The Eocene is an enigmatic and interesting period due to the critical thermal events that occurred during the gradual global cooling, which have been demonstrated in the marine realm but remain ...poorly reported in terrestrial basins. In this study, a continuous ~404-m interval of the Middle Eocene terrestrial succession in Bohai Bay Basin, eastern China, was recovered from Well Fanye-1 in the Shengli Oilfield. This interval provides a unique record that can be used to better clarify the terrestrial sedimentary responses to astronomically forced climate changes, especially the Middle Eocene Climatic Optimum (MECO). Here, a high-resolution cyclostratigraphic framework from the lower third member (Es3l) to the upper fourth chun member (Es4cu) of the Shahejie Formation (Middle Eocene) was constructed by using magnetic susceptibility (MS) as a palaeoenvironmental proxy, in association with new paleomagnetic data. Power spectral analysis of the MS series reveal that the wavelength ratios of stratigraphic cycles are ~43.1–25:15.3–7.5:4.5–3:2.2–1.4, consistent with the period ratios of astronomical cycles. Moreover, a high-resolution astronomical time scale (ATS) for Well Fanye-1 was established by tuning the MS curves to the astronomical solution in combination with the magnetic stratigraphic framework. The method for establishing a high-resolution ATS with magnetostratigraphy and cyclostratigraphy was well applied in Well Fanye-1, making it possible to recalculate the ages in the Jiyang Depression. Finally, the terrestrial record across the MECO event was constructed and characterized based on the widespread “interbedded” argillaceous limestone. The resulting record is consistent with the time frame based on marine records and highlights the apparently primary role of the MECO event in shaping Asian paleoenvironments.
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•A cyclostratigraphic analysis of a middle Eocene lacustrine succession from the Bohai Bay Basin in eastern China was accomplished.•The method to establish an ATS with magnetostratigraphy and cyclostratigraphy is well applied in Well Fanye-1.•The terrestrial record across the MECO event was constructed and characterized based on the “interbedded” argillaceous limestone.
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•Lacustrine shale has strong heterogeneity in terms of its mineral composition.•Seven types of lithofacies developed in the Jiyang Depression.•Three types of lithofacies assemblages ...are present in the study area.•The Type C lithofacies assemblage is the most favorable exploration target.
There are multiple sets of lacustrine source rocks in the Paleogene of the Jiyang Depression, Bohai Bay Basin, Eastern China, which are main targets in the terrestrial shale oil exploration. Compared with marine shales, lacustrine fine-grained rocks are more complex in their mineralogical compositions, sedimentary structures and vertical stacking patterns. Therefore, it is of great theoretical and practical significance to carry out petrological characterization and lithofacies classification in lacustrine fine-grained rocks. Based on observations in cores and thin sections as well as elemental and organic geochemical analyses, this study systematically analyzes petrological characteristics of Eocene lacustrine fine-grained sedimentary rocks in the Jiyang Depression from perspectives of mineralogical compositions, sedimentary structures and organic matter abundance. Three end members (carbonate minerals, clay minerals and terrigenous clastic minerals), together with organic matter abundance and sedimentary structure, are employed to establish a lithofacies classification scheme that is suitable for fine-grained rocks in the Jiyang Depression, Eastern China. A total of 7 lithofacies types are recognized, such as the organic matter-rich laminated calcareous mudstone lithofacies and the moderately organic matter-rich layered calcareous mudstone lithofacies. Through analysis of lithofacies from the bottom to the top of the drilling well, sixth-order sequence units are found to have good correspondence to lithofacies assemblages. Based on consideration of magnetic susceptibility, mineral content, and geochemical proxies, these sixth-order sequence units are divided into three types of lithofacies assemblages, namely the Type A lithofacies assemblage corresponding to the dominantly rising base level, Type B lithofacies assemblage corresponding to the dominantly falling base level, and Type C lithofacies assemblage with the isostatic base level. Among them, the Type C lithofacies assemblage is the most favorable for shale oil exploration and development. Results of this study are expected to not only deepen understanding of lithofacies and its genesis and origin of lacustrine fine-grained rocks, but also provide a theoretical basis for shale oil exploration and development.
