochronous.Using flooding surface markers as a reference,a progradational sequence stratigraphic architecture is reconstructed for the middle-upper part of Yanchang Formation,and divided into seven clinoform units(CF1-CF7).Second,progradation predominantly occurs in semi-deep to deep lake environments,with the depositional center not always coinciding with the thickest strata.The lacustrine basin underwent an evolution of“oscillatory regression-progradational infilling-multi-phase superimposition”.Third,the case study of Qingcheng Oilfield reveals that the major pay zones consist of“isochronous but heterochronous”gravity-flow sandstone complexes.Guided by the progradational sequence stratigraphic architecture,horizontal well oil-layer penetration rates remain above 82%.The progradational sequence stratigraphic architecture and associated geological insights are more consistent with the sedimentary infilling mechanisms of large-scale continental depressed lacustrine basins and actual drilling results.The research results provide crucial theoretical and technical support for subsequent refined exploration and development of the Yanchang Formation,and are expected to offer a reference for research and production practice in similar continental lacustrine basins.展开更多
Fluvial systems play a crucial role in coastal and riverine ecosystems, making it essential to understand their responses to sea level changes for preserving biodiversity and managing natural resources. The evolution ...Fluvial systems play a crucial role in coastal and riverine ecosystems, making it essential to understand their responses to sea level changes for preserving biodiversity and managing natural resources. The evolution of the modern Indus River Delta offers a rare opportunity to study the interplay between sea level fluctuations, tectonism, sediment supply, and the corresponding fluvial responses. This study employs the ‘SedSim' stratigraphic forward model to simulate the delta's evolution from 200 kyr to the next5 kyr, drawing on data from field observations, Landsat imagery, digital elevation models, and previous studies. The model consists of 205 layers, each representing a 1-kyr time step, covering the last two glacial-interglacial cycles. Between 200 kyr and 130 kyr, during a lowstand period, sedimentation on the delta plain continued due to partial flow from the Indus River. During the last interglacial(130–60 kyr), rising sea levels led to peak sediment deposition, characteristic of a highstand phase. From 60 kyr to 18 kyr, sea levels dropped to their lowest during the Last Glacial Maximum(LGM), resulting in extensive erosion and minimal deposition on the delta plain. From 18 kyr to the present, rapidly rising sea levels, coupled with intensified monsoon activity, increased sedimentation rates and triggered avulsion and aggradation processes. The model accurately predicted depositional thickness across the delta plain, indicating a maximum of ca. 200 m at the shoreline platform, ca. 175 m in the northeastern delta, and ca. 100 m in the central delta. The study underscores the delta's vulnerability to future sea level rise, which–at a projected rate of 1 m/kyr–could significantly influence the densely populated, low-lying delta plain. These findings offer valuable insights into the geomorphic evolution of the Indus Delta and emphasize the socioeconomic implications of sea level change, underscoring the importance of proactive management and adaptation strategies.展开更多
Stratigraphic correlations are essential for the fine-scale characterization of reservoirs.However,conventional data-driven methods that rely solely on log data struggle to construct isochronous stratigraphic framewor...Stratigraphic correlations are essential for the fine-scale characterization of reservoirs.However,conventional data-driven methods that rely solely on log data struggle to construct isochronous stratigraphic frameworks for complex sedimentary environments and multi-source geological settings.In response,this study proposed an intelligent,automatic,log-seismic integrated stratigraphic correlation method that incorporates wavelet frequency-division transform(WFT)and dynamic time warping(DTW)(also referred to as the WFT-DTW method).This approach integrates seismic data as constraints into stratigraphic correlations,enabling accurate tracking of the seismic marker horizons through WFT.Under the constraints of framework construction,a DTW algorithm was introduced to correlate sublayer boundaries automatically.The effectiveness of the proposed method was verified through a stratigraphic correlation experiment on the SA0 Formation of the Xingshugang block in the Lasaxing oilfield,the Songliao Basin,China.In this block,the target layer exhibits sublayer thicknesses ranging from 5 m to 8 m,an average sandstone thickness of 2.1 m,and pronounced heterogeneity.The verification using 1760 layers in 160 post-test wells indicates that the WFT-DTW method intelligently compared sublayers in zones with underdeveloped faults and distinct marker horizons.As a result,the posterior correlation of 1682 layers was performed,with a coincidence rate of up to 95.6%.The proposed method can complement manual correlation efforts while also providing valuable technical support for the lithologic and sand body characterization of reservoirs.展开更多
Challenges in stratigraphic modeling arise from underground uncertainty.While borehole exploration is reliable,it remains sparse due to economic and site constraints.Electrical resistivity tomography(ERT)as a cost-eff...Challenges in stratigraphic modeling arise from underground uncertainty.While borehole exploration is reliable,it remains sparse due to economic and site constraints.Electrical resistivity tomography(ERT)as a cost-effective geophysical technique can acquire high-density data;however,uncertainty and nonuniqueness inherent in ERT impede its usage for stratigraphy identification.This paper integrates ERT and onsite observations for the first time to propose a novel method for characterizing stratigraphic profiles.The method consists of two steps:(1)ERT for prior knowledge:ERT data are processed by soft clustering using the Gaussian mixture model,followed by probability smoothing to quantify its depthdependent uncertainty;and(2)Observations for calibration:a spatial sequential Bayesian updating(SSBU)algorithm is developed to update the prior knowledge based on likelihoods derived from onsite observations,namely topsoil and boreholes.The effectiveness of the proposed method is validated through its application to a real slope site in Foshan,China.Comparative analysis with advanced borehole-driven methods highlights the superiority of incorporating ERT data in stratigraphic modeling,in terms of prediction accuracy at borehole locations and sensitivity to borehole data.Informed by ERT,reduced sensitivity to boreholes provides a fundamental solution to the longstanding challenge of sparse measurements.The paper further discusses the impact of ERT uncertainty on the proposed model using time-lapse measurements,the impact of model resolution,and applicability in engineering projects.This study,as a breakthrough in stratigraphic modeling,bridges gaps in combining geophysical and geotechnical data to address measurement sparsity and paves the way for more economical geotechnical exploration.展开更多
