Crude oil has been discovered in the Paleogene and Neogene units of the Weixinan Sag in the Beibu Gulf Basin.To determine the source and accumulation mode of this crude oil,12 crude oil samples and 27 source rock samp...Crude oil has been discovered in the Paleogene and Neogene units of the Weixinan Sag in the Beibu Gulf Basin.To determine the source and accumulation mode of this crude oil,12 crude oil samples and 27 source rock samples were collected and an extensive organic geochemical analysis was conducted on them.Based on the geological conditions and the analytical results,the types,origins and accumulation patterns of crude oil in the study area were elucidated.Except for a shallowly-buried and biodegraded crude oil deposit in Neogene rocks,the crude oil samples in the study area were normal.All of the crude oils were derived from lacustrine source rocks.According to biomarker compositions,the crude oils could be divided into two families,A and B,distinctions that were reinforced by differences in carbon isotope composition and spatial distribution.Oil-source correlation analysis based on biomarkers revealed that Family A oils were derived from the mature oil shale at the bottom of the second member of the Liushagang Formation,while the Family B oils formed in the mature shale of the Liushagang Formation.The Family A oils,generated by oil shale,mainly migrated laterally along sand bodies and were then redistributed in adjacent reservoirs above and below the oil shale layer,as well as in shallow layers at high structural positions,occupying a wide distribution range.The Family B oils were generated by other shale units before migrating vertically along faults to form reservoirs nearby,resulting in a narrow distribution range.展开更多
The mechanisms of lacustrine organic-rich shale formation have attracted attention due to its association with global shale oil and shale gas exploration.Samples of general-quality and excellent-quality source rocks,a...The mechanisms of lacustrine organic-rich shale formation have attracted attention due to its association with global shale oil and shale gas exploration.Samples of general-quality and excellent-quality source rocks,and oil shale from the Beibu Gulf Basin were analyzed to investigate their organic geochemistry,palynofacies,and trace elements.Hydrocarbon potential was higher in the oil shale(29.79 mg/g)than in the general-quality source rock(3.82 mg/g),and its kerogen type wasⅠ-Ⅱ2.Hydrogen-rich liptinite(cutinite and sporinite)components derived from terrigenous higher plants provided most of the hydrocarbon potential of excellent-quality source rock and oil shale.Under the influence of depressioncontrolling fault activity,a deeper subsidence center promotes the deposition of excellent-quality source rock and oil shale in brackish-hypoxic bottom water.A shallower subsidence center,due to subsag-controlling fault activity,promotes the formation of excellent-quality source rock under freshbrackish and weak oxidation-weak reducing conditions.The local uplift and shallow-slope led to the formation of general-quality source rock,under freshwater weak-oxidation conditions.A model was established for organic matter(OM)accumulation in organic-rich shales,accounting for fault activity,terrigenous hydrogen-rich OM,and the preservation conditions,to predict the development of excellent-quality source rock from areas with low levels of exploration.展开更多
The Leidong depression is one of the secondary tectonic units and the least explored part of the Beibu Gulf Basin,northern South China Sea.Exploration activities in the basin reveal that the Middle Eocene deposition w...The Leidong depression is one of the secondary tectonic units and the least explored part of the Beibu Gulf Basin,northern South China Sea.Exploration activities in the basin reveal that the Middle Eocene deposition was controlled by NE-SW-striking faults and the second member of the Eocene Liushagang Formation(LII)consists of high-quality source rocks.The nature and origin of this depression has remained enigmatic due to the complex fault structures as compared to those in other basins.It is important to identify whether LII occurs in the Leidong depression in the context of exploration.Here we analyze available geological,seismic,and drilling data of the depression and the controlling factors among faults,deposition,lithology,and hydrocarbon distribution in the basin.Measures such as stress fracture analysis,fault growth index analysis,and sedimentary strata characterization were used to construct an Eocene sedimentary model controlled by NW-SE striking faults.The model with integrated seismic profile characteristics comparison and velocity analysis results was then used to determine whether the Eocene strata in the west of the depression contain the high-quality source rocks that are widely distributed elsewhere in the basin.Finally,calculations were performed to quantify the intensity of hydrocarbon generation and amount of hydrocarbon generated in the depression based on available data of the source rocks,including their distribution and thickness.The results confirmed the assumption that the Middle Eocene strata in the Leidong depression were controlled by NW-SE strike-slip faults and contain high-quality LII source rocks,thus providing an important foundation for future exploration.展开更多
文摘Crude oil has been discovered in the Paleogene and Neogene units of the Weixinan Sag in the Beibu Gulf Basin.To determine the source and accumulation mode of this crude oil,12 crude oil samples and 27 source rock samples were collected and an extensive organic geochemical analysis was conducted on them.Based on the geological conditions and the analytical results,the types,origins and accumulation patterns of crude oil in the study area were elucidated.Except for a shallowly-buried and biodegraded crude oil deposit in Neogene rocks,the crude oil samples in the study area were normal.All of the crude oils were derived from lacustrine source rocks.According to biomarker compositions,the crude oils could be divided into two families,A and B,distinctions that were reinforced by differences in carbon isotope composition and spatial distribution.Oil-source correlation analysis based on biomarkers revealed that Family A oils were derived from the mature oil shale at the bottom of the second member of the Liushagang Formation,while the Family B oils formed in the mature shale of the Liushagang Formation.The Family A oils,generated by oil shale,mainly migrated laterally along sand bodies and were then redistributed in adjacent reservoirs above and below the oil shale layer,as well as in shallow layers at high structural positions,occupying a wide distribution range.The Family B oils were generated by other shale units before migrating vertically along faults to form reservoirs nearby,resulting in a narrow distribution range.
