The geological characteristics and enrichment laws of the shale oil in the third submember of the seventh member of Triassic Yanchang Formation(Chang 7_(3)) in the Ordos Basin were analyzed by using the information of...The geological characteristics and enrichment laws of the shale oil in the third submember of the seventh member of Triassic Yanchang Formation(Chang 7_(3)) in the Ordos Basin were analyzed by using the information of core observations, experiments and logging, and then the exploration potential and orientation of the Chang 7_(3) shale oil were discussed. The research findings are obtained in three aspects. First, two types of shale oil, i.e. migratory-retained and retained, are recognized in Chang 7_(3). The former is slightly better than the latter in quality. The migratory-retained shale oil reservoir is featured with the frequent interbedding and overlapping of silty-sandy laminae caused by sandy debris flow and low-density turbidity current and semi-deep-deep lacustrine organic-rich shale laminae. The retained shale oil reservoir is composed of black shale with frequent occurrence of bedding and micro-laminae. Second, high-quality source rocks provide a large quantity of hydrocarbon-rich high-quality fluids with high potential energy. The source-reservoir pressure difference provides power for oil accumulation in thin interbeds of organic-poor sandstones with good seepage conditions and in felsic lamina, tuffaceous lamina and bedding fractures in shales. Hydrocarbon generation-induced fractures, bedding fractures and microfractures provide high-speed pathways for oil micro-migration. Frequent sandstone interlayers and felsic laminae provide a good space for large-scale hydrocarbon accumulation, and also effectively improve the hydrocarbon movability. Third, sand-rich areas around the depression are the main targets for exploring migratory-retained shale oil. Mature deep depression areas are the main targets for exploring retained oil with medium to high maturity. Theoretical research and field application of in-situ conversion in low-mature deep depression areas are the main technical orientations for exploring retained shale oil with low to medium maturity.展开更多
To explore the method of improving development effect and solving the problem of water breakthrough and water out for ultralow permeability fractured reservoirs, an indoor evaluation method of dynamic imbibition for f...To explore the method of improving development effect and solving the problem of water breakthrough and water out for ultralow permeability fractured reservoirs, an indoor evaluation method of dynamic imbibition for fracture-matrix system was established taking the Chang 8 reservoir in southern Yanchang Oilfield as a research target. Key factors for the imbibition effect were obtained, an imbibition's rate expression was obtained, a model considering the double effects of imbibition-displacement was built and optimal injection and production parameters for the research area were obtained as well. The results show that an optimum displacement rate that maximizes the oil displacement efficiency exists in the water displacing oil process, and the optimal displacing rate becomes smaller as the permeability decreases. The imbibition displacement efficiency increases as the reservoir quality index and water wettability index of rock become bigger. But the larger the initial water saturation or oil-water viscosity ratio is, the smaller the imbibition displacement efficiency is. The optimal injection-production ratio for the Chang 8 reservoir of southern Yanchang Oilfield is 0.95, and the predicted recovery is 17.2% when the water cut is 95%, it is 2.9% higher than the recovery of conventional injection-production ratio 1.2. By using the moderate water injection technique based on the double effects of imbibition-displacement mechanism, the water injection development effect for the ultra-low permeability fractured reservoirs can be improved significantly.展开更多
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 S...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.展开更多