The widely distributed loess deposits in the Yellow River Basin exhibit unique engineering geological characteristics.The variations in their thickness and stratigraphic structure significantly amplify ground motion p...The widely distributed loess deposits in the Yellow River Basin exhibit unique engineering geological characteristics.The variations in their thickness and stratigraphic structure significantly amplify ground motion parameters,directly influencing the regional seismic hazard risk level.This study methodically conducted on-site studies and observations of building collapses and damages resulting from seismic amplification effects,using the Wenchuan M_(S)8.0 earthquake as a case study.Comprehensive experimental and numerical simulation studies were carried out.A large-scale shaking table test was performed,and numerical models for 14 different loess sites types were established.Various types of seismic waves were incorporated into these models for systematic numerical simulation calculations.The research reveals the mechanisms by which loess deposit thickness and stratigraphic structure in the Yellow River Basin affect seismic ground motion amplification.The results indicate that as the epicentral distance increases,the peak ground motion shows a marked attenuation trend,with the horizontal component attenuating substantially faster than the vertical component.As the overlying loess layer thickness increases from 50 to 100 m,the seismic intensity may escalate by 3−4 degrees,and the peak acceleration may amplify by 1.5−2.2 times.With the augmentation of loess deposit thickness and the proliferation of soil layers,both the peak acceleration response spectrum and the characteristic period demonstrate an upward tendency,exhibiting slight fluctuations contingent upon the seismic wave type.展开更多
In active rift basins, tectonism is extremely important for sequence stratigraphic patterns, affecting both the sequence architecture and internal makeup. Sequence stratigraphic framework of a Paleogene rift successio...In active rift basins, tectonism is extremely important for sequence stratigraphic patterns, affecting both the sequence architecture and internal makeup. Sequence stratigraphic framework of a Paleogene rift succession in Qiongdongnan Basin, northern South China Sea, was built using seismic profiles, complemented by well logs and cores. One first-order and three second-order sequences were identified on the basis of basin-scale unconformities, and seven third-order sequences are defined by unconformities along the basin margins and correlative conformities within the central basin. Through unconformity analysis and backstripping procedure, the Paleogene synrift tectonic evolution of deep- water area of Qiongdongnan Basin was proved to be episodic, which can be divided into rifting stage-I, rifting stage-II and rifting stage-III. Episodic rifting resulted in the formation of various types of struc- tural slope break belts, which controlled different architectures and internal makeup of sequences. This study enhances the understanding of the control of tectonic evolution on sequence stratigraphic pat- terns and establishes relevant patterns in a typical rift basin, and further proposes the favorable sand- stone reservoirs developing in different sequence stratigraphic patterns, which will be pretty helpful for subtle pool exploration in deepwater area of petroliferous basins.展开更多
The onshore oil and gas exploration has stepped into a new stage in China, with equal attention paid to both stratigraphic and subtle reservoirs and structural reservoirs. In the past few years, the increases in oil r...The onshore oil and gas exploration has stepped into a new stage in China, with equal attention paid to both stratigraphic and subtle reservoirs and structural reservoirs. In the past few years, the increases in oil reserves in most basins were found mainly in the stratigraphic and subtle reservoirs. Latest resource evaluation shows that the onshore stratigraphic and subtle reservoirs in China account for 42% of the total remaining resource, the highest in the four major exploration regions. Therefore, these reservoirs will be the most practical, potential and prevalent fields for long-lasting oil and gas exploration in onshore China. Among PetroChina's annual oil geologic reserves of 4.3 × 108t^4.6× 108t, the stratigraphic and subtle reservoirs account for more than 50%. In such basins as Songliao, Ordos, Bohai Bay, Junggar, Tarim, Sichuan and Erlian basins, stratigraphic and subtle reservoirs with geologic reserves ranging from 5×107t to 3×108t were discovered, including Ansai, Jing'an, Daqingzijing, Liuxi, well-21 area in Shinan, and Hadexun. Stratigraphic and subtle reservoirs in the four types of inland basins differ from each other in the formation conditions and the distribution patterns. While continental basins are controlled by unconformity surface, maximum flooding surface and fracture surface, the Paleozoic marine basins are influenced by paleouplift, unconformity surface, and fluctuation of the sea level. Through exploration practices and research, PetroChina has formed its own technique series focused on 3-D seismics and sequence stratigraphy.展开更多
To improve the success rate of locating hydrocarbon reservoirs in pre-Cenozoic inland compressional basins, taking the Early Yanshanian succession of eastern Yihezhuang salient as an example, this paper studied the se...To improve the success rate of locating hydrocarbon reservoirs in pre-Cenozoic inland compressional basins, taking the Early Yanshanian succession of eastern Yihezhuang salient as an example, this paper studied the sedimentary facies and sequence stratigraphic patterns. First, through seismic profiles, well logs, cores and outcrops, the sequence framework was established and internal sedimentary facies were identified. Further, according to analysis of single-wells and connecting-wells, the vertical evolution and horizontal distribution of sedimentation inside the sequence frameworks were discussed. The following results were acquired:(1) meandering river characterized by dual structures superposing each other was developed, and the dual structures can be further divided into three kinds;(2) the entire Early Yanshanian succession was interpreted as one first-order sequence, composed of three third-order sequences, including SQ-Fz1, SQ-Fz2 and SQ-St from bottom to top. Each third-order sequence can be further divided into three system tracts;(3) in different system tracts, different types of dual structures developed separately, and sedimentary bodies showed different horizontal distribution scales and vertical superposition patterns. Finally, the model of sequence stratigraphic patterns was established. This study enhanced the use of sequence stratigraphy to inland tectonically active basins, and would be helpful to predict reservoirs in pre-Cenozoic residual basins.展开更多
This paper presents a unique and formal method of quantifying the similarity or distance between sedimentary facies successions from measured sections in outcrop or drilled wells and demonstrates its first application...This paper presents a unique and formal method of quantifying the similarity or distance between sedimentary facies successions from measured sections in outcrop or drilled wells and demonstrates its first application in inverse stratigraphic modeling. A sedimentary facies succession is represented with a string of symbols, or facies codes in its natural vertical order, in which each symbol brings with it one attribute such as thickness for the facies. These strings are called attributed strings. A similarity measure is defined between the attributed strings based on a syntactic pattern-recognition technique. A dynamic programming algorithm is used to calculate the similarity. Inverse stratigraphic modeling aims to generate quantitative 3D facies models based on forward stratigraphic modeling that honors observed datasets. One of the key techniques in inverse stratigraphic modeling is how to quantify the similarity or distance between simulated and observed sedimentary facies successions at data locations in order for the forward model to condition the simulation results to the observed dataset such as measured sections or drilled wells. This quantification technique comparing sedimentary successions is demonstrated in the form of a cost function based on the defined distance in our inverse stratigraphic modeling implemented with forward modeling optimization.展开更多
