An intelligent automatic correlation method of oilbearing strata based on pattern constraints:An example of accretionary stratigraphy of Shishen 100 block in Shinan Oilfield of Bohai Bay Basin,East China

Aiming at the problem that the data-driven automatic correlation methods which are difficult to adapt to the automatic correlation of oil-bearing strata with large changes in lateral sedimentary facies and strata thickness,an intelligent automatic correlation method of oil-bearing strata based on pattern constraints is formed.We propose to introduce knowledge-driven in automatic correlation of oil-bearing strata,constraining the correlation process by stratigraphic sedimentary patterns and improving the similarity measuring machine and conditional constraint dynamic time warping algorithm to automate the correlation of marker layers and the interfaces of each stratum.The application in Shishen 100 block in the Shinan Oilfield of the Bohai Bay Basin shows that the coincidence rate of the marker layers identified by this method is over 95.00%,and the average coincidence rate of identified oil-bearing strata reaches 90.02% compared to artificial correlation results,which is about 17 percentage points higher than that of the existing automatic correlation methods.The accuracy of the automatic correlation of oil-bearing strata has been effectively improved.

Devonian Frasnian-Famennian Transitional Milankovitch Cycles and High-Resolution Stratigraphic Correlation

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.

Carbon Isotope Features of the Sugetbrak Section in the Aksu-Wushi Area, Northwest China: Implications for the Precambrian/Cambrian Stratigraphic Correlations

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.

Late Carboniferous-Early Permian Volcanic Event Deposits and Stratigraphic Correlation in Shandong Province and Its Adjacent Regions

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.

Stratigraphical Time——Correlation and Mass Extinction Event Near Permian——Triassic Boundary in South China

Shaw's method used to correlate 40 sections across the Permo-Triassic boundary in South China is applied in the paper. Two steps are adopted to get an Integral Composite Section (ICS) by synthesizing these data : First , South China is divided into five areas and composite section developed for each area . Then the second step . the Changxing composite section is regarded as a composite standard (CSRS) while the ICS is produced by matching the CSRS with composite sections of the other areas. Three biozones in the Changxingian and two biozones in the Griesbachian can be discerned on the basis of computing Z values in the ICS. These biozones are marked by the Z values which quantitatively represent their time ranges ; therefore , they may increase accuracy of stratigraphic time correlation . The mass extinction at the end of the Permian is an abrupt event that is supported by the relative rate of extinction near the P/T boundary . About 90% of invertebrate species died out by the end of the Permian . The duration of the mass extinction is rather short ,approximately 0.018Ma .

Hierarchical delineation and multivariate statistical discrimination of chemozones of the Cauvery Basin,south India:Implications on spatio-temporal scales of stratigraphic correlation

Success in locating oil pools in the Cauvery Basin,south India had been found to be based on the ability to delineate precisely the stratigraphic traps resulting from frequent sea level changes.However,recognition and delineation of them in terms of depositional units through conventional stratigraphic methods have been elusive owing to the limitations of such methods and lack of unified stratigraphic markers that could be traced at regional and basinal scale.This paper attempts to recognize depositional units in terms of chemozones,chronologic and lithostratigraphic units by assigning distinct geochemical signatures.Geochemical signatures were assigned through hierarchical delineation and discriminant function analysis.It is observed that individual depositional units could be recognized statistically with whole-rock geochemical composition.The strata under study show two second order chemozones comprising six major chemozones that in turn correspond to third order sea level cycles and minor chemozones at the scale of fourth order and/or further shorter sea level cycles.The geochemical signatures showed 100% distinctness between sample populations categorized according to chronostratigraphy and lithostratigraphy.The durations of these stratigraphic units range from 18 million years to less than a million years and indicate distinct geochemical compositional change at different time slices.By implication and also due to the close correspondence between sea level variations reported from this basin and global sea level cycles,it is suggested that recognition and correlation of individual depositional units with distal counterparts could be made accurately.Implication of these results is that stratigraphic units,at varying scales either temporally or spatially,could be assigned with unique geochemical signature,with which accurate prediction and correlation of similar units elsewhere is possible with measurable accuracy.

