2016 Vol. 34, No. 2
Display Method:
2016, 34(2): 207-221.
doi: 10.14027/j.cnki.cjxb.2016.02.001
Abstract:
Imbricate structure is a common sedimentary structure. Yet, so far, the research on imbricate structure is mainly confined in gravel, and no systematic study of sand grains is conducted. Actually, just like conglomerate, sand grains also develop imbricate structure, and are very perfect. Meanwhile, their imbricate structure contains much more geologic information than that of gravels. Therefore, the study of sand grains' imbricate structure is much more significant.
In this study, we preceded detailed work at Dang River and Aksai River of Dunhuang, Gansu in recent years and found that there also develop imbricate structure in sand grains of modern marginal bank, which is far more complicated than that in gravel. First, according to research, the dip angle of sand grains' imbricate structure varies larger than that of gravel grains', ranging from some 10° to 50°~60°. The maximum can reach 70°~80°, and the average is 45°~50°, in total, which is obviously larger than the dip angle, 34°, of gravel' in the same channel segment. Second, compared with the gravel' trend, the sand grains' trend is not so stable, and sometimes it can appear double trend in small scope. Third, sand grains' imbricate structure can be controlled by lamina, presenting as lamellar. Fourth, according to the contact relation of sand grains, there are two types of imbricate structure, namely grain-braced imbricate structure and matrix-braced imbricate structure. Furthermore, the grain-braced imbricate structure also can be divided into two kinds:lamina-controlled imbricate structure and folium-controlled imbricate structure, both of which develop in "clean water" environment and form in pluvial stabilization period. Meanwhile, matrix-braced sand grains' imbricate structure develops in "muddy water" environment and maybe form in pluvial peak period.
The study of sand grain imbricate structure has significant meaning to sedimentary environment research, paleocurrent analysis and reservoir study. And the grain-braced sand imbricate structure can shape peculiar shield pore and become fine reservoir space, which is the root of sandstone reservoir's emerging of anisotropy.
Imbricate structure is a common sedimentary structure. Yet, so far, the research on imbricate structure is mainly confined in gravel, and no systematic study of sand grains is conducted. Actually, just like conglomerate, sand grains also develop imbricate structure, and are very perfect. Meanwhile, their imbricate structure contains much more geologic information than that of gravels. Therefore, the study of sand grains' imbricate structure is much more significant.
In this study, we preceded detailed work at Dang River and Aksai River of Dunhuang, Gansu in recent years and found that there also develop imbricate structure in sand grains of modern marginal bank, which is far more complicated than that in gravel. First, according to research, the dip angle of sand grains' imbricate structure varies larger than that of gravel grains', ranging from some 10° to 50°~60°. The maximum can reach 70°~80°, and the average is 45°~50°, in total, which is obviously larger than the dip angle, 34°, of gravel' in the same channel segment. Second, compared with the gravel' trend, the sand grains' trend is not so stable, and sometimes it can appear double trend in small scope. Third, sand grains' imbricate structure can be controlled by lamina, presenting as lamellar. Fourth, according to the contact relation of sand grains, there are two types of imbricate structure, namely grain-braced imbricate structure and matrix-braced imbricate structure. Furthermore, the grain-braced imbricate structure also can be divided into two kinds:lamina-controlled imbricate structure and folium-controlled imbricate structure, both of which develop in "clean water" environment and form in pluvial stabilization period. Meanwhile, matrix-braced sand grains' imbricate structure develops in "muddy water" environment and maybe form in pluvial peak period.
The study of sand grain imbricate structure has significant meaning to sedimentary environment research, paleocurrent analysis and reservoir study. And the grain-braced sand imbricate structure can shape peculiar shield pore and become fine reservoir space, which is the root of sandstone reservoir's emerging of anisotropy.
2016, 34(2): 222-235.
doi: 10.14027/j.cnki.cjxb.2016.02.002
Abstract:
Changchang-Heshan depression, located in southwest Zhu-IV subbasin of Pearl River Mouth Basin, extends in NE-SW direction. It is an important strategic exploration block after oil and gas exploration breakthrough in Baiyun and Liwan depression in deep water area. Changchang-Heshan depression is a new area to oil and gas exploration and has no wells, so the basic geological research is particularly important. Based on fault interpretation and formation thickness analysis, rift stages and structural characteristics were studied in detail. Wenchang and Enping Formation experienced two successive tectonic stages, which respectively corresponded to intensive rift stage and weak rift stage. A variety of different levels and types of structural transfer zones were identified at the same time. Guided by the theory of classic sequence stratigraphy, Wenchang and Enping Formation were divided into two second-order sequences and seven third-order sequences based on the two-dimensional seismic data. According to the characteristics of the seismic reflection, transfer the classic seismic facies to sedimentary facies within the sequence framework, and then rebuilt the process of sedimentary system evolution in the study area. Classified two levels(Ⅰ and Ⅱ) and six types of structural transfer zones(syntropy non-overlapping, syntropy non-overlapping, syntropy parallel, syntropy collineation, opposite overlapping and back to back overlapping). The degree of the fault activity controlled the sequence evolution and sedimentation system. Furthermore, structural transfer zone and slope break controlled the distribution and scale of sand bodies. The study area is a new region for oil and gas exploration, this method is focused on the close relation between tectonism and sedimentation. Finally, it offers reliable evidence for favourable region exploration and supports a solid scientific evidence for the low degree oil and gas exploration in deep water area.
Changchang-Heshan depression, located in southwest Zhu-IV subbasin of Pearl River Mouth Basin, extends in NE-SW direction. It is an important strategic exploration block after oil and gas exploration breakthrough in Baiyun and Liwan depression in deep water area. Changchang-Heshan depression is a new area to oil and gas exploration and has no wells, so the basic geological research is particularly important. Based on fault interpretation and formation thickness analysis, rift stages and structural characteristics were studied in detail. Wenchang and Enping Formation experienced two successive tectonic stages, which respectively corresponded to intensive rift stage and weak rift stage. A variety of different levels and types of structural transfer zones were identified at the same time. Guided by the theory of classic sequence stratigraphy, Wenchang and Enping Formation were divided into two second-order sequences and seven third-order sequences based on the two-dimensional seismic data. According to the characteristics of the seismic reflection, transfer the classic seismic facies to sedimentary facies within the sequence framework, and then rebuilt the process of sedimentary system evolution in the study area. Classified two levels(Ⅰ and Ⅱ) and six types of structural transfer zones(syntropy non-overlapping, syntropy non-overlapping, syntropy parallel, syntropy collineation, opposite overlapping and back to back overlapping). The degree of the fault activity controlled the sequence evolution and sedimentation system. Furthermore, structural transfer zone and slope break controlled the distribution and scale of sand bodies. The study area is a new region for oil and gas exploration, this method is focused on the close relation between tectonism and sedimentation. Finally, it offers reliable evidence for favourable region exploration and supports a solid scientific evidence for the low degree oil and gas exploration in deep water area.