Taking member one of Yingcheng Formation of Cretaceous in Xudong area, Xushen Gas Field of Songliao Basin for an example and aimed at the diachronous problem generally existed in vol- canic reservoir division, firstly...Taking member one of Yingcheng Formation of Cretaceous in Xudong area, Xushen Gas Field of Songliao Basin for an example and aimed at the diachronous problem generally existed in vol- canic reservoir division, firstly advanced the method of two steps and two unites in the researches of volcanic reservoir finely division that guided by the method that sources controlled and founded the stratigraphic trellis. In this process, volcanic edifices and bodies were identified and traced. The results indicated that aimed strata in study areas could be carved up to six layers of YCII1, YCII2, YCII-II, YCIIlI, YCIII2 and YCIIII from the top to the bottom. Analyzing causes and firmly united of well data and seismic data could achieve fine stratigraphic division of volcanic reservoir. Surfaces of layers and volcanic bodies were basically unanimous in side direction. Stratum inclination gradually reduced with the distances increased from craters. The results of volcanic reservoir division had preferable con- sistency with lithologies and volcanic lithofacies and dynamic development data. The researches offered a useful method to stratigraphic division of volcanic reservoir and it had very important significance to effective development of volcanic reservoir in practice.展开更多
The ultra-deep Cambrian System in the Tarim Basin is an important field for petroleum exploration,while fine division of the Cambrian strata remains controversial.In recent years,carbon isotope stratigraphy of the Cam...The ultra-deep Cambrian System in the Tarim Basin is an important field for petroleum exploration,while fine division of the Cambrian strata remains controversial.In recent years,carbon isotope stratigraphy of the Cambrian System has been established and widely used.Here,we report an integrated profile of carbonate and organic carbon isotopic values(δ^(13)C_(carb)andδ^(13)C_(org))from cuttings of the Tadong2 Well in the eastern Tarim Basin.Three carbon isotope anomalies of BACE,ROECE and SPICE were recognized on theδ^(13)C_(carb)profile.Three apogees and a nadir on theδ^(13)C_(org)profile and the onset of ROECE on theδ^(13)C_(carb)profile were suggested as boundaries of the present four series of the Cambrian System.Suggested boundaries are easily identifiable on the gamma logging profile and is consistent with the previous division scheme,based on biostratigraphic evidence in outcrop sections.Abnormal carbon cycle perturbations and organic carbon burials during the BACE and SPICE events might be related to the reduction and expansion of a huge dissolved organic carbon reservoir in the deep ocean of the ancient Tarim Basin.展开更多
In recent years, with the development of terrestrial sequence stratigraphy, more attention has been focused on the study of the terrestrial lacustrine sequence stratigraphic model globally. Different viewpoints are pr...In recent years, with the development of terrestrial sequence stratigraphy, more attention has been focused on the study of the terrestrial lacustrine sequence stratigraphic model globally. Different viewpoints are preferred by researchers. Under the guidance of the theory of sequence stratigraphy, the findings of this paper indicate that climate is a major factor controlling the formation of the fourth-order sequence, based upon the study of the sequence stratigraphy in the Green River Formation of the Uinta basin in the USA. It also divides the fourth-order sequence in the terrestrial lacustrine basin into two system tracts： the wet （rising） half-cycle and the dry （falling） half- cycle, establishing a new-style fourth-order sequence stratigraphic model for the terrestrial lacustrine basin, that is, the climate-genetic sequence stratigraphic model. As a result, the theory of sequence stratigraphy is greatly enriched.展开更多
Isotopic ages of synsedimentary clay minerals were directly determined with the ultrasonicscattering-settlement separation-K-Ar dilution technique. The apparent age of black mudstoneis 123 Ma for the Quantou Formation...Isotopic ages of synsedimentary clay minerals were directly determined with the ultrasonicscattering-settlement separation-K-Ar dilution technique. The apparent age of black mudstoneis 123 Ma for the Quantou Formation, 111.9-89.0 Ma for the Qingshankou Formation and77.6-76.8 Ma for the upper part of the Nenjiang Formation. The Rb-Sr isochrone age of themuddy limestone-mudstone sequence of the lower part of the Nenjiang Formation is 81 Ma andthat of the muddy evaporite of the middle part of the Quantou Formation is 122.2 Ma. On thebasis of the above isotopic ages, the authors propose a modified scheme of stratigraphic classifi-cation of the Cretaceous of the Songliao basin.展开更多
The upper Qigeblaq Formation （Fm） dolostones and the Yurtus Fm phosphatic cherts, black shales, limestones, and dolostones are widely distributed in the Precambrian/Cambrian transitional succession of the Aksu-Wushi...The upper Qigeblaq Formation （Fm） dolostones and the Yurtus Fm phosphatic cherts, black shales, limestones, and dolostones are widely distributed in the Precambrian/Cambrian transitional succession of the Aksu-Wushi area. Negative δ13C excursion above the Yurtus Fm/ Qigeblaq Fm boundary was determined in this study. The pronounced negative carbon isotope excursion occurs in the phosphatic chert layers at the bottom of the Cambrian Yurtus Fm, below which the first appearance of the Asteridium- Heh＇osphaeridium-Comasphaeridium （AHC） acritarch assemblage zone. The δ13C curve of the lower part of the Yurtus Fm in the Aksu-Wushi area was found to be correlated with the early Cambrian δ13C curves of the Zhujiaqing Fm （Daibu Member）, the lower part of the Yanjiahe Fm on the Yangtze Platform in China, the lower Tal Fm in India, the Sukharikha Fm in Siberia, and the upper part of the Tsagaan Oloom Fm in Mongolia through biostigraphy. The lower part of the Yurtus Fm in the Tarim Basin is at the Nemakit-Daldynian stage, and the Precambrian/Cambrian boundary of the Aksu-Wushi area may be located in the phosphatic chert unit which just below the first appearance AHC acritarch assemblage zone. The negative δ13C excursion （N1） across the Precambrian/Cambrian boundary in the studied section may have resulted from oceanic overturning and sea level rise.展开更多
Four hierarchical cyclothems, superbundlesets, bundlesets, bundles and laminae, have been identified from the Devonian Frasnian-Famennian carbonate strata in Guangxi, South China. Their hierarchical structures, ratio ...Four hierarchical cyclothems, superbundlesets, bundlesets, bundles and laminae, have been identified from the Devonian Frasnian-Famennian carbonate strata in Guangxi, South China. Their hierarchical structures, ratio relationships and sequence in conodont zones are continuous and stable and can be traced across different facies zones and sedimentary basins. Our data show that hierarchically organized superbundlesets, bundlesets, bundles and laminae correspond to the long eccentricity, eccentricity, obliquity or precession and sub-Milankovitch cycles respectively. Their periods were 400,000, 100,000, 33,333, 16,667 and 8,000–17,000 a, respectively. The ratios of long eccentricity to eccentricity, eccentricity to obliquity, and eccentricity to precession in the Devonian are 1:4, 1:3 and 1:6 respectively. Using these hierarchical Milankovitch cyclothems, chronostratigraphical division and correlation can be realized at a resolution of 100 ka or 10 ka at the Frasnian-Famennian transition. The time intervals of the Upper rhenana Zone, linguiformis Zone, and the Lower, Middle and Upper triangularis Zone are 0.6, 0.8, 0.3, 0.3 and 0.3 Ma, respectively. Sea-level changes of the Frasnian-Famennian transition were not coherent and synchronous at the resolution of 100 ka or 10 ka in the basin-slope carbonate sequences of Guangxi, South China.展开更多
