The East China Sea Shelf Basin generated a series of back-arc basins with thick successions of marine-and terrestrial-facies sediments during Cenozoic.It is enriched with abundant oil and gas resources and is of great...The East China Sea Shelf Basin generated a series of back-arc basins with thick successions of marine-and terrestrial-facies sediments during Cenozoic.It is enriched with abundant oil and gas resources and is of great significance to the petroleum exploration undertakings.Therein,the Lishui Sag formed fan delta,fluvial delta and littoral-to-neritic facies sediments during Paleocene–Eocene,and the research on its sedimentary environment and sediment source was controversial.This study analyzed the paleontological combination characteristics,and conducted a source-to-sink comparative analysis to restore the sedimentary environment and provenance evolution of the Lishui Sag during Paleocene–Eocene based on the integration of detrital zircon U-Pb age spectra patterns with paleontological assemblages.The results indicated that Lishui Sag was dominated by littoral and neritic-facies environment during time corroborated by large abundance of foraminifera,calcareous nannofossils and dinoflagellates.Chronological analysis of detrital zircon U-Pb revealed that there were significant differences in sediment sources between the east and west area of the Lishui Sag.The western area was featured by deeper water depths in the Paleocene–Eocene,and the sediment was characterized by a single Yanshanian peak of zircon U-Pb age spectra,and mainly influenced from Yanshanian magmatic rocks of South China Coast and the surrounding paleo-uplifts.However,its eastern area partly showed Indosinian populations.In particular,the upper Eocene Wenzhou sediments were featured by increasingly plentiful Precambrian zircons in addition to the large Indosinian-Yanshanian peaks,indicating a possible impact from the Yushan Low Uplift to the east.Therefore,it is likely that the eastern Lishui Sag generated large river systems as well as deltas during time.Due to the Yuquan Movement,the Lishui Sag experienced uplifting and exhumation in the late stage of the late Eocene and was not deposited with sediments until Miocene.Featured by transitional-facies depositions of Paleocene–Eocene,the Lishui Sag thus beared significant potential for source rock and oil-gas reservoir accumulation.展开更多
The restoration of the denudation thickness is the basis for quantitatively analyzing the basin burial history,thermal evolution history and hydrocarbon accumulation conditions.The well data is not sufficient to do th...The restoration of the denudation thickness is the basis for quantitatively analyzing the basin burial history,thermal evolution history and hydrocarbon accumulation conditions.The well data is not sufficient to do this in the southern Lishui Sag with only 5 wells,so the new,high-quality three-dimensional(3D)seismic data is essential.The methods employed to determine the eroded thicknesses of key unconformities in the study area are the mudstone acoustic time difference(AC)method,vitrinite reflectance(Ro%)method and stratigraphic trend comparison method.On the basis of the structural evolution,the restoration of the paleogeomorphology is carried out.The results show that the Wenzhou formation(E2 w)in the entire study area has been all denuded.The denudation thickness is in the range of 0–550 m,and decreases gradually from west,thicker than 200 m,to east.The erosion of the upper Lingfeng formation(E1l)are mainly occurred in the N-P-1 structural trap(N-P-1),the N-P-2 structural trap(N-P-2)and the N-P-3 structural trap(N-P-3).Among them,the eroded area in N-P-1(near well S-1)and N-P-2 is 200–230 km^2,and the denudation thickness is 0–600 m,which increases from south to north,even up to 200–400 m in the region around well S-1.In N-P-3,the extent of denudation is 30–50 km^2,and the denudation thickness is 0–400 m.In the early stage of the upper E1 l,one north-south strike slip fault began to develop in the southern study area.Affected by this fault,the southern Lingfeng bulge was offset,forming a gorge,and the eastern and western sides of the concave belt connected to each other.On the basis of the paleo-geomorphological characteristics,it is shown that the sedimentary center of the west subsag began to migrate to the south.展开更多
