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Petroleum Science 2024年第3期21卷 1524-1538页

作者： Bin Bai Jing-Yue Hao Ling Fu Yu-Xi Liu Jian-Peng Wang Lan Wang Kevin G.Taylor Lin Ma PetroChina Research Institute of Petroleum Exploration and Development Department of Earth and Environmental Sciences University of Manchester College of Earth Sciences Jilin University Department of Chemical Engineering University of Manchester

The mineralogical development and diagenetic sequence of lacustrine shales in the Chang 7 Member of the yanchang formation in the Ordos Basin are detailed studied. A model of their depositional system and a diagenetic diagram are proposed in this study. Through detailed petrographic, mineralogical, and elemental analyses, four distinct shale types are identified: argillaceous shale, siliceous shale, calcareous shale, and carbonate, clay, and silt-bearing shale. The main diagenetic process in argillaceous shale is the transformation of illite to smectite, negatively impacting shale porosity. Siliceous shale undergoes carbonate cementation and quartz dissolution, contributing to increased porosity, particularly in mesopores.Calcareous shale experiences diagenesis characterised by carbonate formation and dissolution, with a prevalence of siderite. In carbonate, clay, and silt-bearing shale, the dissolution of K-feldspar contributes to illitization of kaolinite. Argillaceous shale, characterised by more clay minerals and lower mesopore volume, is identified as a potential hydrocarbon seal. Siliceous shale, with the highest pore volume and abundant inter-mineral pores, emerges as a promising shale oil reservoir. These findings contribute to a comprehensive understanding of shale properties, aiding in the prediction of shale oil exploration potential in the studied area.

关键词： Ordos Basin yanchang formation Chang 7 Member Diagenesis Microfacies

Geological characteristics and exploration of shale oil in Chang 7 Member of Triassic yanchang formation, Ordos Basin, NW China

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Petroleum Exploration and Development 2020年第5期47卷 931-945页

作者： FU Jinhua LI Shixiang NIU Xiaobing DENG Xiuqin ZHOU Xinping National Engineering Laboratory for Exploration and Development of Low-Permeability Oil&Gas Fields Xi’an 710018China PetroChina Changqing Oilfield Company Xi’an 710018China Exploration and Development Research Institute of PetroChina Changqing Oilfield Company Xi’an 710018China No.8 Oil Production Plant PetroChina Changqing Oilfield CompanyXi’an 710000China China University of Petroleum(East China) Qingdao 266580China

A set of shale-dominated source rocks series were deposited during the heyday of lake basin development in the Member 7 of Triassic yanchang formation,Ordos Basin,and the thickness is about 110 m.Aimed at whether this layer can form large-scale oil enrichment of industrial value,comprehensive geological research and exploration practice have been carried out for years and obtained the following important geologic findings.Firstly,widely distributed black shale and dark mudstone with an average organic matter abundance of 13.81%and 3.74%,respectively,lay solid material foundation for the formation of shale oil.Secondly,sandy rocks sandwiched in thick organic-rich shale formations constitute an oil-rich"sweet spot",the average thickness of thin sandstone is 3.5 m.Thirdly,fine-grained sandstone and siltstone reservoirs have mainly small pores of 2–8μm and throats of 20–150 nm in radius,but with a large number of micro-pores and nano-throats,through fracturing,the reservoirs can provide good conductivity for the fluid in it.Fourthly,continued high-intensity hydrocarbon generation led to a pressure difference between the source rock and thin-layer reservoir of up to 8–16 MPa during geological history,driven by the high pressure,the oil charged into the reservoirs in large area,with oil saturation reaching more than 70%.Under the guidance of the above theory,in 2019,the Qingcheng Oilfield with geologic oil reserves of billion ton order was proved in the classⅠmulti-stage superimposed sandstone shale reservoir of Chang 7 Member by the Changqing Oilfield Branch through implementation of overall exploration and horizontal well volume fracturing.Two risk exploration horizontal wells were deployed for the classⅡthick layer mud shale interbedded with thin layers of silt-and fine-sandstones reservoir in the Chang 73 submember,and they were tested high yield oil flows of more than 100 tons per day,marking major breakthroughs in petroleum exploration in classⅠshale reservoirs.The new discoveries have expanded the domain of unco