The Baxian depression is a typical half-graben located in the Jizhong sub-basin, north China. Commercial petroleum traps have been discovered in the Jizhong sub-basin. However, the 3rd and 4th members of the Shahejie ...The Baxian depression is a typical half-graben located in the Jizhong sub-basin, north China. Commercial petroleum traps have been discovered in the Jizhong sub-basin. However, the 3rd and 4th members of the Shahejie Formation in this sub-basin have been poorly explored. These two members, belonging to the Lower Paleogene age, are buried deeply in the depression. Favorable petroleum reservoir conditions exist in such deep intervals of the half-graben due to the presence of different types and extent of deltas and turbidity fans in various areas. In fact, three types of turbidite fans are developed in the sag below the transitional belt on the eastern gentle slope. This work summarized three stratigraphic trap belts, i.e., the steep slope, gentle slope, and sag. On the steep slope, structural- stratigraphic traps with small-scale delta fronts and turbidite sandbodies are well developed. On the gentle slope, hydrocarbons generally accumulate in the large-scale delta front, onlapping beds and those sandbodies adjacent to unconformities. In the sag, petroleum trap models are typically characterized by pinched-out turbidite sandbodies. Stratigraphic traps were easily formed in turbidite fans below the eastern transitional belt. The petroleum traps that have already been discovered or predicted in the study area indicate that stratigraphic traps have favorable petroleum exploration potential in deeply buried areas （depth 〉5000 m） in a half-graben basin or depression.展开更多
Well logging curves serve as indicators of strata attribute changes and are frequently utilized for stratigraphic analysis and comparison.Deep learning,known for its robust feature extraction capabilities,has seen con...Well logging curves serve as indicators of strata attribute changes and are frequently utilized for stratigraphic analysis and comparison.Deep learning,known for its robust feature extraction capabilities,has seen continuous adoption by scholars in the realm of well logging stratigraphic correlation tasks.Nonetheless,current deep learning algorithms often struggle to accurately capture feature changes occurring at layer boundaries within the curves.Moreover,when faced with data imbalance issues,neural networks encounter challenges in accurately modeling the one-hot encoded curve stratification positions,resulting in significant deviations between predicted and actual stratification positions.Addressing these challenges,this study proposes a novel well logging curve stratigraphic comparison algorithm based on uniformly distributed soft labels.In the training phase,a label smoothing loss function is introduced to comprehensively account for the substantial loss stemming from data imbalance and to consider the similarity between diff erent layer data.Concurrently,spatial attention and channel attention mechanisms are incorporated into the shallow and deep encoder stages of U²-Net,respectively,to better focus on changes in stratification positions.During the prediction phase,an optimized confidence threshold algorithm is proposed to constrain stratification results and solve the problem of reduced prediction accuracy because of occasional layer repetition.The proposed method is applied to real-world well logging data in oil fields.Quantitative evaluation results demonstrate that within error ranges of 1,2,and 3 m,the accuracy of well logging curve stratigraphic division reaches 87.27%,92.68%,and 95.08%,respectively,thus validating the eff ectiveness of the algorithm presented in this paper.展开更多
Yulin section is a typical sedimentary record for reflecting the environmental evolution of Ordos Desert, China in the past 1.1Ma. By analyzing its sequence and grain-size composition some views have been put forward ...Yulin section is a typical sedimentary record for reflecting the environmental evolution of Ordos Desert, China in the past 1.1Ma. By analyzing its sequence and grain-size composition some views have been put forward in this paper as follows. The layers of sand, loess and palaeosol in Yulin section were respectively formed by wind and the pedogenesis on parent material of the sand and loess. Since 1.1Ma B. P., Ordos Desert has alternately experienced 11 stages of shifting dunes under extreme cold-dry climatic environment, 7 stages of fixed and semi-fixed dunes and 8 stages of dust (loess) under cold-dry climatic condition; and the pedogenesis environment under 15 times of warm-humid climate and 3 times of temperate-humid climate (brownish-drab soils and black soils formed respectively). The aeolian sand had already existed in Ordos Desert at latest by 1.1Ma B. P., and from that time on it has undergone a series of alternative processes of shifting sands, fixed and semi-fixed dunes, loess and soils. Ordos Desert has been situated in the transitional belt of the Mongolian High Pressure and margin of the southeast summer monsoon since 1.1Ma B. P., and influenced repeatedly by migration of the lithofacies belts of shifting sands, fixed and semi-fixed dunes, loess and soils, which have been caused by the climatic fluctuations of glacial and interglacial periods.展开更多
Deposits of 10 volcanic events of 6 stages have been discovered by the authors after detailed field and lab studies of the Benxi and Taiyuan Formations in Shandong Province and its adjacent regions. They show certain ...Deposits of 10 volcanic events of 6 stages have been discovered by the authors after detailed field and lab studies of the Benxi and Taiyuan Formations in Shandong Province and its adjacent regions. They show certain temporal-spatial distribution characteristics. Volcanic fragments were probably derived from two different volcanic sources north and south of the North China Platform, while the magma of the two volcanic sources was probably derived from the lower crust. A new stratigraphic correlation scheme is put forward for the Benxi and Taiyuan Formations in this region on the basis of previous biostratigraphic work with the regionally widespread volcanic event layers as the marker bed for the isochronous stratigraphic correlation on a super-regional scale and in conjunction with the maximum transgressive event layers.展开更多
基金supported by the National Natural Science Foundation of China (Nos. 41806073, 41530963)the Natural Science Foundation of Shandong Province (No. ZR 2017BD014)+1 种基金the Shandong Provincial Key Laboratory of Depositional Mineralization & Sedimentary Minerals, Shandong University of Science and Technology (No. DMSM 2017042)the Fundamental Research Funds for the Central Universities (Nos. 201964016, 201851023)
文摘Many evidences for gas hydrate bearing sediments had been found in the continental slope of the East China Sea,such as bottom simulating reflections(BSRs),undersea gas springs,pyrite associated with methane leakage,mud diapirs/mud volcanos,bottom-water methane anomalies and so on.In this study,six key stratigraphic interfaces including T_0(seafloor),T_1(LGM,23 kyr B.P.),T_2(2.58 Myr),T_3(5.33 Myr),T_4(11.02 Myr)and T_5(16.12 Myr)were identified,and then five third-order sequences of SQIII1 to SQIII5 were divided.However,T5 in southern continental slope is not found,which shows that the middle-northern Okinawa Trough had begun to rift in the early Miocene,earlier than the southern segment.Four system tracts including lowstand systems tract(LST),transgressive systems tract(TST),highstand systems tract(HST)and falling stage systems tract(FSST)are further divided.The marine erosion interface of 11.02 Myr and regressive unconformity interface of 23 kyr B.P.indicate two large-scale sea level drop events in the research area.Seven typical seismic facies identified in the continental slope are continental shelf-edge deltas,littoral fluvial-delta plains,incised channels or submarine canyons,slope fans,submarine fans or coastal sandbars,littoral-neritic finegrained sediments,mud volcanos and some other geological bodies respectively.The minimum water depth for hydrate occurrence in the Okinawa Trough is 630 m,and the thickness of gas hydrate stability zone in continental slope is between 0 and 590 m.The calculated bottom boundary of hydrate stability zone is slightly deeper than BSRs on the seismic sections.The re-depositional turbidite sand bodies,such as canyon channels,slope fans and submarine fans developed in Quaternary strata,are the predominant hydrate reservoirs.According to developing process,the dynamic accumulation of hydrate systems can be divided into three evolutionary stages including canyon erosion and hydrate stability zone migration stage,sediments destabilizing and methane leakage stage,and channel filling and hydrate re-occurrence stage.
