2019 Vol. 37, No. 2
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2019, 37(2): 225-238.
doi: 10.14027/j.issn.1000-0550.2018.152
Abstract:
"Mixed siliciclastic and carbonate sediments" have been a focus in sedimentology during recent years. This paper systematically examines the new research advances of "mixed sediments" in China and abroad and discusses several critical issues at the present stage. The mixed sediment research process can be divided into four stages:1) phenomenal description; 2) basic theory research; 3) research in marine environments; and 4) research in continental and other environments. There are various, but no universal standard, petrographic classifications for the mixed sediments due to different geological settings. The genetic types of mixed sediments generally include punctuated mixing, facies mixing, in situ mixing, and source mixing. The mixing process is actually quite common and can occur in marine environments, freshwater lacustrine basins, and saline lacustrine basins. Consequently, the mixed sedimentary models are varied. The mixing process is generally controlled by siliciclastic supply, climate and water environment, eustatic (lake level) changes, paleogeomorphology features, tectonic forces, and hydrodynamic conditions. Mixed sedimentation is of great petroleum geological significance. Near-source mixed sediments are associated with delta systems, and mixed sediments on underwater uplift far from the source and algal mixed sediments could be excellent lacustrine reservoirs. There are several disadvantages in current mixed sediment research:1) inconformity of lithologic classification schemes; 2) lack of comparison research with outcrops and modern sedimentation; 3) unclarity of the mixing process in the sequence stratigraphic framework; 4) inapplicability of the traditional genetic type on complicated continental mixing processes; and 5) nonidentification of seismic responses of mixed sediments. The recovery of the paleogeographic environment, analysis of sedimentary dynamics, and petroleum exploration by comprehensive and in-depth study on mixed sediments are of great significance.
"Mixed siliciclastic and carbonate sediments" have been a focus in sedimentology during recent years. This paper systematically examines the new research advances of "mixed sediments" in China and abroad and discusses several critical issues at the present stage. The mixed sediment research process can be divided into four stages:1) phenomenal description; 2) basic theory research; 3) research in marine environments; and 4) research in continental and other environments. There are various, but no universal standard, petrographic classifications for the mixed sediments due to different geological settings. The genetic types of mixed sediments generally include punctuated mixing, facies mixing, in situ mixing, and source mixing. The mixing process is actually quite common and can occur in marine environments, freshwater lacustrine basins, and saline lacustrine basins. Consequently, the mixed sedimentary models are varied. The mixing process is generally controlled by siliciclastic supply, climate and water environment, eustatic (lake level) changes, paleogeomorphology features, tectonic forces, and hydrodynamic conditions. Mixed sedimentation is of great petroleum geological significance. Near-source mixed sediments are associated with delta systems, and mixed sediments on underwater uplift far from the source and algal mixed sediments could be excellent lacustrine reservoirs. There are several disadvantages in current mixed sediment research:1) inconformity of lithologic classification schemes; 2) lack of comparison research with outcrops and modern sedimentation; 3) unclarity of the mixing process in the sequence stratigraphic framework; 4) inapplicability of the traditional genetic type on complicated continental mixing processes; and 5) nonidentification of seismic responses of mixed sediments. The recovery of the paleogeographic environment, analysis of sedimentary dynamics, and petroleum exploration by comprehensive and in-depth study on mixed sediments are of great significance.
2019, 37(2): 239-253.
doi: 10.14027/j.issn.1000-0550.2018.168
Abstract:
Deformation bedding is a relatively common and important example of a particular type of soft sediment deformation structure (SSDS). These have recently been the research focus of various disciplines, such as sedimentology, engineering geology, seismology and structural geology. The main difficulty and problem at present concerns the recognition of seismic and non-seismic SSDS. A large number of studies have shown a considerable amount of deformation bedding in the lower reaches of the Yellow River, and there is strong evidence that it is by no means always the result of earthquake activity. The study of deformation bedding in detail is of importance for developing identification and division criteria between seismic and non-seismic SSDS.