The Upper Triassic oil accumulations in the Ordos Basin is the most successful tight oil play in China,with average porosity values of less than 10% and permeability values below 1.0 mD.This study investigated the geo...The Upper Triassic oil accumulations in the Ordos Basin is the most successful tight oil play in China,with average porosity values of less than 10% and permeability values below 1.0 mD.This study investigated the geological characteristics and origin of the tight oil accumulations in the Chang 6 member of the Upper Triassic Yanchang Formation in the Shanbei area based on over 50,000 petrological,source-rock analysis,well logging and production data.The tight oil accumulation of the Chang 6 member is distributed continuously in the basin slope and the centre of the basin.The oilwater relationships are complex.Laumontite dissolution pores are the most important storage spaces,constituting 30%-60% of total porosity and showing a strong positive relationship with oil production.The pore-throat diameter is less than 1 μm,and the calculated critical height of the oil column is much larger than the tight sand thickness,suggesting that the buoyancy was probably of limited importance for oil migration.The pressure difference between the source rocks and sandstone reservoirs is inferred to have provided driving force for hydrocarbon migration.Two factors of source-reservoir configuration and laumontite dissolution contributed to the formation of the Chang 6 tight oil accumulations.Intense hydrocarbon generation and continuous sand bodies close to the hydrocarbon kitchen are the foundation for the large-scale oil distribution.Dissolution of feldspar-laumontite during the process of organic matter evolution generated abundant secondary pores and improved the reservoir quality.展开更多
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 o...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.展开更多
The Chang 73 sub-member of Triassic Yanchang Formation in the Ordos Basin was taken as an example and the lamina types and combinations,reservoir space features and shale oil enrichment patterns in organic-rich shale ...The Chang 73 sub-member of Triassic Yanchang Formation in the Ordos Basin was taken as an example and the lamina types and combinations,reservoir space features and shale oil enrichment patterns in organic-rich shale strata were investigated using core observation,thin section analysis,XRF element measurement,XRD analysis,SEM,high solution laser Raman spectroscopy analysis,and micro-FTIR spectroscopy analysis,etc.According to the mineral composition and thickness of the laminae,the Chang 73 organic-rich shales have four major types of laminae,tuff-rich lamina,organic-rich lamina,silt-grade feldspar-quartz lamina and clay lamina.They have two kinds of shale oil-bearing layers,"organic-rich lamina+silt-grade feldspar-quartz lamina"and"organic-rich lamina+tuff-rich lamina"layers.In the"organic-rich+silt-grade feldspar-quartz"laminae combination shale strata,oil was characterized by relative high maturation,and always filled in K-feldspar dissolution pores in the silt-grade feldspar-quartz laminae,forming oil generation,migration and accumulation process between laminae inside the organic shales.In the"organic-rich+tuff-rich lamina"binary laminae combination shale strata,however,the reservoir properties were poor in organic-rich shales,the oil maturation was relatively lower,and mainly accumulated in the intergranular pores of interbedded thin-layered sandstones.The oil generation,migration and accumulation mainly occurred between organic-rich shales and interbedded thin-layered sandstones.展开更多