2016, 34(2): 236-249.
doi: 10.14027/j.cnki.cjxb.2016.02.003
Abstract:
Petrographic characteristics and geochemical analysis reveal that there exist three types of dolomites in dolostones in Maokou Formation, Lower Permian, central Sichuan Basin:①idiotopic fine crystal-dolomite(IFD)(δ13CPDB=3.06‰, δ18OPDB=-6.81‰; Fe:1×10-6, Mn:negative, Sr:150×10-6);②xenotopic coarse crystal-saddle dolomite(XCSD)(δ13CPDB=3.22‰, δ18OPDB=-7.82‰; Fe:149×10-6, Mn:185×10-6, Sr:85×10-6); ③xenotopic fine crystal-dolomite(XFD)(δ13CPDB=3.49‰, δ18OPDB=-9.45‰; Th=123℃, S=133‰~139‰NaCl; Fe:58×10-6, Mn:59×10-6, Sr:76×10-6).This study demonstrates that two episodes of dolomitization fluids in the study area:①early burial-dolomitization fluid formed by compaction(T=37.4℃; S=29.8‰NaCl); ②late hydrotherm-dolomitization fluid controlled by structure(Th=114.8℃; S=153‰~226‰NaCl).The origin of the dolostone is illustrated that:①IFD is replacive by early burial-dolomitization fluid; ②XFD is the product of hydrothermal alteration on IFD; ③XCSD is precipitated directly from hydrothermal fluid.Based on the achievement, corresponding model of dolomitization has been established.
Petrographic characteristics and geochemical analysis reveal that there exist three types of dolomites in dolostones in Maokou Formation, Lower Permian, central Sichuan Basin:①idiotopic fine crystal-dolomite(IFD)(δ13CPDB=3.06‰, δ18OPDB=-6.81‰; Fe:1×10-6, Mn:negative, Sr:150×10-6);②xenotopic coarse crystal-saddle dolomite(XCSD)(δ13CPDB=3.22‰, δ18OPDB=-7.82‰; Fe:149×10-6, Mn:185×10-6, Sr:85×10-6); ③xenotopic fine crystal-dolomite(XFD)(δ13CPDB=3.49‰, δ18OPDB=-9.45‰; Th=123℃, S=133‰~139‰NaCl; Fe:58×10-6, Mn:59×10-6, Sr:76×10-6).This study demonstrates that two episodes of dolomitization fluids in the study area:①early burial-dolomitization fluid formed by compaction(T=37.4℃; S=29.8‰NaCl); ②late hydrotherm-dolomitization fluid controlled by structure(Th=114.8℃; S=153‰~226‰NaCl).The origin of the dolostone is illustrated that:①IFD is replacive by early burial-dolomitization fluid; ②XFD is the product of hydrothermal alteration on IFD; ③XCSD is precipitated directly from hydrothermal fluid.Based on the achievement, corresponding model of dolomitization has been established.
2016, 34(2): 250-259.
doi: 10.14027/j.cnki.cjxb.2016.02.004
Abstract:
To study the relationship between diagenesis-fluid evolution and uranium mineralization of J2t sandstone in Liuhuanggou area, the southern margin of Junggar basin, finally assessing the metallogenetic potentiality. By means of microscope, X-diffraction and scaning electron microscopy, the author conducted that the studied rock are mainly rock-fragment fine sandstone, which underwent shallow burial period, deep burial period and hypergene-thermal period diagenetic evolution, finally suffered from relatively strong compaction, cementation and dissolution. The clay minerals are mainly kaolinite. There are also some fine sparry and micrite carbonate minerals, a few of siliceous cementations, fine grain pyrite and limonite locally. The diagenetic environment may experienced acid-weak alkalicy-acid and syngenetic oxidation-reduction in the shallow burial period-0xidation/reduction in the transitory elevation period-reduction enhancing in the deep burial period-oxidation in the period of large scale lifting evolutionary process. Simultaneously, hydrocarbon charging on the sandstone were proved by the following evidence:field investigating, oil and gas inclusions verificating, total acidolysis hydrocarbon range from 5.72 μL/kg to 449.14 μL/kg, mainly for the methane, C-O stable isotope values of calcite are -25‰~-6.7‰, 11.1‰~18.9‰, respectively, which influenced the geochemical properties(Eh and pH) of sandstone. The above diagenetic and hydrocarbon evolution controlled the migration, accumulation and localization of uranium, namely it formated and locatly conserved some small interlayer oxidation type uranium deposits in the early phase and formed some groundsurface phreatic oxidation type uranium deposits in the later preiod.
To study the relationship between diagenesis-fluid evolution and uranium mineralization of J2t sandstone in Liuhuanggou area, the southern margin of Junggar basin, finally assessing the metallogenetic potentiality. By means of microscope, X-diffraction and scaning electron microscopy, the author conducted that the studied rock are mainly rock-fragment fine sandstone, which underwent shallow burial period, deep burial period and hypergene-thermal period diagenetic evolution, finally suffered from relatively strong compaction, cementation and dissolution. The clay minerals are mainly kaolinite. There are also some fine sparry and micrite carbonate minerals, a few of siliceous cementations, fine grain pyrite and limonite locally. The diagenetic environment may experienced acid-weak alkalicy-acid and syngenetic oxidation-reduction in the shallow burial period-0xidation/reduction in the transitory elevation period-reduction enhancing in the deep burial period-oxidation in the period of large scale lifting evolutionary process. Simultaneously, hydrocarbon charging on the sandstone were proved by the following evidence:field investigating, oil and gas inclusions verificating, total acidolysis hydrocarbon range from 5.72 μL/kg to 449.14 μL/kg, mainly for the methane, C-O stable isotope values of calcite are -25‰~-6.7‰, 11.1‰~18.9‰, respectively, which influenced the geochemical properties(Eh and pH) of sandstone. The above diagenetic and hydrocarbon evolution controlled the migration, accumulation and localization of uranium, namely it formated and locatly conserved some small interlayer oxidation type uranium deposits in the early phase and formed some groundsurface phreatic oxidation type uranium deposits in the later preiod.
2016, 34(2): 260-267.
doi: 10.14027/j.cnki.cjxb.2016.02.005
Abstract:
A multiproxy record, including grain size, organic carbon and nitrogen, and the stable isotope compositions of organic carbon(δ13C) obtained from Core BDQ06 in the marginal Hoh Xil area, Tibet Plateau, provided evidence for climate change since mid-Pleistocene. The influencing factors and variation characteristics of organic carbon isotope were reviewed. The organic carbon content is controlled by autophyte from lake. The variation of organic carbon isotope is mainly related to the ratio of emergent plant to submerged plant, indicating fluctuation of lake level. Variations of the δ13C can be used to estimate various sources of organic matter in the aquatic environment. The higher δ13C values and lower C/N ratios show the dominance of the submerged plant in the lake, and may reflect higher lake level and more moderate climate. The lower δ13C values is attributed to contributor of emergent aquatic plant and planktont, which used atmospheric CO2 for photosynthesis, indicating lower lake level and drier climate. Additionally, in certain phases, lower δ13C values corresponding to the C/N ratios of more than 10 may be related to the input of terrestrial higher plant.
