The Shanan sag in the central-western Bohai Bay Basin hosts high-quality Paleogene source rocks within the Shahejie Formation’s third member(E_(2)s_(3)).Despite hydrocarbon indications in Cenozoic strata,no commercia...The Shanan sag in the central-western Bohai Bay Basin hosts high-quality Paleogene source rocks within the Shahejie Formation’s third member(E_(2)s_(3)).Despite hydrocarbon indications in Cenozoic strata,no commercial accumulations have been discovered.An integrated approach combining geochemical analysis,fluid inclusion thermometry,apatite fission-track(AFT)thermochronology,and basin modeling was employed to unravel the paleo-geothermal regime and hydrocarbon generation history of E_(2)s_(3) source rocks.AFT data from the Shahejie Formation’s second member(E_(2)s_(2))reveal a tectonothermal event at 25 Ma that accelerated E_(2)s_(3) maturation.Outside three sub-sag depocenters,current E_(2)s_(2) reservoir temperatures remain below the 25 Ma paleo-geothermal maxima despite subsequent Neogene burial.Hydrocarbon-bearing brine inclusions in E_(2)s_(2) reservoirs exhibit peak homogenization temperatures(Th)at 25 Ma,with minimal high-temperature signals,indicating that E_(2)s_(3) hydrocarbon generation peaked during the Paleogene thermal event,with limited late-stage accumulation.The regional effects of the Dongying Movement necessitate thick Neogene sedimentation to compensate for the 25 Ma paleo-geothermal anomaly.Our findings emphasize targeting Neogene depocenters in petroleum exploration to mitigate the inhibitory effects of high paleo-heat flow on late hydrocarbon generation,thereby enhancing current accumulation potential.展开更多
To accurately investigate the evolution characteristics and generation mechanism of retained oil,the study analyzed organic-rich lacustrine shale samples from the Paleogene Kongdian Formation in Cangdong Sag,Bohai Bay...To accurately investigate the evolution characteristics and generation mechanism of retained oil,the study analyzed organic-rich lacustrine shale samples from the Paleogene Kongdian Formation in Cangdong Sag,Bohai Bay Basin.This analysis involves Rock-Eval pyrolysis,pyrolysis simulation experiments,Gas Chromatograph Mass Spectrometer(GC-MS),and reactive molecular dynamics simulations(ReaxFF).The results revealed the retained oil primarily consisted of n-alkanes with carbon numbers ranging from C14 to C36.The generation of retained oil occurred through three stages.A slow growth stage of production rate was observed before reaching the peak of oil production in Stage Ⅰ.Stage Ⅱ involved a rapid increase in oil retention,with C12-C17 and C24-C32 serving as the primary components,increasing continuously during the pyrolysis process.The generation process involved the cleavage of weak bonds,including bridging bonds(hydroxyl,oxy,peroxy,imino,amino,and nitro),ether bonds,and acid amides in the first stage(Ro=0.50%-0.75%).The carbon chains in aromatic ring structures with heteroatomic functional groups breaks in the second stage(R_(o)=0.75%-1.20%).In the third stage(R_(o)=1.20%-2.50%),the ring structures underwent ring-opening reactions to synthesize iso-short-chain olefins and radicals,while further breakdown of aliphatic chains occurred.By coupling pyrolysis simu-lation experiments and molecular simulation technology,the evolution characteristics and bond breaking mechanism of retained oil in three stages were revealed,providing a reference for the for-mation and evolution mechanism of retained oil.展开更多
The Xihu Depression,situated in the northeastern East China Sea Basin,represents the most significant natural gas-producing region in Eastern China.An insufficient understanding of reservoir heterogeneity in petroleum...The Xihu Depression,situated in the northeastern East China Sea Basin,represents the most significant natural gas-producing region in Eastern China.An insufficient understanding of reservoir heterogeneity in petroleum geological conditions―particularly within structural zones beyond the well-explored Pinghu Slope and Ningbo Anticline Belt―has hindered comprehensive hydrocarbon exploration across the sag.Critical knowledge gaps persist in characterizing the geothermal field,reconstructing thermal evolution histories,and constraining hydrocarbon generation phases.These limitations directly impede systematic evaluations of basin selection criteria,reservoir delineation,and their dynamic relationships within petroleum systems.This study analyzes the present geothermal gradient at a unified depth(4000-5000 m),the geothermal heat flow,the geothermal temperature at a unified depth(3000-6000 m),and the plan distribution characteristics of the geothermal temperatures of the exploration strata in the key study area in the Xihu Depression―the Western Slope and the Central Anticlinal Belt.The research in this study is based on present bottom-hole temperature measurements and temperature data for testing for oil,using a one-dimensional steady-state heat conduction equation and the Bullard method.The results indicate that the present geothermal gradient in the Xihu Depression,between a unified depth of 4000 m and 5000 m,ranges from 16.7◦C/km to 44.6℃/km,with an average of 30.6℃/km.The present geothermal heat flow is between 32.23 mW/m^(2)and 90.13 mW/m^(2),with an average of 52.03 mW/m^(2),indicating a typical cold basin.The formation temperature gradually increases with burial depth,from 3000 m to 6000 m.In the plane,the formation temperature gradually increases from the south to the north and from the edge of the depression to the center of the depression.The burial history and thermal evolution of the key plays of the Xihu Depression were reconstructed using apatite fission tracks and zircon U-Th/He data,combined with vitrinite reflectance,which revealed that