In the south of the Ordos Basin, the oil source of the Upper Triassic Yanchang Formation is confused all the time, which affects further exploration. In this study, oil sources from the oil layers of Ch6, Ch8 and Ch9 ...In the south of the Ordos Basin, the oil source of the Upper Triassic Yanchang Formation is confused all the time, which affects further exploration. In this study, oil sources from the oil layers of Ch6, Ch8 and Ch9 are all analyzed and confirmed. Through their carbon isotope value and biomarkers, characteristics of crude oils from the Yanchang Formation are analyzed. Then, the oil–source relation is discussed, with the source rocks' features.Finally, the oil–source relation is calculated through cluster analysis. It is believed that the oils from the Yanchang Formation deposit in a similar redox environment, with weak oxidation–weak reduction, and have all entered maturity stage. Ch9 crude oil is more mature than crude oils from Ch6 and Ch8, and has more advanced plants and fewer algae. Gas chromatography(GC) and gas chromatography–mass spectrometry(GC–MS) analysis show that crude oils from Ch6 and Ch8 may come from Ch7, and Ch9 crude oil may not. Cluster analysis displays that crude oils from Ch6 and Ch8 have closer squared Euclidean distance with Ch7 source rocks than Ch9 crude oil does,indicating crude oils from Ch6 and Ch8 stem from Ch7 source rocks. And Ch9 crude oil has rather close squared Euclidean distance with Ch9 source rocks, illustrating Ch9 crude oil may be from Ch9 source rocks. This research may provide the theoretical basis for the next exploration deploy in the south of Ordos Basin.展开更多
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
综合利用地球化学、扫描电镜、岩心薄片、测井等资料以及油井生产数据等,对鄂尔多斯盆地陕北地区三叠系延长组7段储层特征、烃源岩特征和致密油分布特征进行了分析,从烃源岩展布、输导体系和源-储组合关系3个方面对致密油差异富集控制...综合利用地球化学、扫描电镜、岩心薄片、测井等资料以及油井生产数据等,对鄂尔多斯盆地陕北地区三叠系延长组7段储层特征、烃源岩特征和致密油分布特征进行了分析,从烃源岩展布、输导体系和源-储组合关系3个方面对致密油差异富集控制因素进行了探讨,并总结了成藏模式。研究结果表明:(1)陕北地区长7段致密砂岩储层主要分布在一亚段(长71)和二亚段(长72),以灰色—灰白色长石砂岩和岩屑长石砂岩为主,长71和长72平均孔隙度分别为5.56%和7.32%,平均渗透率分别为0.097 m D和0.110 m D,长72储层物性更好;孔隙空间以溶孔为主,发育少量粒间孔。(2)研究区烃类主要来源于本地长72顶部和长73这2套烃源岩,平均厚度大于20 m,有机质丰度高,平均TOC值为3.02%,干酪根类型以Ⅰ型和Ⅱ1型为主,处于生烃高峰期,平均生烃量为270.2×10^(4)t/km^(2),长73烃源岩生烃潜力更大,供烃至长72储层,长71致密油来源于长72烃源岩;新安边地区三角洲前缘亚相末端的长72储层中致密油由湖盆烃源岩侧向供烃。(3)研究区致密油富集受烃源岩展布、砂体连通性以及源-储组合共同控制,在长72更富集,在新安边地区分布面积最大,安塞地区无大规模致密油聚集;纵向上和平面上致密油的聚集差异受控于烃源岩厚度和源-储组合关系,下生上储、上下生油而中间储集和砂泥互层时含油性更好;新安边地区三角洲前缘亚相末端的长72致密油聚集规模大于三角洲前缘主体,是由于三角洲前缘末端发育的局部连通砂体阻碍了湖盆烃类物质的侧向运移。(4)研究区致密油为“源控-砂控”成藏模式,远源河道优势砂体尖灭处和近源局部连通的砂体是有利勘探区。展开更多
基金Supported by the CNPC Science and Technology Project (2021DJ1806)the National Key Basic Research and Development Program (973 Program),China (2014CB239003)。
文摘The geological characteristics and enrichment laws of the shale oil in the third submember of the seventh member of Triassic Yanchang Formation(Chang 7_(3)) in the Ordos Basin were analyzed by using the information of core observations, experiments and logging, and then the exploration potential and orientation of the Chang 7_(3) shale oil were discussed. The research findings are obtained in three aspects. First, two types of shale oil, i.e. migratory-retained and retained, are recognized in Chang 7_(3). The former is slightly better than the latter in quality. The migratory-retained shale oil reservoir is featured with the frequent interbedding and overlapping of silty-sandy laminae caused by sandy debris flow and low-density turbidity current and semi-deep-deep lacustrine organic-rich shale laminae. The retained shale oil reservoir is composed of black shale with frequent occurrence of bedding and micro-laminae. Second, high-quality source rocks provide a large quantity of hydrocarbon-rich high-quality fluids with high potential energy. The source-reservoir pressure difference provides power for oil accumulation in thin interbeds of organic-poor sandstones with good seepage conditions and in felsic lamina, tuffaceous lamina and bedding fractures in shales. Hydrocarbon generation-induced fractures, bedding fractures and microfractures provide high-speed pathways for oil micro-migration. Frequent sandstone interlayers and felsic laminae provide a good space for large-scale hydrocarbon accumulation, and also effectively improve the hydrocarbon movability. Third, sand-rich areas around the depression are the main targets for exploring migratory-retained shale oil. Mature deep depression areas are the main targets for exploring retained oil with medium to high maturity. Theoretical research and field application of in-situ conversion in low-mature deep depression areas are the main technical orientations for exploring retained shale oil with low to medium maturity.
