2016 Vol. 34, No. 5
Display Method:
2016, 34(5): 811-818.
doi: 10.14027/j.cnki.cjxb.2016.05.001
Abstract:
In order to clarify the characteristic of the Cambrian carbonate paleo-ocean environment, to reveal the potential contact of diagenetic fluid and karstification, and predict favorable reservoir development zone, based on the measured carbonate rock outcrop and the system samples, using the trace elements, strontium, carbon and oxygen isotopes and casting thin section data, geochemistry and petrology method, discuss the carbonate paleo-ocean environment and the geological significance. The results show that Qingxudong Formation-Loushanguan Formation of the Cambrian as a whole for the Marine environment in the Dianqianbei depression, the ancient ocean temperature between 12.82℃~32.84℃, subject to warm or hot subtropical climate. Sea level has a main shock downward trend, there are 8 periods of sea level change cycle, development of the corresponding lithofacies combination, and isotope evolution curve can be taken as the basis of stratigraphic classification. Trace element geochemical characteristics confirmed the Loushanguan Formation karstification relative development, diagenetic fluid mixed with strong oxidizing atmosphere water at low temperature, favorable reservoir are mainly distributed in the sea level falling high part of the cycle.
In order to clarify the characteristic of the Cambrian carbonate paleo-ocean environment, to reveal the potential contact of diagenetic fluid and karstification, and predict favorable reservoir development zone, based on the measured carbonate rock outcrop and the system samples, using the trace elements, strontium, carbon and oxygen isotopes and casting thin section data, geochemistry and petrology method, discuss the carbonate paleo-ocean environment and the geological significance. The results show that Qingxudong Formation-Loushanguan Formation of the Cambrian as a whole for the Marine environment in the Dianqianbei depression, the ancient ocean temperature between 12.82℃~32.84℃, subject to warm or hot subtropical climate. Sea level has a main shock downward trend, there are 8 periods of sea level change cycle, development of the corresponding lithofacies combination, and isotope evolution curve can be taken as the basis of stratigraphic classification. Trace element geochemical characteristics confirmed the Loushanguan Formation karstification relative development, diagenetic fluid mixed with strong oxidizing atmosphere water at low temperature, favorable reservoir are mainly distributed in the sea level falling high part of the cycle.
2016, 34(5): 819-829.
doi: 10.14027/j.cnki.cjxb.2016.05.002
Abstract:
The study of lacustrine carbonate is in the stage of continuous exploration and understanding. In recent years, a large number of lacustrine carbonate reservoirs are found in China and abroad. This makes the study of lacustrine carbonate which learns from the theory of marine carbonate get more concerned and achieved certain results. The Cretaceous lacustrine algal stromatolite reef of Brazil's Santos Basin is a special type of reservoir. This study enriched lacustrine carbonate theory. Through the seismic reflection structure, and properties of three-dimensional seismic sections, core deposit structure, containing material, core and thin section diagenetic porosity and permeability analysis, drilling lithological profile, logging curve reflects the change and cycle characteristics graded phenomenon comprehensive analysis, summed up the main characteristics and controlling factors of the Cretaceous algal stromatolite reef. Algal stromatolite reefs are stacked by stromatolite and bonded by algae, making large areas of cement reef. The algal stromatolite reef has good porosity and permeability. It is a good reservoir. The development and distribution of algal stromatolite reef are mainly controlled by four factors, including sediment supply, the ancient uplift, water changes and algae development. Algal stromatolite reef developed on the eastern uplift belt with saltwater environment,low debris impaction and transgressive systems tract.
The study of lacustrine carbonate is in the stage of continuous exploration and understanding. In recent years, a large number of lacustrine carbonate reservoirs are found in China and abroad. This makes the study of lacustrine carbonate which learns from the theory of marine carbonate get more concerned and achieved certain results. The Cretaceous lacustrine algal stromatolite reef of Brazil's Santos Basin is a special type of reservoir. This study enriched lacustrine carbonate theory. Through the seismic reflection structure, and properties of three-dimensional seismic sections, core deposit structure, containing material, core and thin section diagenetic porosity and permeability analysis, drilling lithological profile, logging curve reflects the change and cycle characteristics graded phenomenon comprehensive analysis, summed up the main characteristics and controlling factors of the Cretaceous algal stromatolite reef. Algal stromatolite reefs are stacked by stromatolite and bonded by algae, making large areas of cement reef. The algal stromatolite reef has good porosity and permeability. It is a good reservoir. The development and distribution of algal stromatolite reef are mainly controlled by four factors, including sediment supply, the ancient uplift, water changes and algae development. Algal stromatolite reef developed on the eastern uplift belt with saltwater environment,low debris impaction and transgressive systems tract.
2016, 34(5): 830-841.
doi: 10.14027/j.cnki.cjxb.2016.05.003
Abstract:
This is the first time to report storm deposit in the Tongzi Formation, Lower Ordovician in the northwest Hunan Province. Meanwhile, the author demonstrates the distribution and manifestation of the sedimentary deposits systematically. Based on careful field observation and laboratory analysis, indications of the tidal flat environment such as hemispheric stromatolites, Herringbone cross bedding are widely present in the succession. The sedimentary structures of the storm deposit such as erosion -tear structure, graded bedding, rhythmic bedding, deformed bedding and the sand grain-wave bedding have been identified, excluding hummocky cross-stratification. Based on the analysis, the storm deposit in this Formation is the tidal flat storm deposit. And, four types of storm deposits have been recognized. Meanwhile, big slump gravity flow deposits are identified in Tongzi Formation, which must be the different material records of the same hurricane in different environments. Study of the storm deposit indicates that the tempestites carry important poleoclimate inFormation and frequent occurrences of storms responded to climate changes from late Cambrian to lower Ordovician. The discovery of tempestite, the storm turbidite and slump breccias provide new lines of evidence for the Western Hubei platform depression in this period and suitable reference for fine stratigraphic division and correlation of ore-containing block Formation as well as more reliable reference data for the analysis of the north draft of the South China Plate.
This is the first time to report storm deposit in the Tongzi Formation, Lower Ordovician in the northwest Hunan Province. Meanwhile, the author demonstrates the distribution and manifestation of the sedimentary deposits systematically. Based on careful field observation and laboratory analysis, indications of the tidal flat environment such as hemispheric stromatolites, Herringbone cross bedding are widely present in the succession. The sedimentary structures of the storm deposit such as erosion -tear structure, graded bedding, rhythmic bedding, deformed bedding and the sand grain-wave bedding have been identified, excluding hummocky cross-stratification. Based on the analysis, the storm deposit in this Formation is the tidal flat storm deposit. And, four types of storm deposits have been recognized. Meanwhile, big slump gravity flow deposits are identified in Tongzi Formation, which must be the different material records of the same hurricane in different environments. Study of the storm deposit indicates that the tempestites carry important poleoclimate inFormation and frequent occurrences of storms responded to climate changes from late Cambrian to lower Ordovician. The discovery of tempestite, the storm turbidite and slump breccias provide new lines of evidence for the Western Hubei platform depression in this period and suitable reference for fine stratigraphic division and correlation of ore-containing block Formation as well as more reliable reference data for the analysis of the north draft of the South China Plate.
