Sediments in the Liushagang Formation of Late Eocene form a group of key hydrocarbon play fairways in the Beibuwan Basin,South China Sea.As an important reservoir-forming combination,the Liushagang Formation consists ...Sediments in the Liushagang Formation of Late Eocene form a group of key hydrocarbon play fairways in the Beibuwan Basin,South China Sea.As an important reservoir-forming combination,the Liushagang Formation consists of deltaic siliciclastic and show clear sedimentary cyclicity.According to paleontology research and stratigraphic correlation,the boundary between Liushagang Formation(Els)and Weizhou Formation(Ewz)is regarded as the Eocene-Oligocene boundary.The oxygen isotope dating for well cores from the top of the first Member of Liushagang Formation(Els1)and the bottom of the third Member of Weizhou Formation(Ewz3)give an isochron age of 35.2 Ma.Here,we use GR logging data as a paleoenvironmental proxy to conduct a detailed cyclostratigraphic study of the Els1 in the Bailian Sag,Fushan Depression.Power spectra,evolutionary fast Fourier transformation and wavelet analysis all reveal significant sedimentary cycles in Els1.The ratios of cycle wavelengths in these stratigraphic units are 21?5?2.8?1.2?1,and are interpreted as Milankovitch cycles of 400 ka and 96 ka eccentricity,52 ka obliquity,22ka and 19 ka precession cycles,respectively.An astronomical time scale is established by tuning filtered 96 ka eccentricity cycles to a target curve of Well L2 in the Bailian Sag.Based on regional stratigraphic framework,combined with seismic,cores and logging data,the HST of the first member of the Liushagang Formation(Els1)delta in Well L2 was divided into six parasequence sets named Ps1-Ps6.According to the spectrum analysis by Simple Lomb periodogram from PAST program packages,the sediment accumulation rate of each parasequence sets first increased and then decreased as time went by.The sediment accumulation rate of Ps4 reached the maximum(0.127 m/ka)during the most prosperous period of delta prograding.Finally,the duration of each period of parasequence sets and more accurate geological age were calculated on the basis of sediment accumulation rate.The ages of each depth are precisely estimated and provide new constraints on the Late Eocene.展开更多
Effective carrier system comprises carrier beds which transport hydrocarbons. The spatial and temporal effectiveness of carrier system is identified according to the relevance of hydrocarbon show, hydrocarbon inclusio...Effective carrier system comprises carrier beds which transport hydrocarbons. The spatial and temporal effectiveness of carrier system is identified according to the relevance of hydrocarbon show, hydrocarbon inclusion and sealing ability of fault to hydrocarbons distribution, together with matching relation of activity history of fault and hydrocarbon generation history of source rock. On the basis of the above considerations, transporting ability of effective carrier system can be evaluated using parameters such as fluid potential, porosity and permeability, spatial coefficient of effective pathway as well as activity rate of fault. Additionally, a new concept of＂transporting threshold porosity＂ was proposed. Five styles of effective carrier systems were established in Gaoyou Sag, displaying either layered or zonal distribution characteristics, and transporting time ranges from the sedimentary time of Ezdz to early stage of sanduo uplift. Effective carrier systems can be described to be lowly-efficient and highly-efficient. Major faults （convex or steep fault plane） with activity rate greater than 20 m/Ma and structure ridges of sand layers with spatial coefficient of effective pathway greater than 25% are defined to be highly-efficient carrier beds. Hydrocarbons are concentrated around high-efficient carrier beds and E1 f traps of northern shanian area are predicted to have great potential.展开更多
The oblique transfer zone in the Fushan Sag, a syndepositional dome sandwiched between the Bailian and Huangtong sub-sags, has been the most important exploration target. The major oil observation occurs in the E_2l_1...The oblique transfer zone in the Fushan Sag, a syndepositional dome sandwiched between the Bailian and Huangtong sub-sags, has been the most important exploration target. The major oil observation occurs in the E_2l_1^(L+M) and the E_2l_3~U. 46 oil and rock samples reveal that the oil in the transfer zone is mostly contributed by the Bailian sub-sag, though the source rock conditions, hydrocarbon generation and expulsion histories of the Bailian and Huangtong sub-sags are similar. The E_2l_3~U oil, characterized by high maturity, Pr/Ph ratio and oleanane/C_(30)-hopane ratio, shows a close genetic affinity with the E_2l_3~b source rocks, while the E_2l_1^(L+M) oil, characterized by lower maturity, Pr/Ph ratio and oleanane/C_(30)-hopane ratio, is suggested to be derived from the E_2l_(1+2)~b source rocks. The homogenization temperatures of aqueous fluid inclusions, taking the burial history of the reservoirs into account, reflect that the oil charge mainly occurred from mid-Miocene to Pliocene in the oblique transfer zone. The oil transporting passages include connected sand bodies, unconformities and faults in the Fushan Sag. Of these, the faults are the most complicated and significant. The faults differ sharply in the west area, the east area and the oblique transfer zone, resulting in different influence on the oil migration and accumulation. During the main hydrocarbon charge stage, the faults in the west area are characterized by bad vertical sealing and spatially dense distribution. As a result, the oil generated by the Huangtong source rocks is mostly lost along the faults during the vertical migration in the west area. This can be the mechanism proposed to explain the little contribution of the Huangtong source rocks to the oil in the oblique transfer zone. Eventually, an oil migration and accumulation model is built in the oblique transfer zone, which may provide theoretical and practical guides for the oil exploration.展开更多