基金Supported by the National Science and Technology Major Project(2017ZX05001)CNPC Technology Project(2023YQX20111).
文摘To address the discrepancies between well and seismic data in stratigraphic correlation of the Triassic Yanchang Formation in the Ordos Basin,NW China,traditional stratigraphic classification schemes,the latest 3D seismic and drilling data,and reservoir sections are thoroughly investigated.Guided by the theory of sequence stratigraphy,the progradational sequence stratigraphic framework of the Yanchang Formation is systematically constructed to elucidate new deposition mechanisms in the depressed lacustrine basin,and it has been successfully applied to the exploration and development practices in the Qingcheng Oilfield.Key findings are obtained in three aspects.First,the seismic progradational reflections,marker tuff beds,and condensed sections of flooding surfaces in the Yanchang Formation are consistent and isochronous.Using flooding surface markers as a reference,a progradational sequence stratigraphic architecture is reconstructed for the middle-upper part of Yanchang Formation,and divided into seven clinoform units(CF1-CF7).Second,progradation predominantly occurs in semi-deep to deep lake environments,with the depositional center not always coinciding with the thickest strata.The lacustrine basin underwent an evolution of“oscillatory regression-progradational infilling-multi-phase superimposition”.Third,the case study of Qingcheng Oilfield reveals that the major pay zones consist of“isochronous but heterochronous”gravity-flow sandstone complexes.Guided by the progradational sequence stratigraphic architecture,horizontal well oil-layer penetration rates remain above 82%.The progradational sequence stratigraphic architecture and associated geological insights are more consistent with the sedimentary infilling mechanisms of large-scale continental depressed lacustrine basins and actual drilling results.The research results provide crucial theoretical and technical support for subsequent refined exploration and development of the Yanchang Formation,and are expected to offer a reference for research and production practice in similar continental lacustrine basins.
基金the Science and Technology Innovation Project of the Laoshan Laboratory (No. LSKJ202203402)the Major Research Project on the Tethys Geodynamic System from the National Science Foundation of China (No. 92055204)。
文摘Fluvial systems play a crucial role in coastal and riverine ecosystems, making it essential to understand their responses to sea level changes for preserving biodiversity and managing natural resources. The evolution of the modern Indus River Delta offers a rare opportunity to study the interplay between sea level fluctuations, tectonism, sediment supply, and the corresponding fluvial responses. This study employs the ‘SedSim' stratigraphic forward model to simulate the delta's evolution from 200 kyr to the next5 kyr, drawing on data from field observations, Landsat imagery, digital elevation models, and previous studies. The model consists of 205 layers, each representing a 1-kyr time step, covering the last two glacial-interglacial cycles. Between 200 kyr and 130 kyr, during a lowstand period, sedimentation on the delta plain continued due to partial flow from the Indus River. During the last interglacial(130–60 kyr), rising sea levels led to peak sediment deposition, characteristic of a highstand phase. From 60 kyr to 18 kyr, sea levels dropped to their lowest during the Last Glacial Maximum(LGM), resulting in extensive erosion and minimal deposition on the delta plain. From 18 kyr to the present, rapidly rising sea levels, coupled with intensified monsoon activity, increased sedimentation rates and triggered avulsion and aggradation processes. The model accurately predicted depositional thickness across the delta plain, indicating a maximum of ca. 200 m at the shoreline platform, ca. 175 m in the northeastern delta, and ca. 100 m in the central delta. The study underscores the delta's vulnerability to future sea level rise, which–at a projected rate of 1 m/kyr–could significantly influence the densely populated, low-lying delta plain. These findings offer valuable insights into the geomorphic evolution of the Indus Delta and emphasize the socioeconomic implications of sea level change, underscoring the importance of proactive management and adaptation strategies.
基金funded by the Major Science and Technology Project of China National Petroleum Corporation(No.2023ZZ22YJ01).
文摘Stratigraphic correlations are essential for the fine-scale characterization of reservoirs.However,conventional data-driven methods that rely solely on log data struggle to construct isochronous stratigraphic frameworks for complex sedimentary environments and multi-source geological settings.In response,this study proposed an intelligent,automatic,log-seismic integrated stratigraphic correlation method that incorporates wavelet frequency-division transform(WFT)and dynamic time warping(DTW)(also referred to as the WFT-DTW method).This approach integrates seismic data as constraints into stratigraphic correlations,enabling accurate tracking of the seismic marker horizons through WFT.Under the constraints of framework construction,a DTW algorithm was introduced to correlate sublayer boundaries automatically.The effectiveness of the proposed method was verified through a stratigraphic correlation experiment on the SA0 Formation of the Xingshugang block in the Lasaxing oilfield,the Songliao Basin,China.In this block,the target layer exhibits sublayer thicknesses ranging from 5 m to 8 m,an average sandstone thickness of 2.1 m,and pronounced heterogeneity.The verification using 1760 layers in 160 post-test wells indicates that the WFT-DTW method intelligently compared sublayers in zones with underdeveloped faults and distinct marker horizons.As a result,the posterior correlation of 1682 layers was performed,with a coincidence rate of up to 95.6%.The proposed method can complement manual correlation efforts while also providing valuable technical support for the lithologic and sand body characterization of reservoirs.
基金the financial support from the National Key R&D Program of China(Grant No.2021YFC3001003)Science and Technology Development Fund,Macao SAR(File No.0056/2023/RIB2)Guangdong Provincial Department of Science and Technology(Grant No.2022A0505030019).