2016, 34(5): 842-852.
doi: 10.14027/j.cnki.cjxb.2016.05.004
Abstract:
The buried depth of karst paleo-caves in Tahe oilfield, Tarim basin is deeper than others throughout the world. But little is known about the reason why it did not collapse. In order to explore the preservation mechanism of Ordovician deep buried karst paleo-caves in Tahe oilfield, by comparing burial history with the buried caves of Ordovician in Fort Worth basin, we noticed that there are a large number of calcite fillings in caves and fractures in Tahe oilfield. Based on statistical and comprehensive analysis of geochemical data, taking calcite genesis as the pointcut, the tectonic background, volcanogenic hydrothermal activities, oil and gas filling, occurrence of calcite and cave stress distribution are analyzed and a preservation mechanism of deep buried caves is put forward. Calcite precipitated in the near-surface filled part of the caves and rock fractures. Calcite is mainly precipitated in atmospheric fresh water environment, and a small amount of calcite formed under seawater environment. Calcite was also reconstructed by dissolution fluid (magmatic hydrothermal and organic acid) during burial process. They shared the overlying strata pressure in the process of strata subsidence, so that the caves have not been fully filled by collapsed breccia. Calcite added the pressure resistance of caves. Calcite filled in fractures of cave ceiling "healed" cracks near the cave, which strengthened the cave roof, increased stability of caves. Before the cave collapse, calcite occupied part of the cave space. When caves were deeply buried, dissolution fluids corroded part of calcite in caves preferentially through the cave system and fracture system. Therefore, filled caves have been recovered partly. So, the calcite filling in surface and near-surface is "retention diagenesis" of carbonate cavern reservoir.
The buried depth of karst paleo-caves in Tahe oilfield, Tarim basin is deeper than others throughout the world. But little is known about the reason why it did not collapse. In order to explore the preservation mechanism of Ordovician deep buried karst paleo-caves in Tahe oilfield, by comparing burial history with the buried caves of Ordovician in Fort Worth basin, we noticed that there are a large number of calcite fillings in caves and fractures in Tahe oilfield. Based on statistical and comprehensive analysis of geochemical data, taking calcite genesis as the pointcut, the tectonic background, volcanogenic hydrothermal activities, oil and gas filling, occurrence of calcite and cave stress distribution are analyzed and a preservation mechanism of deep buried caves is put forward. Calcite precipitated in the near-surface filled part of the caves and rock fractures. Calcite is mainly precipitated in atmospheric fresh water environment, and a small amount of calcite formed under seawater environment. Calcite was also reconstructed by dissolution fluid (magmatic hydrothermal and organic acid) during burial process. They shared the overlying strata pressure in the process of strata subsidence, so that the caves have not been fully filled by collapsed breccia. Calcite added the pressure resistance of caves. Calcite filled in fractures of cave ceiling "healed" cracks near the cave, which strengthened the cave roof, increased stability of caves. Before the cave collapse, calcite occupied part of the cave space. When caves were deeply buried, dissolution fluids corroded part of calcite in caves preferentially through the cave system and fracture system. Therefore, filled caves have been recovered partly. So, the calcite filling in surface and near-surface is "retention diagenesis" of carbonate cavern reservoir.
2016, 34(5): 853-867.
doi: 10.14027/j.cnki.cjxb.2016.05.005
Abstract:
Suhongtu depression is in the northern part of the Yingen-Ejinaqi basin, stratigraphic framework here is still unclear because of the low degree of exploration, especially, there is a big controversy on the location of the deep stratum with volcanic rock. The volcanic rocks in the study area are very developed, volcanic activity has larger influence on hydrocarbon accumulation, but activity times of volcanic remains unclear. In this study, systematic sampling has been carried out from a drilling well in Suhongtu depression. The samples were both shallow sedimentary rocks and deep volcanic rocks. Then, the U-Pb geochronology of the samples was studied, expecting it will provide evidence for the solution of the above problem. The results showed that:①Whether detrital zircon or volcanic zircons, except that a few old age zircons belonged to metamorphic origin, and the rest younger zircons belonged to the magmatic origin. Zircon ages of each sample were concentrated in three groups, and some of the age groups overlapped in different samples. ②The formation age of deep volcanic rocks was early Cretaceous, it provided some restraints on the formation with deep volcanic rocks. ③The age of all the younger magmatic zircons for every samples can be divided into four age groups:132.6±0.7 Ma, 237.9±3.2 Ma, 255.4±6.2 Ma~263.7±2.2 Ma and 314.1±2.3 Ma~328.5 Ma. The four age groups represented four volcanic activities since late Paleozoic, and the corresponding age were early Carboniferous, late Permian, middle Triassic and early Cretaceous, respectively, among these the most widely and strongly volcanic activity was late Permian. The research provided a strong basis for stratigraphic division and volcanic prediction in the study area.
Suhongtu depression is in the northern part of the Yingen-Ejinaqi basin, stratigraphic framework here is still unclear because of the low degree of exploration, especially, there is a big controversy on the location of the deep stratum with volcanic rock. The volcanic rocks in the study area are very developed, volcanic activity has larger influence on hydrocarbon accumulation, but activity times of volcanic remains unclear. In this study, systematic sampling has been carried out from a drilling well in Suhongtu depression. The samples were both shallow sedimentary rocks and deep volcanic rocks. Then, the U-Pb geochronology of the samples was studied, expecting it will provide evidence for the solution of the above problem. The results showed that:①Whether detrital zircon or volcanic zircons, except that a few old age zircons belonged to metamorphic origin, and the rest younger zircons belonged to the magmatic origin. Zircon ages of each sample were concentrated in three groups, and some of the age groups overlapped in different samples. ②The formation age of deep volcanic rocks was early Cretaceous, it provided some restraints on the formation with deep volcanic rocks. ③The age of all the younger magmatic zircons for every samples can be divided into four age groups:132.6±0.7 Ma, 237.9±3.2 Ma, 255.4±6.2 Ma~263.7±2.2 Ma and 314.1±2.3 Ma~328.5 Ma. The four age groups represented four volcanic activities since late Paleozoic, and the corresponding age were early Carboniferous, late Permian, middle Triassic and early Cretaceous, respectively, among these the most widely and strongly volcanic activity was late Permian. The research provided a strong basis for stratigraphic division and volcanic prediction in the study area.