There are many types of deformation bedding from different causes in the Yellow River and distributary channels:typical convolute bedding and very irregular general deformation bedding, whose origins include density or gravity inversion, or sliding caused by wave action, or water and sliding sediments traction, or even dragging or pressure carving by blocks of ice. Deformation bedding from different causes each has unique geometrical features that are useful as reliable markers of its genesis, and which may also be used as reliable criteria for recognizing its seismic (or non-seismic) origin. In addition to the complex hydrodynamic and climatic conditions of the lower Yellow River, the development of deformation bedding is mainly related to the extremely fine particle size of the sediments.
Deformation bedding is a relatively common and important example of a particular type of soft sediment deformation structure (SSDS). These have recently been the research focus of various disciplines, such as sedimentology, engineering geology, seismology and structural geology. The main difficulty and problem at present concerns the recognition of seismic and non-seismic SSDS. A large number of studies have shown a considerable amount of deformation bedding in the lower reaches of the Yellow River, and there is strong evidence that it is by no means always the result of earthquake activity. The study of deformation bedding in detail is of importance for developing identification and division criteria between seismic and non-seismic SSDS.
There are many types of deformation bedding from different causes in the Yellow River and distributary channels:typical convolute bedding and very irregular general deformation bedding, whose origins include density or gravity inversion, or sliding caused by wave action, or water and sliding sediments traction, or even dragging or pressure carving by blocks of ice. Deformation bedding from different causes each has unique geometrical features that are useful as reliable markers of its genesis, and which may also be used as reliable criteria for recognizing its seismic (or non-seismic) origin. In addition to the complex hydrodynamic and climatic conditions of the lower Yellow River, the development of deformation bedding is mainly related to the extremely fine particle size of the sediments.
2019, 37(2): 254-267.
doi: 10.14027/j.issn.1000-0550.2018.139
Abstract:
Conglomerate reservoirs in alluvial fans are an important oil and gas reservoir type in the Junggar Basin. However, alluvial fan glutinite reservoirs consist of several lithofacies and poor continuity, which causes the lithofacies interpretation of the alluvial fan facies to be a fundamental and difficult research area. As an example, the lithofacies mechanism and distribution of the modern Poplar River alluvial fan at the northwestern margin of the Junggar Basin is discussed on the basis of a large amount of outcrop data, source rocks, hydrological data and alluvial fan studies reported in the literature. According to the deposition mechanism, the Poplar River alluvial fan is a braided-river alluvial fan with features typical of its large scale (fan total area is 327.6 km2), gentle slope (about 4‰-7‰), and rough sediments. Sixteen lithofacies were recognized; their hydrodynamic differences indicate that they may be classified into five causes:debris flow, high-flow traction current, low-flow traction current, hydrostatic deposition, and aeolian deposition. Debris flow is mainly composed of flood deposits; high-flow traction current mainly includes sheet-flood deposits and turbulent deposits; low-flow traction current is mainly composed of (gravelly) sand channel sediments; hydrostatic deposits are dominated by fine material, and aeolian deposits mainly consist of wind-transported sediments. The lithofacies are divided into four types according to sedimentary structure, granularity and distribution scale. The first type has an obvious sedimentary structure and wide distribution. The second type has obvious sedimentary structural characteristics but limited distribution. The third type, which is present on a large scale, has characteristics in which the sedimentary structures are not apparent. The sedimentary structure and physical properties of the fourth type are also not apparent, and occur only on a limited scale. The first and second types of lithofacies are mainly caused by traction currents that mainly form in the middle and distal parts of the flood period, and in the middle part of the inter-flood stage; those lithofacies form higher-quality reservoirs underground in due course.
