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Formation Mechanism and Numerical Model of Quartz in Fine-Grained Organic-Rich Shales: A Case Study of Wufeng and Longmaxi Formations in Western Hubei Province, South China

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Journal of Earth Science 2020年第2期31卷 354-367页

作者： Bao Zhang Detian Yan Hassan Jasmine Drawarh Xiangrong Yang Jin He Liwei Zhang Key Laboratory of Tectonics and Petroleum Resources of Ministry of Education China University of GeosciencesWuhan 430074China

The difference in quartz types in shales not only affects the porosity and permeability of the rocks,but also reflects the difference in the sedimentary environments.We established the formation mechanism and numerical model of quartz in shales of Wufeng and Longmaxi formations in the Wangjiawan Section,South China,based on thin-section studies using SEM(scanning electron microscope),SEM-CL(cathodoluminescence),XRD(X-ray diffraction)and geochemical analyses.There are two types of quartz in the shales:detrital quartz and authigenic quartz.Detrital quartz is mostly silt-size,typically ranging from 10 to 60μm in size and subangular to angular monocrystal in shape,and brighter than authigenic quartz by CL intensity;authigenic quartz is present in two phases in shape:grain overgrowths and crystallite grains.Overgrowth surfaces are subhedral.Crystallite grains are typically less than 10μm in size,euhedral or subhedral monocrystal in shape.Authigenic quartz can be subdivided into biogenic quartz and clay mineral transformed quartz according to the source of silicon.In the numerical model,the content of detrital quartz is relatively consistent(20%);the content of biogenic quartz ranges from 40%to 70%,with a sharp fall(0–30%)in the Guanyinqiao mudstone.During the Katian,a lower anoxic and dense water column make the dissolution of biogenic silica well preserved.Biogenic quartz is the major contributor to the sediment.During the early Hirnantian interval,due to the drop of sea level and the oxygenation of seafloor,the sediment is mainly composed of clay transformed quartz and detrital quartz.During the latest Hirnatian and Rhuddanian,rapid sea level rise and anoxic ocean enhance the preservation of the biogenic silica,thereby biogenic quartz re-emerges as the major contributors to the sediment.Authigenic crystallite grains and grain overgrowths have filled in primary pore space and have decreased the interparticle porosity,however,as a rigid framework,they can suppress compaction and maintain the internal pore structure.Th

关键词： brittle mineral quartz Wufeng and Longmaxi formations formation mechanism numerical simulation

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Pyrite Concretions in the Lower Cambrian Niutitang Formation,South China:Response to Hydrothermal Activity

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Journal of Earth Science 2023年第4期34卷 1053-1067页

作者： Zixuan Liu Detian Yan Xing Niu key laboratory of tectonics and petroleum resources Ministry of EducationChina University of GeosciencesWuhan 430074China School of Geosciences Yangtze UniversityWuhan 434023China

The Early Cambrian Niutitang Formation is characterized by wide distribution of black shales on Yangtze Block,South China.Here we have reported the pyrite concretions in the bottom of the Niutitang Formation deposited in the slope-basin environment of Yangtze Block.The pyrite concretion was mainly composed of pyrite associated with hydrothermal minerals(barite,hyalophane,tetrahedrite),followed by quartz and organic matter.Trace elements Mo and U displayed significant enrichment(enrichment factors > 10),indicating the euxinic bottom water condition.Cu,Ni,and excess Ba concentrations were relatively high,denoting high primary productivity.In-situ sulfur isotope compositions of pyrite concretions δ34Spy) showed little variations(13.2‰–19.4‰) and small fractionations compared to coeval seawater δ34Sso4.Petrological and geochemical analyses indicated the pyrite concretions were formed in the sediment-water interface during the early diagenesis,with H2S diffusing from the euxinic water,and influenced by hydrothermal activity leading to the coexistence of barite,hyalophane,and tetrahedrite.These results imply euxinic bottom water featured by high primary productivity and increasing riverine flux of sulfate from chemical weathering during the Early Cambrian.

关键词： shale pyrites black shale pyrite concretion depositional environment.