2016, 34(5): 868-880.
doi: 10.14027/j.cnki.cjxb.2016.05.006
Abstract:
The rhodochrosite ores in black shale basins are usually occupied by a large quantity of pyrites, cause the deposit processes of rhodochrosite and pyrite are hard to observe directly, the enrichment relationship of them is not clear currently. To study the correlation between them, this research selected typical profile of Xixibao manganese ore in northeast of Guizhou province as example. It is based on ordinary thin section, TOC analyses and elemental analyses, which analyzed lithological sequence, mineral assemblage and the geochemical characteristics of Mn and Fe in the manganese-bearing rock series and the roof and floor of them, and at the same time carried out comparison analyses with modern rhodochrosite deposit. Reaearch showed that the Xixibao manganese ore did share some similar characteristics with that of modern Baltics Sea on the enrichment relationship of pyrite and rhodochrosite. The Mn content is low in both roof and floor of the manganese-bearing rock series; inner the manganese-bearing rock series the Mn content fluctuated greatly and is negatively correlated with the Fe content. The precipitation of pyrite and rhodochrosite has a sequence, usually the pyrites are precipitated first from the solution and followed by rhodochrosite.
The rhodochrosite ores in black shale basins are usually occupied by a large quantity of pyrites, cause the deposit processes of rhodochrosite and pyrite are hard to observe directly, the enrichment relationship of them is not clear currently. To study the correlation between them, this research selected typical profile of Xixibao manganese ore in northeast of Guizhou province as example. It is based on ordinary thin section, TOC analyses and elemental analyses, which analyzed lithological sequence, mineral assemblage and the geochemical characteristics of Mn and Fe in the manganese-bearing rock series and the roof and floor of them, and at the same time carried out comparison analyses with modern rhodochrosite deposit. Reaearch showed that the Xixibao manganese ore did share some similar characteristics with that of modern Baltics Sea on the enrichment relationship of pyrite and rhodochrosite. The Mn content is low in both roof and floor of the manganese-bearing rock series; inner the manganese-bearing rock series the Mn content fluctuated greatly and is negatively correlated with the Fe content. The precipitation of pyrite and rhodochrosite has a sequence, usually the pyrites are precipitated first from the solution and followed by rhodochrosite.
2016, 34(5): 881-891.
doi: 10.14027/j.cnki.cjxb.2016.05.007
Abstract:
The sieving analysis is a classic and common method used to measure the particle sizes of beach sediments. With the development of scientific technology, grading analysis by dynamic digital imaging has been widely popularized. We analyzed the particle size and the shape of 20 sediment samples from 5 beaches of Hainan Island by the methods of dynamic image analysis and sieving analysis, and then compared the testing results of the particle size analyzing from the two methods. The results of the dynamic image analysis indicate that this technique has good repeatability and high accuracy. By comparing the results obtained from digital dynamic imaging with those from sieving analysis, we can conclude that the results match well:the grading curves intersect, the particle size parameter values are close and their relevance is rather good (R2>0.94). Analyzing the particle shape parameter values from the digital dynamic images, we learn that there are obvious differences between different coastal segments with similar particle sizes. The sphericity and aspect ratio of particles from different parts of the same beach change greatly, while their symmetry and convexity change slightly. The study indicates that the different results obtained from the two methods mainly derived from their different measurement principles and the irregular particle shapes of beach sediments. The digital dynamic imaging method has completely solved the problems caused by particle shape irregularity, so it can nearly replace sieving analysis in measuring particle size, which has a broad application prospect.
The sieving analysis is a classic and common method used to measure the particle sizes of beach sediments. With the development of scientific technology, grading analysis by dynamic digital imaging has been widely popularized. We analyzed the particle size and the shape of 20 sediment samples from 5 beaches of Hainan Island by the methods of dynamic image analysis and sieving analysis, and then compared the testing results of the particle size analyzing from the two methods. The results of the dynamic image analysis indicate that this technique has good repeatability and high accuracy. By comparing the results obtained from digital dynamic imaging with those from sieving analysis, we can conclude that the results match well:the grading curves intersect, the particle size parameter values are close and their relevance is rather good (R2>0.94). Analyzing the particle shape parameter values from the digital dynamic images, we learn that there are obvious differences between different coastal segments with similar particle sizes. The sphericity and aspect ratio of particles from different parts of the same beach change greatly, while their symmetry and convexity change slightly. The study indicates that the different results obtained from the two methods mainly derived from their different measurement principles and the irregular particle shapes of beach sediments. The digital dynamic imaging method has completely solved the problems caused by particle shape irregularity, so it can nearly replace sieving analysis in measuring particle size, which has a broad application prospect.
2016, 34(5): 892-901.
doi: 10.14027/j.cnki.cjxb.2016.05.008
Abstract:
157 sediment samples were collected from Core DLC70-1 in the eastern Bohai Sea.These samples were analyzed for major and trace elements, grain size parameters, C14 dating and OSL dating with the purpose of studying the geochemical characteristics of elements and controlling factors in the eastern Bohai Sea since Late Pleistocene.The results show that sediment sources and depositional environments of the study area remained relatively stable since Late Pleistocene. According to the changing law of element contents, the sediments from Core DLC70-1 can be divided into six layers, reflecting the fluctuation of sea level and the change of sediment sources in Bohai Sea since the late of the last interglacial cycle (warm period).The Al2O3, MgO, TFe2O3, MnO, TiO2, Cu, Zn, Pb, Cr and Rb elements were positively correlated with the fine-grained sediments, and SiO2, Na2O was positively correlated with coarse-grained sediments. There was no significant positive or negative correlation between K2O, Sr and Ba distributions and grain size of sediment. Three groups representing respectively by Mg, Sr and Ba can be derived from R-model factor analysis, corresponding to the impact of the input of fine-grained terrigenous sediments and Yellow River sediment, Haihe River sediments, Luanhe River sediments. Combined with scatter diagram of Ba/Al2O3 vs. Sr/Al2O3, MgO/Al2O3 vs. K2O/Al2O3 were drawn to reveal the source of sediments from Core DLC70-1. The results suggest that the material sources of the core mainly come from the Yellow River, but the sediments in the upper-middle parts of the core were apparently influenced by materials from the Luanhe River and Haihe River.
