To clarify the formation and distribution of feldspar dissolution pores and predict the distribution of high-quality reservoir in gravity flow sandstone of the 7^(th) member of Triassic Yanchang Formation(Chang 7 Memb...To clarify the formation and distribution of feldspar dissolution pores and predict the distribution of high-quality reservoir in gravity flow sandstone of the 7^(th) member of Triassic Yanchang Formation(Chang 7 Member)in the Ordos Basin,thin sections,scanning electron microscopy,energy spectrum analysis,X-ray diffraction whole rock analysis,and dissolution experiments are employed in this study to investigate the characteristics and control factors of feldspar dissolution pores.The results show that:(1)Three types of diagenetic processes are observed in the feldspar of Chang 7 sandstone in the study area:secondary overgrowth of feldspar,replacement by clay and calcite,and dissolution of detrital feldspar.(2)The feldspar dissolution of Chang 7 tight sandstone is caused by organic acid,and is further affected by the type of feldspar,the degree of early feldspar alteration,and the buffering effect of mica debris on organic acid.(3)Feldspars have varying degrees of dissolution.Potassium feldspar is more susceptible to dissolution than plagioclase.Among potassium feldspar,orthoclase is more soluble than microcline,and unaltered feldspar is more soluble than early kaolinized or sericitized feldspar.(4)The dissolution experiment demonstrated that the presence of mica can hinder the dissolution of feldspar.Mica of the same mass has a significantly stronger capacity to consume organic acids than feldspar.(5)Dissolution pores in feldspar of Chang 7 Member are more abundant in areas with low mica content,and they improve the reservoir physical properties,while in areas with high mica content,the number of feldspar dissolution pores decreases significantly.展开更多
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 ...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.展开更多
1 Introduction Shale formations bear abundant mineral resource and*unconventional petroleum resource,and the unconventional petroleum resource that contain in the shale formation should be integrated and researched.
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...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 unconventional petroleum exploration.展开更多
Based on analysis of main controlling factors of Chang 9, the source rock, driving force of migration, migration and accumulation modes, reservoir forming stages and model and enrichment law of Chang 9 reservoir were ...Based on analysis of main controlling factors of Chang 9, the source rock, driving force of migration, migration and accumulation modes, reservoir forming stages and model and enrichment law of Chang 9 reservoir were examined. The study showed that the oil of Chang 9 reservoir in the Jiyuan and Longdong(Eastern Gansu) areas came primarily from the source rock of Chang 7 Member, but the oil of Chang 9 reservoir in the Zhidan area came primarily from the source rock of Chang 9 Member. There developed lithologic-structural oil reservoirs in Gufengzhuang-Mahuangshan area in northwest Jiyuan, structural-lithologic oil reservoirs in east Jiyuan, and lithologic reservoirs in Huachi–Qingcheng area and Zhidan area. The overpressure of Chang 7 Member was the driving force of oil migration. The burial history showed that Chang 9 Member experienced two stages of reservoir forming, the reservoir formed in the Late Jurassic was smaller in charging scope and scale, and the Early Cretaceous was the period when the source rock generated oil and gas massively and the Chang 9 reservoir came into being. Along with the tectonic movements, Chang 7 bottom structure turned from high in the west and lower in the East in the sedimentary stage to high in the east and lower in the west in the hydrocarbon accumulation stage and at last to gentle western-leaning monoclinal structure at present. In Early Cretaceous, the Chang 7 bottom structure was the lowest in the west of Huanxian-Huachi-Wuqi-Dingbian areas, so the oil migrated laterally towards the higher positions around after entering the reservoir. In the main reservoir forming period, Chang 7 bottom had an ancient anticline in Mahuangshan-Hongjingzi area of west Jiyuan, controlling the oil reservoir distribution in west Jiyuan.展开更多