基金Projects(41472084,41172123) supported by the National Natural Science Foundation of China
文摘Sediments in the Liushagang Formation of Late Eocene form a group of key hydrocarbon play fairways in the Beibuwan Basin,South China Sea.As an important reservoir-forming combination,the Liushagang Formation consists of deltaic siliciclastic and show clear sedimentary cyclicity.According to paleontology research and stratigraphic correlation,the boundary between Liushagang Formation(Els)and Weizhou Formation(Ewz)is regarded as the Eocene-Oligocene boundary.The oxygen isotope dating for well cores from the top of the first Member of Liushagang Formation(Els1)and the bottom of the third Member of Weizhou Formation(Ewz3)give an isochron age of 35.2 Ma.Here,we use GR logging data as a paleoenvironmental proxy to conduct a detailed cyclostratigraphic study of the Els1 in the Bailian Sag,Fushan Depression.Power spectra,evolutionary fast Fourier transformation and wavelet analysis all reveal significant sedimentary cycles in Els1.The ratios of cycle wavelengths in these stratigraphic units are 21?5?2.8?1.2?1,and are interpreted as Milankovitch cycles of 400 ka and 96 ka eccentricity,52 ka obliquity,22ka and 19 ka precession cycles,respectively.An astronomical time scale is established by tuning filtered 96 ka eccentricity cycles to a target curve of Well L2 in the Bailian Sag.Based on regional stratigraphic framework,combined with seismic,cores and logging data,the HST of the first member of the Liushagang Formation(Els1)delta in Well L2 was divided into six parasequence sets named Ps1-Ps6.According to the spectrum analysis by Simple Lomb periodogram from PAST program packages,the sediment accumulation rate of each parasequence sets first increased and then decreased as time went by.The sediment accumulation rate of Ps4 reached the maximum(0.127 m/ka)during the most prosperous period of delta prograding.Finally,the duration of each period of parasequence sets and more accurate geological age were calculated on the basis of sediment accumulation rate.The ages of each depth are precisely estimated and provide new constraints on the Late Eocene.
基金Project(P08045)supported by Geological Research Institute of Jiangsu Oilfield Company,SINOPEC,China
文摘Effective carrier system comprises carrier beds which transport hydrocarbons. The spatial and temporal effectiveness of carrier system is identified according to the relevance of hydrocarbon show, hydrocarbon inclusion and sealing ability of fault to hydrocarbons distribution, together with matching relation of activity history of fault and hydrocarbon generation history of source rock. On the basis of the above considerations, transporting ability of effective carrier system can be evaluated using parameters such as fluid potential, porosity and permeability, spatial coefficient of effective pathway as well as activity rate of fault. Additionally, a new concept of＂transporting threshold porosity＂ was proposed. Five styles of effective carrier systems were established in Gaoyou Sag, displaying either layered or zonal distribution characteristics, and transporting time ranges from the sedimentary time of Ezdz to early stage of sanduo uplift. Effective carrier systems can be described to be lowly-efficient and highly-efficient. Major faults （convex or steep fault plane） with activity rate greater than 20 m/Ma and structure ridges of sand layers with spatial coefficient of effective pathway greater than 25% are defined to be highly-efficient carrier beds. Hydrocarbons are concentrated around high-efficient carrier beds and E1 f traps of northern shanian area are predicted to have great potential.
基金Project(41272122)supported by the National Natural Science Foundation of China
文摘The oblique transfer zone in the Fushan Sag, a syndepositional dome sandwiched between the Bailian and Huangtong sub-sags, has been the most important exploration target. The major oil observation occurs in the E_2l_1^(L+M) and the E_2l_3~U. 46 oil and rock samples reveal that the oil in the transfer zone is mostly contributed by the Bailian sub-sag, though the source rock conditions, hydrocarbon generation and expulsion histories of the Bailian and Huangtong sub-sags are similar. The E_2l_3~U oil, characterized by high maturity, Pr/Ph ratio and oleanane/C_(30)-hopane ratio, shows a close genetic affinity with the E_2l_3~b source rocks, while the E_2l_1^(L+M) oil, characterized by lower maturity, Pr/Ph ratio and oleanane/C_(30)-hopane ratio, is suggested to be derived from the E_2l_(1+2)~b source rocks. The homogenization temperatures of aqueous fluid inclusions, taking the burial history of the reservoirs into account, reflect that the oil charge mainly occurred from mid-Miocene to Pliocene in the oblique transfer zone. The oil transporting passages include connected sand bodies, unconformities and faults in the Fushan Sag. Of these, the faults are the most complicated and significant. The faults differ sharply in the west area, the east area and the oblique transfer zone, resulting in different influence on the oil migration and accumulation. During the main hydrocarbon charge stage, the faults in the west area are characterized by bad vertical sealing and spatially dense distribution. As a result, the oil generated by the Huangtong source rocks is mostly lost along the faults during the vertical migration in the west area. This can be the mechanism proposed to explain the little contribution of the Huangtong source rocks to the oil in the oblique transfer zone. Eventually, an oil migration and accumulation model is built in the oblique transfer zone, which may provide theoretical and practical guides for the oil exploration.