文摘Challenges in stratigraphic modeling arise from underground uncertainty.While borehole exploration is reliable,it remains sparse due to economic and site constraints.Electrical resistivity tomography(ERT)as a cost-effective geophysical technique can acquire high-density data;however,uncertainty and nonuniqueness inherent in ERT impede its usage for stratigraphy identification.This paper integrates ERT and onsite observations for the first time to propose a novel method for characterizing stratigraphic profiles.The method consists of two steps:(1)ERT for prior knowledge:ERT data are processed by soft clustering using the Gaussian mixture model,followed by probability smoothing to quantify its depthdependent uncertainty;and(2)Observations for calibration:a spatial sequential Bayesian updating(SSBU)algorithm is developed to update the prior knowledge based on likelihoods derived from onsite observations,namely topsoil and boreholes.The effectiveness of the proposed method is validated through its application to a real slope site in Foshan,China.Comparative analysis with advanced borehole-driven methods highlights the superiority of incorporating ERT data in stratigraphic modeling,in terms of prediction accuracy at borehole locations and sensitivity to borehole data.Informed by ERT,reduced sensitivity to boreholes provides a fundamental solution to the longstanding challenge of sparse measurements.The paper further discusses the impact of ERT uncertainty on the proposed model using time-lapse measurements,the impact of model resolution,and applicability in engineering projects.This study,as a breakthrough in stratigraphic modeling,bridges gaps in combining geophysical and geotechnical data to address measurement sparsity and paves the way for more economical geotechnical exploration.
基金supported by the Earthquake Science and Technology Spark Plan Project(No.XH23041C)The Natural Science Foundation of Gansu Province(No.22JR11RA090)Gansu Lanzhou Geophysics National Observation and Research Station(No.2021Y14).
文摘The widely distributed loess deposits in the Yellow River Basin exhibit unique engineering geological characteristics.The variations in their thickness and stratigraphic structure significantly amplify ground motion parameters,directly influencing the regional seismic hazard risk level.This study methodically conducted on-site studies and observations of building collapses and damages resulting from seismic amplification effects,using the Wenchuan M_(S)8.0 earthquake as a case study.Comprehensive experimental and numerical simulation studies were carried out.A large-scale shaking table test was performed,and numerical models for 14 different loess sites types were established.Various types of seismic waves were incorporated into these models for systematic numerical simulation calculations.The research reveals the mechanisms by which loess deposit thickness and stratigraphic structure in the Yellow River Basin affect seismic ground motion amplification.The results indicate that as the epicentral distance increases,the peak ground motion shows a marked attenuation trend,with the horizontal component attenuating substantially faster than the vertical component.As the overlying loess layer thickness increases from 50 to 100 m,the seismic intensity may escalate by 3−4 degrees,and the peak acceleration may amplify by 1.5−2.2 times.With the augmentation of loess deposit thickness and the proliferation of soil layers,both the peak acceleration response spectrum and the characteristic period demonstrate an upward tendency,exhibiting slight fluctuations contingent upon the seismic wave type.
基金supported by the National Science Foundation of China (NSFC) (Nos. 41272122, 41202074 and 41172123)the Major National Science and Technology Programs in the "Twelfth Five-Year" Plan of China (No. 2011ZX05009-002-02)+1 种基金the Open Research Program Foundation of Teaching Laboratory of China University of Geosciencesthe Foundation of Key Laboratory of Tectonics and Petroleum Resources (China University of Geosciences) of Ministry of Education (No. TPR-2013-14)
文摘In active rift basins, tectonism is extremely important for sequence stratigraphic patterns, affecting both the sequence architecture and internal makeup. Sequence stratigraphic framework of a Paleogene rift succession in Qiongdongnan Basin, northern South China Sea, was built using seismic profiles, complemented by well logs and cores. One first-order and three second-order sequences were identified on the basis of basin-scale unconformities, and seven third-order sequences are defined by unconformities along the basin margins and correlative conformities within the central basin. Through unconformity analysis and backstripping procedure, the Paleogene synrift tectonic evolution of deep- water area of Qiongdongnan Basin was proved to be episodic, which can be divided into rifting stage-I, rifting stage-II and rifting stage-III. Episodic rifting resulted in the formation of various types of struc- tural slope break belts, which controlled different architectures and internal makeup of sequences. This study enhances the understanding of the control of tectonic evolution on sequence stratigraphic pat- terns and establishes relevant patterns in a typical rift basin, and further proposes the favorable sand- stone reservoirs developing in different sequence stratigraphic patterns, which will be pretty helpful for subtle pool exploration in deepwater area of petroliferous basins.
文摘The onshore oil and gas exploration has stepped into a new stage in China, with equal attention paid to both stratigraphic and subtle reservoirs and structural reservoirs. In the past few years, the increases in oil reserves in most basins were found mainly in the stratigraphic and subtle reservoirs. Latest resource evaluation shows that the onshore stratigraphic and subtle reservoirs in China account for 42% of the total remaining resource, the highest in the four major exploration regions. Therefore, these reservoirs will be the most practical, potential and prevalent fields for long-lasting oil and gas exploration in onshore China. Among PetroChina's annual oil geologic reserves of 4.3 × 108t^4.6× 108t, the stratigraphic and subtle reservoirs account for more than 50%. In such basins as Songliao, Ordos, Bohai Bay, Junggar, Tarim, Sichuan and Erlian basins, stratigraphic and subtle reservoirs with geologic reserves ranging from 5×107t to 3×108t were discovered, including Ansai, Jing'an, Daqingzijing, Liuxi, well-21 area in Shinan, and Hadexun. Stratigraphic and subtle reservoirs in the four types of inland basins differ from each other in the formation conditions and the distribution patterns. While continental basins are controlled by unconformity surface, maximum flooding surface and fracture surface, the Paleozoic marine basins are influenced by paleouplift, unconformity surface, and fluctuation of the sea level. Through exploration practices and research, PetroChina has formed its own technique series focused on 3-D seismics and sequence stratigraphy.
基金supported by the National Natural Science Foundation of China (NSFC) (No. 41472216)the Natural Science Foundation of Shandong Province (No. ZR2016DB29)+3 种基金the Project supported by Shandong Provincial Key Laboratory of Depositional Mineralization & Sedimentary Mineral, Shandong University of Science and Technology (No. DMSM2017015)the Water Conservancy Scientific Research and Technology Promotion Projects of Shandong Province (No. SDSLKY201808)the Natural Science Foundation of Jinan University (No. XBS1647)Petroleum Development Centre of the Shengli Oilfield Company for their support
文摘To improve the success rate of locating hydrocarbon reservoirs in pre-Cenozoic inland compressional basins, taking the Early Yanshanian succession of eastern Yihezhuang salient as an example, this paper studied the sedimentary facies and sequence stratigraphic patterns. First, through seismic profiles, well logs, cores and outcrops, the sequence framework was established and internal sedimentary facies were identified. Further, according to analysis of single-wells and connecting-wells, the vertical evolution and horizontal distribution of sedimentation inside the sequence frameworks were discussed. The following results were acquired:(1) meandering river characterized by dual structures superposing each other was developed, and the dual structures can be further divided into three kinds;(2) the entire Early Yanshanian succession was interpreted as one first-order sequence, composed of three third-order sequences, including SQ-Fz1, SQ-Fz2 and SQ-St from bottom to top. Each third-order sequence can be further divided into three system tracts;(3) in different system tracts, different types of dual structures developed separately, and sedimentary bodies showed different horizontal distribution scales and vertical superposition patterns. Finally, the model of sequence stratigraphic patterns was established. This study enhanced the use of sequence stratigraphy to inland tectonically active basins, and would be helpful to predict reservoirs in pre-Cenozoic residual basins.