Stratigraphic Correlation And Division of the Salite Strata

1 Introduction Stratigraphic correlation is the most important basic work in oil and gas exploration and development,Scientific and reasonable stratigraphic correlation is the premise of developing fine reservoir description,and it is

Stratigraphic Correlation of Middle TriassicSequences among Different Paleogeographic Sedimentary Facies in South China

Affected by the Indosinian movement, the sediments in the main part of South China, Yangtze platform, started to transform from marine to continental during the Middle Triassic. In the meantime, a noticeable paleogeographic and sedimentary facies differentiation occurred in the marginal regions of the platforms and produced completely different lithologic and paleontologic sequences in various paleogeographic gradients and sedimentary facies areas, which brought about the difficulties for the stratigraphic correlation based on the traditional stratigraphies. This paper proposes to use some characteristic environmental events as the markers of the stratigraphic correlation across various paleogeographic sedimentary facies, considering that some distinctive regional environmental events should have affected at the same time on the entire basin or the connected sedimentary regions and produced some closely related sedimentary records in the stratigraphic sequences though the affected intensity and recorded pattern might be different among the regions. The change of violent relative sea level (generally water depth) and the alteration of tectonic activity summarized from the dynamic mechanism of sedimentation are the best markers of environmental events for stratigraphic correlation. Based on the analysis and recognition of some significant environmental events at the typical stratigraphic sequences from various paleogeographic sedimentary facies and combined with the consideration of the variations in expressed form and strength of the events among different paleogeographic gradients and sedimentary facies, the stratigraphic sequences from different sedimentary facies can be easily correlated directly. Furthermore, the evolutionary history of the whole sedimentary basin can be clearly established.

The Discovery of the Bivalve Fossil Arguniella from the Lower Cretaceous Shangkuli Formation in Northern Greater Khingan Mountains, China: Implications for Stratigraphic Correlation

Objective Typical Early Cretaceous non-marine bivalve fossils from Eastern Asia are represented by the Arguniella-Sphaerium assemblage,and they were important members of the Jehol Biota.Historically,the genus Arguniella in western Liaoning had been mistakenly identified as the Jurassic Ferganoconcha,re-identified as Arguniella with。

Automated stratigraphic correlation of well logs using Attention Based Dense Network

The stratigraphic correlation of well logs plays an essential role in characterizing subsurface reservoirs.However,it suffers from a small amount of training data and expensive computing time.In this work,we propose the Attention Based Dense Network(ASDNet)for the stratigraphic correlation of well logs.To implement the suggested model,we first employ the attention mechanism to the input well logs,which can effectively generate the weighted well logs to serve for further feature extraction.Subsequently,the DenseNet is utilized to achieve good feature reuse and avoid gradient vanishing.After model training,we employ the ASDNet to the testing data set and evaluate its performance based on the well log data set from Northwest China.Finally,the numerical results demonstrate that the suggested ASDNet provides higher prediction accuracy for automated stratigraphic correlation of well logs than state-of-the-art contrastive UNet and SegNet.

Early Cambrian carbon isotope stratigraphy in the Tarim Basin and a correlation with the Yangtze Platform

Carbon isotope chemostratigraphy has been used worldwide for stratigraphic correlation.In this study,δ13Ccarb values are estimated for the Early Cambrian Sugaitebulake section in the Tarim Basin,Xinjiang Autonomous Region,China.As a result,one positive and two negative carbon isotope excursions in the studied section were iden-tified.The δ13Ccarb values reached the maximum negative excursion(N1:-12.39‰) at the basal of the Yuertusi For-mation,and then increased to P1.After P1,δ13Ccarb values sharply decreased to about-7.06‰(N2) in the studied section.The pattern of δ13Ccarb in the Early Cambrian is comparable to the synchronous records of other sections,such as the Laolin section,the Xiaotan section and the Anjiahe section of the Yangtze Platform.It is concluded that the Early Cambrian Yuertusi Formation from the Tarim Basin is within the Nemakit-Daldynian stage,and the lower strata of the Yuertusi Formation may belong to the Zhujiaqing Formation(Meishucun Formation) of the Yangtze Platform.The Ediacaran/Cambrian boundary of the Tarim Block should be located in cherts and phosphorites suc-cessions at the basal of the Yuertusi Formation.The δ13Ccarb negative excursion N1 is just across the PC/C boundary,and may be related to certain biomass extinction due to anoxic sedimentary environment,transgression and/or the oceanic overturn.The second δ13Ccarb negative excursion N2 may account for the sea-level falling in the Early Cam-brian.