157 sediment samples were collected from Core DLC70-1 in the eastern Bohai Sea.These samples were analyzed for major and trace elements, grain size parameters, C14 dating and OSL dating with the purpose of studying the geochemical characteristics of elements and controlling factors in the eastern Bohai Sea since Late Pleistocene.The results show that sediment sources and depositional environments of the study area remained relatively stable since Late Pleistocene. According to the changing law of element contents, the sediments from Core DLC70-1 can be divided into six layers, reflecting the fluctuation of sea level and the change of sediment sources in Bohai Sea since the late of the last interglacial cycle (warm period).The Al2O3, MgO, TFe2O3, MnO, TiO2, Cu, Zn, Pb, Cr and Rb elements were positively correlated with the fine-grained sediments, and SiO2, Na2O was positively correlated with coarse-grained sediments. There was no significant positive or negative correlation between K2O, Sr and Ba distributions and grain size of sediment. Three groups representing respectively by Mg, Sr and Ba can be derived from R-model factor analysis, corresponding to the impact of the input of fine-grained terrigenous sediments and Yellow River sediment, Haihe River sediments, Luanhe River sediments. Combined with scatter diagram of Ba/Al2O3 vs. Sr/Al2O3, MgO/Al2O3 vs. K2O/Al2O3 were drawn to reveal the source of sediments from Core DLC70-1. The results suggest that the material sources of the core mainly come from the Yellow River, but the sediments in the upper-middle parts of the core were apparently influenced by materials from the Luanhe River and Haihe River.
2016, 34(5): 902-911.
doi: 10.14027/j.cnki.cjxb.2016.05.009
Abstract:
The East China Sea continental shelf is an area characterized by complicated hydrodynamic conditions and large variability in sediment texture. Detrital mineral examinations were carried out on 69 surface sediment samples (0~5 cm) collected from the East China Sea continental shelf to investigate the spatial variations of sediment composition and their underlying mechanisms. The average content of heavy minerals in the study area is 16.3%. The high value zone is located in the middle and outer continental shelf while the inner shelf and the southwest of Jeju Island have much lower content. A total of 49 species of heavy minerals were discovered in the study area, dominated by hornblende and followed by epidote, schistose mineral and carbonate mineral; metallic minerals and pyroxene are in the third row; the rest are tremolite, garnet, sphene, zircon, olivine, glauconite, andalusite and so on. Light minerals mainly consist of feldspar followed by quartz; schistose minerals and calcite are respectively in the third and fourth row. According to the characteristics of detrital mineral assemblages, the East China Sea continental shelf can be divided into three districts:Inner-shelf area (Unit I), Outer-shelf area (Unit Ⅱ) and Tiger Reef area (Unit Ⅲ). Sediments in Unit I are mainly from the Yangtze River and the Fujian and Zhejiang coastal rivers. Hydrodynamic sorting is the primary factor that controls the distribution of detrital minerals in this unit; besides human activities also have a certain impact. However the long-term separation is the main control factor of the distribution of heavy minerals in Unite Ⅱ. In the vicinity of the 29°N, fine-grained sediments from the modern Yangtze River were spreading to the northeast into the sea make an obvious effect on the detrital mineral composition in Unit Ⅱ. Unit Ⅲ has relatively varied provenances and complicated hydrodynamic environment. The materials from the Yellow River, the Yangtze River and submarine volcanos both influence there. Thus it has a bigger difference in detrital mineral assemblages with the first two.
The East China Sea continental shelf is an area characterized by complicated hydrodynamic conditions and large variability in sediment texture. Detrital mineral examinations were carried out on 69 surface sediment samples (0~5 cm) collected from the East China Sea continental shelf to investigate the spatial variations of sediment composition and their underlying mechanisms. The average content of heavy minerals in the study area is 16.3%. The high value zone is located in the middle and outer continental shelf while the inner shelf and the southwest of Jeju Island have much lower content. A total of 49 species of heavy minerals were discovered in the study area, dominated by hornblende and followed by epidote, schistose mineral and carbonate mineral; metallic minerals and pyroxene are in the third row; the rest are tremolite, garnet, sphene, zircon, olivine, glauconite, andalusite and so on. Light minerals mainly consist of feldspar followed by quartz; schistose minerals and calcite are respectively in the third and fourth row. According to the characteristics of detrital mineral assemblages, the East China Sea continental shelf can be divided into three districts:Inner-shelf area (Unit I), Outer-shelf area (Unit Ⅱ) and Tiger Reef area (Unit Ⅲ). Sediments in Unit I are mainly from the Yangtze River and the Fujian and Zhejiang coastal rivers. Hydrodynamic sorting is the primary factor that controls the distribution of detrital minerals in this unit; besides human activities also have a certain impact. However the long-term separation is the main control factor of the distribution of heavy minerals in Unite Ⅱ. In the vicinity of the 29°N, fine-grained sediments from the modern Yangtze River were spreading to the northeast into the sea make an obvious effect on the detrital mineral composition in Unit Ⅱ. Unit Ⅲ has relatively varied provenances and complicated hydrodynamic environment. The materials from the Yellow River, the Yangtze River and submarine volcanos both influence there. Thus it has a bigger difference in detrital mineral assemblages with the first two.
2016, 34(5): 912-923.
doi: 10.14027/j.cnki.cjxb.2016.05.010
Abstract:
Affected by multi-period karst cumulated influence, the original rock fabric of Ma51+2 member of Ordovician in the northeastern Ordos basin have suffered a great destruction which restricted the reconstructing study of original palaeoenvironment and sedimentary facies. Based on core, thin section, cathode luminescence and the recovery of the protolith, five original rock types and seven rock products of diagenesis are recognized, and it can be divided into five rock type combinations, which represents about five sedimentary environment in restricted and evaporate platform of study area in the following:grain beach, beach interaction sea, mound-shoal complex, platform inner flat and restricted lagoon. Those rock type combinations constitutes four typical sedimentary sequences in vertical which reflects a drop in sea level, including restricted lagoon- platform inner shoals- platform inner flat and restricted lagoon- mound-shoal complex- platform inner flat. The results show that the grainstones and gypsum mould pore contained mud(bread flour)-crystal dolomitite form the two major kinds of original rock types in Ma51+2 member of Ordovician in northestern Ordos basin, a certain scale of algal binding rock and mud(bread flour)-crystal dolomitite are also found. Besides, the gypsum mould pore contained mud(bread flour)-crystal dolomitite shows a close relationship with the upward shoaling succession of mounds and shoals. These new recognition can provide the basis for in-depth study of palaeoenvironment and reservoir rocks in the study area.