Conglomerate reservoirs in alluvial fans are an important oil and gas reservoir type in the Junggar Basin. However, alluvial fan glutinite reservoirs consist of several lithofacies and poor continuity, which causes the lithofacies interpretation of the alluvial fan facies to be a fundamental and difficult research area. As an example, the lithofacies mechanism and distribution of the modern Poplar River alluvial fan at the northwestern margin of the Junggar Basin is discussed on the basis of a large amount of outcrop data, source rocks, hydrological data and alluvial fan studies reported in the literature. According to the deposition mechanism, the Poplar River alluvial fan is a braided-river alluvial fan with features typical of its large scale (fan total area is 327.6 km2), gentle slope (about 4‰-7‰), and rough sediments. Sixteen lithofacies were recognized; their hydrodynamic differences indicate that they may be classified into five causes:debris flow, high-flow traction current, low-flow traction current, hydrostatic deposition, and aeolian deposition. Debris flow is mainly composed of flood deposits; high-flow traction current mainly includes sheet-flood deposits and turbulent deposits; low-flow traction current is mainly composed of (gravelly) sand channel sediments; hydrostatic deposits are dominated by fine material, and aeolian deposits mainly consist of wind-transported sediments. The lithofacies are divided into four types according to sedimentary structure, granularity and distribution scale. The first type has an obvious sedimentary structure and wide distribution. The second type has obvious sedimentary structural characteristics but limited distribution. The third type, which is present on a large scale, has characteristics in which the sedimentary structures are not apparent. The sedimentary structure and physical properties of the fourth type are also not apparent, and occur only on a limited scale. The first and second types of lithofacies are mainly caused by traction currents that mainly form in the middle and distal parts of the flood period, and in the middle part of the inter-flood stage; those lithofacies form higher-quality reservoirs underground in due course.
2019, 37(2): 268-277.
doi: 10.14027/j.issn.1000-0550.2018.132
Abstract:
After the PTB's biggest extinction in the world, the Lower Triassic is considered to be the golden era of microbial growth and reproduction. A shallow-water environment is the most favorable for microbial activity and microbial rock formation. Spectral analysis of high-resolution scanning electron microscopy and energy showed three types of microbial mineralized fabric in oolitic limestone, which is the origin of a shallow-water carbonate platform margin on the western side of the Kaijiang-Liangping Trough. These are:cavity-shaped mineralized fabric; micro-nodule-shaped mineralized fabric; and arrow-shaped mineralized fabric. Following comprehensive sedimentological, petrological and geochemical analyses, it is considered that micro-nodule-shaped mineralized fabric consists of dolomitic nanospheroids formed by microbial metabolism. The arrow-shaped mineralized fabric is made up of extracellular polymeric substances (EPS). Cavity-shaped mineralized fabric are microorganism individuals. In addition, a large number of micropores on the surface of calcite crystals were found to be caused by microbial dissolution. The discovery of these microbial mineralized fabrics provides direct evidence of a microbial outbreak in the Lower Triassic. It is assumed that microbial activity is a direct cause of the rapid carbonate deposition phenomenon of the Lower Triassic which led to the rapid Lower Triassic infilling of the Late Permian intracratonic rift in the Kaijiang-Liangping Trough.
After the PTB's biggest extinction in the world, the Lower Triassic is considered to be the golden era of microbial growth and reproduction. A shallow-water environment is the most favorable for microbial activity and microbial rock formation. Spectral analysis of high-resolution scanning electron microscopy and energy showed three types of microbial mineralized fabric in oolitic limestone, which is the origin of a shallow-water carbonate platform margin on the western side of the Kaijiang-Liangping Trough. These are:cavity-shaped mineralized fabric; micro-nodule-shaped mineralized fabric; and arrow-shaped mineralized fabric. Following comprehensive sedimentological, petrological and geochemical analyses, it is considered that micro-nodule-shaped mineralized fabric consists of dolomitic nanospheroids formed by microbial metabolism. The arrow-shaped mineralized fabric is made up of extracellular polymeric substances (EPS). Cavity-shaped mineralized fabric are microorganism individuals. In addition, a large number of micropores on the surface of calcite crystals were found to be caused by microbial dissolution. The discovery of these microbial mineralized fabrics provides direct evidence of a microbial outbreak in the Lower Triassic. It is assumed that microbial activity is a direct cause of the rapid carbonate deposition phenomenon of the Lower Triassic which led to the rapid Lower Triassic infilling of the Late Permian intracratonic rift in the Kaijiang-Liangping Trough.