In this study, the differences in reservoir parameters, such as pore radius, throat radius, and pore-throat ratio, between the east and west subsags of the Lishui Sag are analyzed by using data obtained from a constan...In this study, the differences in reservoir parameters, such as pore radius, throat radius, and pore-throat ratio, between the east and west subsags of the Lishui Sag are analyzed by using data obtained from a constant-rate mercury injection experiment. Furthermore, the quality of the reservoirs in the two subsags is systematically evaluated. Results show that the throat radius of the Lishui west subsag is larger than that of the east subsag, and this parameter has a positive correlation with reservoir quality. However, the pore-throat ratio of the east subsag is larger than that of the west subsag, which has an inverse relationship with reservoir quality. The main reasons for this reservoir difference can be attributed to sedimentation and diagenesis. The sedimentary facies types of the Lishui east subsag are the fan delta, shore lake, shallow lake, and shore shallow lake;their sandstone composition maturity is low;the clay mineral content is high;and the rock has undergone strong diagenesis. Therefore, the physical conditions of the reservoir are poor. However, the sandstones in the Lishui west subsag have weak cementation and compaction, mainly with an intergranular pore structure type, which leads to good connectivity between pores. Therefore, the storage performance and seepage capacity of the Lishui west subsag are better than those of the east subsag;the west subsag is the main area of oil and gas accumulation, as confirmed in the process of exploration and development.展开更多
Estimation of base level changes in geological records is an important topic for petroleum geologists.Taking the Paleocene Upper Lingfeng Member of Lishui Sag as an example,this paper conducted a base level reconstruc...Estimation of base level changes in geological records is an important topic for petroleum geologists.Taking the Paleocene Upper Lingfeng Member of Lishui Sag as an example,this paper conducted a base level reconstruction based on Basin Filling Modelling(BFM).The reconstruction was processed on the ground of a previously interpreted seismic stratigraphic framework with several assumptions and simplification.The BFM is implemented with a nonlinear diffusion equation solver written in R coding that excels in shallow marine stratigraphic simulation.The modeled results fit the original stratigraphy very well.The BFM is a powerful tool for reconstructing the base level,and is an effective way to check the reasonableness of previous interpretations.Although simulation solutions may not be unique,the BFM still provides us a chance to gain some insights into the mechanism and dynamic details of the stratigraphy of sedimentary basins.展开更多
The Lishui Sag,in the East China Sea Shelf Basin,is rich in hydrocarbons,with the major hydrocarbon-bearing layers being the Paleocene Mingyuefeng clastic rocks.Analysis of the implicit geologic background information...The Lishui Sag,in the East China Sea Shelf Basin,is rich in hydrocarbons,with the major hydrocarbon-bearing layers being the Paleocene Mingyuefeng clastic rocks.Analysis of the implicit geologic background information of these Paleocene clastic rocks using petrological and geochemical methods has significant practical importance.These Paleocene sandstones are mainly lithic arenite,lithic arkose and greywacke,composed of K-feldspar,plagioclase,authigenic clays,silica and carbonates.As continental deposits,Yueguifeng clastic rocks have high aluminosilicate and mafic detritus contents,while the Lingfeng and Mingyuefeng Formations are rich in silica due to an oscillating coastal marine depositional environment The major element contents of these Paleocene sandstones are low and have a concentrated distribution,indicating that the geochemical composition is non-epigenetic,transformed by sedimentary processes and diagenesis.The Yueguifeng detritus comprises recycled sediments,controlled by moderate weathering and erosion,while the Lingfeng and Mingyuefeng detritus is interpreted as primarily first-cycle materials due to low chemical weathering.In the Late Cretaceous to Early Paleocene,the Pacific Plate began subducting under the Eurasian Plate,causing an orogeny by plate collision and magma eruption due to the melting of subducted oceanic crust.This resulted in the dual tectonic settings of"active margin"and"continental island arc"in the East China Sea Shelf Basin.During the Late Paleocene,the Pacific Plate margin migrated eastward along with development of the Philippine Ocean Plate,and the tectonic setting of the Lishui Sag gradually turned into a passive continental margin.Detrital sources included both orogenic continental blocks and continental island arcs,and the parent rocks are primarily felsic volcanic rocks and granites.展开更多