基金supported by the Certificate of National Science and Technology Major Project of the Ministry of Science and Technology of China(2016ZX05006-007-004)National Natural Science Foundation of China(41702139,41772138,41602142,42072130)the Fundamental Research Funds for the Central Universities(18CX02008A)。
文摘The mechanisms of lacustrine organic-rich shale formation have attracted attention due to its association with global shale oil and shale gas exploration.Samples of general-quality and excellent-quality source rocks,and oil shale from the Beibu Gulf Basin were analyzed to investigate their organic geochemistry,palynofacies,and trace elements.Hydrocarbon potential was higher in the oil shale(29.79 mg/g)than in the general-quality source rock(3.82 mg/g),and its kerogen type wasⅠ-Ⅱ2.Hydrogen-rich liptinite(cutinite and sporinite)components derived from terrigenous higher plants provided most of the hydrocarbon potential of excellent-quality source rock and oil shale.Under the influence of depressioncontrolling fault activity,a deeper subsidence center promotes the deposition of excellent-quality source rock and oil shale in brackish-hypoxic bottom water.A shallower subsidence center,due to subsag-controlling fault activity,promotes the formation of excellent-quality source rock under freshbrackish and weak oxidation-weak reducing conditions.The local uplift and shallow-slope led to the formation of general-quality source rock,under freshwater weak-oxidation conditions.A model was established for organic matter(OM)accumulation in organic-rich shales,accounting for fault activity,terrigenous hydrogen-rich OM,and the preservation conditions,to predict the development of excellent-quality source rock from areas with low levels of exploration.
基金funded by the National Science and Technology Major Project for China’s 13th-Five-Year-Plan:High-temperature and high-pressure natural gas enrichment laws and key Technologies for Exploration and Development in Ying-Qiong Basin(Phase III)(Project NO.2016ZX05024-005).
文摘The Leidong depression is one of the secondary tectonic units and the least explored part of the Beibu Gulf Basin,northern South China Sea.Exploration activities in the basin reveal that the Middle Eocene deposition was controlled by NE-SW-striking faults and the second member of the Eocene Liushagang Formation(LII)consists of high-quality source rocks.The nature and origin of this depression has remained enigmatic due to the complex fault structures as compared to those in other basins.It is important to identify whether LII occurs in the Leidong depression in the context of exploration.Here we analyze available geological,seismic,and drilling data of the depression and the controlling factors among faults,deposition,lithology,and hydrocarbon distribution in the basin.Measures such as stress fracture analysis,fault growth index analysis,and sedimentary strata characterization were used to construct an Eocene sedimentary model controlled by NW-SE striking faults.The model with integrated seismic profile characteristics comparison and velocity analysis results was then used to determine whether the Eocene strata in the west of the depression contain the high-quality source rocks that are widely distributed elsewhere in the basin.Finally,calculations were performed to quantify the intensity of hydrocarbon generation and amount of hydrocarbon generated in the depression based on available data of the source rocks,including their distribution and thickness.The results confirmed the assumption that the Middle Eocene strata in the Leidong depression were controlled by NW-SE strike-slip faults and contain high-quality LII source rocks,thus providing an important foundation for future exploration.
