Salinity is a crucial property of water body and is essential for the restoration of paleoecology and paleoenvironment.However,the theoretical method of application of elemental geochemical proxies to paleosalinity re...Salinity is a crucial property of water body and is essential for the restoration of paleoecology and paleoenvironment.However,the theoretical method of application of elemental geochemical proxies to paleosalinity reconstruction is still underdeveloped.Moreover,accurate determination and reconstruction of paleosalinity and its variation in an offshore lacustrine basin have been extremely challenging thus far.This study presents detailed elemental geochemical investigations from the Zhanhua Sag in the southern Bohai Bay Basin to reconstruct the salinity variation in the Paleogene Eocene Shahejie Formation(50.8-33.9 Ma).Based on the variation of strontium barium ratio(Sr/Ba)and boron gallium ratio(B/Ga),we determined three typical salinity types of water body:salty water(Sr/Ba>0.5,B/Ga>6),brackish water(0.2<Sr/Ba<0.5,3<B/Ga<6),and fresh water(Sr/Ba<0.2,B/Ga<3),after eliminating carbonate-sourced strontium(Sr).The salinity values following Couch’s paleosalinometer r anged from 3.1 to 11.9,reflecting the overall characteristics of oligohaline(0.5<salinity value<5)to mesohaline(5<salinity value<18)brackish water.All proxies yielded similar trends in paleosalinity variation,demonstrating a clear trend of rising and then declining from 50.8 Ma to 33.9 Ma.We considered that the B/Ga ratio had the highest reliability and resolution in determining the salinity types of water body in the study area.The environmental factors causing paleosalinity variation were also thoroughly analysed based on the temporal relationship among the salinity types of watermasses,paleoclimate characteristics from pollen records,and marine transgression events from marine fossils.Our research established a model of paleoclimatic and eustatic mechanisms to explain paleosalinity variation,providing reasonable and integral driving forces for the salinity variation of all offshore lacustrine basins.展开更多
The controlling factors of organic-rich shale accumulation is essential for the exploration and development of shale oil and gas resources.The sedimentary environment plays a vital role in the formation of organic-ric...The controlling factors of organic-rich shale accumulation is essential for the exploration and development of shale oil and gas resources.The sedimentary environment plays a vital role in the formation of organic-rich sediments in lacustrine facies.This article unravels the mineralogy,geochemistry,and paleoenvironmental evolution during the deposition of the Paleogene Shahejie Formation(Es_(3)^(L)).It discusses the effects of paleoclimate,paleosalinity,paleoredox conditions,paleowater depth,and paleoproductivity on organic matter(OM)enrichment.Finally,the OM enrichment model was established.The results show that the mineralogical compositions are mainly composed of calcite(avg.40.13%),quartz(avg.21.64%)and clay minerals(avg.24.07%),accompanied by dolomite(avg.7.07%),feldspar(avg.6.36%)and pyrite(avg.2.95%).The Es_(3)^(L) shale has a high abundance of OM,with total organic carbon(TOC)ranging from 1.07%to 5.12%.The organic matter type is mainly composed of type I-II_(1) kerogen,which is generally considered a good-quality source rock.The source of OM is a mixture of lower bacteria,algae,and plants.During the early sedimentary period,the paleoclimate was dry and cold,with high salinity,intense reducibility,and relatively low productivity.During the late sedimentary period,the climate became warmer and more humid.As a result,the salinity decreased to a level that was suitable for biological reproduction,and productivity increased gradually due to the input of terrigenous plants.Paleosalinity and paleoclimate determined the environment of the sedimentary period,in addition,paleoproductivity and paleoredox condition indicated the formation and preservation conditions of OM.The warm and humid climate,brackish water,suitable reduction conditions and high productivity are the favorable conditions for the generation and preservation of organic matter.The research results may have implications for the genetic mechanisms of organic matter accumulation.They will provide theoretical and technical insights into the exploration and development of shale oil.展开更多
Researches into shale lithofacies,their sedimentary environments and relationship benefit understanding both of sedimentary cycle division and unconventional hydrocarbon exploration in lacustrine basins.Based on a 100...Researches into shale lithofacies,their sedimentary environments and relationship benefit understanding both of sedimentary cycle division and unconventional hydrocarbon exploration in lacustrine basins.Based on a 100~300-m-thick dark shale,mudstone and limestone encountered in the lower third member of the Eocene Shahejie Formation(Es3l member)in Zhanhua Sag,Bohai Bay Basin,eastern China,routine core analysis,thin sectioning,scanning electron microscopy(SEM),mineralogical and geochemical measurements were used to understand detailed facies characterization and paleoclimate in the member.This Es3l shale sediment includes three sedimentary cycles(C3,C2 and C1),from bottom to top,with complex sedimentary characters and spatial distribution.In terms of the