基金financially was supported by Colorado School of Minessupported by the Science and Technology Ministry of China (2016ZX05033003)+1 种基金China Academy of Sciences (XDA14010204)Sinopec (G5800-15-ZS-KJB016)
文摘This paper presents a unique and formal method of quantifying the similarity or distance between sedimentary facies successions from measured sections in outcrop or drilled wells and demonstrates its first application in inverse stratigraphic modeling. A sedimentary facies succession is represented with a string of symbols, or facies codes in its natural vertical order, in which each symbol brings with it one attribute such as thickness for the facies. These strings are called attributed strings. A similarity measure is defined between the attributed strings based on a syntactic pattern-recognition technique. A dynamic programming algorithm is used to calculate the similarity. Inverse stratigraphic modeling aims to generate quantitative 3D facies models based on forward stratigraphic modeling that honors observed datasets. One of the key techniques in inverse stratigraphic modeling is how to quantify the similarity or distance between simulated and observed sedimentary facies successions at data locations in order for the forward model to condition the simulation results to the observed dataset such as measured sections or drilled wells. This quantification technique comparing sedimentary successions is demonstrated in the form of a cost function based on the defined distance in our inverse stratigraphic modeling implemented with forward modeling optimization.
基金sponsored by the Magnitude Project of Ministry of Science and Technology of China (No. 2008ZX05016-001)the China Postdoctoral Science Foundation (No. 20100480344)Youth Innovation Fund of Research Institute of Petroleum Exploration and Development of PetroChina (No. 2009-B-10-03)
文摘Taking member one of Yingcheng Formation of Cretaceous in Xudong area, Xushen Gas Field of Songliao Basin for an example and aimed at the diachronous problem generally existed in vol- canic reservoir division, firstly advanced the method of two steps and two unites in the researches of volcanic reservoir finely division that guided by the method that sources controlled and founded the stratigraphic trellis. In this process, volcanic edifices and bodies were identified and traced. The results indicated that aimed strata in study areas could be carved up to six layers of YCII1, YCII2, YCII-II, YCIIlI, YCIII2 and YCIIII from the top to the bottom. Analyzing causes and firmly united of well data and seismic data could achieve fine stratigraphic division of volcanic reservoir. Surfaces of layers and volcanic bodies were basically unanimous in side direction. Stratum inclination gradually reduced with the distances increased from craters. The results of volcanic reservoir division had preferable con- sistency with lithologies and volcanic lithofacies and dynamic development data. The researches offered a useful method to stratigraphic division of volcanic reservoir and it had very important significance to effective development of volcanic reservoir in practice.
基金financially supported by the National Key Research and Development Program of China(2017YFC0603101)the Strategic Priority Research Program of the Chinese Academy of Sciences(XDA14010101)the National Natural Science Foundation of China(41872125,42102146,42002158)。
文摘The ultra-deep Cambrian System in the Tarim Basin is an important field for petroleum exploration,while fine division of the Cambrian strata remains controversial.In recent years,carbon isotope stratigraphy of the Cambrian System has been established and widely used.Here,we report an integrated profile of carbonate and organic carbon isotopic values(δ^(13)C_(carb)andδ^(13)C_(org))from cuttings of the Tadong2 Well in the eastern Tarim Basin.Three carbon isotope anomalies of BACE,ROECE and SPICE were recognized on theδ^(13)C_(carb)profile.Three apogees and a nadir on theδ^(13)C_(org)profile and the onset of ROECE on theδ^(13)C_(carb)profile were suggested as boundaries of the present four series of the Cambrian System.Suggested boundaries are easily identifiable on the gamma logging profile and is consistent with the previous division scheme,based on biostratigraphic evidence in outcrop sections.Abnormal carbon cycle perturbations and organic carbon burials during the BACE and SPICE events might be related to the reduction and expansion of a huge dissolved organic carbon reservoir in the deep ocean of the ancient Tarim Basin.
基金These research results are part of a key international cooperation project carried out during 2003 and 2005 and financially supported by SINOPEC.
文摘In recent years, with the development of terrestrial sequence stratigraphy, more attention has been focused on the study of the terrestrial lacustrine sequence stratigraphic model globally. Different viewpoints are preferred by researchers. Under the guidance of the theory of sequence stratigraphy, the findings of this paper indicate that climate is a major factor controlling the formation of the fourth-order sequence, based upon the study of the sequence stratigraphy in the Green River Formation of the Uinta basin in the USA. It also divides the fourth-order sequence in the terrestrial lacustrine basin into two system tracts： the wet （rising） half-cycle and the dry （falling） half- cycle, establishing a new-style fourth-order sequence stratigraphic model for the terrestrial lacustrine basin, that is, the climate-genetic sequence stratigraphic model. As a result, the theory of sequence stratigraphy is greatly enriched.
基金Note:The study was supported by the China National Natural Science Foundation Grant No 49172107.
文摘Isotopic ages of synsedimentary clay minerals were directly determined with the ultrasonicscattering-settlement separation-K-Ar dilution technique. The apparent age of black mudstoneis 123 Ma for the Quantou Formation, 111.9-89.0 Ma for the Qingshankou Formation and77.6-76.8 Ma for the upper part of the Nenjiang Formation. The Rb-Sr isochrone age of themuddy limestone-mudstone sequence of the lower part of the Nenjiang Formation is 81 Ma andthat of the muddy evaporite of the middle part of the Quantou Formation is 122.2 Ma. On thebasis of the above isotopic ages, the authors propose a modified scheme of stratigraphic classifi-cation of the Cretaceous of the Songliao basin.
基金financially supported by the National Natural Science Foundation of China (Grant No.41203023)National Basic Research Program of China (Grant No.2007CB411301)
文摘The upper Qigeblaq Formation （Fm） dolostones and the Yurtus Fm phosphatic cherts, black shales, limestones, and dolostones are widely distributed in the Precambrian/Cambrian transitional succession of the Aksu-Wushi area. Negative δ13C excursion above the Yurtus Fm/ Qigeblaq Fm boundary was determined in this study. The pronounced negative carbon isotope excursion occurs in the phosphatic chert layers at the bottom of the Cambrian Yurtus Fm, below which the first appearance of the Asteridium- Heh＇osphaeridium-Comasphaeridium （AHC） acritarch assemblage zone. The δ13C curve of the lower part of the Yurtus Fm in the Aksu-Wushi area was found to be correlated with the early Cambrian δ13C curves of the Zhujiaqing Fm （Daibu Member）, the lower part of the Yanjiahe Fm on the Yangtze Platform in China, the lower Tal Fm in India, the Sukharikha Fm in Siberia, and the upper part of the Tsagaan Oloom Fm in Mongolia through biostigraphy. The lower part of the Yurtus Fm in the Tarim Basin is at the Nemakit-Daldynian stage, and the Precambrian/Cambrian boundary of the Aksu-Wushi area may be located in the phosphatic chert unit which just below the first appearance AHC acritarch assemblage zone. The negative δ13C excursion （N1） across the Precambrian/Cambrian boundary in the studied section may have resulted from oceanic overturning and sea level rise.
