To solve the problems in restoring sedimentary facies and predicting reservoirs in loose gas-bearing sediment,based on seismic sedimentologic analysis of the first 9-component S-wave 3D seismic dataset of China,a four...To solve the problems in restoring sedimentary facies and predicting reservoirs in loose gas-bearing sediment,based on seismic sedimentologic analysis of the first 9-component S-wave 3D seismic dataset of China,a fourth-order isochronous stratigraphic framework was set up and then sedimentary facies and reservoirs in the Pleistocene Qigequan Formation in Taidong area of Qaidam Basin were studied by seismic geomorphology and seismic lithology.The study method and thought are as following.Firstly,techniques of phase rotation,frequency decomposition and fusion,and stratal slicing were applied to the 9-component S-wave seismic data to restore sedimentary facies of major marker beds based on sedimentary models reflected by satellite images.Then,techniques of seismic attribute extraction,principal component analysis,and random fitting were applied to calculate the reservoir thickness and physical parameters of a key sandbody,and the results are satisfactory and confirmed by blind testing wells.Study results reveal that the dominant sedimentary facies in the Qigequan Formation within the study area are delta front and shallow lake.The RGB fused slices indicate that there are two cycles with three sets of underwater distributary channel systems in one period.Among them,sandstones in the distributary channels of middle-low Qigequan Formation are thick and broad with superior physical properties,which are favorable reservoirs.The reservoir permeability is also affected by diagenesis.Distributary channel sandstone reservoirs extend further to the west of Sebei-1 gas field,which provides a basis to expand exploration to the western peripheral area.展开更多
A correct understanding of organic matter abundance is key to understanding the conditions necessary for generating biogenic gas,seeking favorable exploration intervals and fields and evaluating resources correctly.Th...A correct understanding of organic matter abundance is key to understanding the conditions necessary for generating biogenic gas,seeking favorable exploration intervals and fields and evaluating resources correctly.The Qigequan Formation shale of the Quaternary in the Sanhu Depression of the Qaidam Basin is taken as the research object.The abundance of dissolved organic matter was determined through total carbon,pyrolysis and other experiments.The evaluation criteria were established and applied.The resource quality is calculated.The results are as follows.(1)Dissolved organic matter is the basis for biogenic gas generation and should be emphasized in the evaluation.(2)The shale has a relatively high dissolved organic carbon(DOC)content,with an average of 2.48 times that of insoluble organic carbon.(3)The DOC of the good source rock is more than 0.60%,that of the medium is 0.25~0.60%,and that of the poor is less than 0.25%.(4)The distribution of good source rocks is influenced by the position and depth of the water column and the paleoclimate.Favorable intervals are mainly in the upper sections of K10,K9 and K8 and the middle section of K7.The favorable areas are mainly the Tainan,Sebei and Sedong areas.展开更多
Influenced by neo-tectonic movement, the Sanhu area of China＇s Qaidam Basin formed in the Quaternary in response to migration of its depocentre. A study of core material from the Qijia 1 Well reveals novel Quaternary...Influenced by neo-tectonic movement, the Sanhu area of China＇s Qaidam Basin formed in the Quaternary in response to migration of its depocentre. A study of core material from the Qijia 1 Well reveals novel Quaternary aqueously deposited aeolian sandstones in the Qigequan Formation of the Sanhu area. Here we report the sedimentary petrology and geochemistry data of these deposits that constrain their depositional history. Evidence for aeolian influence during deposition includes： sorting and roundness, pure quartz sand with single mode grain size distribution and few suspension materials,very fine sand grain size distribution indicating sorting by saltation and suspension transport, dish-shaped and crescentshaped pits in grain surfaces indicating aeolian transport and chemical composition similar to that observed in active or recent dune deposits, namely enrichment in Si O_2, Na_2 O, and Mg O relative to the sand dam sediment in the lakeshore.Identification of these aqueously deposited aeolian sandstones expands the range of sedimentary deposit types found in the Sanhu area and improves understanding of its paleoclimatic history.展开更多