基金Supported by Science Coordination New Project(2016KTCL01-12)
文摘To explore the method of improving development effect and solving the problem of water breakthrough and water out for ultralow permeability fractured reservoirs, an indoor evaluation method of dynamic imbibition for fracture-matrix system was established taking the Chang 8 reservoir in southern Yanchang Oilfield as a research target. Key factors for the imbibition effect were obtained, an imbibition's rate expression was obtained, a model considering the double effects of imbibition-displacement was built and optimal injection and production parameters for the research area were obtained as well. The results show that an optimum displacement rate that maximizes the oil displacement efficiency exists in the water displacing oil process, and the optimal displacing rate becomes smaller as the permeability decreases. The imbibition displacement efficiency increases as the reservoir quality index and water wettability index of rock become bigger. But the larger the initial water saturation or oil-water viscosity ratio is, the smaller the imbibition displacement efficiency is. The optimal injection-production ratio for the Chang 8 reservoir of southern Yanchang Oilfield is 0.95, and the predicted recovery is 17.2% when the water cut is 95%, it is 2.9% higher than the recovery of conventional injection-production ratio 1.2. By using the moderate water injection technique based on the double effects of imbibition-displacement mechanism, the water injection development effect for the ultra-low permeability fractured reservoirs can be improved significantly.
文摘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.
基金granted by the National Program on Key Basic Research Project(973 Program)(grant No. 2014CB239000)State Oil and Gas Major Project(grant No.2011ZX05001)+1 种基金CNPC Major Project(grant No. 2016B-0301-04)financially supported by the Ministry of Science and Technology of China
文摘The Upper Triassic oil accumulations in the Ordos Basin is the most successful tight oil play in China,with average porosity values of less than 10% and permeability values below 1.0 mD.This study investigated the geological characteristics and origin of the tight oil accumulations in the Chang 6 member of the Upper Triassic Yanchang Formation in the Shanbei area based on over 50,000 petrological,source-rock analysis,well logging and production data.The tight oil accumulation of the Chang 6 member is distributed continuously in the basin slope and the centre of the basin.The oilwater relationships are complex.Laumontite dissolution pores are the most important storage spaces,constituting 30%-60% of total porosity and showing a strong positive relationship with oil production.The pore-throat diameter is less than 1 μm,and the calculated critical height of the oil column is much larger than the tight sand thickness,suggesting that the buoyancy was probably of limited importance for oil migration.The pressure difference between the source rocks and sandstone reservoirs is inferred to have provided driving force for hydrocarbon migration.Two factors of source-reservoir configuration and laumontite dissolution contributed to the formation of the Chang 6 tight oil accumulations.Intense hydrocarbon generation and continuous sand bodies close to the hydrocarbon kitchen are the foundation for the large-scale oil distribution.Dissolution of feldspar-laumontite during the process of organic matter evolution generated abundant secondary pores and improved the reservoir quality.
基金financial supports are from the National Natural Science Foundation of China (41702130 and 41971335)China Postdoctoral Science Foundation (2017T100419 and 2019M660269)Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD)。
文摘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.
基金Supported by the National Natural Fund Petrochemical Joint Fund Key Project(U1762217)Fundamental Scientific Research Operations Project of China Central Universities(19CX02009A)
文摘The Chang 73 sub-member of Triassic Yanchang Formation in the Ordos Basin was taken as an example and the lamina types and combinations,reservoir space features and shale oil enrichment patterns in organic-rich shale strata were investigated using core observation,thin section analysis,XRF element measurement,XRD analysis,SEM,high solution laser Raman spectroscopy analysis,and micro-FTIR spectroscopy analysis,etc.According to the mineral composition and thickness of the laminae,the Chang 73 organic-rich shales have four major types of laminae,tuff-rich lamina,organic-rich lamina,silt-grade feldspar-quartz lamina and clay lamina.They have two kinds of shale oil-bearing layers,"organic-rich lamina+silt-grade feldspar-quartz lamina"and"organic-rich lamina+tuff-rich lamina"layers.In the"organic-rich+silt-grade feldspar-quartz"laminae combination shale strata,oil was characterized by relative high maturation,and always filled in K-feldspar dissolution pores in the silt-grade feldspar-quartz laminae,forming oil generation,migration and accumulation process between laminae inside the organic shales.In the"organic-rich+tuff-rich lamina"binary laminae combination shale strata,however,the reservoir properties were poor in organic-rich shales,the oil maturation was relatively lower,and mainly accumulated in the intergranular pores of interbedded thin-layered sandstones.The oil generation,migration and accumulation mainly occurred between organic-rich shales and interbedded thin-layered sandstones.