A multiproxy record, including grain size, organic carbon and nitrogen, and the stable isotope compositions of organic carbon(δ13C) obtained from Core BDQ06 in the marginal Hoh Xil area, Tibet Plateau, provided evidence for climate change since mid-Pleistocene. The influencing factors and variation characteristics of organic carbon isotope were reviewed. The organic carbon content is controlled by autophyte from lake. The variation of organic carbon isotope is mainly related to the ratio of emergent plant to submerged plant, indicating fluctuation of lake level. Variations of the δ13C can be used to estimate various sources of organic matter in the aquatic environment. The higher δ13C values and lower C/N ratios show the dominance of the submerged plant in the lake, and may reflect higher lake level and more moderate climate. The lower δ13C values is attributed to contributor of emergent aquatic plant and planktont, which used atmospheric CO2 for photosynthesis, indicating lower lake level and drier climate. Additionally, in certain phases, lower δ13C values corresponding to the C/N ratios of more than 10 may be related to the input of terrestrial higher plant.
2016, 34(2): 268-280.
doi: 10.14027/j.cnki.cjxb.2016.02.006
Abstract:
This paper studies the sedimentary characteristics, stratigraphic sequence, sequence boundary and environmental evolution of the Late Quaternary incised-valley fills in the Nantong area, Jiangsu Province, based on the detailed analyses of core lithology, paleontology, 14C dating, and so on. The results show that there are three episodes of incised valley developed in the study area resulting in the formation of distinct sedimentary sequences, which correlate to the early stage, the middle stage, and late stage of late Quaternary, respectively, and showing three episodic sea-level change "low sea level-transgression-high sea level-regression". The early two systems are incomplete due to the late strong incision and erosion, and are characterized by the superposition of fluvial sediments; while the last postglacial sequence is relatively complete with five sedimentary facies generated, i.e., the fluvial channel, floodplain, estuary, shallow marine, and delta. The basal erosional surface of the lastglacial incised valley fill, which was formed during the Last Glacial Maximum due to fluvial incision, can be correlated with the surface of stiff clay on the interfluves, indicating a significant chronostratigraphic nature.
This paper studies the sedimentary characteristics, stratigraphic sequence, sequence boundary and environmental evolution of the Late Quaternary incised-valley fills in the Nantong area, Jiangsu Province, based on the detailed analyses of core lithology, paleontology, 14C dating, and so on. The results show that there are three episodes of incised valley developed in the study area resulting in the formation of distinct sedimentary sequences, which correlate to the early stage, the middle stage, and late stage of late Quaternary, respectively, and showing three episodic sea-level change "low sea level-transgression-high sea level-regression". The early two systems are incomplete due to the late strong incision and erosion, and are characterized by the superposition of fluvial sediments; while the last postglacial sequence is relatively complete with five sedimentary facies generated, i.e., the fluvial channel, floodplain, estuary, shallow marine, and delta. The basal erosional surface of the lastglacial incised valley fill, which was formed during the Last Glacial Maximum due to fluvial incision, can be correlated with the surface of stiff clay on the interfluves, indicating a significant chronostratigraphic nature.
2016, 34(2): 281-291.
doi: 10.14027/j.cnki.cjxb.2016.02.007
Abstract:
The Early Holocene is an important period of Solar radiation strengthening, global warming and along with ice sheets melting. The cause of the colder events and the weaker summer monsoon in the Asian monsoon region during the Early Holocene has always been the focus of research. It has important significance for the study of the links among the Asian monsoon, ocean and polar regions. Based on 28 U/Th dates and 535 oxygen isotopic data of stalagmite LHD5 from Lianhua Cave, Hunan province, China, a Holocene Asian monsoon evolution record was reconstructed, and the average resolution is 8 year in the Early Holocene. From the LHD5 stalagmite record, the end of Younger Dryas was at 11748±30 a B.P., the start of the Holocene was at 11684±39 a B.P., and the conversion time is about 64 years, which is consistent with the records of the gicc05 ice core from Greenland in the error range. The central age of the six weak summer monsoon events were at 11461±34 a B.P.(1.08‰), 10354±36 a B.P.(0.94‰), 9957±25 a B.P.(0.66‰), 9062±36 a B.P.(0.90‰), 8744±23 a B.P.(0.55‰) and 8144±24 a B.P.(1.02‰) in the record of the stalagmite LHD5 during the Early Holocene, respectively. These weaker summer monsoon events in the Asian monsoon region have a common regional significance. In addition to the 8.2 ka event, the weaker summer monsoon events before 10 ka B.P. were not only affected by the summer insolation but also by the ice-rafted debris (IRD) events in the North Atlantic, but the following weak summer monsoon events were mostly influenced by solar activity and the southward migration of the mean position of the Inter-Tropical Convergence Zone.
The Early Holocene is an important period of Solar radiation strengthening, global warming and along with ice sheets melting. The cause of the colder events and the weaker summer monsoon in the Asian monsoon region during the Early Holocene has always been the focus of research. It has important significance for the study of the links among the Asian monsoon, ocean and polar regions. Based on 28 U/Th dates and 535 oxygen isotopic data of stalagmite LHD5 from Lianhua Cave, Hunan province, China, a Holocene Asian monsoon evolution record was reconstructed, and the average resolution is 8 year in the Early Holocene. From the LHD5 stalagmite record, the end of Younger Dryas was at 11748±30 a B.P., the start of the Holocene was at 11684±39 a B.P., and the conversion time is about 64 years, which is consistent with the records of the gicc05 ice core from Greenland in the error range. The central age of the six weak summer monsoon events were at 11461±34 a B.P.(1.08‰), 10354±36 a B.P.(0.94‰), 9957±25 a B.P.(0.66‰), 9062±36 a B.P.(0.90‰), 8744±23 a B.P.(0.55‰) and 8144±24 a B.P.(1.02‰) in the record of the stalagmite LHD5 during the Early Holocene, respectively. These weaker summer monsoon events in the Asian monsoon region have a common regional significance. In addition to the 8.2 ka event, the weaker summer monsoon events before 10 ka B.P. were not only affected by the summer insolation but also by the ice-rafted debris (IRD) events in the North Atlantic, but the following weak summer monsoon events were mostly influenced by solar activity and the southward migration of the mean position of the Inter-Tropical Convergence Zone.
2016, 34(2): 292-307.
doi: 10.14027/j.cnki.cjxb.2016.02.008
Abstract:
Remote sensing has been widely used to research suspended sediment concentration on sea surface. The hydrology and inherent optical properties of sea waters are very complex in the eastern China seas, which makes building retrieval models from satellite images more difficult. By comparing and summarizing former researches, some conclusions and suggestions about establishing inversion models have been offered. It can improve accuracy to build models separately in different time and regions identified by in-situ data. Areas containing different SSC have their own optimal bands combination to be used in models. In the coastal areas with high SSC, using the combination of the second peak of water reflectance and the increasing part before the first peak as proportional input factors and choosing inverse proportional input factor based on specific spectrum feature of water can offer the best bands' choice. In offshore waters with low SSC, optimal bands' combination are the first peak of reflectance of water and the increasing part before it. And taking sediment grain size into models can also increase accuracy and may break the depth limitation of remote sensing in shallow sea. It's better to use determination coefficient, mean relative error, mean absolute error and root mean square error as the assessment criterion of models' results and its stability can be certified by error sensitivity analysis. Though semi-analytical and neural network models have more explicit physical foundations, empirical models have better precision and applicability. There is a promising trench using remote sensing to study instantaneous oceanic events due to the advancement of high spatial-and-temporal resolution satellites.