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Markers and Genetic Mechanisms of Primary and Epigenetic Oxidation of an Aeolian Depositional System of the Luohandong Formation,Ordos Basin

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Journal of Earth Science 2022年第2期33卷 358-372页

作者： Yao Xiang Yangquan Jiao Liqun Wu Hui Rong Fan Zhang Key Laboratory of Tectonics and Petroleum Resources of Ministry of Education China University of GeosciencesWuhan 430074China Faculty of Earth resources China University of GeosciencesWuhan 430074China

Uranium exploration breakthrough was extremely rare in an aeolian depositional system.In order to know the complicate characteristics of oxidation associated closely with uranium mineralization in the aeolian depositional system,petrology and mineralogy markers of the oxidation and its genetic mechanisms are identified and illustrated by fieldwork,thin section analysis and scanning electron microscopy test,based on 2 field outcrops in Zhenyuan County in the southwest of the Tianhuan depression in the Ordos Basin and the core of 2 wells in the north and south of Ordos Basin.The results showed:the typical macroscopic indicator of primary oxidation was the red fine sediments in the aeolian interdune with a thickness of 10-50 cm,and the microscopic characteristics of primary oxidation were the minerals such as hematite,ilmenite,and the irony matrix rich in fine-grained dolomite and biotite;the phreatic oxidation was manifested as the red sandstone with limonite horizontal layer with a thickness of 1-4 cm and a width of 60 cm-1 m,and the circular limonite nodules with a diameter of 3-7 cm,in which there was intergranular limonite cement;the interlayer oxidation was characterized by lenticular tongue and tapered red sandstone with a length of 1-10 m and a width of 10 cm-5m,in which detrital particles are coated with hematite and hematite was distributed inside the rhombus dolomite.The paleoclimate of the sedimentary period,the water-table movement and the pore and permeability conditions of the sand body were the key factors for the formation of different oxidation types in the aeolian depositional system.

关键词： Ordos Basin aeolian depositional system primary oxidation epigenetic oxidation sandstone-type uranium exploration ore deoposit geology

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Relations of Uranium Enrichment and Metal Sulfides within the Shuanglong Uranium Deposit,Southern Ordos Basin

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Journal of Earth Science 2022年第2期33卷 395-408页

作者： Yuhan Sun Yangquan Jiao LiqunWu Hui Rong key laboratory of tectonics and petroleum resources China University of GeosciencesMinistry of EducationWuhan 430074China School of Earth resources China University of GeosciencesWuhan 430074China

Large quantities of metal sulfides are widely distributed in uranium ores from the Middle Jurassic Zhiluo Formation of the Shuanglong uranium deposit,southern Ordos Basin,providing a convenient condition to study the relationship between metal sulfides and uranium minerals.The morphology and composition of uranium minerals and metal sulfides are illustrated to study uranium mineralization and mechanisms of metallogenesis.Uranium minerals can be broadly categorized as pitchblende,coffinite and brannerite.Metal sulfides associated with uranium minerals are pyrite,sphalerite,chalcopyrite and galena.Some assemblages of various metal sulfides and uranium minerals indicate that they are coeval,but the order of formation is different.Based on mineralogical observations,paragenetic sequences for mineral assemblages are discussed.Alteration of Fe-Ti oxides forms Ti oxides,brannerite and pyrite.The formation of chalcopyrite was later than that of pyrite.Clausthalite(Pb Se)replaces sphalerite or shows isomorphism with galena.There are three genetic types of galena,of which typeⅠis related to tectonic thermal events and can interact with uranyl ions to form uranium oxides and Pb;.When sulfur activity is relatively high,Pb;can form new anhedral galena,that is,typeⅡ.TypeⅢof galena is related to the decay of uranium minerals.The genetic order of the main minerals was determined as follows:Fe-Ti oxides>Ti oxides/sphalerite/pyrite>clausthalite/galenaⅠ/chalcopyrite>galenaⅡ/uranium minerals>galenaⅢduring the diagenetic stage.Hydrogen sulfide(H;S)is a decisive factor in the interaction between metal sulfides and uranium.Metal ions can react with H;S,accompanied by precipitation and enrichment of uranium minerals.

关键词： uranium mineralization metal sulfides hydrogen sulfide paragenetic sequences Shuanglong uranium deposit ore deposit geology

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Quantitative Estimation on Methane Storage Capacity of Organic-Rich Shales from the Lower Silurian Longmaxi Formation in the Eastern Sichuan Basin, China

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Journal of Earth Science 2023年第6期34卷 1851-1860页

作者： Xiaowen Guo Tao Luo Tian Dong Rui Yang Yuanjia Han Jizheng Yi Sheng He Zhiguo Shu Hanyong Bao key laboratory of tectonics and petroleum resources Ministry of EducationChina University of GeosciencesWuhan 430074China Jianghan Oilfield Branch Company SINOPECWuhan 430223China

