Diagenetic traps in conglomerate in nearshore subaqueous fans in the steep slope zones of rift basins have been important exploration targets for subtle reservoirs in eastern China. However, the mechanism of how those...Diagenetic traps in conglomerate in nearshore subaqueous fans in the steep slope zones of rift basins have been important exploration targets for subtle reservoirs in eastern China. However, the mechanism of how those traps were formed is not clear, which inhibits further exploration for this type of reservoir. In order to solve the problem, we take as an example nearshore subaqueous fans in the upper part of the fourth member of the Shahejie Formation(Es4s) on the north slope of the Minfeng Subsag in the Dongying Sag. Combining different research methods, such as core observation, thin section examination, scanning electron microscope(SEM) observation, fluid-inclusion analysis, carbon and oxygen isotope analysis of carbonate cements, and analysis of core properties, we studied the genetic mechanisms of diagenetic traps on the basis of diagenetic environment evolution and diagenetic evolution sequence in different sub/micro-facies. Conglomerate in Es4 s in the north Minfeng Subsag experienced several periods of transition between alkaline and acidic environments as "alkaline–acidic–alkaline–acidic–weak alkaline". As a result, dissolution and cementation are also very complex, and the sequence is "early pyrite cementation / siderite cementation / gypsum cementation / calcite and dolomite cementation——feldspar dissolution / quartz overgrowth——quartz dissolution / ferroan calcite cementation / ankerite cementation / lime-mud matrix recrystallization / feldspar overgrowth——carbonate dissolution / feldspar dissolution / quartz overgrowth / pyrite cementation". The difference in sedimentary characteristics between different sub/micro-facies of nearshore subaqueous fans controls diagenetic characteristics. Inner fan conglomerates mainly experienced compaction and lime-mud matrix recrystallization, with weak dissolution, which led to a reduction in the porosity and permeability crucial to reservoir formation. Lime-mud matrix recrystallization results in a rapid decrease in porosity and permeability in inner fan conglomerates in middle-to-deep layers. Because acid dissolution reworks reservoirs and hydrocarbon filling inhibits cementation, reservoirs far from mudstone layers in middle fan braided channels develop a great number of primary pores and secondary pores, and are good enough to be effective reservoirs of hydrocarbon. With the increase of burial depth, both the decrease of porosity and permeability of inner fan conglomerates and the increase of the physical property difference between inner fans and middle fans enhance the quality of seals in middle-to-deep layers. As a result, inner fan conglomerates can be sealing layers in middle-to-deep buried layers. Reservoirs adjacent to mudstones in middle fan braided channels and reservoirs in middle fan interdistributaries experienced extensive cementation, and tight cemented crusts formed at both the top and bottom of conglomerates, which can then act as cap rocks. In conclusion, diagenetic traps in conglomerates of nearshore subaqueous fans could be developed with inner fan conglomerates as lateral or vertical sealing layers, tight carbonate crusts near mudstone layers in middle fan braided channels as well as lacustrine mudstones as cap rocks, and conglomerates far from mudstone layers in middle fan braided channels as reservoirs. Lime-mud matrix recrystallization of inner fan conglomerates and carbonate cementation of conglomerates adjacent to mudstone layers in middle fan braided channels took place from 32 Ma B.P. to 24.6 Ma B.P., thus the formation of diagenetic traps was from 32 Ma B.P. to 24.6 Ma B.P. and diagenetic traps have a better hydrocarbon sealing ability from 24 Ma B.P.. The sealing ability of inner fans gradually increases with the increase of burial depth and diagenetic traps buried more than 3,200 m have better seals.展开更多
Methodologies have been developed for calculating cutoffs of reservoir intervals with production capacity(RIPC) and reservoir intervals with accumulation capacity(RIAC) according to the types of pore throat structures...Methodologies have been developed for calculating cutoffs of reservoir intervals with production capacity(RIPC) and reservoir intervals with accumulation capacity(RIAC) according to the types of pore throat structures and dynamic force by using data from petrophysical analysis, production tests and mercury injection. The data are from clastic reservoirs in the third member(Es3) and the fourth member(Es4) of the Shahejie Formation in the Shengtuo area on the North Slope of the Dongying Sag, Jiyang Depression, China. The method of calculating cutoffs of RIPC is summarized as follows: 1) determination of permeability cutoffs of RIPC; 2) classification of types of pore-throat structures according to mercury injection data and then relating porosity to permeability and determining the relationship between porosity