2019, 37(2): 278-291.
doi: 10.14027/j.issn.1000-0550.2018.108
Abstract:
The black rock series of the Lower Cambrian in northwestern Jiangxi is an important source of uranium and other metals. The carbonaceous-siliceous mudstone of the Guanyintang Formation is a typical black rock type. This study of the element geochemistry and paleoenvironmental evolution characteristics of the carbonaceous-siliceous mudstone shows that the clay mineral content of the rock is 55%-59%, with average contents of SiO2 69.47%; Al2O3 11.39%; Fe2O3 3.32%; K2O 2.76%; MgO 1.57%; and TOC 5.82%. The chemical composition is characterized by high silicon, low aluminum, low potassium and low magnesium. It is rich in carbon. Comparison with the argillaceous rocks in eastern China shows that this carbonaceous-siliceous mudstone is relatively enriched in Ni, V, U, Ba, Cd, In, Tl, Se, W, Mo, Cu, Zn, Au, Ag, As, Sb and so on. From the upper to lower levels, SiO2, Na2O, Ni and Mo content increases gradually, and Al2O3, K2O, TiO2, H2O, LOI, Cr, Th, Ba, Ga, Li, Be, Rb, Sc, Sn, Bi, Cu, Pb, Zn, Ag and REE decrease gradually. The discriminant parameters or diagrams of the major or trace elements show that the source of the sedimentary material was terrigenous clastic rocks in a stable deep-water reducing environment and a low deposition rate. From early to late, the weathering effect of the source area has gradually been enhanced, the climate is becoming wetter, and the water in the basin is becoming increasingly desalinized.
The black rock series of the Lower Cambrian in northwestern Jiangxi is an important source of uranium and other metals. The carbonaceous-siliceous mudstone of the Guanyintang Formation is a typical black rock type. This study of the element geochemistry and paleoenvironmental evolution characteristics of the carbonaceous-siliceous mudstone shows that the clay mineral content of the rock is 55%-59%, with average contents of SiO2 69.47%; Al2O3 11.39%; Fe2O3 3.32%; K2O 2.76%; MgO 1.57%; and TOC 5.82%. The chemical composition is characterized by high silicon, low aluminum, low potassium and low magnesium. It is rich in carbon. Comparison with the argillaceous rocks in eastern China shows that this carbonaceous-siliceous mudstone is relatively enriched in Ni, V, U, Ba, Cd, In, Tl, Se, W, Mo, Cu, Zn, Au, Ag, As, Sb and so on. From the upper to lower levels, SiO2, Na2O, Ni and Mo content increases gradually, and Al2O3, K2O, TiO2, H2O, LOI, Cr, Th, Ba, Ga, Li, Be, Rb, Sc, Sn, Bi, Cu, Pb, Zn, Ag and REE decrease gradually. The discriminant parameters or diagrams of the major or trace elements show that the source of the sedimentary material was terrigenous clastic rocks in a stable deep-water reducing environment and a low deposition rate. From early to late, the weathering effect of the source area has gradually been enhanced, the climate is becoming wetter, and the water in the basin is becoming increasingly desalinized.
2019, 37(2): 292-300.
doi: 10.14027/j.issn.1000-0550.2018.125
Abstract:
There are two opposing views about the origin of the ore bearing rocks of the Jinding superlarge lead-zinc mine in Yunnan, Lanping:normal deposition and abnormal deposition. To determine the origin, firstly observation and description of the mining outcrop and drill cores in the mining area were carried out, based on geological mapping of the mining area, and secondly by analyzing the petrological characteristics, granularity and sedimentary facies of the ore bearing rock. It is believed that the ore bearing rock was deposited as a sublacustrine fan dominated by debris flows, identified both as a non-channel system of liquefied particle flow and as a channel system of sand debris flow with turbidity currents, and further subdivided into inner, middle and outer fan facies. The plane distribution of the sublacustrine fan shows that the grain size clearly changes from coarse to fine from east to west of the mining area. The lithology consists of thick-blocky limestone rock composed of breccia facies, gradually transitioning to cross-bedding in sandstone. The sand debris flow deposits have good reservoir properties and are also important ore bearing rocks with broad exploration prospects.