关键词： Triassic yanchang formation Chang 7 Member shale oil main controlling factors of enrichment Qingcheng Oilfield Ordos Basin

Impact of chlorites on the wettability of tight oil sandstone reservoirs in the Upper Triassic yanchang formation,Ordos Basin,China

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Science China Earth Sciences 2021年第6期64卷 951-961页

作者： Zhongnan WANG Xiaorong LUO Keyu LIU Yuchen FAN Xiangzeng WANG Key Laboratory of Deep Oil and Gas China University of Petroleum(East China)Qingdao266580China School of Geosciences China University of Petroleum(East China)Qingdao266580China Key Laboratory of Petroleum Resources Research Institute of Geology and GeophysicsChinese Academy of SciencesBeijing100029China Laboratory for Marine Mineral Resources Qingdao National Laboratory for Marine Science and TechnologyQingdao266071China Shanxi yanchang Petroleum(Group)Co. Ltd.Xi’an710075China

Wettability is an essential property of reservoirs that is of great importance for enhancing oil recovery(EOR)and oil migration.The wettability of reservoirs is generally believed to be strongly affected by mineral compositions but it is not always the case.An integrated study of petrography and wettability was carried out to determine the impact of chlorite minerals on the wettability of the sandstone reservoirs in the Upper Triassic yanchang formation.Chlorites are found to be commonly present in the reservoir sandstones as detrital grains,rim-shaped cements,and biotite-chloritized forms with the pore peripheries being largely coated by chlorite,which is the main mineral in direct contact with pores.At pore scale,the wetting state of chlorites can either be oil-wet or water-wet in the tight sandstone reservoirs depending on wettability alteration by oil charge.Chlorites in contact with pores occupy a large of proportions of oil-wet pore walls and are crucial for the formation of oil-wetting state of reservoir sandstones.At core scale,the contents of chlorites in direct contact with pores do not correlate well with the AmottHarvey index due to other factors such as heterogeneity,oil-bearing degrees of samples.

关键词： Wettability Chlorite Pore scale Core scale yanchang formation Ordos Basin

Nanoscale pore morphology and distribution of lacustrine shale reservoirs:Examples from the Upper Triassic yanchang formation,Ordos Basin

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Journal of Energy Chemistry 2015年第4期24卷 512-519页

作者： Yang Wang Yanming Zhu Hongyan Wang Guangjun Feng Key Laboratory of Coalbed Methane Resources and Reservoir formation Process Ministry of Education School of Resources and Earth Science China University of Mining and Technology Langfang Branch Petro China Exploration and Development Research Institute

Pore structure plays an important role in the gas storage and flow capacity of shale gas reservoirs. Fieldemission environmental scanning electron microscopy（FE-SEM） in combination with low-pressure carbon dioxide gas adsorption（CO2GA）,nitrogen gas adsorption（N2GA）,and high-pressure mercury intrusion（HPMI） were used to study the nanostructure pore morphology and pore-size distributions（PSDs） of lacustrine shale from the Upper Triassic yanchang formation,Ordos Basin. Results show that the pores in the shale reservoirs are generally nanoscale and can be classified into four types： organic,interparticle,intraparticle,and microfracture. The interparticle pores between clay particles and organic-matter pores develop most often,l with pore sizes that vary from several to more than 100 nm. Mercury porosimetry analysis shows total porosities ranging between 1.93 and 7.68%,with a mean value of 5.27%. The BET surface areas as determined by N2 adsorption in the nine samples range from 10 to 20 m2/g and the CO2 equivalent surface areas（2 nm）vary from 18 to 71 m2/g. Together,the HPMI,N2 GA,and CO2 GA curves indicate that the pore volumes are mainly due to pores 100 nm in size. In contrast,however,most of the specific surface areas are provided by the micropores. The total organic carbon（TOC） and clay minerals are the primary controls of the structures of nanoscale pores（especially micropores and mesopores）. Micropores are predominantly determined by the content of the TOC,and mesopores are possibly related to the content of clay minerals,particularly the illite-montmorillonite mixed-layer content.