The assessment of gas storage capacity is crucial to furthering shale gas exploration and development in the eastern Sichuan Basin,China.Eleven organic-rich shale samples were selected to carry out the high pressure methane sorption,low-pressure N_(2)/CO_(2) gas adsorption,and bulk and skeletal density measurements to investigate the methane storage capacity(MSC).Based on the relative content of clay,carbonates,quartz+feldspar,we grouped the 11 samples into three lithofacies:silica-rich argillaceous shale(CM-1),argillaceous/siliceous mixed shale(M-2),and clay-rich siliceous shale(S-3).The total porosity of the shale samples varies from 3.4% to 5.6%,and gas saturation ranges from 47% to 89%.The measured total gas amount ranges from 1.84 mg/g to 4.22 mg/g with the ratio of free gas to total gas amount ranging from 52.7% to 70.8%.Free gas with high content in the eastern Sichuan Basin may be the key factor controlling amount of shale gas production.The TOC content critically controls the MSC of shales,because micropore,mesopore volumes and the specific surface areas associated with organic matter provide the storage sites for the free and adsorbed gas.The methane sorption capacities of samples from different lithofacies are also affected by clay minerals and moisture content.Clay minerals can provide additional surface areas for methane sorption,and water can cause a 7.1%-42.8% loss of methane sorption capacity.The total porosity,gas-bearing porosity,water saturation,free gas and adsorbed gas number of samples from different lithofacies show subtle differences if the shale samples had similar TOC contents.Our results suggest that,in the eastern Sichuan Basin,clay-rich shale lithofacies is also prospecting targets for shale gas production.

关键词： methane shale gas Longmaxi Formation Sichuan Basin

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Bedding-parallel fractures in ultradeep tight sandstone reservoirs in Jurassic and Cretaceous of Yongjin Oil Field,Junggar Basin,China

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Frontiers of Earth Science 2022年第4期16卷 975-988页

作者： Hongping LIU Changmin ZHANG Li ZHANG Yang LUO School of Geosciences Yangtze UniversityWuhan 430100China key laboratory of tectonics and petroleum resources(ministry of education) China University of GeosciencesWuhan 430074China

Bedding-parallel fractures are fractures that are parallel to rock bedding structure planes and have been widely accepted as a key factor for oil and gas production in tight sandstone and shale reservoirs.However,the formation mechanisms of these parallel-bedding fractures are still under debate.In this study,bedding-parallel fractures in Yongjin Oil Field were analyzed using methods including core and microscopic observations,element geochemistry,and carbon and oxygen isotope analysis.Their origin and relations to reservoir quality,faults,and rock mechanical properties were examined.The discovery of bedding-parallel fractures in both the Upper Jurassic and Lower Cretaceous formations indicates that the BPFs are generated later than the early Cretaceous.The filling state of bedding-parallel fractures that with no bitumen and carbonate cement indicate that they formed after oil charging and carbonate cementation.The tensile fracture characteristics in core and thin section observa-tions,and the fact that overburden stress exceeds the pore pressure indicate that the bedding-parallel fractures were neither generated from tectonic compression nor over-pressure.The most likely generation mechanism is stress relief during core drilling under high in situ stress conditions.High in situ stress and low tensile strength lead to thinner fracture spacing.The existence of high bedding-parallel fracture density is an indicator of good reservoir quality and result in high oil/gas production.

关键词： Bedding-parallel fractures ultradeep reservoirs tight sandstone fracture origin Junggar Basin

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A fractal approach to low velocity non-Darcy flow in a low permeability porous medium

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Chinese Physics B 2014年第4期23卷 385-389页

作者：蔡建超 Institute of Geophysics and Geomatics Key Laboratory of Tectonics and Petroleum Resources of Ministry of Education China University of Geosciences

In this paper, the mechanism for fluid flow at low velocity in a porous medium is analyzed based on plastic flow of oil in a reservoir and the fractal approach. The analytical expressions for flow rate and velocity of non-Newtonian fluid flow in the low permeability porous medium are derived, and the threshold pressure gradient （TPG） is also obtained. It is notable that the TPG （J） and permeability （K） of the porous medium analytically exhibit the scaling behavior J ~ K-D＇r/（l＋Or）, where DT is the fractal dimension for tortuous capillaries. The fractal characteristics of tortuosity for capillaries should be considered in analysis of non-Darcy flow in a low permeability porous medium. The model predictions of TPG show good agreement with those obtained by the available expression and experimental data. The proposed model may be conducible to a better understanding of the mechanism for nonlinear flow in the low permeability porous medium.