Natural gases discovered up to now in Lishui Sag,the East China Sea Basin,differ greatly in gaseous compositions,of which hydrocarbon gases amount to 2%―94%while non-hydrocarbon gases are dominated by CO2.Their hydro...Natural gases discovered up to now in Lishui Sag,the East China Sea Basin,differ greatly in gaseous compositions,of which hydrocarbon gases amount to 2%―94%while non-hydrocarbon gases are dominated by CO2.Their hydrocarbon gases,without exception,contain less than 90%of methane and over 10%of C2 + heavier hydrocarbons,indicating a wet gas.Carbon isotopic analyses on these hydrocarbon gases showed thatδ13C 1 ,δ13C 2 andδ13C 3 are basically lighter than-44‰,-29‰and-26‰, respectively.The difference in carbon isotopic values between methane and ethane is great,suggesting a biogenic oil-type gas produced by the mixed organic matter at peak generation.δ13C CO2 values of nonhydrocarbon gases are all heavier than-10‰,indicating a typical abiogenic gas.The simulation experiment on hydrocarbon generation of organic matter in a closed gold-tube system showed that the proportion of methane in natural gases produced by terrigenous organic matter in the Lingfeng Formation marine deposit is obviously higher than that in natural gases derived from the aquatic and terrigenous mixed organic matter in the Yueguifeng Formation lacustrine deposit,consequently the proportion of heavier hydrocarbons of the former is remarkably lower than that of the latter.Moreover, δ13C 1 values of natural gases produced by terrigenous organic matter in the Lingfeng Formation marine deposit are about 5‰heavier than those of natural gases derived from the aquatic and terrigenous mixed organic matter in the Yueguifeng Formation lacustrine deposit whileδ13C 2 andδ13C 3 values of the former are over 9‰heavier than those of the latter.Currently the LS36-1 oil-gas pool is the only commercial oil-gas reservoir in Lishui Sag,where carbon isotopic compositions of various hydrocarbon components differ greatly from those of natural gases produced by the Lingfeng Formation organic matter but are very similar to those of natural gases derived from the Yueguifeng Formation organic matter,therefore,natural gases in the LS36-1 oil-gas pool are mainly derived from the Yueguifeng Formation lacustrine source rock rather than the Lingfeng Formation marine or Mingyuefeng Formation coal-measures source rocks.展开更多
基金The National Natural Science Foundation of China under contract Nos 42076066 and 92055203。
文摘The East China Sea Shelf Basin generated a series of back-arc basins with thick successions of marine-and terrestrial-facies sediments during Cenozoic.It is enriched with abundant oil and gas resources and is of great significance to the petroleum exploration undertakings.Therein,the Lishui Sag formed fan delta,fluvial delta and littoral-to-neritic facies sediments during Paleocene–Eocene,and the research on its sedimentary environment and sediment source was controversial.This study analyzed the paleontological combination characteristics,and conducted a source-to-sink comparative analysis to restore the sedimentary environment and provenance evolution of the Lishui Sag during Paleocene–Eocene based on the integration of detrital zircon U-Pb age spectra patterns with paleontological assemblages.The results indicated that Lishui Sag was dominated by littoral and neritic-facies environment during time corroborated by large abundance of foraminifera,calcareous nannofossils and dinoflagellates.Chronological analysis of detrital zircon U-Pb revealed that there were significant differences in sediment sources between the east and west area of the Lishui Sag.The western area was featured by deeper water depths in the Paleocene–Eocene,and the sediment was characterized by a single Yanshanian peak of zircon U-Pb age spectra,and mainly influenced from Yanshanian magmatic rocks of South China Coast and the surrounding paleo-uplifts.However,its eastern area partly showed Indosinian populations.In particular,the upper Eocene Wenzhou sediments were featured by increasingly plentiful Precambrian zircons in addition to the large Indosinian-Yanshanian peaks,indicating a possible impact from the Yushan Low Uplift to the east.Therefore,it is likely that the eastern Lishui Sag generated large river systems as well as deltas during time.Due to the Yuquan Movement,the Lishui Sag experienced uplifting and exhumation in the late stage of the late Eocene and was not deposited with sediments until Miocene.Featured by transitional-facies depositions of Paleocene–Eocene,the Lishui Sag thus beared significant potential for source rock and oil-gas reservoir accumulation.