and permeability according to each type of pore-throat structure; and 3) calculating porosity cutoffs of RIPC using established correlation between porosity and permeability according to the type of pore throat structure. The method of calculating cutoffs of RIAC includes: 1) establishing a functional relationship between oil-water interfacial tension and formation temperature; 2) calculating limiting values of maximum connected pore-throat radii according to formation temperature and dynamic forces of each reservoir interval; 3) correlating permeability with maximum connected pore-throat radius and then obtaining permeability cutoffs of RIAC; and 4) calculating porosity cutoffs on the basis of permeability cutoffs according to specific correlations, suitable for the type of porethroat structure. The results of this study show that porosity and permeability cutoffs of clastic reservoirs decrease with depth. For a fixed permeability cutoff, the porosity cutoff of RIPC varies because the type of pore throat is different. At a fixed temperature, porosity and permeability cutoffs of RIAC decrease as dynamic force increases. For a fixed permeability cutoff of effective hydrocarbon accumulation, the porosity cutoff also varies with different types of pore throat.展开更多
The main oil-bearing formation of Area 4 of Tahe oilfield is in Yingshan Group of Ordovician consisted of thick pure limestone. The types of the pore space contain the pore, fissure, cave as well as fracture formed by...The main oil-bearing formation of Area 4 of Tahe oilfield is in Yingshan Group of Ordovician consisted of thick pure limestone. The types of the pore space contain the pore, fissure, cave as well as fracture formed by solution collapse. The primary porosity and tectonic fracture are of poor growth. Therefore, the formation growth is mainly controlled by hydraulic units of the palaeo-karst. There are three palaeo-hydraulic zones: vadose zone (including infiltration sub-zone and percolation sub-zone), phreatic zone and tranquil zone. They are identified by retrieving the palaeo-geographical karst environment. The pore space of the infiltration zone is mainly solution fissures, small solution cavities and solution pores. The growth and lateral connection of the formation are favorable. The reservoir/formation ratio is 0.54. The pore space of the phreatic zone developed large size cavities and fractures related to cave collapse. The height of the cavity can reach 71m. The fractures by collapse have a influencing range of more than 100m, and its reservoir/formation ratio is 0. 51. But the lateral connection is unfavorable. The percolation subzone and the tranquil zone are of relatively poor growth with the reservoir/tormation ratio less than 0. 3.展开更多
Analyses of the original and pyrolytic products of coccolithophore at various temperatures suggest that the contribution of coccolithophore to the formation of large immature oil reservoirs should attract keen interes...Analyses of the original and pyrolytic products of coccolithophore at various temperatures suggest that the contribution of coccolithophore to the formation of large immature oil reservoirs should attract keen interest. Through biochemical processes algae can change inorganic sulphur into organic sulphur, which could be one of the most important precursors of organic sulphur compounds in oil and source rocks. When Methylphenanthrene Index (MPI) and Methylphenanthrene Ratio (MPR) indices were used to evaluate the evolution degree of source rocks and oil maturity, other maturity indices must be used together for correction. In low maturity, the relative abundances of diben-zothiophene (DBT), fluorine (F) and dibenzofuran (DBF) can be used to identify the oxidation-reduction environments.展开更多
Fine-grained rocks(FGR) are the important source rocks and reservoirs of shale hydrocarbon which is the prospect hotspot at present. Widely distributed fine-grained sediments(FGS) of the upper fourth member of Shaheji...Fine-grained rocks(FGR) are the important source rocks and reservoirs of shale hydrocarbon which is the prospect hotspot at present. Widely distributed fine-grained sediments(FGS) of the upper fourth member of Shahejie Formation in Dongying depression are taken as an example to study the space-time evolution and controlling factor of FGS in this paper. Based on the analysis of well cores, thin sections, inorganic and organic geochemistry indicators, FGR are divided into 7 types of lithofacies. Through the study of ‘point-line-plane', this study shows that FGS has the characteristics of rhythum, diversity and succession. The first stage is characterized by clayey FGS(massive claystone). The second stage is characterized by carbonate FGS(low-TOC laminated limestone) and dolomitic FGS(dolomitic-silty shale) formed by transgression. The third stage is characterized by organic-rich carbonate FGS(middle/high-TOC laminated limestone) distributed in cycle. The fourth stage is characterized by FGS mixed carbonate and siliciclastic sediments(calcareous-silty shale). A variety of space-time evolution of FGS are controlled by multiple factors including tectonism, climate and lake conditions.展开更多