There are two opposing views about the origin of the ore bearing rocks of the Jinding superlarge lead-zinc mine in Yunnan, Lanping:normal deposition and abnormal deposition. To determine the origin, firstly observation and description of the mining outcrop and drill cores in the mining area were carried out, based on geological mapping of the mining area, and secondly by analyzing the petrological characteristics, granularity and sedimentary facies of the ore bearing rock. It is believed that the ore bearing rock was deposited as a sublacustrine fan dominated by debris flows, identified both as a non-channel system of liquefied particle flow and as a channel system of sand debris flow with turbidity currents, and further subdivided into inner, middle and outer fan facies. The plane distribution of the sublacustrine fan shows that the grain size clearly changes from coarse to fine from east to west of the mining area. The lithology consists of thick-blocky limestone rock composed of breccia facies, gradually transitioning to cross-bedding in sandstone. The sand debris flow deposits have good reservoir properties and are also important ore bearing rocks with broad exploration prospects.
2019, 37(2): 301-308.
doi: 10.14027/j.issn.1000-0550.2018.123
Abstract:
Obvious 23 000-year-long cycles have been identified in stalagmite oxygen isotope records, but 100 000-year cycles are also widely recorded in other geological records. Based on the analysis of isotopic data for 20 stalagmites from Sanbao Cave, Hubei, it is found that the initial 234U/238U ratio has a strong cycle of 100 000 years in the period 640.3-299.6 ka B.P. The values of (234U/238U)0 increases during interglacial periods and decreases in glacial periods. The 100 000-year cycle of (234U/238U)0 corresponds closely with changes in global ice volume, loess grain size and atmospheric CO2 concentration. This coherence indicates that the changes of global ice volume and CO2 concentration had important effects on the enrichment and migration of geochemical elements in karst areas. These observations indicate that the oxygen isotope record for the precession cycle in stalagmites is independent of the influences of high-northern-latitude ice volume and global greenhouse gases, suggesting a direct effect of solar radiation change on low-latitude water circulation. Corresponding changes of (234U/238U)0, oxygen isotope and insolation in terminations support the hypothesis that the northern hemisphere summer insolation modulate the glacial to interglacial cycle.
Obvious 23 000-year-long cycles have been identified in stalagmite oxygen isotope records, but 100 000-year cycles are also widely recorded in other geological records. Based on the analysis of isotopic data for 20 stalagmites from Sanbao Cave, Hubei, it is found that the initial 234U/238U ratio has a strong cycle of 100 000 years in the period 640.3-299.6 ka B.P. The values of (234U/238U)0 increases during interglacial periods and decreases in glacial periods. The 100 000-year cycle of (234U/238U)0 corresponds closely with changes in global ice volume, loess grain size and atmospheric CO2 concentration. This coherence indicates that the changes of global ice volume and CO2 concentration had important effects on the enrichment and migration of geochemical elements in karst areas. These observations indicate that the oxygen isotope record for the precession cycle in stalagmites is independent of the influences of high-northern-latitude ice volume and global greenhouse gases, suggesting a direct effect of solar radiation change on low-latitude water circulation. Corresponding changes of (234U/238U)0, oxygen isotope and insolation in terminations support the hypothesis that the northern hemisphere summer insolation modulate the glacial to interglacial cycle.
2019, 37(2): 309-319.
doi: 10.14027/j.issn.1000-0550.2018.129
Abstract:
The Loess Plateau with eolian accumulation is the most widespread and most continuous area in western China. Based on the loess-paleosol sequence and research of the underlying red clay, a series of advances have been made in determining the inland aridity, the evolution of the paleo-monsoon, and its constraints on the uplift of the plateau. The eolian deposits found in the western part of China also provide indispensable data for inland aridity research. Based on previous field investigations, this paper takes the Neogene red clay in the Altun Mountain area on the northeastern margin of Qinghai-Tibet Plateau as the research focus, and based on the magnetic stratigraphy, substitution indices of paleoclimatology, such as magnetic susceptibility, particle size, etc, are used to reconstruct the palaeoclimate evolution process of the Altun area and explore its indicative significance for the aridity of the Asian interior. In this paper, grain size analysis is carried out on the basis of the existing magnetic stratigraphic constraints and the paleo-climatic environment information for the inversion of the Altun Neogene red clay records. The sediment grain size End Member Model (EMM) was decomposed. It can be divided into three End Members:EM1 (mode particle size 5.2 μm) has a concentration size distribution in 2-6 μm, grain size distribution in the westerlies of the North Pacific Ocean, and grain size distribution of Chinese loess. EM2 (Mode Size 20 μm) shows a negative skewed asymmetric distribution, and the Mode Size is between 32-16 μm. It is the dust material, which is moved by the low-level westerly over short distances. The distribution of EM3 is a double main peak, and the particle sizes are 57 μm and 2.5 μm, representing the intensity of near-source variation of wind-stroke dynamics during the duststorm event reflecting the mixed depositional characteristics. During 10.8-10.3 Ma, 8-6 Ma, 5.2-4.3 Ma, and 3.6-2.8 Ma, the particle content of End-Member 1 gradually decreased while the granularity percent content of End-Member 2 shows a gradually increasing trend and medium particle size. The Altun red clay records show that the intensity of the inland drought has gone through four stages:10.8-10.3 Ma, 8-6 Ma, 5.2-4.3 Ma, and 3.6-2.8 Ma. Combined with previous studies of other geological records for the profile and related geological records of the adjacent areas, the onset time of inland drought may be 11 Ma. The westerly wind is dominant in this area, global cooling is the leading factor of the intensification of inland drought, and the stage uplift of the Tibei-Plateau is promoted.