Discovery of Pseudofrenelopsis gansuensis from the Lower Cretaceous of Wangqing,Jilin Province,and Its Significance in Correlation of Cretaceous Red Beds in China

New data from abundant vegetative shoots and cuticular analysis are provided for the Cretaceous cheirolepidiaceous conifer Pseudofrenelopsis gansuensis Deng, Yang et Lu. The material was found from a new locality of the Lower Cretaceous strata in the Luozigou Basin, Wangqing, Jilin Province, northeastern China. Pseudofrenelopsis is a common plant in the Dalazi Formation of the Yanji Basin about 150 km from Wangqing, but there exists different species, Pseudofrenelopsis dalatzensis only. Both P. dalatzensis and P. gansuensis have been recorded from the Lower Cretaceous of Jiuquan, Gansu Province, but they are in different stratigraphic horizons. The Lower Cretaceous plant-bearing strata in Luozigou have used to correlate with the Dalazi Formation of the Yanji Basin. The discovery of P. gansuensis, which is lower in horizon than P. dalatzensis in Jiuquan, may indicate that they are also different in horizon in Jilin. Cheirolepidiaceous conifers are among the few fossils of red beds of the Early Cretaceous in China. The present discovery of Pseudofrenelopsis gansuensis provides important evidence for classification, correlation and determination of geological ages of the Early Cretaceous non-marine red deposits of the two separate basins in remote areas of North China.

Stratigraphic Framework of the Cryogenian in China

The Cryogenian is a critical period in the history of the Earth. It is marked by multiple extreme climate changes that caused alternating global glacial and interglacial intervals. These dramatically changed the sedimentary system, and metal ores and source rocks distributed widely during this period. Therefore, studying the Cryogenian stratigraphic framework and sedimentary basins is important to improve the stratigraphic resolution for metal mineral and hydrocarbon prospecting and exploration in China. This review paper firstly divides three tectonic-stratigraphic regions in China in the Cryogenian, including the tectonic-stratigraphic regions of Great South China, Xingmeng-Tarim, and North China. Secondly, geochronologic data and geological records are combined to clearly depict the Cryogenian sedimentary sequence of continental blocks and micro-continental blocks in different tectonic-stratigraphic regions. The results were used to propose a new comparison scheme of stratigraphy for the Cryogenian in China. Finally, according to differences of sedimentary evolution and tectonic evolvement, sedimentary basins and their lithofacies paleogeography are identified and summarized, respectively.

Stratigraphic framework of late Paleozoic in northeastern China

Late Paleozoic strata in northeastern China are distributed in a zonal pattern around the old-land on the Jiamusi-Mongolia Block. They are composed of active deposits in the regular distributed tectonic lithofacies zones. This indicates that the late Paleozoic strata belong to continental margin deposits. According to the strong conformability of the sedimentary strata in the same continental margin and distinct differences among the three continental margins, three stratigraphical regions of the Jiamusi-Mongolia Stratigraphical Province are recognized along the northern, southern and eastern margins of the Jiamusi-Mongolia Block, named respectively as Xing＇an Stratigraphical Region, Inner Mongolia grass-Songhua River Stratigraphical Region and Baoqing-Hunchun Stra- tigraphical Region. Due to the characteristics of continental margin deposits and active sediments, the strata can be correlated on the level of formation by the methods of analysing the rock association in the same stratigraphic region. Therefore, some revisions of the lithologieal formations of the late Paleozoic strata in northeastern China have been made, and a new chart of lithostratigraphic correlation has been proposed. Furthermore, the present stratigraphic framework is setting on the International Stratigraphic Chart on the level of stage, after comprehen- sive researches to lithostratigraphy, biostratigraphy and chronostratigraphy, especially the conodont biostratigra- phy and isotopic ages of volcanic rocks obtained in recent years.