关键词： Pore morphology Pore-size distributions Lacustrine shale yanchang formation Ordos Basin

Palynology of yanchang formation of Middle and Late Triassic in Eastern Gansu Province and Its Paleoclimatic Significance

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Journal of China University of Geosciences 2006年第3期17卷 209-220页

作者：吉利明孟凡巍 Lanzhou Institute of Geology Chinese Academy of Sciences Graduate School China University of Geosciences Wuhan 430074 China Nanjing Institute of Geology and Palaeontology Chinese Academy of Sciences

Xifeng （西峰） oilfield was recently found in the southwest of the Ordos basin. The oil source rocks are the Chang 7 Section of yanchang （延长） formation. In order to study the paleoclimate that controlled the formation of source rocks, a systemically palynological research on related beds in yanchang formation has been carried out. The core samples were analyzed with classical palynological techniques and the organic-walled sporomorphs from these samples were observed, identified and photographed under a light microscopy and a fluorescence microscopy. Abundant sporopollen were found in drilling cores from Chang 8 and Chang 7 sections, and two assemblages were distinguished： the Aratisporites-Punctatisporites assemblage and the Asseretospora-Walchiites assemblage. Their characteristics are similar to those of the assemblage of Tongchuan （铜川） formation and the assemblage of yanchang formation in southeast Ordos basin, respectively. Their geological times are Ladinian of late Middle Triassic and Carnian of early Late Triassic, respectively. The correlation of palynoflora with their parent plants suggests the paleoclimate of eastern Gansu （甘肃） Province in the Middle and Late Triassic was warm and rainy with prosperous vegetation. The palynoflora indicated the area was in a temperate to subtropical zone then. Both the ecological types and differentiation degree curves of sporopollen indicated the period during Chang 8 and Chang 7 sections was warm and wet, and the phase accorded with large-scale lake transgression in Chang 8 Section and the largest lake area in Chang 7 Section. North China in Middle and Late Triassic was located in a warm and rainy, temperate and subtropi- cal zone. The palynofloras in Chang 8 and Chang 7 sections have the characteristics of North China flora, however they also indicate wetter and warmer climate due to their proximity to the large lakes. The period of Chang 8 to Chang 7 sections is the climax of the expansion of the lake, and the bloom of fresh algae during the period, which helped form

关键词： Ordos basin eastern Gansu Province yanchang formation source rock sporopollen assemblage paleoclimate.

Features of Sandy Debris Flows of the yanchang formation in the Ordos Basin and Its Oil and Gas Exploration Significance

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Acta Geologica Sinica(English Edition) 2011年第5期85卷 1187-1202页

作者： LI Xiangbo CHEN Qilin LIU Huaqing WAN Yanrong WEI Lihua LIAO Jianbo LONG Liwen Northwest Branch Research Institute of Petroleum Exploration and DevelopmentChina National Petroleum CorporationLanzhou 730020China