关键词： fractal porous media non-Darcy flow threshold pressure gradient scaling law

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Uranium Metallogeny in Fault-Depression Transition Region:A Case Study of the Tamusu Uranium Deposit in the Bayingobi Basin

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Journal of Earth Science 2022年第2期33卷 409-421页

作者： Liqun Wu Yangquan Jiao Yunbiao Peng Hui Rong key laboratory of tectonics and petroleum resources Ministry of EducationChina University of GeosciencesWuhan 430074China Geologic Party No.208 BOGCNNCBaotou 014040China

Compared to the sandstone-type uranium deposits in the Ordos Basin and the Songliao Basin,the Tamusu uranium deposit in the Bayingobi Basin formed in fault-depression transition region displays distinctive features.First,the uranium-bearing sandstones and their interlayer oxidation zone extend longitudinally no more than ten kilometers.Second,gravity flow sediments are more common in the uranium-bearing strata.Comprehensive facies analysis indicates that the Upper Member(orebearing horizon)of the Bayingobi Formation was largely deposited in fan deltas that prograded into lakes during period of relatively dry paleoclimate.Spatial distribution patterns of five facies associations along with two depositional environments(fan delta,lake)were reconstructed in this study.The results demonstrated that the depositional systems and their inner genetic facies played different roles in uranium reservoir sandstone,confining beds(isolated barrier beds)and reduction geologic bodies during uranium mineralization process.

关键词： sandstone-type uranium deposit fan delta lake fault-depression transition Tamusu uranium deposit Bayingobi Basin ore deposit geology

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Control of differential tectonic evolution on petroleum occurrence in Bohai Bay Basin

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Science China Earth Sciences 2014年第4期57卷 1117-1128页

作者： TENG ChangYu ZOU HuaYao HAO Fang State key laboratory of petroleum Resource and Prospecting China University of Petroleum key laboratory of tectonics and petroleum resources Ministry of Education China University of Geosciences

The Bohai Bay Basin(BBB)is the most petroliferous Cenozoic basin in the east of China.It consists of seven depressions.Each depression has been subjected to different stress states and then has experienced varying faulting processes since the Neogene,especially during the Neotectonism(from the Pliocene to the present).On the basis of the investigation of fault patterns,fault densities and fault activity rates(FARs)for each depression,this paper demonstrates the discrepancy of faulting development and evolution across the BBB.The dynamic mechanism for the differences in faulting is also discussed by the analysis of the regional stress state.The Bozhong Depression is just situated in the transtensional zone induced by the two active strike-slip faults,namely Yingkou-Weifang and Beijing-Penglai.In this depression,the major faults which cut through the Paleogene or the Cenozoic have had higher than 10 m/Ma FARs since the Neogene,and the highest FARs have reached or exceeded 25 m/Ma during the Neotectonism.As a result,most of the petroleum has migrated along these major faults and accumulated within the Neogene.In contrast,in the other depressions of the BBB away from the Bozhong Depression,the FARs of the major faults were decreased to lower than 10 m/Ma since the Neogene,and tended to be zero during the Neotectonism.Therefore,the major faults could not serve as vertical conduits for petroleum migration,and the petroleum was entrapped in the Paleogene.Consequently,the faulting since the Neogene,especially during the Neotectonism,controlled the petroleum richness in vertical strata.

关键词：渤海湾盆地构造演化石油控制新构造运动断层活动新生代盆地故障模式

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Numerical Approach for Thermal History Modelling in Multi-Episodic Rifting Basins

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Journal of Earth Science 2014年第3期25卷 519-528页

作者： Bo Kang Xinong Xie Tao Cui Key Laboratory of Tectonics and Petroleum Resources of Ministry of Education China University of Geosciences CSIRO Land and Water

Pre-existing models for thermal history modelling have shown deficiency in explicit algorithms to establish the quantitative relationship between maturity indices and thermal gradients in some sedimentary basins that experienced multi-episodic rifting evolution. In this study, a forward and inverse combination model（FICM） is proposed to estimate the vitrinite reflectance（Ro） and thermal gradients. The forward module is used to calculate Ro values. It couples the EASY%Ro model with burial history reconstruction with consideration of thermal gradient variations during basin evolution. The inverse module reconstructs histoical thermal gradients by calibrating cmputed Ro against measured Ro data. The time-temperature series is a necessary input for both forward and inverse modules. Sample density is a profound factor influencing the accuracy of modelling results. In order to obtain satisfying outputs, a sufficient sample density is required. Thermal gradients are assumed to vary linearly between two given samples. Modelling results of case studies indicate that the sensitivity of heating time to Ro evlution is differnt with thermal gradients depending on geolgoical setting. Three difffernt districts, which include the time-sensitive area, the temperature-sensitive area and the non-sensitive area, can be recognized on the the relationship map among Ro variations, heating time and geothermal gradients. This model can be applied to reconstruct the thermal history and maturation evolution in a basin that has undergone complex multi-episodic rifting.

关键词： thermal history maturity EASY%Ro burial history vitrinite reflectance.

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