Volcanic Event Layers——A Marker Bed of Correlation of Coal Measures

Upper Carboniferous-Lower Permian volcanic event deposits from two cross sections in Nanpiao, Liaoning Province, and the Daqing Mountains, Inner Mongolia, were examined by systematic rock and mineral identification, differential thermal analysis, X-ray diffraction, scanning electron microscopy and trace element and rare earth element quantitative analysis. According to the results, twelve sequences of volcanic event deposits have been distinguished from bottom to top, including 34–39 volcanic event layers. As these layers each have their own distinctive petrological, mineralogical and geochemical characteristics and were derived from the same source, they provide new evidence for further ascertaining the distribution characteristics of volcanic event deposits on the northern margin of the North China plate and carrying out the stratigraphic correlation using volcanic event layers as marker beds.

Correlation methods of base-level cycle based on wavelet neural network

The authors discussed the method of wavelet neural network （WNN） for correlation of base-level cycle. A new vectored method of well log data was proposed. Through the training with the known data set, the WNN can remenber the cycle pattern characteristic of the well log curves. By the trained WNN to identify the cycle pattern in the vectored log data, the ocrrdation process among the well cycles was completed. The application indicates that it is highly efficient and reliable in base-level cycle correlation.

Geochemical Stratigraphy and Microvertebrate Assemblage Sequences across the Silurian/Devonian Transition in South China

Carbon isotope （δ13Corg） analyses of non-marine clastic rocks and neritic carbonates and black shales spanning the Silurian/Devonian transition are compared from two richly fossiliferous sequences in Qujing of East Yunnan and Zoige of Sichuan, South China. The two sections, Xishancun and Putonggou sections in South China, reveal positive δ13Corg shifts happening in the Upper Pridoli and Lower Devonian and reaching peak values as heavy as -25.2‰ （Xishancun） and -19.9‰（Putonggou） in the lowermost Lochkovian following the first occurrence of the thelodont Parathelodus and the conodont Icriodus woschmidti woschmidti （only in Putonggou Section and together with Protathyris-Lanceomyonia brachiopod fauna）. These results replicate a globally known positive shift in δ13Corg from the uppermost Silurian to the lowermost Devonian. The δ13Corg variations across the Silurian/Devonian Boundary （SDB） at the two sections in South China exhibit a shift in carbon isotopic composition similar to the detailed SDB curves from the borehole Klonk-1 drilled at top of the Klonk Global Standard Stratotype-Section and Point （GSSP） in the Prague Basin, Czech Republic. In addition, four microvertebrate assemblages, including the Liaojiaoshan, Xishancun, Yanglugou and Xiaputonggou assemblages, are recognized from the Silurian/Devonian transition exposed in the Xishancun and Putonggou sections, respectively. The results from both carbon isotope stratigraphy and microvertebrate assemblage sequences suggest that the SDB in South China is located at the base of the Xishancun Formation （between sample QX-20 and sample QX-21） in the Xishancun Section and the lower part of the Xiaputonggou Formation （between sample ZP-09 and sample ZP-10） in the Putonggou Section. The isotopic trend for organic carbon together with the changes of microvertebrate remains across the SDB can offer an approach to a potential correlation of the SDB from different sedimentary facies, which help to correlate the marine with non-marine deposits.