Trace elements and rare earth elements(REEs)of two kinds of organic facies samples representing marginal and more basin-center deposits from Pleistocene lacustrine mudstones in the central Qaidam Basin were studied to...Trace elements and rare earth elements(REEs)of two kinds of organic facies samples representing marginal and more basin-center deposits from Pleistocene lacustrine mudstones in the central Qaidam Basin were studied to understand the provenance,palaeotectonic setting,hydrothermal activity,palaeoredox conditions and sedimentary rate.The results show that the lacustrine mudstones were mainly derived from felsic sources with little contribution from ancient crustal sediments and no ultramafic(ophiolitic)source.The mudstones were deposited in a continental island arc tectonic setting,which is consistent with the tectonic evolution of the Cenozoic basin.Both two organic facies samples were hydrothermal in origin based on the ternary diagram of Ni–Zn–Co and normalized REE patterns.However,this does not mean that the water column in paleolake was affected by hydrothermal fluids in situ.This signal might indicate hydrothermal origins from hot springs related to active faults around the basin rather than the deep hydrothermal fluids entering the sediments via deep faculties based on the comprehensive analyses of normalized REE patterns,negative E_(uanom)(Eu anomaly),Y/Ho,Sm/Yb,and Eu/Sm.Redox proxies including U/Th,Ni/Co,and Mnanom values,are more sensitive for the studied samples indicating that most of the organic facies A samples were deposited under an oxygen-depleted condition,while the organic facies B samples were deposited under oxygen-rich conditions.Redox proxies of Ceanom values are unavailable for the organic facies B samples due to hypersaline environments,and V/C_(r)and V/(V+Ni)are invalid for the organic facies A samples,possibly because of their organism composition.The low Lan/Ybn values indicate high sedimentation rates,which is consistent with the average sedimentation rates of approximately 0.43 to 1.1 km/Ma.However,the La_(n)/Yb_(n) is more likely affected by the provenance of the studied samples,so it should be used with caution.展开更多
基金Supported by the CNPC Science and Technology Projects(2022-N/G-47808,2023-N/G-67014)RIPED International Cooperation Project(19HTY5000008).
文摘To solve the problems in restoring sedimentary facies and predicting reservoirs in loose gas-bearing sediment,based on seismic sedimentologic analysis of the first 9-component S-wave 3D seismic dataset of China,a fourth-order isochronous stratigraphic framework was set up and then sedimentary facies and reservoirs in the Pleistocene Qigequan Formation in Taidong area of Qaidam Basin were studied by seismic geomorphology and seismic lithology.The study method and thought are as following.Firstly,techniques of phase rotation,frequency decomposition and fusion,and stratal slicing were applied to the 9-component S-wave seismic data to restore sedimentary facies of major marker beds based on sedimentary models reflected by satellite images.Then,techniques of seismic attribute extraction,principal component analysis,and random fitting were applied to calculate the reservoir thickness and physical parameters of a key sandbody,and the results are satisfactory and confirmed by blind testing wells.Study results reveal that the dominant sedimentary facies in the Qigequan Formation within the study area are delta front and shallow lake.The RGB fused slices indicate that there are two cycles with three sets of underwater distributary channel systems in one period.Among them,sandstones in the distributary channels of middle-low Qigequan Formation are thick and broad with superior physical properties,which are favorable reservoirs.The reservoir permeability is also affected by diagenesis.Distributary channel sandstone reservoirs extend further to the west of Sebei-1 gas field,which provides a basis to expand exploration to the western peripheral area.
基金supported by the Natural Science Foundation of China(No.41872135)the China Scholarship Council.