基金supported with funding from the National Natural Science Foundation of China(No.41173055)
文摘In the south of the Ordos Basin, the oil source of the Upper Triassic Yanchang Formation is confused all the time, which affects further exploration. In this study, oil sources from the oil layers of Ch6, Ch8 and Ch9 are all analyzed and confirmed. Through their carbon isotope value and biomarkers, characteristics of crude oils from the Yanchang Formation are analyzed. Then, the oil–source relation is discussed, with the source rocks' features.Finally, the oil–source relation is calculated through cluster analysis. It is believed that the oils from the Yanchang Formation deposit in a similar redox environment, with weak oxidation–weak reduction, and have all entered maturity stage. Ch9 crude oil is more mature than crude oils from Ch6 and Ch8, and has more advanced plants and fewer algae. Gas chromatography(GC) and gas chromatography–mass spectrometry(GC–MS) analysis show that crude oils from Ch6 and Ch8 may come from Ch7, and Ch9 crude oil may not. Cluster analysis displays that crude oils from Ch6 and Ch8 have closer squared Euclidean distance with Ch7 source rocks than Ch9 crude oil does,indicating crude oils from Ch6 and Ch8 stem from Ch7 source rocks. And Ch9 crude oil has rather close squared Euclidean distance with Ch9 source rocks, illustrating Ch9 crude oil may be from Ch9 source rocks. This research may provide the theoretical basis for the next exploration deploy in the south of Ordos Basin.
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.
文摘综合利用地球化学、扫描电镜、岩心薄片、测井等资料以及油井生产数据等,对鄂尔多斯盆地陕北地区三叠系延长组7段储层特征、烃源岩特征和致密油分布特征进行了分析,从烃源岩展布、输导体系和源-储组合关系3个方面对致密油差异富集控制因素进行了探讨,并总结了成藏模式。研究结果表明:(1)陕北地区长7段致密砂岩储层主要分布在一亚段(长71)和二亚段(长72),以灰色—灰白色长石砂岩和岩屑长石砂岩为主,长71和长72平均孔隙度分别为5.56%和7.32%,平均渗透率分别为0.097 m D和0.110 m D,长72储层物性更好;孔隙空间以溶孔为主,发育少量粒间孔。(2)研究区烃类主要来源于本地长72顶部和长73这2套烃源岩,平均厚度大于20 m,有机质丰度高,平均TOC值为3.02%,干酪根类型以Ⅰ型和Ⅱ1型为主,处于生烃高峰期,平均生烃量为270.2×10^(4)t/km^(2),长73烃源岩生烃潜力更大,供烃至长72储层,长71致密油来源于长72烃源岩;新安边地区三角洲前缘亚相末端的长72储层中致密油由湖盆烃源岩侧向供烃。(3)研究区致密油富集受烃源岩展布、砂体连通性以及源-储组合共同控制,在长72更富集,在新安边地区分布面积最大,安塞地区无大规模致密油聚集;纵向上和平面上致密油的聚集差异受控于烃源岩厚度和源-储组合关系,下生上储、上下生油而中间储集和砂泥互层时含油性更好;新安边地区三角洲前缘亚相末端的长72致密油聚集规模大于三角洲前缘主体,是由于三角洲前缘末端发育的局部连通砂体阻碍了湖盆烃类物质的侧向运移。(4)研究区致密油为“源控-砂控”成藏模式,远源河道优势砂体尖灭处和近源局部连通的砂体是有利勘探区。