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Selective core-shell doping enabling high performance 4.6 V-LiCoO2

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Journal of Energy Chemistry 2024年第8期95卷 684-693页

作者： Yueming Xia Jianrui Feng Jinhui Li Yan Li Zhengfeng Zhang Xiaoqi Wang Jianli Shao Manling Sui Pengfei Yan Beijing Key Laboratory of Microstructure and Property of Solids College of Materials Science & Engineering Beijing University of Technology Petro China research institute of petroleum exploration & development State Key Laboratory of Explosion Science and Technology Beijing Institute of Technology

Constructing robust surface and bulk structure is the prerequisite for realizing high performance high voltage LiCoO2（LCO）.Herein,we manage to synthesize a surface Mg-doping and bulk Al-doping coreshell structured LCO,which demonstrates excellent cycling performance.Half-cell shows 94.2% capacity retention after 100 cycles at 3.0-4.6 V（vs.Li/Li+） cycling,and no capacity decay after 300 cycles for fullcell test（3.0-4.55 V）.Based on comprehensive microanalysis and theoretical calculations,the degradation mechanisms and doping effects are systematically revealed.For the undoped LCO,high voltage cycling induces severe interfacial and bulk degradations,where cracks,stripe defects,fatigue H2 phase,and spinel phase are identified in grain bulk.For the doped LCO,Mg-doped surface shell can suppress the interfacial degradations,which not only stabilizes the surface structure by forming a thin rock-salt layer but also significantly improves the electronic conductivity,thus enabling superior rate performance.Bulk Al-doping can suppress the lattice "breathing" effect and the detrimental H3 to H1-3 phase transition,which minimizes the internal strain and defects growth,maintaining the layered structure after prolonged cycling.Combining theoretical calculations,this work deepens our understanding of the doping effects of Mg and Al,which is valuable in guiding the future material design of high voltage LCO.

关键词： Doping effect Electron microscopy Failure mechanism High-voltage LiCoO2 Lithium-ion battery

Controls of strike-slip fault on fractures:Insight from 3D discrete element simulation

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Science China Earth Sciences 2024年第1期67卷 146-164页

作者： Lianbo ZENG Zhe MAO Guoping LIU He TIAN Yingtao YAO Kewei ZU Shaoqun DONG Mehdi OSTADHASSAN State Key Laboratory of petroleum Resources and Prospecting China University of Petroleum(Beijing)Beijing 102249China College of Geosciences China University of Petroleum(Beijing)Beijing 102249China institute of Energy Peking UniversityBeijing 100871China exploration and development research institute Zhongyuan Oilfield Branch CompanySINOPECZhengzhou 457001China Northeast petroleum University Daqing 163318China

The fracture-cave reservoirs controlled by strike-slip faults are the main targets for oil and gas exploration of ultradeep carbonate in the Tarim Basin.It is of great significance to clarify the distribution rules of fractures related to strike-slip faults for guiding the exploration and development of ultra-deep oil and gas.In this study,six groups of strike-slip fault 3D models based on discrete element numerical simulation method have been created to investigate characteristics of fault-related fracture development and distribution law.In addition,we compared the modeling results to the measurement of fractures from the outcrop of a strike-slip fault in the Northern Tarim Basin to verify their validity.The results show that the stress environment is stable in the simple strike-slip section,and fractures intersecting with the strike-slip direction at a small angle are the principal fracture.In the releasing stepover and double-bend sections,the maximum principal stress changes from horizontal to vertical during the formation of pull-apart zones,where the principal fractures intersect the strike-slip direction at a large angle.The maximum principal stress in the restraining stepover and double-bend section remains horizontal,but their strikes change significantly with the increment of fault displacement.Thus,fractures intersecting the strike-slip direction at a small angle will become principal fractures early on,while those parallel to or anti-intersecting the strike-slip direction at a small angle will become principal fractures later.There are obvious differences in the development of fractures in different structural positions of strike-slip faults.Fractures are mainly concentrated in the fault tips,connections,and fault plane,and the magnitude of the fault damage zone is relatively larger in the first two.Compared with fault displacement,the principal damage zone(PDZ)shows stronger control on the distribution and development intensity of fractures.With the increment of fault displacement,the width of the f

关键词： Strike-slip fault Fault-related fracture Stepover Double-bend Discrete element method

development characteristics and controlling factors of fractures in lacustrine shale and their geological significance for evaluating shale oil sweet spots in the third member of the Shahejie Formation in the Qikou Sag, Bohai Bay Basin

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petroleum Science 2024年第2期21卷 791-805页

作者： Xu Zeng Tao Yang Jian-Wei Feng Cong-Sheng Bian Ming Guan Wei Liu Bing-Cheng Guo Jin Dong research institute of petroleum exploration and development China National Petroleum CorporationBeijing100083China College of Geosciences China University of Petroleum(Beijing)Beijing102249China Key Laboratory of petroleum Resources and Prospecting China University of Petroleum(Beijing)Beijing102249China School of Earth Sciences China University of PetroleumQingdao266400ShandongChina