文摘A correct understanding of organic matter abundance is key to understanding the conditions necessary for generating biogenic gas,seeking favorable exploration intervals and fields and evaluating resources correctly.The Qigequan Formation shale of the Quaternary in the Sanhu Depression of the Qaidam Basin is taken as the research object.The abundance of dissolved organic matter was determined through total carbon,pyrolysis and other experiments.The evaluation criteria were established and applied.The resource quality is calculated.The results are as follows.(1)Dissolved organic matter is the basis for biogenic gas generation and should be emphasized in the evaluation.(2)The shale has a relatively high dissolved organic carbon(DOC)content,with an average of 2.48 times that of insoluble organic carbon.(3)The DOC of the good source rock is more than 0.60%,that of the medium is 0.25~0.60%,and that of the poor is less than 0.25%.(4)The distribution of good source rocks is influenced by the position and depth of the water column and the paleoclimate.Favorable intervals are mainly in the upper sections of K10,K9 and K8 and the middle section of K7.The favorable areas are mainly the Tainan,Sebei and Sedong areas.
基金funding support from the Qinghai Oilfield Company of the China National Petroleum Corporation
文摘Influenced by neo-tectonic movement, the Sanhu area of China＇s Qaidam Basin formed in the Quaternary in response to migration of its depocentre. A study of core material from the Qijia 1 Well reveals novel Quaternary aqueously deposited aeolian sandstones in the Qigequan Formation of the Sanhu area. Here we report the sedimentary petrology and geochemistry data of these deposits that constrain their depositional history. Evidence for aeolian influence during deposition includes： sorting and roundness, pure quartz sand with single mode grain size distribution and few suspension materials,very fine sand grain size distribution indicating sorting by saltation and suspension transport, dish-shaped and crescentshaped pits in grain surfaces indicating aeolian transport and chemical composition similar to that observed in active or recent dune deposits, namely enrichment in Si O_2, Na_2 O, and Mg O relative to the sand dam sediment in the lakeshore.Identification of these aqueously deposited aeolian sandstones expands the range of sedimentary deposit types found in the Sanhu area and improves understanding of its paleoclimatic history.
基金The study was granted financial support by the National Natural Science Foundation of China(Grant Nos.42202154 and 42002050)the Science Foundation of China University of Petroleum,Beijing(No.ZX20220074).
文摘Trace elements and rare earth elements(REEs)of two kinds of organic facies samples representing marginal and more basin-center deposits from Pleistocene lacustrine mudstones in the central Qaidam Basin were studied to understand the provenance,palaeotectonic setting,hydrothermal activity,palaeoredox conditions and sedimentary rate.The results show that the lacustrine mudstones were mainly derived from felsic sources with little contribution from ancient crustal sediments and no ultramafic(ophiolitic)source.The mudstones were deposited in a continental island arc tectonic setting,which is consistent with the tectonic evolution of the Cenozoic basin.Both two organic facies samples were hydrothermal in origin based on the ternary diagram of Ni–Zn–Co and normalized REE patterns.However,this does not mean that the water column in paleolake was affected by hydrothermal fluids in situ.This signal might indicate hydrothermal origins from hot springs related to active faults around the basin rather than the deep hydrothermal fluids entering the sediments via deep faculties based on the comprehensive analyses of normalized REE patterns,negative E_(uanom)(Eu anomaly),Y/Ho,Sm/Yb,and Eu/Sm.Redox proxies including U/Th,Ni/Co,and Mnanom values,are more sensitive for the studied samples indicating that most of the organic facies A samples were deposited under an oxygen-depleted condition,while the organic facies B samples were deposited under oxygen-rich conditions.Redox proxies of Ceanom values are unavailable for the organic facies B samples due to hypersaline environments,and V/C_(r)and V/(V+Ni)are invalid for the organic facies A samples,possibly because of their organism composition.The low Lan/Ybn values indicate high sedimentation rates,which is consistent with the average sedimentation rates of approximately 0.43 to 1.1 km/Ma.However,the La_(n)/Yb_(n) is more likely affected by the provenance of the studied samples,so it should be used with caution.