Affected by multi-period karst cumulated influence, the original rock fabric of Ma51+2 member of Ordovician in the northeastern Ordos basin have suffered a great destruction which restricted the reconstructing study of original palaeoenvironment and sedimentary facies. Based on core, thin section, cathode luminescence and the recovery of the protolith, five original rock types and seven rock products of diagenesis are recognized, and it can be divided into five rock type combinations, which represents about five sedimentary environment in restricted and evaporate platform of study area in the following:grain beach, beach interaction sea, mound-shoal complex, platform inner flat and restricted lagoon. Those rock type combinations constitutes four typical sedimentary sequences in vertical which reflects a drop in sea level, including restricted lagoon- platform inner shoals- platform inner flat and restricted lagoon- mound-shoal complex- platform inner flat. The results show that the grainstones and gypsum mould pore contained mud(bread flour)-crystal dolomitite form the two major kinds of original rock types in Ma51+2 member of Ordovician in northestern Ordos basin, a certain scale of algal binding rock and mud(bread flour)-crystal dolomitite are also found. Besides, the gypsum mould pore contained mud(bread flour)-crystal dolomitite shows a close relationship with the upward shoaling succession of mounds and shoals. These new recognition can provide the basis for in-depth study of palaeoenvironment and reservoir rocks in the study area.
2016, 34(5): 924-929.
doi: 10.14027/j.cnki.cjxb.2016.05.011
Abstract:
Pinghu Formation in Xihu Depression is obviously affected by tide, but no tidal ridges are documented which are the typical sedimentary type in the tide-dominated environment. Through comprehensive application of cores, logs and seismic data, tidal sand ridges are discovered in Pinghu Formation, Xihu Depression. In the RMS amplitude attribute map, the topographic expression of ridges is banded. In the core, the tidal sand ridge is typically coarsing upwards. In the upper part, tabular cross bedding and scour which show the strong hydrodynamic force during the sedimentation are common; while in the lower part, the sediments are fine, and tidal beddings and bioturbation structures are frequent. There is a sharp base of the ridge in well logs and the heavy minerals are rich in ridges area. Tidal ridges are excellent quality reservoir and always surrounded by mud, so the ridges are good stratigraphic trapping potentials. Whether Xihu Depression is connected with the southern open sea or not can be known by tidal ridges coverage, so the study of tidal ridges are also helpful in palaeogeographical reconstruction.
Pinghu Formation in Xihu Depression is obviously affected by tide, but no tidal ridges are documented which are the typical sedimentary type in the tide-dominated environment. Through comprehensive application of cores, logs and seismic data, tidal sand ridges are discovered in Pinghu Formation, Xihu Depression. In the RMS amplitude attribute map, the topographic expression of ridges is banded. In the core, the tidal sand ridge is typically coarsing upwards. In the upper part, tabular cross bedding and scour which show the strong hydrodynamic force during the sedimentation are common; while in the lower part, the sediments are fine, and tidal beddings and bioturbation structures are frequent. There is a sharp base of the ridge in well logs and the heavy minerals are rich in ridges area. Tidal ridges are excellent quality reservoir and always surrounded by mud, so the ridges are good stratigraphic trapping potentials. Whether Xihu Depression is connected with the southern open sea or not can be known by tidal ridges coverage, so the study of tidal ridges are also helpful in palaeogeographical reconstruction.
2016, 34(5): 930-939.
doi: 10.14027/j.cnki.cjxb.2016.05.012
Abstract:
By study of heavy mineral, paleocurrent direction, pebble content and the glutenite percentage, this paper discussed the provenance and the content of material source rock of Baikouquan Formation in the area around Mahu depression. By the method of Q-type clustering analysis, Paleocurrent direction analysis combine ZTR map, it shows that there are three distinct sediment sources of Baikouquan Formation in the study area:the northern Xiazijie provenance, the western Huangyangquan provenance and the eastern Xiayan provenance. The hauling distance of western provenance and eastern provenance are longer than northern provenance's. By analysis of pebble content and heavy mineral combination, it shows that there exist difference of material source rock content between northern provenance and western provenance. The content of northern provenance are primarily tuff, intermediate-acid volcanic rock, while the content of western provenance are tuff, sedimentary rock and granite. As the western provenance has higher content granite, so do the higher content hard particle, and which makes the reservoir has stronger ability to resist the compaction. The directions of different sediment sources identified are in accordance with the main building directions of fans delta. Using comprehensive analysis with several methods to identify source area in the study area is quite effective.
By study of heavy mineral, paleocurrent direction, pebble content and the glutenite percentage, this paper discussed the provenance and the content of material source rock of Baikouquan Formation in the area around Mahu depression. By the method of Q-type clustering analysis, Paleocurrent direction analysis combine ZTR map, it shows that there are three distinct sediment sources of Baikouquan Formation in the study area:the northern Xiazijie provenance, the western Huangyangquan provenance and the eastern Xiayan provenance. The hauling distance of western provenance and eastern provenance are longer than northern provenance's. By analysis of pebble content and heavy mineral combination, it shows that there exist difference of material source rock content between northern provenance and western provenance. The content of northern provenance are primarily tuff, intermediate-acid volcanic rock, while the content of western provenance are tuff, sedimentary rock and granite. As the western provenance has higher content granite, so do the higher content hard particle, and which makes the reservoir has stronger ability to resist the compaction. The directions of different sediment sources identified are in accordance with the main building directions of fans delta. Using comprehensive analysis with several methods to identify source area in the study area is quite effective.
Forming Mechanism of the Slope-confined Submarine Canyons in the Baiyun Sag, Pearl River Mouth Basin
2016, 34(5): 940-950.
doi: 10.14027/j.cnki.cjxb.2016.05.013
Abstract:
The bathymetric map shows that there are 17 NNW-SSE trending submarine canyons in the northern slope of the Baiyun Sag in the Pearl River Mouth Basin, with the heads terminated on the slope, composing the slope-confined submarine canyons. Based on the high resolution 2D seismic profiles, the Quaternary sequence stratigraphic framework was established by external morphology, internal structure and other reflection characters. The depositional fillings can be divided into three systems tracts, including LST (lowstand systems tract, LST), TST (transgressive systems tract, TST) and HST (highstand systems tract, HST).The HST could be further divided into two sedimentary units, HST-I and HST-Ⅱ, according to the prograding styles of the slope, the vertical stacking patterns, the change of erosion features, and the continuity of high-amplitude seismic reflectors. The results illustrated that, the slope-confined submarine canyons were developed in the later HST sedimentary unit (HST-Ⅱ). Besides, some factors controlling the formation and development of canyons were also discussed, such as sediment supply, sedimentary failures, seafloor topographic features, and fluids leakage. Since Quaternary, abundant sediments from the Pearl River in the north would be transported via shelf to slope and basinfloor, supplying the sufficient sediments for slope-confined submarine canyons. Controlled by some negative paleo-topographic features formed in the earlier HST sedimentary unit (HST-I), during the northward transportation of these sediments, erosions and sedimentary failures were developed, inducing the formations of slope-confined submarine canyons. In the study area, the widely distributed gas chimneys, implied the vertical migrations and leakages of gas-bearing fluids, which might contribute to the evolution of submarine canyons.