基金supported by the National Science and Technology Major Projects(No.2016ZX05027-001-006)
文摘The restoration of the denudation thickness is the basis for quantitatively analyzing the basin burial history,thermal evolution history and hydrocarbon accumulation conditions.The well data is not sufficient to do this in the southern Lishui Sag with only 5 wells,so the new,high-quality three-dimensional(3D)seismic data is essential.The methods employed to determine the eroded thicknesses of key unconformities in the study area are the mudstone acoustic time difference(AC)method,vitrinite reflectance(Ro%)method and stratigraphic trend comparison method.On the basis of the structural evolution,the restoration of the paleogeomorphology is carried out.The results show that the Wenzhou formation(E2 w)in the entire study area has been all denuded.The denudation thickness is in the range of 0–550 m,and decreases gradually from west,thicker than 200 m,to east.The erosion of the upper Lingfeng formation(E1l)are mainly occurred in the N-P-1 structural trap(N-P-1),the N-P-2 structural trap(N-P-2)and the N-P-3 structural trap(N-P-3).Among them,the eroded area in N-P-1(near well S-1)and N-P-2 is 200–230 km^2,and the denudation thickness is 0–600 m,which increases from south to north,even up to 200–400 m in the region around well S-1.In N-P-3,the extent of denudation is 30–50 km^2,and the denudation thickness is 0–400 m.In the early stage of the upper E1 l,one north-south strike slip fault began to develop in the southern study area.Affected by this fault,the southern Lingfeng bulge was offset,forming a gorge,and the eastern and western sides of the concave belt connected to each other.On the basis of the paleo-geomorphological characteristics,it is shown that the sedimentary center of the west subsag began to migrate to the south.
基金supported by the National Natural Science Foundation of China (Nos. 51504143 and 51674156)the SDUST Research Fund (No. 2015DJH101)the Major National R&D Projects of China (No. 2016ZX0 5027-001-006)。
文摘In this study, the differences in reservoir parameters, such as pore radius, throat radius, and pore-throat ratio, between the east and west subsags of the Lishui Sag are analyzed by using data obtained from a constant-rate mercury injection experiment. Furthermore, the quality of the reservoirs in the two subsags is systematically evaluated. Results show that the throat radius of the Lishui west subsag is larger than that of the east subsag, and this parameter has a positive correlation with reservoir quality. However, the pore-throat ratio of the east subsag is larger than that of the west subsag, which has an inverse relationship with reservoir quality. The main reasons for this reservoir difference can be attributed to sedimentation and diagenesis. The sedimentary facies types of the Lishui east subsag are the fan delta, shore lake, shallow lake, and shore shallow lake;their sandstone composition maturity is low;the clay mineral content is high;and the rock has undergone strong diagenesis. Therefore, the physical conditions of the reservoir are poor. However, the sandstones in the Lishui west subsag have weak cementation and compaction, mainly with an intergranular pore structure type, which leads to good connectivity between pores. Therefore, the storage performance and seepage capacity of the Lishui west subsag are better than those of the east subsag;the west subsag is the main area of oil and gas accumulation, as confirmed in the process of exploration and development.
基金the Initial Fund for Young Scholars of Qingdao University of Science and Technology and the National Natural Science Foundation of China(No.51804325)。
文摘Estimation of base level changes in geological records is an important topic for petroleum geologists.Taking the Paleocene Upper Lingfeng Member of Lishui Sag as an example,this paper conducted a base level reconstruction based on Basin Filling Modelling(BFM).The reconstruction was processed on the ground of a previously interpreted seismic stratigraphic framework with several assumptions and simplification.The BFM is implemented with a nonlinear diffusion equation solver written in R coding that excels in shallow marine stratigraphic simulation.The modeled results fit the original stratigraphy very well.The BFM is a powerful tool for reconstructing the base level,and is an effective way to check the reasonableness of previous interpretations.Although simulation solutions may not be unique,the BFM still provides us a chance to gain some insights into the mechanism and dynamic details of the stratigraphy of sedimentary basins.