基金The study was jointly supported by the National Natural Science Foundation of China(Grants 49472086 and 40072041)the Ministry of Science and Technology(the SSER project).
文摘Four hierarchical cyclothems, superbundlesets, bundlesets, bundles and laminae, have been identified from the Devonian Frasnian-Famennian carbonate strata in Guangxi, South China. Their hierarchical structures, ratio relationships and sequence in conodont zones are continuous and stable and can be traced across different facies zones and sedimentary basins. Our data show that hierarchically organized superbundlesets, bundlesets, bundles and laminae correspond to the long eccentricity, eccentricity, obliquity or precession and sub-Milankovitch cycles respectively. Their periods were 400,000, 100,000, 33,333, 16,667 and 8,000–17,000 a, respectively. The ratios of long eccentricity to eccentricity, eccentricity to obliquity, and eccentricity to precession in the Devonian are 1:4, 1:3 and 1:6 respectively. Using these hierarchical Milankovitch cyclothems, chronostratigraphical division and correlation can be realized at a resolution of 100 ka or 10 ka at the Frasnian-Famennian transition. The time intervals of the Upper rhenana Zone, linguiformis Zone, and the Lower, Middle and Upper triangularis Zone are 0.6, 0.8, 0.3, 0.3 and 0.3 Ma, respectively. Sea-level changes of the Frasnian-Famennian transition were not coherent and synchronous at the resolution of 100 ka or 10 ka in the basin-slope carbonate sequences of Guangxi, South China.
基金supported by "the Major State Science and Technology Research Program" (grant No.2016ZX05010001-003)"the Chinese National Natural Science Fund Project" (grant No.41572080)
文摘The Baxian depression is a typical half-graben located in the Jizhong sub-basin, north China. Commercial petroleum traps have been discovered in the Jizhong sub-basin. However, the 3rd and 4th members of the Shahejie Formation in this sub-basin have been poorly explored. These two members, belonging to the Lower Paleogene age, are buried deeply in the depression. Favorable petroleum reservoir conditions exist in such deep intervals of the half-graben due to the presence of different types and extent of deltas and turbidity fans in various areas. In fact, three types of turbidite fans are developed in the sag below the transitional belt on the eastern gentle slope. This work summarized three stratigraphic trap belts, i.e., the steep slope, gentle slope, and sag. On the steep slope, structural- stratigraphic traps with small-scale delta fronts and turbidite sandbodies are well developed. On the gentle slope, hydrocarbons generally accumulate in the large-scale delta front, onlapping beds and those sandbodies adjacent to unconformities. In the sag, petroleum trap models are typically characterized by pinched-out turbidite sandbodies. Stratigraphic traps were easily formed in turbidite fans below the eastern transitional belt. The petroleum traps that have already been discovered or predicted in the study area indicate that stratigraphic traps have favorable petroleum exploration potential in deeply buried areas （depth 〉5000 m） in a half-graben basin or depression.
基金supported by the CNPC Advanced Fundamental Research Projects(No.2023ycq06).
文摘Well logging curves serve as indicators of strata attribute changes and are frequently utilized for stratigraphic analysis and comparison.Deep learning,known for its robust feature extraction capabilities,has seen continuous adoption by scholars in the realm of well logging stratigraphic correlation tasks.Nonetheless,current deep learning algorithms often struggle to accurately capture feature changes occurring at layer boundaries within the curves.Moreover,when faced with data imbalance issues,neural networks encounter challenges in accurately modeling the one-hot encoded curve stratification positions,resulting in significant deviations between predicted and actual stratification positions.Addressing these challenges,this study proposes a novel well logging curve stratigraphic comparison algorithm based on uniformly distributed soft labels.In the training phase,a label smoothing loss function is introduced to comprehensively account for the substantial loss stemming from data imbalance and to consider the similarity between diff erent layer data.Concurrently,spatial attention and channel attention mechanisms are incorporated into the shallow and deep encoder stages of U²-Net,respectively,to better focus on changes in stratification positions.During the prediction phase,an optimized confidence threshold algorithm is proposed to constrain stratification results and solve the problem of reduced prediction accuracy because of occasional layer repetition.The proposed method is applied to real-world well logging data in oil fields.Quantitative evaluation results demonstrate that within error ranges of 1,2,and 3 m,the accuracy of well logging curve stratigraphic division reaches 87.27%,92.68%,and 95.08%,respectively,thus validating the eff ectiveness of the algorithm presented in this paper.
基金Undertheauspices of the National Basic Research Program of China(No. 2004CB720206) and theproject of Chin-ese AcademyofSciences (No. KZCX2-SW-118)
文摘Yulin section is a typical sedimentary record for reflecting the environmental evolution of Ordos Desert, China in the past 1.1Ma. By analyzing its sequence and grain-size composition some views have been put forward in this paper as follows. The layers of sand, loess and palaeosol in Yulin section were respectively formed by wind and the pedogenesis on parent material of the sand and loess. Since 1.1Ma B. P., Ordos Desert has alternately experienced 11 stages of shifting dunes under extreme cold-dry climatic environment, 7 stages of fixed and semi-fixed dunes and 8 stages of dust (loess) under cold-dry climatic condition; and the pedogenesis environment under 15 times of warm-humid climate and 3 times of temperate-humid climate (brownish-drab soils and black soils formed respectively). The aeolian sand had already existed in Ordos Desert at latest by 1.1Ma B. P., and from that time on it has undergone a series of alternative processes of shifting sands, fixed and semi-fixed dunes, loess and soils. Ordos Desert has been situated in the transitional belt of the Mongolian High Pressure and margin of the southeast summer monsoon since 1.1Ma B. P., and influenced repeatedly by migration of the lithofacies belts of shifting sands, fixed and semi-fixed dunes, loess and soils, which have been caused by the climatic fluctuations of glacial and interglacial periods.
基金This study was supported by the National Natural Science Foundation of China Grant No. 4880102
文摘Deposits of 10 volcanic events of 6 stages have been discovered by the authors after detailed field and lab studies of the Benxi and Taiyuan Formations in Shandong Province and its adjacent regions. They show certain temporal-spatial distribution characteristics. Volcanic fragments were probably derived from two different volcanic sources north and south of the North China Platform, while the magma of the two volcanic sources was probably derived from the lower crust. A new stratigraphic correlation scheme is put forward for the Benxi and Taiyuan Formations in this region on the basis of previous biostratigraphic work with the regionally widespread volcanic event layers as the marker bed for the isochronous stratigraphic correlation on a super-regional scale and in conjunction with the maximum transgressive event layers.