the tectonic uplift that occurred during the Late Miocene Longjing Movement was a critical event in trap formation and hydrocarbon filling.The thermal-hydrocarbon generation history indicates that the Xihu Depression has mostly entered a high maturity stage,with gas condensate and condensate charging occurring between 16.4 Ma and 13 Ma and natural gas filling occurring at 5.3 Ma up to now.Hydrocarbon generation and expulsion in the Xihu Depression occurred early in the north and late in the south,with two stages in the north and one stage in the south.A study of the burial history-thermal history-hydrocarbon generation history based on the reconstruction of geothermal fields demonstrates the matching relationship between hydrocarbon generation,distribution,and accumulation in the Xihu Depression―an understanding that is vital for oil and gas exploration in the Xihu Depression.展开更多
Pyrolysis experiments were conducted on lacustrine organic-rich shale from Cangdong Sag in Bohai Bay Basin,China,to investigate the impact of hydrocarbon generation on shale pore structure evolution.Thermal evolution ...Pyrolysis experiments were conducted on lacustrine organic-rich shale from Cangdong Sag in Bohai Bay Basin,China,to investigate the impact of hydrocarbon generation on shale pore structure evolution.Thermal evolution is found to control the transformation of organic matter,hydrocarbon products characteristics,and pore structure changes.Furthermore,pore volume and specific surface area increase with increasing maturity.In low-mature stage,the retained oil content begins to increase,pore volumes show slight changes,and primary pores are occluded by the generated crude oil of high molecular weight and density.In the oil-window stage,the retained oil content rapidly increases and reaches maximum,and pore volumes gradually increase with increasing thermal maturity.At high mature stage,the retained oil content begins to decrease,and the pore volume increases considerably owing to the expulsion of liquid hydrocarbon.In over mature stage,natural gas content significantly increases and kerogen transforms to asphalt.Numerous organic pores are formed and the pore size gradually increases,resulting from the connection of organic pores caused the increasing thermal stress.This study lays a foundation for understanding variation of hydrocarbon products during the thermal evolution of lacustrine shales and its relationship with the evolution of shale reservoirs.展开更多
基金the National Natural Science Foundation(41802169)Key Laboratory of Polar Geology and Marine Mineral Resources Foudation(HNPY-202506)for supporting this study.
文摘The Shanan sag in the central-western Bohai Bay Basin hosts high-quality Paleogene source rocks within the Shahejie Formation’s third member(E_(2)s_(3)).Despite hydrocarbon indications in Cenozoic strata,no commercial accumulations have been discovered.An integrated approach combining geochemical analysis,fluid inclusion thermometry,apatite fission-track(AFT)thermochronology,and basin modeling was employed to unravel the paleo-geothermal regime and hydrocarbon generation history of E_(2)s_(3) source rocks.AFT data from the Shahejie Formation’s second member(E_(2)s_(2))reveal a tectonothermal event at 25 Ma that accelerated E_(2)s_(3) maturation.Outside three sub-sag depocenters,current E_(2)s_(2) reservoir temperatures remain below the 25 Ma paleo-geothermal maxima despite subsequent Neogene burial.Hydrocarbon-bearing brine inclusions in E_(2)s_(2) reservoirs exhibit peak homogenization temperatures(Th)at 25 Ma,with minimal high-temperature signals,indicating that E_(2)s_(3) hydrocarbon generation peaked during the Paleogene thermal event,with limited late-stage accumulation.The regional effects of the Dongying Movement necessitate thick Neogene sedimentation to compensate for the 25 Ma paleo-geothermal anomaly.Our findings emphasize targeting Neogene depocenters in petroleum exploration to mitigate the inhibitory effects of high paleo-heat flow on late hydrocarbon generation,thereby enhancing current accumulation potential.
基金financially supported by the National Natural Science Foundation of China (Grant No. 42072150)
文摘To accurately investigate the evolution characteristics and generation mechanism of retained oil,the study analyzed organic-rich lacustrine shale samples from the Paleogene Kongdian Formation in Cangdong Sag,Bohai Bay Basin.This analysis involves Rock-Eval pyrolysis,pyrolysis simulation experiments,Gas Chromatograph Mass Spectrometer(GC-MS),and reactive molecular dynamics simulations(ReaxFF).The results revealed the retained oil primarily consisted of n-alkanes with carbon numbers ranging from C14 to C36.The generation of retained oil occurred through three stages.A slow growth stage of production rate was observed before reaching the peak of oil production in Stage Ⅰ.Stage Ⅱ involved a rapid increase in oil retention,with C12-C17 and C24-C32 serving as the primary components,increasing continuously during the pyrolysis process.The generation process involved the cleavage of weak bonds,including bridging bonds(hydroxyl,oxy,peroxy,imino,amino,and nitro),ether bonds,and acid amides in the first stage(Ro=0.50%-0.75%).The carbon chains in aromatic ring structures with heteroatomic functional groups breaks in the second stage(R_(o)=0.75%-1.20%).In the third stage(R_(o)=1.20%-2.50%),the ring structures underwent ring-opening reactions to synthesize iso-short-chain olefins and radicals,while further breakdown of aliphatic chains occurred.By coupling pyrolysis simu-lation experiments and molecular simulation technology,the evolution characteristics and bond breaking mechanism of retained oil in three stages were revealed,providing a reference for the for-mation and evolution mechanism of retained oil.