The Paleogene strata of the Bohai Bay Basin include multiple sets of lacustrine fine-grained sediments, which provide a detailed record of the climate changes that occurred in the lake basin. Early ...Paleogene fine-grained sedimentary rocks are the main target layers of continental shale oil exploration in eastern China. Therefore, studies of the geological responses to astronomical factors have important theoretical and practical significance for understanding the depositional process of lacustrine fine-grained sedimentary rocks. In this paper, we focus on the lower Es3 (Es3l)-upper Es4 (Es4u) units in four shale oil wells in the Dongying Sag of the Bohai Bay Basin. Based on the previous establishment of a high-resolution astronomical time scale in this area, we have further studied the petrological characteristics and lithofacies of the fine-grained sedimentary rocks. Then the geological responses to astronomical cycles on different scales are investigated, and the models for the depositional process of fine-grained sedimentary rocks under the control of astronomical factors are revealed. The results indicate that the cyclic changes in mineral content and lithofacies in fine-grained sedimentary rocks in the Dongying Sag are controlled by short eccentricity and precession cycles. Periods near the maximum short eccentricity range had large precession amplitudes, humid climates, and the development of organic-rich laminated calcareous mudstone lithofacies. In contrast, periods near the minimum short eccentricity range had small precession amplitudes, a dry climates, and the development of organic-containing layered muddy limestone lithofacies. This study explores the depositional process of fine-grained sedimentary rocks from the perspective of astronomical cycles, which is conducive to the comprehensive prediction of favorable shale oil layers.
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•High-resolution geochemical and sedimentary record of orbital cyclicity in Bohai Bay Basin.•The depositional process of lacustrine fine-grained sedimentary rocks is mainly affected by eccentricity and precession.•Two depositional models of lacustrine fine-grained sediments controlled by astronomical factors were established.
High-resolution measurements of magnetic susceptibility (MS) (8029 samples) and X-ray fluorescence (XRF) elements (4367 samples) were performed on the ~403-m-thick Shahejie Formation in the Bohai Bay ...Basin, eastern China. The power spectral and fast Fourier transform (FFT) spectrogram analyses of the MS series reveal that the wavelength ratios of the stratigraphic cycles are ~20:5:2:1, which is consistent with the period ratios of astronomical cycles (long eccentricity, short eccentricity, obliquity, and precession). A floating-point time scale (FPTS) was developed by tuning the magnetostratigraphic susceptibility (MSS) zonation to the standard reference zonation (SRZ) established by using the same interval of semi-long eccentricity (200 kyr). The depositional durations of the lower third member (Es3l) and upper fourth member (Es4u) of the Eocene Shahejie Formation were estimated to be 2.03 ± 0.2 Myr and 1.97 ± 0.2 Myr, respectively. The sedimentary accumulation rates (SARs) during different stages were calculated based on the FPTS; the SAR of the deep to semi-deep lacustrine deposits was generally lower than 10 cm/kyr, while that of the shallow lacustrine deposits was higher than 10 cm/kyr. The significant ~1.2-Myr cycles, which were related to the planetary secular frequencies s4-s3, were coincident with the periodic climatic variation in the study area, while the ~0.84-Myr cycles may have been long-period astronomical cycles unique to the Dongying Sag. Furthermore, both of these cycles may have controlled the enrichment of the hydrocarbon source rocks in eastern China.
•A record of astronomically forced climate changes in the lower Paleogene terrestrial succession in the Bohai Bay Basin was conformed.•Construction of the floating point time scale (FPTS) for Es3l to Es4u.•Long-period ~1.2- and ~0.84-Myr cycles were identified in the Bohai Bay Basin of eastern China, East Asia.