The bathymetric map shows that there are 17 NNW-SSE trending submarine canyons in the northern slope of the Baiyun Sag in the Pearl River Mouth Basin, with the heads terminated on the slope, composing the slope-confined submarine canyons. Based on the high resolution 2D seismic profiles, the Quaternary sequence stratigraphic framework was established by external morphology, internal structure and other reflection characters. The depositional fillings can be divided into three systems tracts, including LST (lowstand systems tract, LST), TST (transgressive systems tract, TST) and HST (highstand systems tract, HST).The HST could be further divided into two sedimentary units, HST-I and HST-Ⅱ, according to the prograding styles of the slope, the vertical stacking patterns, the change of erosion features, and the continuity of high-amplitude seismic reflectors. The results illustrated that, the slope-confined submarine canyons were developed in the later HST sedimentary unit (HST-Ⅱ). Besides, some factors controlling the formation and development of canyons were also discussed, such as sediment supply, sedimentary failures, seafloor topographic features, and fluids leakage. Since Quaternary, abundant sediments from the Pearl River in the north would be transported via shelf to slope and basinfloor, supplying the sufficient sediments for slope-confined submarine canyons. Controlled by some negative paleo-topographic features formed in the earlier HST sedimentary unit (HST-I), during the northward transportation of these sediments, erosions and sedimentary failures were developed, inducing the formations of slope-confined submarine canyons. In the study area, the widely distributed gas chimneys, implied the vertical migrations and leakages of gas-bearing fluids, which might contribute to the evolution of submarine canyons.
2016, 34(5): 951-962.
doi: 10.14027/j.cnki.cjxb.2016.05.014
Abstract:
Three intervals were identified in the Penglaiba Section of Keping area, and every interval has different facies associations and sedimentary characteristics:the lower interval is coarse grains intraclast wackestone or packstone limestones with a little of terrigenous mud; the middle interval is the association of sparry silt and fine grains intraclast grainstone limestones and laminites limestones; the upper interval is medium thickness peloids micrite limestones. And the intra-platform shoals are found in the lower and middle interval. The Keping cement plant cross-section also can be divided into three intervals, but the boundary is not clear, the sparry intraclast limestones and micrite intraclast limestones appearing in rotation overall. According to outcrop observation, thin section identification and sedimentary microfacies analysis to the Penglaiba cross-section and Keping Cement Plant cross-section, we clarified the types of rock and facies association and built up the sediment models of Yingshan Formation:According to the water depth and energy, the Keping area developed four types facies belts-high energy shoals belt, middle-low energy shoals belt, inter-shoals despressions sediment belt, and open shallow marine sediment belt. The high energy shoals belt developed sparry fine-middle grains intraclast shoals and the middle-lower energy shoals belts developed micrite middle-coarse grains intraclast shoal, and every shoal can be divided into three subfacies-shoal body, shoal wing and inner-shoal depression; The Keping area was located in shallow marine environment with extensive microbial peloids and it was a special stage of Ordovician that the carbonate rock transformed from microbial constructions to metazoan constructions in Tarim Basin, so the formation and reform of sediment was affected by microbial activity. On the one hand, microbial action of the Ordovician Yingshan Formation based the material condition for the shoals. On the other hand, it controlled the carbonate sedimentary characteristics of Yingshan Formation.
Three intervals were identified in the Penglaiba Section of Keping area, and every interval has different facies associations and sedimentary characteristics:the lower interval is coarse grains intraclast wackestone or packstone limestones with a little of terrigenous mud; the middle interval is the association of sparry silt and fine grains intraclast grainstone limestones and laminites limestones; the upper interval is medium thickness peloids micrite limestones. And the intra-platform shoals are found in the lower and middle interval. The Keping cement plant cross-section also can be divided into three intervals, but the boundary is not clear, the sparry intraclast limestones and micrite intraclast limestones appearing in rotation overall. According to outcrop observation, thin section identification and sedimentary microfacies analysis to the Penglaiba cross-section and Keping Cement Plant cross-section, we clarified the types of rock and facies association and built up the sediment models of Yingshan Formation:According to the water depth and energy, the Keping area developed four types facies belts-high energy shoals belt, middle-low energy shoals belt, inter-shoals despressions sediment belt, and open shallow marine sediment belt. The high energy shoals belt developed sparry fine-middle grains intraclast shoals and the middle-lower energy shoals belts developed micrite middle-coarse grains intraclast shoal, and every shoal can be divided into three subfacies-shoal body, shoal wing and inner-shoal depression; The Keping area was located in shallow marine environment with extensive microbial peloids and it was a special stage of Ordovician that the carbonate rock transformed from microbial constructions to metazoan constructions in Tarim Basin, so the formation and reform of sediment was affected by microbial activity. On the one hand, microbial action of the Ordovician Yingshan Formation based the material condition for the shoals. On the other hand, it controlled the carbonate sedimentary characteristics of Yingshan Formation.
2016, 34(5): 963-972.
doi: 10.14027/j.cnki.cjxb.2016.05.015
Abstract:
Based on core, thin section and physical properties, the sedimentary characteristics and reservoir significance of microbial carbonate in Ma51+2 member of Ordovician in northestern Ordos Basin were studied. Different scale of microbial carbonates constructions formed by cyanobacteria community were found in the study area. Algal flat and microbial mound are found in Ma51+2 member, formed by stromatolite, cyanobacteria laminar dolomitite, cyanobacteria thrombolite and some grainstone connected with microbes. The microbial mound develops on a small scale in vertical, mostly less than 1 m thick per cycle. And, the microbial mound has a depositional model of mound base-core-flat in vertical which reflects a drop in sea level, formed by piebald clastic dolomite, cyanobacteria thrombolite, algal bound sand-clastic dolomitite and cyanobacteria laminar dolomitite. Besides, it also develops into the mound-shoal complex together with grain beach. Fenestral pores and intergranular dissolved pores were found in cyanobacteria thrombolite and algal bound sand-clastic dolomitite which shows the characteristics of medium porosity and low permeability totally. It can be one of the reservoir rocks in northestern Ordos Basin.