Sandy debris flow is a new genetic type of sand bodies,which has gained much attention in recent years and its corresponding theory is proved to be a significant improvement and even partial denial to the 'Bouma Sequence' and 'turbidite fan' deep-water sedimentary theories to some point. Oil exploration researchers are highly concerned with sandy debris flows for its key role in controlling oil and gas accumulation processes.In this article,by applying sandy debris flows theory and combining a lot work of core,outcrop observation and analysis plus seismic profile interpretation,we recognized three types of sedimentary gravity flows that are sandy debris flows,classic turbidites and slumping rocks in chang-6 member of yanchang formation in the deep-water area of central Ordos Basin.Among the three types,the sandy debris flows are the most prominent and possesses the best oil bearing conditions.On the contrary,the classic turbidites formed by turbidity currents are limited in distribution;therefore,previous yanchang formation deep-water sedimentary studies have exaggerated the importance of turbidite currents deposition.Further study showed that the area distribution of deep water gravity flow sand bodies in yanchang formation were controlled by the slope of the deep-water deposits and the flows had vast distribution,huge depth and prevalent advantages for oil forming,which make it one of the most favorable new areas for Ordos Basin prospecting.

关键词： sandy debris flows sedimentary characteristics oil and gas prospecting values yanchang formation Ordos Basin

Genesis of the high gamma sandstone of the yanchang formation in the Ordos Basin,China:A reply

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Petroleum Science 2013年第1期10卷 55-57页

作者： Zhang Xiaoli Feng Qiao Feng Qianghan Liu Jingjing Liu Guangwei Yan Yuanzi State Key Laboratory of Continental Dynamics/Department of Geology Northwest University College of Geological Science&Engineering Shandong University of Science and Technology State Key Laboratory for Exploration and Development of Low-permeability Oil and Gas Fields Oil&Gas Technology Research InstituteChangqing Oilfield Company

The authors of ＇Genesis of the high gamma sandstone of the yanchang formation in the Ordos Basin, China＇ questioned the viewpoint that high-gamma-ray sandstone might be caused by homochronous sedimentary volcano tuff ash or previous tuff. The authors argued that the main reason for the high-gamma-ray sandstone should be from high Th and U contents in zircon. In reply, we discuss the problems with the authors from the category of high-gamma-ray sandstones, rock characteristics, and possible sources of radioactivity. The results still indicate that the high gamma ray characteristics might be caused by homochronous sedimentary volcano tuff ash or reworked previous turfs.

关键词： High-gamma-ray sandstone provenance event deposit yanchang formation Ordos Basin

Predicting the present-day in situ stress distribution within the yanchang formation Chang 7 shale oil reservoir of Ordos Basin, central China

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Petroleum Science 2020年第4期17卷 912-924页

作者： Wei Ju Xiao-Bing Niu Sheng-Bin Feng Yuan You Ke Xu Geof Wang Hao-Ran Xu Key Laboratory of Coalbed Methane Resources and Reservoir formation Process Ministry of EducationChina University of Mining and TechnologyXuzhou 221008JiangsuChina Shandong Provincial Key Laboratory of Depositional Mineralization and Sedimentary Mineral Shandong University of Science and TechnologyQingdao 266590ShandongChina School of Resources and Geosciences China University of Mining and TechnologyXuzhou 221116JiangsuChina Institute of Exploration and Development PetroChina Changqing Oilfeld CompanyXi’an 710018ShaanxiChina PetroChina Tarim Oilfeld Company Korla 841000XinjiangChina School of Chemical Engineering The University of QueenslandBrisbaneQueensland 4072Australia

The yanchang formation Chang 7 oil-bearing layer of the Ordos Basin is important in China for producing shale oil.The present-day in situ stress state is of practical implications for the exploration and development of shale oil;however,few studies are focused on stress distributions within the Chang 7 reservoir.In this study,the present-day in situ stress distribution within the Chang 7 reservoir was predicted using the combined spring model based on well logs and measured stress data.The results indicate that stress magnitudes increase with burial depth within the Chang 7 reservoir.Overall,the horizontal maximum principal stress(SHmax),horizontal minimum principal stress(Shmin) and vertical stress(Sv) follow the relationship of Sv≥SHmax>Shmin,indicating a dominant normal faulting stress regime within the Chang 7 reservoir of Ordos Basin.Laterally,high stress values are mainly distributed in the northwestern parts of the studied region,while low stress values are found in the southeastern parts.Factors influencing stress distributions are also analyzed.Stress magnitudes within the Chang 7 reservoir show a positive linear relationship with burial depth.A larger value of Young's modulus results in higher stress magnitudes,and the differential horizontal stress becomes higher when the rock Young's modulus grows larger.