Lacustrine shale is an important target for the exploration of unconventional oil and gas in China beyond marine shale gas. However, the formation environment of lacustrine shale differs from that of ...marine shale, resulting in a different reservoir composition, organic matter, oil and gas content, and hydrocarbon mobility. In this study, the Chang 7 shale of the Yanchang Formation in the Ordos Basin was used to analyze the effect of volcanic activity on the paleoproductivity and preservation conditions during the formation of lacustrine shale. The results show that algae and bacteria were developed before the eruption. After the eruption, the number of bacteria declined, but the increased prosperity of algae reflects that the volcanic activity enhanced ancient productivity. The sulfate generated by volcanic activity promotes bacterial sulfate reduction, and the produced H
2
S leads to a strong reducing environment in the waterbody, which is conducive to the preservation of organic matter. Organic geochemical analysis shows that the black shale in the shale strata has a high total organic carbon (TOC) content and strong hydrocarbon generation potential, whereas the tuff has a low TOC content and can scarcely generate hydrocarbons, indicating that the tuff deposited by volcanic activity cannot be considered as effective source rock. In terms of storage space, shale is mainly laminar and dispersed, and it includes organic and inorganic pores. The development of organic pores is affected by thermal maturity, whereas inorganic pores mainly occur between detrital particles and crystals. Tuff is mainly supported by heterogeneous matrix and associated with alteration. Its pores include inter- and intragranular mineral pores. The development of tight sandstone pores is affected by compaction, cementation, and dissolution, which mainly consist of intra- and intergranular pores. The Chang 7 lacustrine shale generally contains oil, but different lithologies have different oil drainage efficiencies. Sandstone and shale exhibit the best and worst oil drainage efficiency, respectively. It is mainly affected by the pore size distribution, fluid properties, and rock wettability. Therefore, the development of shale oil should mainly focus on lacustrine shale formations with interbeds. The mutual dissolution of organic matter and hydrocarbons in the shale section leads to the poor mobility and difficult development of hydrocarbons.
The micropore-throat structure of a tight oil reservoir is complex, and its movable fluid distribution differs from that of a conventional reservoir. By using nuclear magnetic resonance (NMR) and ...centrifugation, the movable fluid distribution in the Chang 7 tight reservoir in the Xin'anbian Block of the Ordos Basin was quantitatively evaluated. Combined with the results of the physical property and high-pressure mercury intrusion experiments, the effects of the porosity, permeability, pore size distribution and micropore-throat structure on the movable fluid distribution in the Chang 7 tight reservoir were analyzed. The NMR results show that the T2 spectral morphology of the Chang 7 tight oil reservoir in the Xin'anbian Block can be characterized by three main patterns with different amplitudes of front and post peaks. The front peak corresponds to the scale of small pores and the post peak corresponds to the scale of large pores. Based on the three T2 spectrum patterns, the Chang 7 tight reservoir can be divided into three types: type 1 reservoir with more small pores and fewer large pores, type 2 reservoir with similar amounts of small and large pores, and type 3 reservoir with fewer small pores and more large pores. Thus, the characteristics of these three types of reservoirs can be determined. The movable fluid parameters were calculated by NMR and centrifugation. The movable fluid saturation of the type 1 reservoir is low, with an average of 20.38%, and the average movable fluid porosity is 1.47%. The type 2 and type 3 reservoirs have higher movable fluid contents of 40.79% and 47.04%, respectively. The average movable fluid porosities of the type 2 and type 3 reservoirs are 3.37% and 3.48%, respectively. The greater number of small pores and smaller number of large pores in the type 1 reservoir result in weak correlations of the movable fluid with the physical properties and pore-throat structure parameters. The movable fluid saturation is negatively correlated with the maximum pore radius, mainstream throat radius and maximum mercury saturation and is strongly positively correlated only with the porosity of the large pores. As the number of large pores increases, the movable fluid saturation strongly correlates with the property parameters, pore size distribution, and pore-throat structure parameters in the type 2 and type 3 reservoirs. The movable fluid saturations are positively affected by the maximum pore radius, median radius, mainstream throat radius, and effective porosity but are strongly negatively correlated only with the radius mean value. These results indicate that the fluid mobility of these two types of reservoirs can be promoted by the pore-throat system to obtain favorable seepage characteristics.
•Bimodal distribution is the main pattern of T2 spectrum and three typical types responding to three types of reservoirs.•The movable fluid parameters of different types of reservoirs exhibit considerable differences and strong heterogeneity.•Controlled by the pore distribution, the micro pore-throat structures of different types of reservoirs show a difference.•The fluid movability of type 2 and type 3 reservoirs is controlled by the pore throat system, enabling favorable seepage.