Remote sensing has been widely used to research suspended sediment concentration on sea surface. The hydrology and inherent optical properties of sea waters are very complex in the eastern China seas, which makes building retrieval models from satellite images more difficult. By comparing and summarizing former researches, some conclusions and suggestions about establishing inversion models have been offered. It can improve accuracy to build models separately in different time and regions identified by in-situ data. Areas containing different SSC have their own optimal bands combination to be used in models. In the coastal areas with high SSC, using the combination of the second peak of water reflectance and the increasing part before the first peak as proportional input factors and choosing inverse proportional input factor based on specific spectrum feature of water can offer the best bands' choice. In offshore waters with low SSC, optimal bands' combination are the first peak of reflectance of water and the increasing part before it. And taking sediment grain size into models can also increase accuracy and may break the depth limitation of remote sensing in shallow sea. It's better to use determination coefficient, mean relative error, mean absolute error and root mean square error as the assessment criterion of models' results and its stability can be certified by error sensitivity analysis. Though semi-analytical and neural network models have more explicit physical foundations, empirical models have better precision and applicability. There is a promising trench using remote sensing to study instantaneous oceanic events due to the advancement of high spatial-and-temporal resolution satellites.
2016, 34(2): 308-314.
doi: 10.14027/j.cnki.cjxb.2016.02.009
Abstract:
Trace elements in marine sediment can be used to reflect anthropogenic influence on marine systems, to trace the origin and transformation of the marine substances, to indicate sedimentary environment and early diagenesis, and even to reconstruct the global change of climate. However, studies of trace elements in marine sediments are rarely reported from east Antarctica. In this case, sixteen surface sediments were collected during the 21st to 27th cruises of Chinese Antarctic Expedition in order to investigate the distribution and source composition of trace elements in the surface sediments from Prydz Bay and east Antarctica. Samples were analyzed using ICP-MS to determine the content of trace elements in the bay. Combined with biogenic silica and grain size of the sediments, the sources of trace elements were discussed based on the enrichment factors and principle component analysis. The results show that the trace metal contents range from 7.9 to 75.6 μg/g for Cu, from 6.7 to 39.0 μg/g for Pb, from 32.8 to 96.6 μg/g for Zn, from 0.25 to 0.44 μg/g for Cd, from 28.0 to 78.2 μg/g for Cr, from 5.1 to 17.8 μg/g for Co, from 1.26% to 3.22% for Al, from 1.31% to 3.30% for Fe and from 158 to 638 μg/g for Mn. The metal contents in the surface sediments from Prydz Bay are comparable to those obtained from the other regions of the Southern Ocean. The contents of Cu, Zn, Cr, Co, Fe and Mn are higher in the open sea and continental slope area; the contents of Al and Pb are higher at the edge of Amery Ice Shelf; while the contents of Cd are higher in the continental shelf area. Pb, Zn, and Cd are significantly enriched in all studied sites; no obvious enrichment is observed for Cu, Cr, Co, Fe and Mn from ice shelf edge and continental shelf area; while all trace elements are variously enriched in the sediments from continental slope and open sea area. The main sources of the trace elements in Prydz Bay are mineral particles derived from the erosion and weathering of the surrounding basement, and marine biological deposition. The trace metals at the edge of the ice shelf and site of P2-9 are primarily from local sourced lithogenic inputs. The trace metals of Cu, Zn, Cr. Co. Fe and Mn in the areas of continental shelf and deep sea are significantly influenced by biological input. The trace element of Cd in the sediments from the bay is suggested to be mainly from biogenic sources, which is assimilated by diatom through the uptake from the water column in the euphotic layer and settled down on the marine floor associated with biogenic silica in the body remains.
Trace elements in marine sediment can be used to reflect anthropogenic influence on marine systems, to trace the origin and transformation of the marine substances, to indicate sedimentary environment and early diagenesis, and even to reconstruct the global change of climate. However, studies of trace elements in marine sediments are rarely reported from east Antarctica. In this case, sixteen surface sediments were collected during the 21st to 27th cruises of Chinese Antarctic Expedition in order to investigate the distribution and source composition of trace elements in the surface sediments from Prydz Bay and east Antarctica. Samples were analyzed using ICP-MS to determine the content of trace elements in the bay. Combined with biogenic silica and grain size of the sediments, the sources of trace elements were discussed based on the enrichment factors and principle component analysis. The results show that the trace metal contents range from 7.9 to 75.6 μg/g for Cu, from 6.7 to 39.0 μg/g for Pb, from 32.8 to 96.6 μg/g for Zn, from 0.25 to 0.44 μg/g for Cd, from 28.0 to 78.2 μg/g for Cr, from 5.1 to 17.8 μg/g for Co, from 1.26% to 3.22% for Al, from 1.31% to 3.30% for Fe and from 158 to 638 μg/g for Mn. The metal contents in the surface sediments from Prydz Bay are comparable to those obtained from the other regions of the Southern Ocean. The contents of Cu, Zn, Cr, Co, Fe and Mn are higher in the open sea and continental slope area; the contents of Al and Pb are higher at the edge of Amery Ice Shelf; while the contents of Cd are higher in the continental shelf area. Pb, Zn, and Cd are significantly enriched in all studied sites; no obvious enrichment is observed for Cu, Cr, Co, Fe and Mn from ice shelf edge and continental shelf area; while all trace elements are variously enriched in the sediments from continental slope and open sea area. The main sources of the trace elements in Prydz Bay are mineral particles derived from the erosion and weathering of the surrounding basement, and marine biological deposition. The trace metals at the edge of the ice shelf and site of P2-9 are primarily from local sourced lithogenic inputs. The trace metals of Cu, Zn, Cr. Co. Fe and Mn in the areas of continental shelf and deep sea are significantly influenced by biological input. The trace element of Cd in the sediments from the bay is suggested to be mainly from biogenic sources, which is assimilated by diatom through the uptake from the water column in the euphotic layer and settled down on the marine floor associated with biogenic silica in the body remains.