Based on core, thin section and physical properties, the sedimentary characteristics and reservoir significance of microbial carbonate in Ma51+2 member of Ordovician in northestern Ordos Basin were studied. Different scale of microbial carbonates constructions formed by cyanobacteria community were found in the study area. Algal flat and microbial mound are found in Ma51+2 member, formed by stromatolite, cyanobacteria laminar dolomitite, cyanobacteria thrombolite and some grainstone connected with microbes. The microbial mound develops on a small scale in vertical, mostly less than 1 m thick per cycle. And, the microbial mound has a depositional model of mound base-core-flat in vertical which reflects a drop in sea level, formed by piebald clastic dolomite, cyanobacteria thrombolite, algal bound sand-clastic dolomitite and cyanobacteria laminar dolomitite. Besides, it also develops into the mound-shoal complex together with grain beach. Fenestral pores and intergranular dissolved pores were found in cyanobacteria thrombolite and algal bound sand-clastic dolomitite which shows the characteristics of medium porosity and low permeability totally. It can be one of the reservoir rocks in northestern Ordos Basin.
2016, 34(5): 973-982.
doi: 10.14027/j.cnki.cjxb.2016.05.016
Abstract:
With vigorous promotion on the exploration for carbonate reef and shoal reservoirs in eastern Sichuan basin, the intra-platform reef shoal reservoir has become one focus in this area, but the study extent is lower. In this paper, based on the study on cores, field profiles and thin section data, it is ascertained that the principal sedimentation type of the study area mainly consists of Changxing Formation carbonate ramp sedimentation developed at early stage, and carbonate platform sedimentation developed at middle and late stages, open platform facies is the main sedimentation. The Changxing Formation can be divided into two third order sequences,the intra-platform reef and shoal bodies are mainly developed in Sq1-HST and Sq2-HST, and lateral distribution is not continuous, longitudinal development of phase changes, the west tectonic zone is mainly developed by Sq2-HST, whereas the east tectonic zone is developed by both Sq1-HST and Sq2-HST, and Sq1-HST is more developed. Physical analytic data show that grain dolomite and powder dolomite are the main reservoir rocks, the intra-platform is the main reservoir facies, sedimentary structure within reefs station controls the distribution of favorable reservoir. But the intra-platform highland plays a vital role in controlling the distribution of reef shoal. The vast majority of reef shoals recognized by geologic and seismic data are distributed along the Sui'ning and Guang'an intra-platform highlands, Wolonghe tectonic zone is already disclosed favorable reservoir zone, and the high zone in the south of the study area may be the important exploration direction of the intra-platform reef shoal reservoirs in this area in the future.
With vigorous promotion on the exploration for carbonate reef and shoal reservoirs in eastern Sichuan basin, the intra-platform reef shoal reservoir has become one focus in this area, but the study extent is lower. In this paper, based on the study on cores, field profiles and thin section data, it is ascertained that the principal sedimentation type of the study area mainly consists of Changxing Formation carbonate ramp sedimentation developed at early stage, and carbonate platform sedimentation developed at middle and late stages, open platform facies is the main sedimentation. The Changxing Formation can be divided into two third order sequences,the intra-platform reef and shoal bodies are mainly developed in Sq1-HST and Sq2-HST, and lateral distribution is not continuous, longitudinal development of phase changes, the west tectonic zone is mainly developed by Sq2-HST, whereas the east tectonic zone is developed by both Sq1-HST and Sq2-HST, and Sq1-HST is more developed. Physical analytic data show that grain dolomite and powder dolomite are the main reservoir rocks, the intra-platform is the main reservoir facies, sedimentary structure within reefs station controls the distribution of favorable reservoir. But the intra-platform highland plays a vital role in controlling the distribution of reef shoal. The vast majority of reef shoals recognized by geologic and seismic data are distributed along the Sui'ning and Guang'an intra-platform highlands, Wolonghe tectonic zone is already disclosed favorable reservoir zone, and the high zone in the south of the study area may be the important exploration direction of the intra-platform reef shoal reservoirs in this area in the future.
2016, 34(5): 983-990.
doi: 10.14027/j.cnki.cjxb.2016.05.017
Abstract:
Tight sandstone gas as a kind of unconventional natural gas which showed a trend of rapid exploration development in China. In order to assess the tight sandstone gas reservoir, however, we still continue to use conventional sandstone reservoir assessing parameters and method. The fact proved that the conventional method used for the assessment of tight sandstone gas is obvious inadaptability. In this paper, by comparing the characteristics and forming mechanism between conventional gas reservoir and tight sandstone gas, we conclude that the throat radius and the gas pressure are the critical factors of tight sandstone migration and enrichment. Using the improvement Windland equation with R35 parameter which is on behalf of the throat radius when mercury saturation arrives 35%, established a preferable assessing methods for tight sandstone gas reservoir in Dibei aera. Assessment results show that the R35=0.17 μm is the boundary of effective reservoir and invalid reservoir;At the same time, on the basis of the R35 size, the effective reservoir can be further divided intoⅠ, Ⅱ and Ⅲ class.
Tight sandstone gas as a kind of unconventional natural gas which showed a trend of rapid exploration development in China. In order to assess the tight sandstone gas reservoir, however, we still continue to use conventional sandstone reservoir assessing parameters and method. The fact proved that the conventional method used for the assessment of tight sandstone gas is obvious inadaptability. In this paper, by comparing the characteristics and forming mechanism between conventional gas reservoir and tight sandstone gas, we conclude that the throat radius and the gas pressure are the critical factors of tight sandstone migration and enrichment. Using the improvement Windland equation with R35 parameter which is on behalf of the throat radius when mercury saturation arrives 35%, established a preferable assessing methods for tight sandstone gas reservoir in Dibei aera. Assessment results show that the R35=0.17 μm is the boundary of effective reservoir and invalid reservoir;At the same time, on the basis of the R35 size, the effective reservoir can be further divided intoⅠ, Ⅱ and Ⅲ class.
2016, 34(5): 991-1002.
doi: 10.14027/j.cnki.cjxb.2016.05.018
Abstract:
Typical tight sandstone oil within hydrocarbon source rocks is considered in Gaotaizi oil-layer of Qingshankou Formation in Qijia Sag, located in central depression area of northern Songliao Basin. Macro- and micro-analysis of oil-bearing property and in-depth study of the main controlling factors have been carried out in reservoir, which show that oil-bearing property of the reservoir of Gaotaizi oil-layer is mainly controlled by sedimentary micro-facies, diagenesis and quality of source rock. Favorable sedimentary microfacies controls oil enrichment in reservoir. Macro pore throats are developed in sandbodies of mouth bars and distal sandbars, where the physical properties are good enough to provide preferential pathways for migration and meanwhile relatively developed storage space can also provide more entrapment habitats. The sedimentary micro-facies is the critical geological factor controlling the distribution of "sweet spots" within Gaotaizi oil-layer. Diagenesis controls the differential distribution of hydrocarbon, and mechanical compaction and cementation led to tightness of reservoir before the large-scale migration-accumulation. While in local sandstones with weak cementation and heavy corrosion developed macro pores and throats. In the later charging process differential entrapment took place in the reservoir sandstones, having different levels of shows. Source rock quality controls the level of oil occurrence within reservoir. Good-excellent quality source rock can provide abundant hydrocarbon and powerful charging dynamics. And, therefore the hydrocarbon can be migrated to and accumulated in reservoir within the source rocks. So, the shows are common even though the sand bodies may be thin and with bad physical properties, showing that the low-limits of physical properties are relatively low. While in bad-middle quality source rock area the sand bodies are thick with better physical properties, but the oil-bearing property is controlled by the combination of source rock quality, sedimentation and diagenesis. So the shows are commonly bad, only the middle part with good physical properties of sand bodies bear oil and more dry sand bodies are discovered, too. "Sweet spot" zones are principally distributed in the mature source rock area where multiple series of oil-layers are staggered and overlapped. A conclusion can be drawn that in the mid-north oil-bearing sand bodies are of thick cumulative thickness and good physical properties, but to the south they get worse. In all the "sweet spot" zones 1.5×108t of resources can be estimated, which offers exciting exploration prospect.