The Middle Triassic was a key period that witnessed the evolution of Earth system processes and the commencement of a terrestrial lake in the Ordos Basin, Central China. A high-precision ...stratigraphic framework is the key to understanding the nature and pattern of critical geological events. Detailed time series analyses of magnetic susceptibility (MS) data were performed on the deep lacustrine shale-dominated Chang 7 Member of the Yanchang Formation from the Y1011 well core. The results reveal well documented cyclic variations with wavelengths of 5.37 m, 1.39–1.78 m, 0.48 m, and 0.24–0.30 m, which are driven by long-eccentricity, short-eccentricity, obliquity, and precession in the Middle Triassic. The stable 405-kyr tuned floating astrochronological time scale (FATS) reveals that the depositional duration of the Chang 7 Member is approximately 5 Myr, and the sedimentation rates range from 0.90 cm/kyr to 1.69 cm/kyr. In particular, the lower part of the Chang 7 Member is characterized by an organic-rich, black shale, called “Zhangjiatan Shale”, whose depositional duration can be estimated at about 1.7 Myr. Along with the published biostratigraphic divisions and UPb age constraints, our FATS further confirms that the Chang 7 Member mainly developed in the Ladinian Stage, and that the upper part of the Chang 7 spanned the Middle/Late Triassic boundary. The duration of the Chang 7 deposition suggests a temporal and genetic linkage between the responses of the Chang 7 shales in the Ordos Basin and the Indosinian Orogeny in the Qinling orogenic belt. The Ladinian Stage of the Middle Triassic probably witnessed a dramatic shift in the evolution of the regional geodynamic system.
•Magnetic susceptibility series reveal the Milankovitch cycles of the Ladinian Stage.•“eCOCO” is used for tracking mean sedimentation rate and cyclostratigraphic assessment.•Duration of the Chang 7 Member of the Yanchang Formation is estimated at 5 Myr.•Temporal formation of Chang 7 shale was linked to the key geological events during the Indosinian Orogeny.
Kerogen was isolated from the source rock of Well L69, Zhanhua depression, Bohai Bay Basin and an artificial pyrolysis experiment was carried out in a closed gold tube system with a heating rate of ...2 °C/h. Products were collected at eleven temperature points every ten degrees from 350 °C to 450 °C. The soluble organic matter and residual kerogens from the experiment were quantified by weighing. Furthermore, the residual kerogens were analysed by element analysis, X-ray photoelectron spectroscopy (XPS) and solid 13C nuclear magnetic resonance (13C NMR) spectroscopy to determine the chemical structural of kerogen during oil generation. Combining the data from the analyses, information on the elemental compositions as well as on how functional groups were connected in residues was obtained. Seven molecular models of initial and residual kerogens were established to trace the structure changes in kerogen with maturity. The results suggest that as the temperature increases, aliphatic chains and small clusters of aromatic groups break down from kerogens, generating soluble hydrocarbons at temperatures of less than 390 °C (Easy% Ro1.15). At higher thermal maturity, a few short aliphatic carbons remain in the structure of residues. The number of aromatic groups increases and their size grows with increasing maturity, with condensation occurring at aromatic groups at high temperature, while these residues have little potential for oil generation.
•Pyrolysis, Element analysis and 13C NMR were performed on kerogen.•Seven kerogen molecular structures with maturity were established.•The calculation method of aromatic cluster size was improved.•The variation in kerogen structures was revealed.
A model predictive control approach is proposed for path following of underactuated surface ships with input saturation, parameters uncertainties, and environmental disturbances. An Euler iterative ...algorithm is used to reduce the calculation amount of model predictive control. The matter of input saturation is addressed naturally and flexibly by taking advantage of model predictive control. The mathematical model group (MMG) model as the internal model improves the control accuracy. A radial basis function neural network is also applied to compensate the total unknowns including parameters uncertainties and environmental disturbances. The numerical simulation results show that the designed controller can force an underactuated ship to follow the desired path accurately in the case of input saturation and time-varying environmental disturbances including wind, current, and wave.
Polymer matrix nanomaterials have revolutionized materials science due to their unique properties resulting from the incorporation of nanoscale fillers into polymer matrices ...
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