Why Terrestrial Stable Carbon-isotope Stratigraphy Works: a Review

Carbon-isotope stratigraphy launched since the early technological development of carbon- isotope measurement in 1950s, however, the emergence and advance of terrestrial carbon-isotope stratigraphy took quite a long way. At early stage the exploration of carbon-isotope stratigraphy based on the marine biological shell carbonates was verified by repeatable carbon-isotope stratigraphic data, laboratory chemical experiments and the later laboratory foraminiferal culture experiments. The breakthrough for testifying the fundamentals of terrestrial carbon-isotope stratigraphy lies on the synchronous fluctuations between the carbon-isotope stratigraphic curves derived from marine biological shell carbonates and those derived from terrestrial C3 plants. The character that carbon-isotope stratigraphic curves can be globally synchronously correlated over the marine and terrestrial/atmospheric reservoir mainly excludes the potential biasing factors, such as diagenetic bias, carbon-isotope variations in intra/inter individual plant in same species or between species, ecological changes, changes in aridity, changes in source input and representative sampling. Therefore, the fundamentals of terrestrial carbon-isotope stratigraphy based on C3 plant successfully established. The terrestrial carbon-isotope stratigraphy can be used for global stratigraphic correlation, reconstructing the evolution of atmospheric CO2 and can further verify the published global carbon-cycle models. The terrestrial carbon-isotope stratigraphy based on the compound specific biomarkers and single-grained pollen may be a promising perspective in future.

Paired δ^13Ccarb-δ^13Corg Evolution of the Dengying Formation from Northeastern Guizhou and Implications for Stratigraphic Correlation and the Late Ediacaran Carbon Cycle

This study provides δ^13C profiles from a lower-slope(Well ZK102)to basin(Bahuang Section)environment to better understand the temporal and spatial variability in δ^13Ccarb-δ^13Corg of the Yangtze Block during the Late Ediacaran.Our new δ^13C profiles together with the reported data suggest that the Upper Ediacaran successions from different depositional environments are generally bounded by negative δ^13Ccarb and/or δ^13Corg excursions in the underlying and overlying strata.Moreover,the Upper Ediacaran δ^13Ccarb profiles generally can be subdivided into two positive excursions and an interjacent negative excursion,whereas the paired δ^13Corg profiles from different depositional environments have individual variation trends.On the other hand,these data show a large surface-to-deep waterδ^13C gradient(~5‰variation in δ^13Ccarb,>10‰variation in δ^13Corg)which can be reasonably explained by the heterogeneity of the biological activities in the redox-stratified water column.Furthermore,the decoupled δ^13Ccarb-δ^13Corg pattern with large δ^13Corg perturbations at the lower slope precluded the existence of a large dissolved organic carbon reservoir at the Yangtze Block during the Late Ediacaran.Thus,the high δ^13Ccarb values in the Upper Ediacaran succession could be balanced by large amounts of buried organic carbon likely associated with high productivity.

Advances in sediment geochemistry and chemostratigraphy for reservoir characterization

Sedimentary sequences preserve the records of changes in major controls of sedimentation namely,tectonics,climate,relative sea level and sediment production and preservation.The potential to characterize these changes in spatial and temporal scales has led to the development of the branch of chemostratigraphy.Chemostratigraphic study of sedimentary sequences commenced from recognizing identical/contrasting geochemical features across major geochronological boundaries,and evolved into one of the essential tools in exploration,characterization,and well development strategies.Chemostratigraphy incorporates applications on continuous,real-time geochemical mapping and direction of lateral drilling,and machine learning,among others.As the sedimentary systems operate on a variety of temporal scales that range from few hours(tidal cycles)to few tens of millions of years,within which many perturbations such as catastrophic and diagenetic events take place,that lead to unique geochemical signature which can be correlated at appropriate spatial and temporal scales.The application of chemostratigraphic technique in hydrocarbon exploration and reservoir characterization has gained momentum in recent years,particularly with the advent of developments in analytical instrumentation.This has also led to the integration of a variety of data from field sedimentary structures,mineralogy,major,trace and isotopic chemical compositions of whole rock,selected components of rocks,organic and inorganic components of oil and gas,etc.,for reservoir characterization more accurately than ever.The geochemical fingerprinting of oil and gas reservoir components plays a major role in the identification of source rocks,discrimination of oil families,characterization of reservoir,source,and seal segments in petroleum systems.Future trends indicate the relevance and growing applications of machine learning techniques,artificial intelligence in real-time assessment,monitoring and planning of hydrocarbon exploration and production.