2016, 34(2): 315-325.
doi: 10.14027/j.cnki.cjxb.2016.02.010
Abstract:
Intertidal sediments in Hangzhou Bay were collected and analyzed by XRD. The clay minerals distribution characteristics and the source and origin of clay minerals in the study area were discussed by means of cluster analysis, combined with the hydrodynamic characteristics of the Hangzhou Bay. The results showed that surficial sediments in the tidal flat of Hangzhou Bay were mainly clayey silt and the others were sandy silt. The complex composition of clay minerals in the study area were mainly illite, kaolinite and chlorite, as well as a few smectite and vermiculite and 1.4nm transitional mineral. According to each clay mineral's content, it could be divided into three kinds of combinations:typeⅠ of illite-kaolinite-chlorite-vermiculite-smectite, typeⅡ of illite-chlorite-kaolinite-smectite-vermiculite, typeⅢ of illite-kaolinite-chlorite-smectite-vermiculite. 0n the spatial distribution, the average contents of smectite and chlorite in the northern shore were higher than which of the southern shore; while the average contents of illite and kaolinite and vermiculite(containing 1.4nm transitional minerals) in the northern shore were lower than which of the southern shore. Smectite in surficial sediments in high tidal flat was greater than in the central tidal flat, and the other clay minerals had no obvious difference. The clay minerals distribution characteristics are closely related to the hydrodynamic and material source. The intertidal sediments in eastern areas of Zhapu in north shore were significantly affected by the tide and Yangtze River coastal current, the sediments were mainly from Yangtze River and the East China Sea. As a result of the input of Caoe River and Yong River, the proportion of deposits from Qiantang River basin of sediments in the southern shore was obviously higher than which of the northern shore. The changes of each clay mineral's content from bottom to top in vertical section sediments reflected the fluctuation of weathering intensity in the source area.
Intertidal sediments in Hangzhou Bay were collected and analyzed by XRD. The clay minerals distribution characteristics and the source and origin of clay minerals in the study area were discussed by means of cluster analysis, combined with the hydrodynamic characteristics of the Hangzhou Bay. The results showed that surficial sediments in the tidal flat of Hangzhou Bay were mainly clayey silt and the others were sandy silt. The complex composition of clay minerals in the study area were mainly illite, kaolinite and chlorite, as well as a few smectite and vermiculite and 1.4nm transitional mineral. According to each clay mineral's content, it could be divided into three kinds of combinations:typeⅠ of illite-kaolinite-chlorite-vermiculite-smectite, typeⅡ of illite-chlorite-kaolinite-smectite-vermiculite, typeⅢ of illite-kaolinite-chlorite-smectite-vermiculite. 0n the spatial distribution, the average contents of smectite and chlorite in the northern shore were higher than which of the southern shore; while the average contents of illite and kaolinite and vermiculite(containing 1.4nm transitional minerals) in the northern shore were lower than which of the southern shore. Smectite in surficial sediments in high tidal flat was greater than in the central tidal flat, and the other clay minerals had no obvious difference. The clay minerals distribution characteristics are closely related to the hydrodynamic and material source. The intertidal sediments in eastern areas of Zhapu in north shore were significantly affected by the tide and Yangtze River coastal current, the sediments were mainly from Yangtze River and the East China Sea. As a result of the input of Caoe River and Yong River, the proportion of deposits from Qiantang River basin of sediments in the southern shore was obviously higher than which of the northern shore. The changes of each clay mineral's content from bottom to top in vertical section sediments reflected the fluctuation of weathering intensity in the source area.
2016, 34(2): 326-335.
doi: 10.14027/j.cnki.cjxb.2016.02.011
Abstract:
Silurian Kepingtage Formation is the key formation of clastic rock exploration in Tahe area. With the implementation of the three-dimensional exploration, showing good potential for further exploration. But lack of intergraded study on sedimentary facies restricts the deep exploration in future and well placement. Core analysis, logging response and seismic data are applied for sedimentary facies identification and source direction in combination of the study of trace elements and grain size in the guidance of Sedimentology, Geophysical and Geochemical. Study suggests that, the lower member of Kepingtage Formation is channel, tidal flat and shallow shelf. And S1k1-1 is channel and mud flat deposition, S1k1-2 is the continental shelf facies, S1k1-3 is sand flat deposition. The origin of rock mainly comes from the igneous and metammorphic rocks of Cambrian in north-west.
Silurian Kepingtage Formation is the key formation of clastic rock exploration in Tahe area. With the implementation of the three-dimensional exploration, showing good potential for further exploration. But lack of intergraded study on sedimentary facies restricts the deep exploration in future and well placement. Core analysis, logging response and seismic data are applied for sedimentary facies identification and source direction in combination of the study of trace elements and grain size in the guidance of Sedimentology, Geophysical and Geochemical. Study suggests that, the lower member of Kepingtage Formation is channel, tidal flat and shallow shelf. And S1k1-1 is channel and mud flat deposition, S1k1-2 is the continental shelf facies, S1k1-3 is sand flat deposition. The origin of rock mainly comes from the igneous and metammorphic rocks of Cambrian in north-west.
2016, 34(2): 336-345.
doi: 10.14027/j.cnki.cjxb.2016.02.012
Abstract:
Types of diagenetic facies and micro-pore structure characteristics of sandstone components of Chang 63 reservoir in Banqiao-Heshui area are systematically studied according to thin section, scanning electron microscope, mercury injection, constant-rate mercury penetration and relative permeability data. Logging response stencil is also established. Moreover, diagenetic facies parallel and planar distribution have been studied. The results show that relationship between quality of diagenetic facies controlled by sedimentary facies, diagenesis and pore structure, especially throat distribution, which is the major factor controlling the reservoir permeability. Reservoirs belonging to hydromica cementation-residual intergranular pore facies and hydromica cementation-feldspar dissolution facies, in which fine or micro-fine throat develops, pore connectivity is good, show the best flow ability and a relatively uniform oil-water percolation. These facies located in flow composite channel turbidite deposition in semi deep lake facies of gravity and oil within pores is easily mined through the throat. Pore throat radius of chlorite cementation facies and hydromica weak ementation dissolution facies is small but uniform distribution, besides this kind of reservoir distributed in the branching channel margin and seepage permeability is middle to poor. Carbonate cementation facies and carbonate+hydromica cementation facies with the worst pore structure mainly developed in the branch between the canal. Due to fine throat and poor pore connectivity, oil enrichment in pore is difficult to pass through fine throat, and recovery ratio of these two kinds of diagenetic facies is very low.
Types of diagenetic facies and micro-pore structure characteristics of sandstone components of Chang 63 reservoir in Banqiao-Heshui area are systematically studied according to thin section, scanning electron microscope, mercury injection, constant-rate mercury penetration and relative permeability data. Logging response stencil is also established. Moreover, diagenetic facies parallel and planar distribution have been studied. The results show that relationship between quality of diagenetic facies controlled by sedimentary facies, diagenesis and pore structure, especially throat distribution, which is the major factor controlling the reservoir permeability. Reservoirs belonging to hydromica cementation-residual intergranular pore facies and hydromica cementation-feldspar dissolution facies, in which fine or micro-fine throat develops, pore connectivity is good, show the best flow ability and a relatively uniform oil-water percolation. These facies located in flow composite channel turbidite deposition in semi deep lake facies of gravity and oil within pores is easily mined through the throat. Pore throat radius of chlorite cementation facies and hydromica weak ementation dissolution facies is small but uniform distribution, besides this kind of reservoir distributed in the branching channel margin and seepage permeability is middle to poor. Carbonate cementation facies and carbonate+hydromica cementation facies with the worst pore structure mainly developed in the branch between the canal. Due to fine throat and poor pore connectivity, oil enrichment in pore is difficult to pass through fine throat, and recovery ratio of these two kinds of diagenetic facies is very low.