Fluorescence properties of Early Cambrian acri-tarchs were investigated using Leica das Mikroskop(DM)microscopy with a mercury lamp.Well-preserved autoflures-cence properties show a correlation between acritarchs morp...Fluorescence properties of Early Cambrian acri-tarchs were investigated using Leica das Mikroskop(DM)microscopy with a mercury lamp.Well-preserved autoflures-cence properties show a correlation between acritarchs morphology and the intensity of emitted fluorescence.In accordance with the fluorescence intensity of organic cell walls,two groups of microfossils were distinguished.Results of observation in this study,which are consistent with those of the previous foreign studies,are in good agreement with regular difference in autofluorescence intensity among paly-nomorphs reported by McPhilemy(1998).Spores and algae,including Botryococcus,have very bright fluorescence while acritarchs often show less intense fluorescence.Dark brown microfossils have been reworked,and have little or no fluorescence.展开更多
Biogenic opal and calcium carbonate contents in the Quaternary fine-grained sediments in the deep sea coral mound area (Hole U1317E and Hole U1318B drilled by IODP Expedition 307) in Porcupine Seabight, southwest off ...Biogenic opal and calcium carbonate contents in the Quaternary fine-grained sediments in the deep sea coral mound area (Hole U1317E and Hole U1318B drilled by IODP Expedition 307) in Porcupine Seabight, southwest off Ireland, were measured to estimate the primary productivity (Pp) of the surface seawater in NE Atlantic. The results from the two holes commonly show relatively high Pp values of 10-30 g cm-2 ky-1, having stratigraphic cyclicity reversely correlated with the δ13C profile. The high Pp could be attributed to the oceanic setting controlled by the Eastern North Atlantic (Central) Water and Shelf Edge Current, which have been strongly influenced by the obliquity forcing of the Milankovitch cycle. A positive covariance was observed between high Pp and the mound development in U1317E, implying that the organic matter was the principal food source for the mound coral community. It is proposed that the pelagic marl matrix of the mound sediments provides information of the surface water productivity that is useful for reconstructing the paleoceanography and the paleoclimate in the NW Atlantic.展开更多
基金co-funded by the National Natural Science Foundation of China (41102058)the National Science and Technology Special Grant (2011ZX05006-003)the Fundamental Research Funds for the Central Universities (12CX04001A)
文摘Diagenetic traps in conglomerate in nearshore subaqueous fans in the steep slope zones of rift basins have been important exploration targets for subtle reservoirs in eastern China. However, the mechanism of how those traps were formed is not clear, which inhibits further exploration for this type of reservoir. In order to solve the problem, we take as an example nearshore subaqueous fans in the upper part of the fourth member of the Shahejie Formation(Es4s) on the north slope of the Minfeng Subsag in the Dongying Sag. Combining different research methods, such as core observation, thin section examination, scanning electron microscope(SEM) observation, fluid-inclusion analysis, carbon and oxygen isotope analysis of carbonate cements, and analysis of core properties, we studied the genetic mechanisms of diagenetic traps on the basis of diagenetic environment evolution and diagenetic evolution sequence in different sub/micro-facies. Conglomerate in Es4 s in the north Minfeng Subsag experienced several periods of transition between alkaline and acidic environments as "alkaline–acidic–alkaline–acidic–weak alkaline". As a result, dissolution and cementation are also very complex, and the sequence is "early pyrite cementation / siderite cementation / gypsum cementation / calcite and dolomite cementation——feldspar dissolution / quartz overgrowth——quartz dissolution / ferroan calcite cementation / ankerite cementation / lime-mud matrix recrystallization / feldspar overgrowth——carbonate dissolution / feldspar dissolution / quartz overgrowth / pyrite cementation". The difference in sedimentary characteristics between different sub/micro-facies of nearshore subaqueous fans controls diagenetic characteristics. Inner fan conglomerates mainly experienced compaction and lime-mud matrix recrystallization, with weak dissolution, which led to a reduction in the porosity and permeability crucial to reservoir formation. Lime-mud matrix recrystallization results in a rapid decrease in porosity and permeability in inner fan conglomerates in middle-to-deep layers. Because acid dissolution reworks reservoirs and hydrocarbon filling inhibits cementation, reservoirs far from mudstone layers in middle fan braided channels develop a great number of primary pores and secondary pores, and are good enough to be effective reservoirs of hydrocarbon. With the increase of burial depth, both the decrease of porosity and permeability