Natural fractures are critical for shale oil and gas enrichment and development. Due to the extremely high heterogeneity of shale, the factors controlling the formation of internal fractures, especially horizontal fractures, remain controversial. In this study, we integrate thin section analysis and microcomputed tomography(CT) data from several lacustrine shale samples from the third member(Es3) of the Shahejie Formation, Qikou Sag, Bohai Bay Basin, to assess the fractures in detail. The goal is to reveal the development characteristics, controlling factors, and geological significance for evaluating sweet spots in a shale oil play. The fractures in the Es3contain high-angle structural and horizontal bed-parallel fractures that are mostly shear and extensional. Various factors influence fracture development,including lithofacies, mineral composition, organic matter content, and the number of laminae. Structural fractures occur predominantly in siltstone, whereas bed-parallel fractures are abundant in laminated shale and layered mudstone. A higher quartz content results in higher shale brittleness, causing fractures, whereas the transformation between clay minerals contributes to the development of bedparallel fractures. Excess pore pressure due to hydrocarbon generation and expulsion during thermal advance can cause the formation of bed-parallel fractures. The density of the bed-parallel and structural fractures increases with the lamina density, and the bed-parallel fractures are more sensitive to the number of laminae. The fractures are critical storage spaces and flow conduits and are indicative of sweet spots. The laminated shale in the Es3with a high organic matter content contains natural fractures and is an organic-rich, liquid-rich, self-sourced shale play. Conversely, the siltstone, massive mudstone, and argillaceous carbonate lithofacies contain lower amounts of organic matter and do not have bed-parallel fractures. However, good reservoirs can form in these areas when structural fractures are present

关键词： Fractures development characteristics Controlling factors Shale oil Sweet spot

research on Quantitative Identification of Three-Dimensional Connectivity of Fractured-Vuggy Reservoirs

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Energy Engineering 2024年第5期121卷 1195-1207页

作者： Xingliang Deng Peng Cao Yintao Zhang Yuhui Zhou Xiao Luo Liang Wang exploration and development research institute PetroChina Tarim Oilfield CompanyKorla841000China PetroChina Hangzhou research institute of Geology Hangzhou310023China School of petroleum Engineering Yangtze UniversityWuhan430100China

The fractured-vuggy carbonate oil resources in the western basin of China are extremely rich.The connectivity of carbonate reservoirs is complex,and there is still a lack of clear understanding of the development and topological structure of the pore space in fractured-vuggy reservoirs.Thus,effective prediction of fractured-vuggy reservoirs is difficult.In view of this,this work employs adaptive point cloud technology to reproduce the shape and capture the characteristics of a fractured-vuggy reservoir.To identify the complex connectivity among pores,fractures,and vugs,a simplified one-dimensional connectivity model is established by using the meshless connection element method(CEM).Considering that different types of connection units have different flow characteristics,a sequential coupling calculation method that can efficiently calculate reservoir pressure and saturation is developed.By automatic history matching,the dynamic production data is fitted in real-time,and the characteristic parameters of the connection unit are inverted.Simulation results show that the three-dimensional connectivity model of the fractured-vuggy reservoir built in this work is as close as 90%of the fine grid model,while the dynamic simulation efficiency is much higher with good accuracy.

关键词： Fractured-vuggy reservoir three-dimensional connectivity connection unit dynamic prediction automatic history matching

Geochemical identification of a source rock affected by migrated hydrocarbons and its geological significance:Fengcheng Formation,southern Mahu Sag,Junggar Basin,NW China

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petroleum Science 2024年第1期21卷 100-114页

作者： Wen-Long Dang Gang Gao Xin-Cai You Ke-Ting Fan Jun Wu De-Wen Lei Wen-Jun He Yong Tang State Key Laboratory of petroleum Resource and Prospecting China University of Petroleum(Beijing)Beijing102249China School of GeoSciences China University of Petroleum(Beijing)Beijing102249China exploration&development institute Xinjiang Oil Field CompanyKaramay834000XinjiangChina