关键词： Present-day in situ stress Chang 7 shale oil reservoir Influencing factor Ordos Basin Stress distribution prediction yanchang formation

Origin and depositional model of deep-water lacustrine sandstone deposits in the 7th and 6th members of the yanchang formation(Late Triassic),Binchang area,Ordos Basin,China

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Petroleum Science 2017年第1期14卷 24-36页

作者： Xi-Xiang Liu Xiao-Qi Ding Shao-Nan Zhang Hao He State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation Southwest Petroleum UniversityChengdu 610500SichuanChina School of Geoscience and Technology Southwest Petroleum UniversityChengdu 610500SichuanChina College of Energy Chengdu University of TechnologyChengdu 610059SichuanChina Second Production Plant Petro China Changqing Oilfield CompanyQinyang 745000GansuChina

Sandstones attributed to different lacustrine sediment gravity flows are present in the 7th and 6th members of the yanchang formation in the Ordos Basin, China. These differences in their origins led to different sandstone distributions which control the scale and connectivity of oil and gas reservoirs. Numerous cores and outcrops were analysed to understand the origins of these sandstones. The main origin of these sandstones was analysed by statistical methods, and well logging data were used to study their vertical and horizontal distributions. Results show that the sandstones in the study area accu- mulated via sandy debris flows, turbidity currents and slumping, and sandy debris flows predominate. The sand- stone associated with a single event is characteristically small in scale and exhibits poor lateral continuity. How- ever, as a result of multiple events that stacked gravity flow-related sandstones atop one another, sandstones are extensive overall, as illustrated in the cross section and isopach maps. Finally, a depositional model was developed in which sandy debris flows predominated and various other types of small-scale gravity flows occurred frequently, resulting in extensive deposition of sand bodies across a large area.

关键词： Sediment gravity flows - Sandy debris flows -Binchang area yanchang formation Ordos Basin

Insights into the Tectonic Fractures in the yanchang formation Interbedded Sandstone-Mudstone of the Ordos Basin Based on Core Data and Geomechanical Models

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Acta Geologica Sinica(English Edition) 2015年第6期89卷 1986-1997页

作者： JU Wei SUN Weifeng HOU Guiting Key Laboratory of Coalbed Methane Resources and Reservoir formation Process Ministry of Education School of Resources and Geoscience China University of Mining and Technology School of Earth and Space Science Peking University The State Key Laboratory of Continental Tectonics and Dynamics Institute of Geology Chinese Academy of Geological Sciences PetroChina Research Institute of Petroleum Exploration and Development

The distribution and intensity of tectonic fractures within geologic units are important to hydrocarbon exploration and development. Taken the Upper Triassic yanchang formation interbedded sandstone-mudstone in the Ordos Basin as an example, this study used the finite element method（FEM） based on geomechanical models to study the development of tectonic fractures. The results show that the sandstones tend to generate tectonic fractures more easily than mudstones with the same layer thickness, and the highest degree of tectonic fractures will be developed when the sandstone-mudstone thickness ratio is about 5.0. A possible explanation is proposed for the tectonic fracture development based on two important factors of rock brittleness and mechanical layer thickness. Generally, larger rock brittleness and thinner layer thickness will generate more tectonic fractures. In interbedded sandstone-mudstone formations, the rock brittleness increases with the increasing mechanical layer thickness, hence, these two factors will achieve a balance for the development of tectonic fractures when the sandstone-mudstone thickness ratio reaches a specific value, and the development degree of tectonic fractures is the highest at this value.

关键词： tectonic fractures interbedded sandstone-mudstone formations sandstone-mudstonethickness ratio yanchang formation rock rupture value Ordos Basin