of inner fan conglomerates and the increase of the physical property difference between inner fans and middle fans enhance the quality of seals in middle-to-deep layers. As a result, inner fan conglomerates can be sealing layers in middle-to-deep buried layers. Reservoirs adjacent to mudstones in middle fan braided channels and reservoirs in middle fan interdistributaries experienced extensive cementation, and tight cemented crusts formed at both the top and bottom of conglomerates, which can then act as cap rocks. In conclusion, diagenetic traps in conglomerates of nearshore subaqueous fans could be developed with inner fan conglomerates as lateral or vertical sealing layers, tight carbonate crusts near mudstone layers in middle fan braided channels as well as lacustrine mudstones as cap rocks, and conglomerates far from mudstone layers in middle fan braided channels as reservoirs. Lime-mud matrix recrystallization of inner fan conglomerates and carbonate cementation of conglomerates adjacent to mudstone layers in middle fan braided channels took place from 32 Ma B.P. to 24.6 Ma B.P., thus the formation of diagenetic traps was from 32 Ma B.P. to 24.6 Ma B.P. and diagenetic traps have a better hydrocarbon sealing ability from 24 Ma B.P.. The sealing ability of inner fans gradually increases with the increase of burial depth and diagenetic traps buried more than 3,200 m have better seals.
基金co-funded by National Natura Science Foundation of China (Grant No. 41102058 Gran No. U1262203)+4 种基金the National Science and Technology Special Grant (No. 2011ZX05006-003)Shandong Natura Science Foundation (Grant No. ZR2011DQ017)the Fundamental Research Funds for the Central Universities (No. 12CX04001A No. 13CX02035A No. 13CX02036A)
文摘Methodologies have been developed for calculating cutoffs of reservoir intervals with production capacity(RIPC) and reservoir intervals with accumulation capacity(RIAC) according to the types of pore throat structures and dynamic force by using data from petrophysical analysis, production tests and mercury injection. The data are from clastic reservoirs in the third member(Es3) and the fourth member(Es4) of the Shahejie Formation in the Shengtuo area on the North Slope of the Dongying Sag, Jiyang Depression, China. The method of calculating cutoffs of RIPC is summarized as follows: 1) determination of permeability cutoffs of RIPC; 2) classification of types of pore-throat structures according to mercury injection data and then relating porosity to permeability and determining the relationship between porosity and permeability according to each type of pore-throat structure; and 3) calculating porosity cutoffs of RIPC using established correlation between porosity and permeability according to the type of pore throat structure. The method of calculating cutoffs of RIAC includes: 1) establishing a functional relationship between oil-water interfacial tension and formation temperature; 2) calculating limiting values of maximum connected pore-throat radii according to formation temperature and dynamic forces of each reservoir interval; 3) correlating permeability with maximum connected pore-throat radius and then obtaining permeability cutoffs of RIAC; and 4) calculating porosity cutoffs on the basis of permeability cutoffs according to specific correlations, suitable for the type of porethroat structure. The results of this study show that porosity and permeability cutoffs of clastic reservoirs decrease with depth. For a fixed permeability cutoff, the porosity cutoff of RIPC varies because the type of pore throat is different. At a fixed temperature, porosity and permeability cutoffs of RIAC decrease as dynamic force increases. For a fixed permeability cutoff of effective hydrocarbon accumulation, the porosity cutoff also varies with different types of pore throat.
文摘The main oil-bearing formation of Area 4 of Tahe oilfield is in Yingshan Group of Ordovician consisted of thick pure limestone. The types of the pore space contain the pore, fissure, cave as well as fracture formed by solution collapse. The primary porosity and tectonic fracture are of poor growth. Therefore, the formation growth is mainly controlled by hydraulic units of the palaeo-karst. There are three palaeo-hydraulic zones: vadose zone (including infiltration sub-zone and percolation sub-zone), phreatic zone and tranquil zone. They are identified by retrieving the palaeo-geographical karst environment. The pore space of the infiltration zone is mainly solution fissures, small solution cavities and solution pores. The growth and lateral connection of the formation are favorable. The reservoir/formation ratio is 0.54. The pore space of the phreatic zone developed large size cavities and fractures related to cave collapse. The height of the cavity can reach 71m. The fractures by collapse have a influencing range of more than 100m, and its reservoir/formation ratio is 0. 51. But the lateral connection is unfavorable. The percolation subzone and the tranquil zone are of relatively poor growth with the reservoir/tormation ratio less than 0. 3.