composition,texture,bedding and thickness,six lithofacies are recognized in this succession.Some geochemical parameters,such as trace elements(Sr/Ba,Na/Al,V/Ni,V/(V+Ni),U/Th),carbon and oxygen isotopes(δ^(18)O,δ^(13)C),and total organic carbon content(TOC)indicate that the shales were deposited in a deep to semi-deep lake,with the water column being salty,stratified,enclosed and reductive.During cycles C3 and C2 of the middle-lower sections,the climate was arid,and the water was salty and stratified.Laminated and laminar mudstone-limestone was deposited with moderate organic matter(average TOC 1.8%)and good reservoir quality(average porosity 6.5%),which can be regarded as favorable reservoir.During the C1 cycle,a large amount of organic matter was input from outside the basin and this led to high productivity with a more humid climate.Massive calcareous mudstone was deposited,and this is characterized by high TOC(average 3.6%)and moderate porosity(average 4%),and provides favorable source rocks.展开更多
The residual oil in the fluvial reservoir of Gudong Oilfield is still widely developed even after decades of development.In order to explore the remaining oil in the subsurface fluvial reservoir,we need to have a bett...The residual oil in the fluvial reservoir of Gudong Oilfield is still widely developed even after decades of development.In order to explore the remaining oil in the subsurface fluvial reservoir,we need to have a better understanding on fluvial sandbody characteristics.This paper aims to demonstrate how to quantify anatomy on meandering fluvial architecture.Sedimentologic data from core descriptions of Guantao Formation in Gudong Oilfield were used to identify architectural elements.The upper Guantao Formation consists of ten lithofacies composing five different types of architectural elements.By integrating the available core,well logs,and seismic data,the fluvial sandbody distribution was analyzed.To characterize the fluvial channel geomorphology,we used seismic inversion to explore the stratigraphic correlation and stacking patterns of different channels,and the sandbody isopach map was obtained by the sandbody thickness in each layer.The architectural elements distribution in the plane was mapped by the sandbody isopach map and its profile characteristics.According to the investigation of meandering fluvial outcrops,subsurface meandering fluvial seismic geomorphology,and modern river morphology,the upstream-bar portions are always eroded because of the downstream channel migration.Statistics on the morphometric parameters(bar width/looplength,upstream deflection angle,downstream deflection angle,etc.)of modern meandering river(Ob River)were obtained from the Google Earth.It is found that the bar width/looplength and upstream deflection angle,upstream deflection angle and downstream deflection angle in modern meandering river have a good relationship,and we can have a quantitative architectural characterization on the point bar.This study quantified lithofacies thickness and proportion in different architectural elements of Guantao Formation,which ensures a high resolution anatomy on the small scale architecture.By using this method,the lithofacies proportion in each architectural element was computed,and through the statistics of architectural elements proportion in the Gudong Oilfield,the different lithofacies proportions in the block 6 can be computed.展开更多
基金Supported by the National Natural Science Foundation of China(No.42272110)。
文摘Salinity is a crucial property of water body and is essential for the restoration of paleoecology and paleoenvironment.However,the theoretical method of application of elemental geochemical proxies to paleosalinity reconstruction is still underdeveloped.Moreover,accurate determination and reconstruction of paleosalinity and its variation in an offshore lacustrine basin have been extremely challenging thus far.This study presents detailed elemental geochemical investigations from the Zhanhua Sag in the southern Bohai Bay Basin to reconstruct the salinity variation in the Paleogene Eocene Shahejie Formation(50.8-33.9 Ma).Based on the variation of strontium barium ratio(Sr/Ba)and boron gallium ratio(B/Ga),we determined three typical salinity types of water body:salty water(Sr/Ba>0.5,B/Ga>6),brackish water(0.2<Sr/Ba<0.5,3<B/Ga<6),and fresh water(Sr/Ba<0.2,B/Ga<3),after eliminating carbonate-sourced strontium(Sr).The salinity values following Couch’s paleosalinometer r anged from 3.1 to 11.9,reflecting the overall characteristics of oligohaline(0.5<salinity value<5)to mesohaline(5<salinity value<18)brackish water.All proxies yielded similar trends in paleosalinity variation,demonstrating a clear trend of rising and then declining from 50.8 Ma to 33.9 Ma.We considered that the B/Ga ratio had the highest reliability and resolution in determining the salinity types of water body in the study area.The environmental factors causing paleosalinity variation were also thoroughly analysed based on the temporal relationship among the salinity types of watermasses,paleoclimate characteristics from pollen records,and marine transgression events from marine fossils.Our research established a model of paleoclimatic and eustatic mechanisms to explain paleosalinity variation,providing reasonable and integral driving forces for the salinity variation of all offshore lacustrine basins.