2016, 34(2): 346-355.
doi: 10.14027/j.cnki.cjxb.2016.02.013
Abstract:
Diagenetic facies is a popular method in the exploration of oil and gas, however, there were different research achievements because of the different definition. Based on the detailed research of petrology and diagenesis of reservoir in He8 section of Shihezi Formation, EastⅡpart of Sulige Gas Field, there were five kinds of diagenetic facies in He8 section of the study area, according to Zou(2008)'s classification and nomenclature of diagenetic facies. Combining with fluid inclusions analysis results, the diagenetic environments in He8 section of East Ⅱ part of Sulige Gas Field were analyzed, and restudied the diagenetic facies according to the diagenetic environments, which improved the forming process and stages of diagenetic facies. The reservoirs in He8 section were undergone three kinds of diagenetic environments:neutral to weak acid atmospheric diagenetic environment, weak acid to acid burial diagenetic environment and weak alkaline burial diagenetic environment, different diagenetic facies were produced in different diagenetic environments. Weak dissolution-compaction facies was formed due to the compaction and weak acid dissolution in the Syndiagenetic-Period A of Early diagenetic stage, with atmosphere and acidic burial environment. There was weak acidic buried environment of Period A-Period B of Early diagenetic stage, due to the enhancing compaction and dissolution, dissolution-compaction facies was formed. Cementation and acid dissolution were the main diagenesis of the Period A-early Period B of Middle diagenetic stage, so dissolution-cementation facies was formed in the stage. And metasomatic facies was dominated by the alkaline metasomatism and cementation in late Period B of Middle diagenetic-Epigenetic stage, so the metasomatic facies was mainly formed in the alkaline burial environment when the diagenetic evolution had been up to the Period B of Middle diagenetic stage. According to the definition that diagenetic facies is the material performance of diagenetic environment, "lithology+diagenetic environment+(physical characteristics)+main diagenesis" is as the basis to divide diagenetic facies. Following the classification scheme, five types of diagenetic facies are divided for the reservoirs in He8 section:Dense compaction facies of greywacke in atmosphere environment, Dissolution-compaction facies of arenite with extra low porosity and permeability in atmosphere and acidic burial environment, Dissolution-cementation facies of arenite with extra low porosity and permeability in acidic burial environment, Dissolution facies of arenite with low porosity and permeability in acidic burial environment, and last, Dense metasomatic facies of arenite in alkaline burial environment.
Diagenetic facies is a popular method in the exploration of oil and gas, however, there were different research achievements because of the different definition. Based on the detailed research of petrology and diagenesis of reservoir in He8 section of Shihezi Formation, EastⅡpart of Sulige Gas Field, there were five kinds of diagenetic facies in He8 section of the study area, according to Zou(2008)'s classification and nomenclature of diagenetic facies. Combining with fluid inclusions analysis results, the diagenetic environments in He8 section of East Ⅱ part of Sulige Gas Field were analyzed, and restudied the diagenetic facies according to the diagenetic environments, which improved the forming process and stages of diagenetic facies. The reservoirs in He8 section were undergone three kinds of diagenetic environments:neutral to weak acid atmospheric diagenetic environment, weak acid to acid burial diagenetic environment and weak alkaline burial diagenetic environment, different diagenetic facies were produced in different diagenetic environments. Weak dissolution-compaction facies was formed due to the compaction and weak acid dissolution in the Syndiagenetic-Period A of Early diagenetic stage, with atmosphere and acidic burial environment. There was weak acidic buried environment of Period A-Period B of Early diagenetic stage, due to the enhancing compaction and dissolution, dissolution-compaction facies was formed. Cementation and acid dissolution were the main diagenesis of the Period A-early Period B of Middle diagenetic stage, so dissolution-cementation facies was formed in the stage. And metasomatic facies was dominated by the alkaline metasomatism and cementation in late Period B of Middle diagenetic-Epigenetic stage, so the metasomatic facies was mainly formed in the alkaline burial environment when the diagenetic evolution had been up to the Period B of Middle diagenetic stage. According to the definition that diagenetic facies is the material performance of diagenetic environment, "lithology+diagenetic environment+(physical characteristics)+main diagenesis" is as the basis to divide diagenetic facies. Following the classification scheme, five types of diagenetic facies are divided for the reservoirs in He8 section:Dense compaction facies of greywacke in atmosphere environment, Dissolution-compaction facies of arenite with extra low porosity and permeability in atmosphere and acidic burial environment, Dissolution-cementation facies of arenite with extra low porosity and permeability in acidic burial environment, Dissolution facies of arenite with low porosity and permeability in acidic burial environment, and last, Dense metasomatic facies of arenite in alkaline burial environment.
2016, 34(2): 356-363.
doi: 10.14027/j.cnki.cjxb.2016.02.014
Abstract:
Based on the observation of drilling core samples and thin sections, the physical property and influencing factors of sandstone reservoir of Lulehe Formation in the Pingtai region of Qaidam Basin were studied. Scanning electron microscopy, X-ray diffraction, reservoir properties and mercury injection and other information were mainly applied on this study. The result shows that the sandstone reservoirs of Lulehe Formation are mainly composed of lithic sandstone and feldspar lithic sandstone, with medium or low compositional maturity and textural maturity. Particle sorting and rounding are medium and poor. The performance of reservoir properties includes two major types:medium pore and permeability, low pore and permeability. Meanwhile, the correlation of the porosity and permeability is good. Pore type is primary intragranular pore, followed by a small amount of intergranular and intragranular dissolved pore. The original porosity of the reservoir were reduced by 31.8% and 29.5%, respectively, by compaction and cementation, which was the main factor for porosity-losing processes. Meanwhile carbonate cements has enhanced the ability of the resistance to compaction of reservoir rock. Therefore, it can effectively prevent compaction damage to the intergranular pore of reservoir rocks in the early diagenetic stage. Moreover, it provides space and material basis for the corrosion and dissolution of acidic fluid, which is beneficial to the formation of secondary corrosion pores and the improvements of reservoir properties.
Based on the observation of drilling core samples and thin sections, the physical property and influencing factors of sandstone reservoir of Lulehe Formation in the Pingtai region of Qaidam Basin were studied. Scanning electron microscopy, X-ray diffraction, reservoir properties and mercury injection and other information were mainly applied on this study. The result shows that the sandstone reservoirs of Lulehe Formation are mainly composed of lithic sandstone and feldspar lithic sandstone, with medium or low compositional maturity and textural maturity. Particle sorting and rounding are medium and poor. The performance of reservoir properties includes two major types:medium pore and permeability, low pore and permeability. Meanwhile, the correlation of the porosity and permeability is good. Pore type is primary intragranular pore, followed by a small amount of intergranular and intragranular dissolved pore. The original porosity of the reservoir were reduced by 31.8% and 29.5%, respectively, by compaction and cementation, which was the main factor for porosity-losing processes. Meanwhile carbonate cements has enhanced the ability of the resistance to compaction of reservoir rock. Therefore, it can effectively prevent compaction damage to the intergranular pore of reservoir rocks in the early diagenetic stage. Moreover, it provides space and material basis for the corrosion and dissolution of acidic fluid, which is beneficial to the formation of secondary corrosion pores and the improvements of reservoir properties.