基金This study was supported by the National Natural Science Foundation of China (Grant No. 39870064) and the State Key Basic Research Development Program (Grant No. G19990433).
文摘Analyses of the original and pyrolytic products of coccolithophore at various temperatures suggest that the contribution of coccolithophore to the formation of large immature oil reservoirs should attract keen interest. Through biochemical processes algae can change inorganic sulphur into organic sulphur, which could be one of the most important precursors of organic sulphur compounds in oil and source rocks. When Methylphenanthrene Index (MPI) and Methylphenanthrene Ratio (MPR) indices were used to evaluate the evolution degree of source rocks and oil maturity, other maturity indices must be used together for correction. In low maturity, the relative abundances of diben-zothiophene (DBT), fluorine (F) and dibenzofuran (DBF) can be used to identify the oxidation-reduction environments.
基金supported by the National Science and Technology Special Grant of China (No. 2017zx05036-004)
文摘Fine-grained rocks(FGR) are the important source rocks and reservoirs of shale hydrocarbon which is the prospect hotspot at present. Widely distributed fine-grained sediments(FGS) of the upper fourth member of Shahejie Formation in Dongying depression are taken as an example to study the space-time evolution and controlling factor of FGS in this paper. Based on the analysis of well cores, thin sections, inorganic and organic geochemistry indicators, FGR are divided into 7 types of lithofacies. Through the study of ‘point-line-plane', this study shows that FGS has the characteristics of rhythum, diversity and succession. The first stage is characterized by clayey FGS(massive claystone). The second stage is characterized by carbonate FGS(low-TOC laminated limestone) and dolomitic FGS(dolomitic-silty shale) formed by transgression. The third stage is characterized by organic-rich carbonate FGS(middle/high-TOC laminated limestone) distributed in cycle. The fourth stage is characterized by FGS mixed carbonate and siliciclastic sediments(calcareous-silty shale). A variety of space-time evolution of FGS are controlled by multiple factors including tectonism, climate and lake conditions.
基金This work was supported by the“Western China Light”Science Foundation(Chinese Academy of Science)(No.0240401)State Key Laboratory of Palaeobiology and Stratigraphy(Nanjing Institute of Geology and Palaeontology,Chinese Academy of Science)(No.073105).
文摘Fluorescence properties of Early Cambrian acri-tarchs were investigated using Leica das Mikroskop(DM)microscopy with a mercury lamp.Well-preserved autoflures-cence properties show a correlation between acritarchs morphology and the intensity of emitted fluorescence.In accordance with the fluorescence intensity of organic cell walls,two groups of microfossils were distinguished.Results of observation in this study,which are consistent with those of the previous foreign studies,are in good agreement with regular difference in autofluorescence intensity among paly-nomorphs reported by McPhilemy(1998).Spores and algae,including Botryococcus,have very bright fluorescence while acritarchs often show less intense fluorescence.Dark brown microfossils have been reworked,and have little or no fluorescence.
基金supported by National Natural Science Foundation of China (Grant Nos. 40772074, 40643017)the Japan Agency for Marine-Earth Science and Technologypartly by the Center for Advanced Marine Core Research, Kochi University
文摘Biogenic opal and calcium carbonate contents in the Quaternary fine-grained sediments in the deep sea coral mound area (Hole U1317E and Hole U1318B drilled by IODP Expedition 307) in Porcupine Seabight, southwest off Ireland, were measured to estimate the primary productivity (Pp) of the surface seawater in NE Atlantic. The results from the two holes commonly show relatively high Pp values of 10-30 g cm-2 ky-1, having stratigraphic cyclicity reversely correlated with the δ13C profile. The high Pp could be attributed to the oceanic setting controlled by the Eastern North Atlantic (Central) Water and Shelf Edge Current, which have been strongly influenced by the obliquity forcing of the Milankovitch cycle. A positive covariance was observed between high Pp and the mound development in U1317E, implying that the organic matter was the principal food source for the mound coral community. It is proposed that the pelagic marl matrix of the mound sediments provides information of the surface water productivity that is useful for reconstructing the paleoceanography and the paleoclimate in the NW Atlantic.