基金supported by the National Natural Science Foundation of China(No.42272110)。
文摘The controlling factors of organic-rich shale accumulation is essential for the exploration and development of shale oil and gas resources.The sedimentary environment plays a vital role in the formation of organic-rich sediments in lacustrine facies.This article unravels the mineralogy,geochemistry,and paleoenvironmental evolution during the deposition of the Paleogene Shahejie Formation(Es_(3)^(L)).It discusses the effects of paleoclimate,paleosalinity,paleoredox conditions,paleowater depth,and paleoproductivity on organic matter(OM)enrichment.Finally,the OM enrichment model was established.The results show that the mineralogical compositions are mainly composed of calcite(avg.40.13%),quartz(avg.21.64%)and clay minerals(avg.24.07%),accompanied by dolomite(avg.7.07%),feldspar(avg.6.36%)and pyrite(avg.2.95%).The Es_(3)^(L) shale has a high abundance of OM,with total organic carbon(TOC)ranging from 1.07%to 5.12%.The organic matter type is mainly composed of type I-II_(1) kerogen,which is generally considered a good-quality source rock.The source of OM is a mixture of lower bacteria,algae,and plants.During the early sedimentary period,the paleoclimate was dry and cold,with high salinity,intense reducibility,and relatively low productivity.During the late sedimentary period,the climate became warmer and more humid.As a result,the salinity decreased to a level that was suitable for biological reproduction,and productivity increased gradually due to the input of terrigenous plants.Paleosalinity and paleoclimate determined the environment of the sedimentary period,in addition,paleoproductivity and paleoredox condition indicated the formation and preservation conditions of OM.The warm and humid climate,brackish water,suitable reduction conditions and high productivity are the favorable conditions for the generation and preservation of organic matter.The research results may have implications for the genetic mechanisms of organic matter accumulation.They will provide theoretical and technical insights into the exploration and development of shale oil.
基金This work is granted by the China State Lithologic Key Program(grant no.2017ZX05001-002-002).
文摘Researches into shale lithofacies,their sedimentary environments and relationship benefit understanding both of sedimentary cycle division and unconventional hydrocarbon exploration in lacustrine basins.Based on a 100~300-m-thick dark shale,mudstone and limestone encountered in the lower third member of the Eocene Shahejie Formation(Es3l member)in Zhanhua Sag,Bohai Bay Basin,eastern China,routine core analysis,thin sectioning,scanning electron microscopy(SEM),mineralogical and geochemical measurements were used to understand detailed facies characterization and paleoclimate in the member.This Es3l shale sediment includes three sedimentary cycles(C3,C2 and C1),from bottom to top,with complex sedimentary characters and spatial distribution.In terms of the composition,texture,bedding and thickness,six lithofacies are recognized in this succession.Some geochemical parameters,such as trace elements(Sr/Ba,Na/Al,V/Ni,V/(V+Ni),U/Th),carbon and oxygen isotopes(δ^(18)O,δ^(13)C),and total organic carbon content(TOC)indicate that the shales were deposited in a deep to semi-deep lake,with the water column being salty,stratified,enclosed and reductive.During cycles C3 and C2 of the middle-lower sections,the climate was arid,and the water was salty and stratified.Laminated and laminar mudstone-limestone was deposited with moderate organic matter(average TOC 1.8%)and good reservoir quality(average porosity 6.5%),which can be regarded as favorable reservoir.During the C1 cycle,a large amount of organic matter was input from outside the basin and this led to high productivity with a more humid climate.Massive calcareous mudstone was deposited,and this is characterized by high TOC(average 3.6%)and moderate porosity(average 4%),and provides favorable source rocks.
基金Research Institute of Exploration and Development of Shengli Oilfield for their support in completing the research and their permission to publish the resultsco-funded by the National Key Oil&Gas Project of China (No. 2011ZX05009-002)+2 种基金the National Science and Technology Major Program of China (No2017ZX05009-002)the Youth Project of Education Department of Liaoning Province (No. LJKQZ20222320)the talent scientific research fund of Liaoning Petrochemical University (No. 2021XJJL-028).
文摘The residual oil in the fluvial reservoir of Gudong Oilfield is still widely developed even after decades of development.In order to explore the remaining oil in the subsurface fluvial reservoir,we need to have a better understanding on fluvial sandbody characteristics.This paper aims to demonstrate how to quantify anatomy on meandering fluvial architecture.Sedimentologic data from core descriptions of Guantao Formation in Gudong Oilfield were used to identify architectural elements.The upper Guantao Formation consists of ten lithofacies composing five different types of architectural elements.By integrating the available core,well logs,and seismic data,the fluvial sandbody distribution was analyzed.To characterize the fluvial channel geomorphology,we used seismic inversion to explore the stratigraphic correlation and stacking patterns of different channels,and the sandbody isopach map was obtained by the sandbody thickness in each layer.The architectural elements distribution in the plane was mapped by the sandbody isopach map and its profile characteristics.According to the investigation of meandering fluvial outcrops,subsurface meandering fluvial seismic geomorphology,and modern river morphology,the upstream-bar portions are always eroded because of the downstream channel migration.Statistics on the morphometric parameters(bar width/looplength,upstream deflection angle,downstream deflection angle,etc.)of modern meandering river(Ob River)were obtained from the Google Earth.It is found that the bar width/looplength and upstream deflection angle,upstream deflection angle and downstream deflection angle in modern meandering river have a good relationship,and we can have a quantitative architectural characterization on the point bar.This study quantified lithofacies thickness and proportion in different architectural elements of Guantao Formation,which ensures a high resolution anatomy on the small scale architecture.By using this method,the lithofacies proportion in each architectural element was computed,and through the statistics of architectural elements proportion in the Gudong Oilfield,the different lithofacies proportions in the block 6 can be computed.