基金supported by the Fundamental Research Funds for the Central Universities of Ocean University of China(201413005)a China National Science and Technology Major Project(2011ZX05023003)Shanghai Branch,China National Offshore Oil Co.,Ltd.(CNOOC)
文摘The Lishui Sag,in the East China Sea Shelf Basin,is rich in hydrocarbons,with the major hydrocarbon-bearing layers being the Paleocene Mingyuefeng clastic rocks.Analysis of the implicit geologic background information of these Paleocene clastic rocks using petrological and geochemical methods has significant practical importance.These Paleocene sandstones are mainly lithic arenite,lithic arkose and greywacke,composed of K-feldspar,plagioclase,authigenic clays,silica and carbonates.As continental deposits,Yueguifeng clastic rocks have high aluminosilicate and mafic detritus contents,while the Lingfeng and Mingyuefeng Formations are rich in silica due to an oscillating coastal marine depositional environment The major element contents of these Paleocene sandstones are low and have a concentrated distribution,indicating that the geochemical composition is non-epigenetic,transformed by sedimentary processes and diagenesis.The Yueguifeng detritus comprises recycled sediments,controlled by moderate weathering and erosion,while the Lingfeng and Mingyuefeng detritus is interpreted as primarily first-cycle materials due to low chemical weathering.In the Late Cretaceous to Early Paleocene,the Pacific Plate began subducting under the Eurasian Plate,causing an orogeny by plate collision and magma eruption due to the melting of subducted oceanic crust.This resulted in the dual tectonic settings of"active margin"and"continental island arc"in the East China Sea Shelf Basin.During the Late Paleocene,the Pacific Plate margin migrated eastward along with development of the Philippine Ocean Plate,and the tectonic setting of the Lishui Sag gradually turned into a passive continental margin.Detrital sources included both orogenic continental blocks and continental island arcs,and the parent rocks are primarily felsic volcanic rocks and granites.
基金the Research Project of CNOOC(Grant No.CT/04-EXP-009)
文摘Natural gases discovered up to now in Lishui Sag,the East China Sea Basin,differ greatly in gaseous compositions,of which hydrocarbon gases amount to 2%―94%while non-hydrocarbon gases are dominated by CO2.Their hydrocarbon gases,without exception,contain less than 90%of methane and over 10%of C2 + heavier hydrocarbons,indicating a wet gas.Carbon isotopic analyses on these hydrocarbon gases showed thatδ13C 1 ,δ13C 2 andδ13C 3 are basically lighter than-44‰,-29‰and-26‰, respectively.The difference in carbon isotopic values between methane and ethane is great,suggesting a biogenic oil-type gas produced by the mixed organic matter at peak generation.δ13C CO2 values of nonhydrocarbon gases are all heavier than-10‰,indicating a typical abiogenic gas.The simulation experiment on hydrocarbon generation of organic matter in a closed gold-tube system showed that the proportion of methane in natural gases produced by terrigenous organic matter in the Lingfeng Formation marine deposit is obviously higher than that in natural gases derived from the aquatic and terrigenous mixed organic matter in the Yueguifeng Formation lacustrine deposit,consequently the proportion of heavier hydrocarbons of the former is remarkably lower than that of the latter.Moreover, δ13C 1 values of natural gases produced by terrigenous organic matter in the Lingfeng Formation marine deposit are about 5‰heavier than those of natural gases derived from the aquatic and terrigenous mixed organic matter in the Yueguifeng Formation lacustrine deposit whileδ13C 2 andδ13C 3 values of the former are over 9‰heavier than those of the latter.Currently the LS36-1 oil-gas pool is the only commercial oil-gas reservoir in Lishui Sag,where carbon isotopic compositions of various hydrocarbon components differ greatly from those of natural gases produced by the Lingfeng Formation organic matter but are very similar to those of natural gases derived from the Yueguifeng Formation organic matter,therefore,natural gases in the LS36-1 oil-gas pool are mainly derived from the Yueguifeng Formation lacustrine source rock rather than the Lingfeng Formation marine or Mingyuefeng Formation coal-measures source rocks.