The Fengcheng Formation is a crucial source rock and the primary reservoir for oil accumulation in the Mahu Sag.Crude oils are distributed throughout the Fengcheng Formation,ranging from the edge to the interior of the sag in the southern Mahu Sag.These crude oils originate from in-situ source rocks in shallowly buried areas and the inner deep sag.During migration,the crude oil from the inner deep sag affects the source rocks close to carrier beds,leading to changes in the organic geochemical characteristics of the source rocks.These changes might alter source rock evaluations and oil-source correlation.Based on data such as total organic carbon(TOC),Rock-Eval pyrolysis of source rocks,and gas chromatography-mass spectrometry(GC-MS)of the saturated fraction,and considering the geological characteristics of the study area,we define the identification characteristics of source rock affected by migrated hydrocarbons and establish the various patterns of influence that migrated hydrocarbons have on the source rock of the Fengcheng Formation in the southern Mahu Sag.The source rocks of the Fengcheng Formation are mostly fair to good,containing mainly Type II organic matter and being thermally mature enough to generate oil.Source rocks affected by migrated hydrocarbons exhibit relatively high hydrocarbon contents(S1/TOC>110 mg HC/g TOC,Extract/TOC>30%,HC:hydrocarbon),relatively low Rock-Eval Tmax values,and relatively high tricyclic terpane contents with a descending and mountain-shaped distribution.Furthermore,biomarker composition parameters indicate a higher thermal maturity than in-situ source rocks.Through a comparison of the extract biomarker fingerprints of adjacent reservoirs and mudstones in different boreholes,three types of influence patterns of migrated hydrocarbons are identified:the edge-influence of thin sandstone-thick mudstone,the mixed-influence of sandstone-mudstone interbedded,and the full-influence of thick sandstone-thin mudstone.This finding reminds us that the influence of migrated hydrocarbons

关键词： Organic geochemistry Source rock Influence of migrated hydrocarbons Fengcheng Formation Southern Mahu Sag

CO_(2)flooding in shale oil reservoir with radial borehole fracturing for CO_(2)storage and enhanced oil recovery

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petroleum Science 2024年第1期21卷 519-534页

作者： Jia-Cheng Dai Tian-Yu Wang Jin-Tao Weng Kang-Jian Tian Li-Ying Zhu Gen-Sheng Li State Key Laboratory of petroleum Resources and Prospecting China University of PetroleumBeijing102249China China National Oil and Gas exploration and development Company Limited Beijing100034China

This study introduces a novel method integrating CO_(2)flooding with radial borehole fracturing for enhanced oil recovery and CO_(2)underground storage,a solution to the limited vertical stimulation reservoir volume in horizontal well fracturing.A numerical model is established to investigate the production rate,reservoir pressure field,and CO_(2)saturation distribution corresponding to changing time of CO_(2)flooding with radial borehole fracturing.A sensitivity analysis on the influence of CO_(2)injection location,layer spacing,pressure difference,borehole number,and hydraulic fractures on oil production and CO_(2)storage is conducted.The CO_(2)flooding process is divided into four stages.Reductions in layer spacing will significantly improve oil production rate and gas storage capacity.However,serious gas channeling can occur when the spacing is lower than 20 m.Increasing the pressure difference between the producer and injector,the borehole number,the hydraulic fracture height,and the fracture width can also increase the oil production rate and gas storage rate.Sensitivity analysis shows that layer spacing and fracture height greatly influence gas storage and oil production.research outcomes are expected to provide a theoretical basis for the efficient development of shale oil reservoirs in the vertical direction.

关键词： Shale oil Radial borehole fracturing Embedded discrete fracture model Enhanced oil recovery Carbon storage

Identification of reservoir types in deep carbonates based on mixedkernel machine learning using geophysical logging data

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petroleum Science 2024年第3期21卷 1632-1648页

作者： Jin-Xiong Shi Xiang-Yuan Zhao Lian-Bo Zeng Yun-Zhao Zhang Zheng-Ping Zhu Shao-Qun Dong Key Laboratory of exploration Technologies for Oil and Gas Resources of the Ministry of Education Yangtze University School of Geosciences Yangtze University College of Geosciences China University of Petroleum (Beijing) petroleum exploration and Production research institute of SINOPEC School of Earth Sciences and Engineering Xi'an Shiyou University

Identification of reservoir types in deep carbonates has always been a great challenge due to complex logging responses caused by the heterogeneous scale and distribution of storage spaces. Traditional cross-plot analysis and empirical formula methods for identifying reservoir types using geophysical logging data have high uncertainty and low efficiency, which cannot accurately reflect the nonlinear relationship between reservoir types and logging data. Recently, the kernel Fisher discriminant analysis(KFD), a kernel-based machine learning technique, attracts attention in many fields because of its strong nonlinear processing ability. However, the overall performance of KFD model may be limited as a single kernel function cannot simultaneously extrapolate and interpolate well, especially for highly complex data cases. To address this issue, in this study, a mixed kernel Fisher discriminant analysis(MKFD) model was established and applied to identify reservoir types of the deep Sinian carbonates in central Sichuan Basin, China. The MKFD model was trained and tested with 453 datasets from 7 coring wells, utilizing GR,CAL, DEN, AC, CNL and RT logs as input variables. The particle swarm optimization(PSO) was adopted for hyper-parameter optimization of MKFD model. To evaluate the model performance, prediction results of MKFD were compared with those of basic-kernel based KFD, RF and SVM models. Subsequently, the built MKFD model was applied in a blind well test, and a variable importance analysis was conducted. The comparison and blind test results demonstrated that MKFD outperformed traditional KFD, RF and SVM in the identification of reservoir types, which provided higher accuracy and stronger generalization. The MKFD can therefore be a reliable method for identifying reservoir types of deep carbonates.