In the Triassic Yanchang Formation, Jiyuan-Wuqi area, Ordos Basin, the Chang 6 reservoir is contacted to the Chang 7 high-quality source rock, but the oil pools are unevenly distributed, and complex in oil and water d...In the Triassic Yanchang Formation, Jiyuan-Wuqi area, Ordos Basin, the Chang 6 reservoir is contacted to the Chang 7 high-quality source rock, but the oil pools are unevenly distributed, and complex in oil and water distribution. Through cores observation and fracture statistics, combined with comprehensive analyses of physical property, mercury injection, logging and geochemical data, and comparisons of the sandbodies scales, reservoir physical properties, argillaceous laminae and fractures between source and reservoir in the eastern and western oil-bearing areas and in the central water producing area, it is found that the hydrocarbon accumulation patterns are different in the eastern, central and western areas, and the characteristics of hydrocarbon migration under the background of double-provenance were sorted out. The study results show that the crude oil in the eastern area has different Pr/Ph and sterane distribution from that in the western area. The oil and gas primarily migrated vertically. The high-quality source rocks and favorable source-reservoir-cap combinations lay the foundation for large-scale oil and gas accumulations. Vertically, the oil and gas enrichment is controlled by the scale of sandbody and the difference of physical properties, while on the plane, it is controlled by the connectivity of sandbodies, the argillaceous laminae between source rock and reservoir, the reservoir physical property and the fractures. The sandbodies of oil-rich zones in the eastern and western areas have large thickness, low shale content, good physical properties, weak heterogeneity, few argillaceous laminae and abundant fractures, all of which are favorable for the vertical migration and accumulation of oil and gas. In contrast, in the middle area with converging provenances, the reservoirs, composed of thin sandbodies, features rapid variation in lithology and physical properties, strong heterogeneity, poor continuity of sandbodies, abundant argillaceous laminae between source rock and reservoir, and few fractures, makes it difficult for the oil and gas to migrate vertically, and results in low oil enrichment degree ultimately. For the exploration of continental multiple-provenance tight reservoirs, not only the good-property source rocks and reservoirs, but more importantly the source-reservoir contact relationship and the effect of fractures on the hydrocarbon migration and accumulation should be considered.展开更多
基金Supported by the National Natural Science Foundation of China(42202176)CNPC-Southwest University of Petroleum Innovation Consortium Cooperation Project(2020CX050103).
文摘To clarify the formation and distribution of feldspar dissolution pores and predict the distribution of high-quality reservoir in gravity flow sandstone of the 7^(th) member of Triassic Yanchang Formation(Chang 7 Member)in the Ordos Basin,thin sections,scanning electron microscopy,energy spectrum analysis,X-ray diffraction whole rock analysis,and dissolution experiments are employed in this study to investigate the characteristics and control factors of feldspar dissolution pores.The results show that:(1)Three types of diagenetic processes are observed in the feldspar of Chang 7 sandstone in the study area:secondary overgrowth of feldspar,replacement by clay and calcite,and dissolution of detrital feldspar.(2)The feldspar dissolution of Chang 7 tight sandstone is caused by organic acid,and is further affected by the type of feldspar,the degree of early feldspar alteration,and the buffering effect of mica debris on organic acid.(3)Feldspars have varying degrees of dissolution.Potassium feldspar is more susceptible to dissolution than plagioclase.Among potassium feldspar,orthoclase is more soluble than microcline,and unaltered feldspar is more soluble than early kaolinized or sericitized feldspar.(4)The dissolution experiment demonstrated that the presence of mica can hinder the dissolution of feldspar.Mica of the same mass has a significantly stronger capacity to consume organic acids than feldspar.(5)Dissolution pores in feldspar of Chang 7 Member are more abundant in areas with low mica content,and they improve the reservoir physical properties,while in areas with high mica content,the number of feldspar dissolution pores decreases significantly.
基金founded by National Natural Science Foundation of China(grant Nos.:42072186 and 42090025)National Science and Technology Major Project,China(grant No.:2016ZX05046001)+3 种基金Science and Technology Research Project of Petro China Company Limited,China(grant No.:2021DJ1806)the fund support from China Scholarship Council(No.201806440002)the International Postdoctoral Exchange Fellowship Program,China(Talent-Introduction Program,No.270152)Lin Ma wishes to acknowledge the fund support from Natural Environment Research Council,United Kingdom(NE/R013527/1)。
文摘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.
基金supported by funding the National Basic Research Program of China (973 Program) and the grant number is 2014CB239000
文摘1 Introduction Shale formations bear abundant mineral resource and*unconventional petroleum resource,and the unconventional petroleum resource that contain in the shale formation should be integrated and researched.