The Loess Plateau with eolian accumulation is the most widespread and most continuous area in western China. Based on the loess-paleosol sequence and research of the underlying red clay, a series of advances have been made in determining the inland aridity, the evolution of the paleo-monsoon, and its constraints on the uplift of the plateau. The eolian deposits found in the western part of China also provide indispensable data for inland aridity research. Based on previous field investigations, this paper takes the Neogene red clay in the Altun Mountain area on the northeastern margin of Qinghai-Tibet Plateau as the research focus, and based on the magnetic stratigraphy, substitution indices of paleoclimatology, such as magnetic susceptibility, particle size, etc, are used to reconstruct the palaeoclimate evolution process of the Altun area and explore its indicative significance for the aridity of the Asian interior. In this paper, grain size analysis is carried out on the basis of the existing magnetic stratigraphic constraints and the paleo-climatic environment information for the inversion of the Altun Neogene red clay records. The sediment grain size End Member Model (EMM) was decomposed. It can be divided into three End Members:EM1 (mode particle size 5.2 μm) has a concentration size distribution in 2-6 μm, grain size distribution in the westerlies of the North Pacific Ocean, and grain size distribution of Chinese loess. EM2 (Mode Size 20 μm) shows a negative skewed asymmetric distribution, and the Mode Size is between 32-16 μm. It is the dust material, which is moved by the low-level westerly over short distances. The distribution of EM3 is a double main peak, and the particle sizes are 57 μm and 2.5 μm, representing the intensity of near-source variation of wind-stroke dynamics during the duststorm event reflecting the mixed depositional characteristics. During 10.8-10.3 Ma, 8-6 Ma, 5.2-4.3 Ma, and 3.6-2.8 Ma, the particle content of End-Member 1 gradually decreased while the granularity percent content of End-Member 2 shows a gradually increasing trend and medium particle size. The Altun red clay records show that the intensity of the inland drought has gone through four stages:10.8-10.3 Ma, 8-6 Ma, 5.2-4.3 Ma, and 3.6-2.8 Ma. Combined with previous studies of other geological records for the profile and related geological records of the adjacent areas, the onset time of inland drought may be 11 Ma. The westerly wind is dominant in this area, global cooling is the leading factor of the intensification of inland drought, and the stage uplift of the Tibei-Plateau is promoted.
2019, 37(2): 320-329.
doi: 10.14027/j.issn.1000-0550.2018.133
Abstract:
The climate evolution of the Paleogene experienced changing from "greenhouse climate" to "ice chamber climate". During this period, three significant climate events occurred:the PETM event, the Oi-L event and the Mi-L event. Using pollen and foraminifera data, we discuss the ancient biological differences in the East China Sea Shelf Basin based on the global palaeoclimate. According to the characteristics of the pollen assemblage with the monsoon climate formed in the Oligocene, we restore the ancient plant and climate patterns in the East China Sea Shelf Basin. Based on this, a comparison was carried out on the temperature and humidity changes in the East China Sea Shelf Basin, with special references to global temperature and sea level changes. We suggest that a certain coupling relationship exists between the climate changes in the East China Sea Shelf Basin and global sea level change, which helps us better understand climate change in the East China Sea Shelf Basin during the Oligocene. The formation of the monsoon climate during the Oligocene led to the humid climate characteristics of the Huagang Formation in the East China Sea Shelf Basin.