2016, 34(2): 364-374.
doi: 10.14027/j.cnki.cjxb.2016.02.015
Abstract:
Taking the Upper Paleozoic tight sandstone reservoir of Well D18 in Daniudi Gas Field as research object, utilizing microscopic methods and reservoir physical property data, we have performed researches on petrologic features, pore types, physical property evaluation characteristics, causes of densification and favorable reservoir main controlling factors. The analyzing results provide some indications. Firstly, Well D18 the Upper Paleozoic reservoir space is mainly dominated by secondary pore including quartz intergranular dissolved pore, quartz intragranular dissolve pore, intercrystal pore, rarely mold pore and oversized pore. Secondly, the reservoir belongs to low porosity and low permeability reservoir:the average porosity is 7.1%, and the average permeability is 0.34×10-3 μm2. Thirdly, compaction is the general background of reservoir densification; siliceous, calcareous and clay cements are the main causes of densification. Lastly, dissolution is the main controlling factor of Well D18 favorable reservoir, especially the quartz dissolution most growing; chlorite cementation can preserve primary pores without increasing reservoir physical property by enhancing the resisting compaction strength of rocks and inhibiting quartz over growth.
Taking the Upper Paleozoic tight sandstone reservoir of Well D18 in Daniudi Gas Field as research object, utilizing microscopic methods and reservoir physical property data, we have performed researches on petrologic features, pore types, physical property evaluation characteristics, causes of densification and favorable reservoir main controlling factors. The analyzing results provide some indications. Firstly, Well D18 the Upper Paleozoic reservoir space is mainly dominated by secondary pore including quartz intergranular dissolved pore, quartz intragranular dissolve pore, intercrystal pore, rarely mold pore and oversized pore. Secondly, the reservoir belongs to low porosity and low permeability reservoir:the average porosity is 7.1%, and the average permeability is 0.34×10-3 μm2. Thirdly, compaction is the general background of reservoir densification; siliceous, calcareous and clay cements are the main causes of densification. Lastly, dissolution is the main controlling factor of Well D18 favorable reservoir, especially the quartz dissolution most growing; chlorite cementation can preserve primary pores without increasing reservoir physical property by enhancing the resisting compaction strength of rocks and inhibiting quartz over growth.
2016, 34(2): 375-385.
doi: 10.14027/j.cnki.cjxb.2016.02.016
Abstract:
The architecture of braided river, especially the muddy intercalation, plays a key role in the enhancement of remaining oil. Based on the outcrop, modern sediments and underground reservoir, taken P oilfield as an example, the different level of the internal architecture elements are studied in order to obtain a qualitative and quantitative distribution pattern of the heterogeneity character of the sandy braided river reservoir. Also, the architecture characterization technique for underground braided river reservoir is studied in this work. Based on the proposed distribution pattern and the related characterization techniques, the different control of architecture element to the distribution of remaining oil is analyzed:① the sandy braided rivers have three filling types, dominated by sandy fillings. The distribution styles of channel bars and braided rivers display "wide bar-narrow channel". The sludge beds within channel bars show two distribution styles as dome-like and horizon-like. ② architectures from 5 to 3 hierarchies are characterized successively. Based on three identification marks, single braded belts are characterized with width of 800~1200 m, thickness of 3~8 m and average width/thickness ratio about 178. Channel bars are characterized by principles of thickness-controlled, scale-constraint and multidimensional interaction. The width ratio of braided rivers and channel bars is about 1:3.8, and width/length ratio of channel bars is about 1:2.2. Single periodic sludge bed within channel bars are horizontally distributed and different periodic sludge beds are parallel with each other. The distribution range of sludge beds from bottom up decreases from bar head to bar tail. The quantity of sludge beds within channel bars are generally low (about 2~4). ③ reservoir architectures of different hierarchies exert different controls on the distribution of remaining oil. The interlayers control the remaining oil directly in the hierarchy of braided river belts. In the hierarchy of channel bars, the sandbodies are connected at the bottom of muddy semi-filling channels, resulting in relatively poor water flooding degree and enriched remaining oil in the upper part. Influenced by sludge beds and petrophysical boundaries, the remaining oil within in channel bars is mainly distributed as "segment-like" at the top of aggraded bodies under the sludge beds and the margin part with poor water flooding. This research has been applied in the optimization of water injection and deployment of wells of oilfields.
The architecture of braided river, especially the muddy intercalation, plays a key role in the enhancement of remaining oil. Based on the outcrop, modern sediments and underground reservoir, taken P oilfield as an example, the different level of the internal architecture elements are studied in order to obtain a qualitative and quantitative distribution pattern of the heterogeneity character of the sandy braided river reservoir. Also, the architecture characterization technique for underground braided river reservoir is studied in this work. Based on the proposed distribution pattern and the related characterization techniques, the different control of architecture element to the distribution of remaining oil is analyzed:① the sandy braided rivers have three filling types, dominated by sandy fillings. The distribution styles of channel bars and braided rivers display "wide bar-narrow channel". The sludge beds within channel bars show two distribution styles as dome-like and horizon-like. ② architectures from 5 to 3 hierarchies are characterized successively. Based on three identification marks, single braded belts are characterized with width of 800~1200 m, thickness of 3~8 m and average width/thickness ratio about 178. Channel bars are characterized by principles of thickness-controlled, scale-constraint and multidimensional interaction. The width ratio of braided rivers and channel bars is about 1:3.8, and width/length ratio of channel bars is about 1:2.2. Single periodic sludge bed within channel bars are horizontally distributed and different periodic sludge beds are parallel with each other. The distribution range of sludge beds from bottom up decreases from bar head to bar tail. The quantity of sludge beds within channel bars are generally low (about 2~4). ③ reservoir architectures of different hierarchies exert different controls on the distribution of remaining oil. The interlayers control the remaining oil directly in the hierarchy of braided river belts. In the hierarchy of channel bars, the sandbodies are connected at the bottom of muddy semi-filling channels, resulting in relatively poor water flooding degree and enriched remaining oil in the upper part. Influenced by sludge beds and petrophysical boundaries, the remaining oil within in channel bars is mainly distributed as "segment-like" at the top of aggraded bodies under the sludge beds and the margin part with poor water flooding. This research has been applied in the optimization of water injection and deployment of wells of oilfields.
2016, 34(2): 386-396.
doi: 10.14027/j.cnki.cjxb.2016.02.017
Abstract:
The microbial reef reservoirs of the 2nd submember in the upper part of the Lower Cambrian Xiaoerbulak Formation have been researched based on outcrop section, thin section identification and experiment analysis in the west of North Tarim to Kelpin area. The microbial reefs were found in south of the study area, of which the largest number and volume growth in Kungaikuotan section, showing a nearly E-W distribution, while less development in Yingersu and Sugaitebulak sections. 6 kinds of reservoir space developed in the microbial reef dolostones:intragranular pores, intergranular pores, dissolved pores, fenestral pores, micro-fractures and stylolites. But the reservoir characteristics are far from expectative goals, the average porosity and permeability are only 1.84% and 0.91×10-3 μm2, belongs to ultra-low porosity and ultra-low permeability reservoirs. It's difficult to the effective reservoirs of Lower Cambrian in Tarim Basin. Combined with previous work, the microbial reefs should not be used as the key objects of hydrocarbon exploration in Lower Cambrian and even older strata, whereas the microbial bank can be used as the next major explorative horizon.