基金Supported by the China National Science and Technology Major Project(2016ZX05050)the National Key Basic Research and Development Program(973 Program),China(2014CB239003)
文摘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 unconventional petroleum exploration.
基金Supported by China National Science and Technology Major Project(2016ZX05050,2017ZX05001002-008)the PetroChina Science and Technology Major Project(2016E-0501)
文摘Based on analysis of main controlling factors of Chang 9, the source rock, driving force of migration, migration and accumulation modes, reservoir forming stages and model and enrichment law of Chang 9 reservoir were examined. The study showed that the oil of Chang 9 reservoir in the Jiyuan and Longdong(Eastern Gansu) areas came primarily from the source rock of Chang 7 Member, but the oil of Chang 9 reservoir in the Zhidan area came primarily from the source rock of Chang 9 Member. There developed lithologic-structural oil reservoirs in Gufengzhuang-Mahuangshan area in northwest Jiyuan, structural-lithologic oil reservoirs in east Jiyuan, and lithologic reservoirs in Huachi–Qingcheng area and Zhidan area. The overpressure of Chang 7 Member was the driving force of oil migration. The burial history showed that Chang 9 Member experienced two stages of reservoir forming, the reservoir formed in the Late Jurassic was smaller in charging scope and scale, and the Early Cretaceous was the period when the source rock generated oil and gas massively and the Chang 9 reservoir came into being. Along with the tectonic movements, Chang 7 bottom structure turned from high in the west and lower in the East in the sedimentary stage to high in the east and lower in the west in the hydrocarbon accumulation stage and at last to gentle western-leaning monoclinal structure at present. In Early Cretaceous, the Chang 7 bottom structure was the lowest in the west of Huanxian-Huachi-Wuqi-Dingbian areas, so the oil migrated laterally towards the higher positions around after entering the reservoir. In the main reservoir forming period, Chang 7 bottom had an ancient anticline in Mahuangshan-Hongjingzi area of west Jiyuan, controlling the oil reservoir distribution in west Jiyuan.
基金Supported by the National Natural Science Foundation of China(41872165,41572137)
文摘In the Triassic Yanchang Formation, Jiyuan-Wuqi area, Ordos Basin, the Chang 6 reservoir is contacted to the Chang 7 high-quality source rock, but the oil pools are unevenly distributed, and complex in oil and water distribution. Through cores observation and fracture statistics, combined with comprehensive analyses of physical property, mercury injection, logging and geochemical data, and comparisons of the sandbodies scales, reservoir physical properties, argillaceous laminae and fractures between source and reservoir in the eastern and western oil-bearing areas and in the central water producing area, it is found that the hydrocarbon accumulation patterns are different in the eastern, central and western areas, and the characteristics of hydrocarbon migration under the background of double-provenance were sorted out. The study results show that the crude oil in the eastern area has different Pr/Ph and sterane distribution from that in the western area. The oil and gas primarily migrated vertically. The high-quality source rocks and favorable source-reservoir-cap combinations lay the foundation for large-scale oil and gas accumulations. Vertically, the oil and gas enrichment is controlled by the scale of sandbody and the difference of physical properties, while on the plane, it is controlled by the connectivity of sandbodies, the argillaceous laminae between source rock and reservoir, the reservoir physical property and the fractures. The sandbodies of oil-rich zones in the eastern and western areas have large thickness, low shale content, good physical properties, weak heterogeneity, few argillaceous laminae and abundant fractures, all of which are favorable for the vertical migration and accumulation of oil and gas. In contrast, in the middle area with converging provenances, the reservoirs, composed of thin sandbodies, features rapid variation in lithology and physical properties, strong heterogeneity, poor continuity of sandbodies, abundant argillaceous laminae between source rock and reservoir, and few fractures, makes it difficult for the oil and gas to migrate vertically, and results in low oil enrichment degree ultimately. For the exploration of continental multiple-provenance tight reservoirs, not only the good-property source rocks and reservoirs, but more importantly the source-reservoir contact relationship and the effect of fractures on the hydrocarbon migration and accumulation should be considered.