关键词： Reservoir type identification Geophysical logging data Kernel Fisher discriminant analysis Mixed kernel function Deep carbonates

Microscopic experiment on efficient construction of underground gas storages converted from water-invaded gas reservoirs

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petroleum exploration and development 2024年第1期51卷 203-212页

作者： JIANG Tongwen QI Huan WANG Zhengmao LI Yiqiang WANG Jinfang LIU Zheyu CAO Jinxin PetroChina Company Limited Beijing 100007China National Key Laboratory of petroleum Resources and Engineering China University of Petroleum(Beijing)Beijing 102249China College of petroleum Engineering China University of Petroleum(Beijing)Beijing 102249China PetroChina petroleum&New Energies Company Beijing 100007China PetroChina research institute of petroleum exploration&development Beijing 100083China

Based on the microfluidic technology,a microscopic visualization model was used to simulate the gas injection process in the initial construction stage and the bottom water invasion/gas injection process in the cyclical injection-production stage of the underground gas storage(UGS)rebuilt from water-invaded gas reservoirs.Through analysis of the gas-liquid contact stabilization mechanism,flow and occurrence,the optimal control method for lifecycle efficient operation of UGS was explored.The results show that in the initial construction stage of UGS,the action of gravity should be fully utilized by regulating the gas injection rate,so as to ensure the macroscopically stable migration of the gas-liquid contact,and greatly improve the gas sweeping capacity,providing a large pore space for gas storage in the subsequent cyclical injection-production stage.In the cyclical injection-production stage of UGS,a constant gas storage and production rate leads to a low pore space utilization.Gradually increasing the gas storage and production rate,that is,transitioning from small volume to large volume,can continuously break the hydraulic equilibrium of the remaining fluid in the porous media,which then expands the pore space and flow channels.This is conducive to the expansion of UGS capacity and efficiency for purpose of peak shaving and supply guarantee.

关键词： water-invaded gas-reservoir underground gas storage cyclical injection-production gas-water contact gas storage and production rate UGS capacity expansion control method

Supramolecular polymer-based gel fracturing fluid with a double network applied in ultra-deep hydraulic fracturing

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petroleum Science 2024年第3期21卷 1875-1888页

作者： Yong-Ping Huang Yong Hu Chang-Long Liu Yi-Ning Wu Chen-Wei Zou Li-Yuan Zhang Ming-Wei Zhao Cai-Li Dai School of petroleum Engineering China University of Petroleum(East China) Shandong Key Laboratory of Oilfield Chemistry China University of Petroleum(East China) SINOPEC petroleum exploration and Production research institute CNOOC China Co Ltd Tianjin Branch

A gel based on polyacrylamide, exhibiting delayed crosslinking characteristics, emerges as the preferred solution for mitigating degradation under conditions of high temperature and extended shear in ultralong wellbores. High viscosity/viscoelasticity of the fracturing fluid was required to maintain excellent proppant suspension properties before gelling. Taking into account both the cost and the potential damage to reservoirs, polymers with lower concentrations and molecular weights are generally preferred. In this work, the supramolecular action was integrated into the polymer, resulting in significant increases in the viscosity and viscoelasticity of the synthesized supramolecular polymer system.The double network gel, which is formed by the combination of the supramolecular polymer system and a small quantity of Zr-crosslinker, effectively resists temperature while minimizing permeability damage to the reservoir. The results indicate that the supramolecular polymer system with a molecular weight of(268—380) × 10～4g/mol can achieve the same viscosity and viscoelasticity at 0.4 wt% due to the supramolecular interaction between polymers, compared to the 0.6 wt% traditional polymer(hydrolyzed polyacrylamide, molecular weight of 1078 × 10～4g/mol). The supramolecular polymer system possessed excellent proppant suspension properties with a 0.55 cm/min sedimentation rate at 0.4 wt%, whereas the0.6 wt% traditional polymer had a rate of 0.57 cm/min. In comparison to the traditional gel with a Zrcrosslinker concentration of 0.6 wt% and an elastic modulus of 7.77 Pa, the double network gel with a higher elastic modulus(9.00 Pa) could be formed only at 0.1 wt% Zr-crosslinker, which greatly reduced the amount of residue of the fluid after gel-breaking. The viscosity of the double network gel was66 m Pa s after 2 h shearing, whereas the traditional gel only reached 27 m Pa s.

关键词： Ultra-deep reservoir Gel fracturing fluid Double network Supramolecular polymer system Proppant suspension property