基金the National Natural Science Foundation of China(No.42430806)CNOOC(China)Co.,Ltd+1 种基金‘14th Five-Year'science and technology major project offshore deep/ultra-deep oil and gas exploration technology(KJGG2022-0402)‘14th Five-Year'national oil and gas resources evaluation CNOOC mining rights area and surrounding blank area oil and gas resources evaluation project(QGYQZYPJ2022-3).
文摘The Xihu Depression,situated in the northeastern East China Sea Basin,represents the most significant natural gas-producing region in Eastern China.An insufficient understanding of reservoir heterogeneity in petroleum geological conditions―particularly within structural zones beyond the well-explored Pinghu Slope and Ningbo Anticline Belt―has hindered comprehensive hydrocarbon exploration across the sag.Critical knowledge gaps persist in characterizing the geothermal field,reconstructing thermal evolution histories,and constraining hydrocarbon generation phases.These limitations directly impede systematic evaluations of basin selection criteria,reservoir delineation,and their dynamic relationships within petroleum systems.This study analyzes the present geothermal gradient at a unified depth(4000-5000 m),the geothermal heat flow,the geothermal temperature at a unified depth(3000-6000 m),and the plan distribution characteristics of the geothermal temperatures of the exploration strata in the key study area in the Xihu Depression―the Western Slope and the Central Anticlinal Belt.The research in this study is based on present bottom-hole temperature measurements and temperature data for testing for oil,using a one-dimensional steady-state heat conduction equation and the Bullard method.The results indicate that the present geothermal gradient in the Xihu Depression,between a unified depth of 4000 m and 5000 m,ranges from 16.7◦C/km to 44.6℃/km,with an average of 30.6℃/km.The present geothermal heat flow is between 32.23 mW/m^(2)and 90.13 mW/m^(2),with an average of 52.03 mW/m^(2),indicating a typical cold basin.The formation temperature gradually increases with burial depth,from 3000 m to 6000 m.In the plane,the formation temperature gradually increases from the south to the north and from the edge of the depression to the center of the depression.The burial history and thermal evolution of the key plays of the Xihu Depression were reconstructed using apatite fission tracks and zircon U-Th/He data,combined with vitrinite reflectance,which revealed that the tectonic uplift that occurred during the Late Miocene Longjing Movement was a critical event in trap formation and hydrocarbon filling.The thermal-hydrocarbon generation history indicates that the Xihu Depression has mostly entered a high maturity stage,with gas condensate and condensate charging occurring between 16.4 Ma and 13 Ma and natural gas filling occurring at 5.3 Ma up to now.Hydrocarbon generation and expulsion in the Xihu Depression occurred early in the north and late in the south,with two stages in the north and one stage in the south.A study of the burial history-thermal history-hydrocarbon generation history based on the reconstruction of geothermal fields demonstrates the matching relationship between hydrocarbon generation,distribution,and accumulation in the Xihu Depression―an understanding that is vital for oil and gas exploration in the Xihu Depression.
基金supported by the National Natural Science Foundation of China(Grant Nos.42072150,41372144)the State Science and Technology Major Project of China(Grant No.2017ZX05049001-008)
文摘Pyrolysis experiments were conducted on lacustrine organic-rich shale from Cangdong Sag in Bohai Bay Basin,China,to investigate the impact of hydrocarbon generation on shale pore structure evolution.Thermal evolution is found to control the transformation of organic matter,hydrocarbon products characteristics,and pore structure changes.Furthermore,pore volume and specific surface area increase with increasing maturity.In low-mature stage,the retained oil content begins to increase,pore volumes show slight changes,and primary pores are occluded by the generated crude oil of high molecular weight and density.In the oil-window stage,the retained oil content rapidly increases and reaches maximum,and pore volumes gradually increase with increasing thermal maturity.At high mature stage,the retained oil content begins to decrease,and the pore volume increases considerably owing to the expulsion of liquid hydrocarbon.In over mature stage,natural gas content significantly increases and kerogen transforms to asphalt.Numerous organic pores are formed and the pore size gradually increases,resulting from the connection of organic pores caused the increasing thermal stress.This study lays a foundation for understanding variation of hydrocarbon products during the thermal evolution of lacustrine shales and its relationship with the evolution of shale reservoirs.