Typical tight sandstone oil within hydrocarbon source rocks is considered in Gaotaizi oil-layer of Qingshankou Formation in Qijia Sag, located in central depression area of northern Songliao Basin. Macro- and micro-analysis of oil-bearing property and in-depth study of the main controlling factors have been carried out in reservoir, which show that oil-bearing property of the reservoir of Gaotaizi oil-layer is mainly controlled by sedimentary micro-facies, diagenesis and quality of source rock. Favorable sedimentary microfacies controls oil enrichment in reservoir. Macro pore throats are developed in sandbodies of mouth bars and distal sandbars, where the physical properties are good enough to provide preferential pathways for migration and meanwhile relatively developed storage space can also provide more entrapment habitats. The sedimentary micro-facies is the critical geological factor controlling the distribution of "sweet spots" within Gaotaizi oil-layer. Diagenesis controls the differential distribution of hydrocarbon, and mechanical compaction and cementation led to tightness of reservoir before the large-scale migration-accumulation. While in local sandstones with weak cementation and heavy corrosion developed macro pores and throats. In the later charging process differential entrapment took place in the reservoir sandstones, having different levels of shows. Source rock quality controls the level of oil occurrence within reservoir. Good-excellent quality source rock can provide abundant hydrocarbon and powerful charging dynamics. And, therefore the hydrocarbon can be migrated to and accumulated in reservoir within the source rocks. So, the shows are common even though the sand bodies may be thin and with bad physical properties, showing that the low-limits of physical properties are relatively low. While in bad-middle quality source rock area the sand bodies are thick with better physical properties, but the oil-bearing property is controlled by the combination of source rock quality, sedimentation and diagenesis. So the shows are commonly bad, only the middle part with good physical properties of sand bodies bear oil and more dry sand bodies are discovered, too. "Sweet spot" zones are principally distributed in the mature source rock area where multiple series of oil-layers are staggered and overlapped. A conclusion can be drawn that in the mid-north oil-bearing sand bodies are of thick cumulative thickness and good physical properties, but to the south they get worse. In all the "sweet spot" zones 1.5×108t of resources can be estimated, which offers exciting exploration prospect.
2016, 34(5): 1003-1010.
doi: 10.14027/j.cnki.cjxb.2016.05.019
Abstract:
Based on the analysis of trace element, maceral and the results of rock pyrolysis of the coal-measure source rock samples from Well Y1, the development regularities of the coal-measure source rock in Ya-3 member of Yanan depression were systematically studied combining the Milankovitch cycle division results of wavelet analysis. This research shows that:(1)Based on the 104 and 260 wavelet scale of Milankovitch cycling, combined with the sequence of core and geological test results, two medium cycles and five short-cycles were identified in Ya-3 member, which points out that the coal-measure source rock tends to thicken visibly in vertical direction, and the proportion of the source rock increases clearly upward in each cycle and it is mainly developed on the top of the medium cycle, in which ⅠA2, ⅠA3 andⅠB2 are the dominant cycles; (2)As for organic macerals, the source rock is vitrinite-rich, inetinite-poor, exinite-poor and sapropelinite-poor. Of all the organic macerals, the average concentration of vitrinite is 83%, which accounts for 44%~100% of the total content. The vitriniteis mainly composed by desmocollinite and vitrodetrinite, and the kerogen types of the source rock are primarily Type Ⅲ (humus type) and some Type Ⅱ (sapropelic-humus type) organic matter. Besides, the source rock generates gas prevailingly, and it is in the initial stage of hydrocarbon generation with low maturity. The average value of Rois is 1.12; (3) The development of the source rock in the study area is controlled by multiple factors, and the period in which the faulted depression basin transformed into a sag basin is a critical tectonic stage of coal formation. The incomplete preservation of the source rock resulted from the process of strong progradation, and the time in which regional sea level rising was also a critical period of coal formation, and the toward-right inflection point of the short-cycle represented layer which was relatively rich in coal-measure source rock.
Based on the analysis of trace element, maceral and the results of rock pyrolysis of the coal-measure source rock samples from Well Y1, the development regularities of the coal-measure source rock in Ya-3 member of Yanan depression were systematically studied combining the Milankovitch cycle division results of wavelet analysis. This research shows that:(1)Based on the 104 and 260 wavelet scale of Milankovitch cycling, combined with the sequence of core and geological test results, two medium cycles and five short-cycles were identified in Ya-3 member, which points out that the coal-measure source rock tends to thicken visibly in vertical direction, and the proportion of the source rock increases clearly upward in each cycle and it is mainly developed on the top of the medium cycle, in which ⅠA2, ⅠA3 andⅠB2 are the dominant cycles; (2)As for organic macerals, the source rock is vitrinite-rich, inetinite-poor, exinite-poor and sapropelinite-poor. Of all the organic macerals, the average concentration of vitrinite is 83%, which accounts for 44%~100% of the total content. The vitriniteis mainly composed by desmocollinite and vitrodetrinite, and the kerogen types of the source rock are primarily Type Ⅲ (humus type) and some Type Ⅱ (sapropelic-humus type) organic matter. Besides, the source rock generates gas prevailingly, and it is in the initial stage of hydrocarbon generation with low maturity. The average value of Rois is 1.12; (3) The development of the source rock in the study area is controlled by multiple factors, and the period in which the faulted depression basin transformed into a sag basin is a critical tectonic stage of coal formation. The incomplete preservation of the source rock resulted from the process of strong progradation, and the time in which regional sea level rising was also a critical period of coal formation, and the toward-right inflection point of the short-cycle represented layer which was relatively rich in coal-measure source rock.