The microbial reef reservoirs of the 2nd submember in the upper part of the Lower Cambrian Xiaoerbulak Formation have been researched based on outcrop section, thin section identification and experiment analysis in the west of North Tarim to Kelpin area. The microbial reefs were found in south of the study area, of which the largest number and volume growth in Kungaikuotan section, showing a nearly E-W distribution, while less development in Yingersu and Sugaitebulak sections. 6 kinds of reservoir space developed in the microbial reef dolostones:intragranular pores, intergranular pores, dissolved pores, fenestral pores, micro-fractures and stylolites. But the reservoir characteristics are far from expectative goals, the average porosity and permeability are only 1.84% and 0.91×10-3 μm2, belongs to ultra-low porosity and ultra-low permeability reservoirs. It's difficult to the effective reservoirs of Lower Cambrian in Tarim Basin. Combined with previous work, the microbial reefs should not be used as the key objects of hydrocarbon exploration in Lower Cambrian and even older strata, whereas the microbial bank can be used as the next major explorative horizon.
2016, 34(2): 397-403.
doi: 10.14027/j.cnki.cjxb.2016.02.018
Abstract:
From the drilling core data in different sags within Bohaiwan Basin, the rhythmic layered mudstone, limestone, dolomite, gypsum which had deposited at the Paleogene Es3-Es4 stage, was inter-layer distribution for each other. The rock thickness, whether or not the missing one, or the prosodic integrity, is inconsistent in the different sags or dips. Through the analysis of pollen data, the weak degree change between drought and wetting can't result in the huge difference of the deposition profile under a condition of the stable ancient climate. According to the deposition record and ancient salinity period of Xialiaohe, Dongying, Zhanhua and Dongpu sags, the result was founded that the different lithological combination is due to the different ancient salinity from each basin. Comprehensive analysis and inference, during the deposition of the Es3-Es4 stage, dynamic fresh water is injected into the basin, from Northeast Xialiaohe sag which is upstream region clamped by uplift and rift valley. Finally, water is collected in the southwest of the low-lying areas, the downstream region, Dongpu sag. The salty environment in the basin is not balanced. In the upstream region, salty environment is diluted by fresh water, single rock type and low thickness. In the downstream region, the high salinity environment is stable, and salt rock and gypsum rock strata are well developed when it comes to a dry climate. In the middle reaches of Dongying and Zhanhua sags, water is sometimes too fresh, sometimes too salty, and sometimes in transient state. Salty environment of high salinity is favorable for the preservation of organic matter, and it is capable of contributing to the early discharge of hydrocarbons. The salty environment is favorable for the formation of the oil and gas resources.
From the drilling core data in different sags within Bohaiwan Basin, the rhythmic layered mudstone, limestone, dolomite, gypsum which had deposited at the Paleogene Es3-Es4 stage, was inter-layer distribution for each other. The rock thickness, whether or not the missing one, or the prosodic integrity, is inconsistent in the different sags or dips. Through the analysis of pollen data, the weak degree change between drought and wetting can't result in the huge difference of the deposition profile under a condition of the stable ancient climate. According to the deposition record and ancient salinity period of Xialiaohe, Dongying, Zhanhua and Dongpu sags, the result was founded that the different lithological combination is due to the different ancient salinity from each basin. Comprehensive analysis and inference, during the deposition of the Es3-Es4 stage, dynamic fresh water is injected into the basin, from Northeast Xialiaohe sag which is upstream region clamped by uplift and rift valley. Finally, water is collected in the southwest of the low-lying areas, the downstream region, Dongpu sag. The salty environment in the basin is not balanced. In the upstream region, salty environment is diluted by fresh water, single rock type and low thickness. In the downstream region, the high salinity environment is stable, and salt rock and gypsum rock strata are well developed when it comes to a dry climate. In the middle reaches of Dongying and Zhanhua sags, water is sometimes too fresh, sometimes too salty, and sometimes in transient state. Salty environment of high salinity is favorable for the preservation of organic matter, and it is capable of contributing to the early discharge of hydrocarbons. The salty environment is favorable for the formation of the oil and gas resources.
2016, 34(2): 404-414.
doi: 10.14027/j.cnki.cjxb.2016.02.019
Abstract:
Carbonate rocks of the Majiagou Formation and mud shale rocks of the Pingliang Formation of the Ordovician system were sampled from 4 sections in the south-western margin of the Ordos Basin. GC-MS analyses were made on the saturated and aromatic hydrocarbons of the dissolved organic matter extracted from the rock samples. Contrasting studies were made on the biomarker characteristics of carbonate of the Majiagou and mud shale of the Pingliang formations. The results show that there exist obvious differences in the n-alkane distribution types, peak patterns, biomarker ratios of Pr/Ph, gamacerane/C30-αβ-hopane, C20-29tricyclic terpanes/(C20-29 tricyclic terpanes+C27-35hopanes), and methylphenanthrene index (MPI) between carbonate of the Majiagou and mud shale of the Pingliang formations. These differences are the results of different depositional environments and thermal maturities of the Majiagou and Pingliang formations and are significant for the discriminating of oils derived from the Majiagou and the Pingliang formations. The corresponding relations among the n-alkane distribution types, the sterane/hopane ratio and the C28/C29ααα20R ratio of steranes in the Majiagou Formation reflect subtle differences in organic matter sources. Correlations between Ts/(Ts+Tm) and gamacerane/C30-αβ-hopane ratios, and between C29-sterane αββ/(αββ+ααα) ratio and abundances of rearranged hopanes and steranes suggest obvious influence of depositional environment on these maturity parameters.
Carbonate rocks of the Majiagou Formation and mud shale rocks of the Pingliang Formation of the Ordovician system were sampled from 4 sections in the south-western margin of the Ordos Basin. GC-MS analyses were made on the saturated and aromatic hydrocarbons of the dissolved organic matter extracted from the rock samples. Contrasting studies were made on the biomarker characteristics of carbonate of the Majiagou and mud shale of the Pingliang formations. The results show that there exist obvious differences in the n-alkane distribution types, peak patterns, biomarker ratios of Pr/Ph, gamacerane/C30-αβ-hopane, C20-29tricyclic terpanes/(C20-29 tricyclic terpanes+C27-35hopanes), and methylphenanthrene index (MPI) between carbonate of the Majiagou and mud shale of the Pingliang formations. These differences are the results of different depositional environments and thermal maturities of the Majiagou and Pingliang formations and are significant for the discriminating of oils derived from the Majiagou and the Pingliang formations. The corresponding relations among the n-alkane distribution types, the sterane/hopane ratio and the C28/C29ααα20R ratio of steranes in the Majiagou Formation reflect subtle differences in organic matter sources. Correlations between Ts/(Ts+Tm) and gamacerane/C30-αβ-hopane ratios, and between C29-sterane αββ/(αββ+ααα) ratio and abundances of rearranged hopanes and steranes suggest obvious influence of depositional environment on these maturity parameters.