The climate evolution of the Paleogene experienced changing from "greenhouse climate" to "ice chamber climate". During this period, three significant climate events occurred:the PETM event, the Oi-L event and the Mi-L event. Using pollen and foraminifera data, we discuss the ancient biological differences in the East China Sea Shelf Basin based on the global palaeoclimate. According to the characteristics of the pollen assemblage with the monsoon climate formed in the Oligocene, we restore the ancient plant and climate patterns in the East China Sea Shelf Basin. Based on this, a comparison was carried out on the temperature and humidity changes in the East China Sea Shelf Basin, with special references to global temperature and sea level changes. We suggest that a certain coupling relationship exists between the climate changes in the East China Sea Shelf Basin and global sea level change, which helps us better understand climate change in the East China Sea Shelf Basin during the Oligocene. The formation of the monsoon climate during the Oligocene led to the humid climate characteristics of the Huagang Formation in the East China Sea Shelf Basin.
2019, 37(2): 330-344.
doi: 10.14027/j.issn.1000-0550.2018.162
Abstract:
In order to explore the identification of the sequence boundary, sequence division, and vertical evolution characteristics of marine shales, and to provide a reference for the study of standardized sequence stratigraphy in shale, as well as the exploration and development of shale gas, we take the Wufeng Formation-Longmaxi Formation marine black shale, which has rich organic matter in southeastern Sichuan Basin, as an example, The comprehensive utilization of the wild section, rock cores and petrographic thin sections, palaeontology graptolites, logging, and geochemical data is carried out. Based on sequence stratigraphy, the marine shale sequence interface recognition and the sequence of the division are investigated. The study established a sequence boundary recognition method for Marine shales with a lithologic interface to reflect the physical characteristics intuitively, with logging to reflect stratigraphic superposition patterns with the concept of limited time of paleograptolite and using geochemical parameter TH/U to the reflect sedimentary environment, where total organic carbon (TOC), TH, U, and K reflect the stratigraphic rotation. Then, the vertical sequence development characteristics and the sequence characteristics of the connecting well are analyzed, and it is clear that the Wufeng Formation-the first section of the Longmaxi Formation experienced three large-scale transgressive-regressive cycles, and three tertiary sequences and seven system tracts are divided. This paper discusses the control effect of the recession-transgression events and glacial climate on relative sea level. In the end, the sequence evolution model of marine transgression is proposed, which is influenced by glacial climate, tectonic uplift, rising ocean currents, and turbidity currents. These system tracts SQ1-TST, SQ2-TST, and SQ2-EHST are the key layers of organic matter enrichment, and SQ3-TST is the secondary organic matter enrichment stratum.
In order to explore the identification of the sequence boundary, sequence division, and vertical evolution characteristics of marine shales, and to provide a reference for the study of standardized sequence stratigraphy in shale, as well as the exploration and development of shale gas, we take the Wufeng Formation-Longmaxi Formation marine black shale, which has rich organic matter in southeastern Sichuan Basin, as an example, The comprehensive utilization of the wild section, rock cores and petrographic thin sections, palaeontology graptolites, logging, and geochemical data is carried out. Based on sequence stratigraphy, the marine shale sequence interface recognition and the sequence of the division are investigated. The study established a sequence boundary recognition method for Marine shales with a lithologic interface to reflect the physical characteristics intuitively, with logging to reflect stratigraphic superposition patterns with the concept of limited time of paleograptolite and using geochemical parameter TH/U to the reflect sedimentary environment, where total organic carbon (TOC), TH, U, and K reflect the stratigraphic rotation. Then, the vertical sequence development characteristics and the sequence characteristics of the connecting well are analyzed, and it is clear that the Wufeng Formation-the first section of the Longmaxi Formation experienced three large-scale transgressive-regressive cycles, and three tertiary sequences and seven system tracts are divided. This paper discusses the control effect of the recession-transgression events and glacial climate on relative sea level. In the end, the sequence evolution model of marine transgression is proposed, which is influenced by glacial climate, tectonic uplift, rising ocean currents, and turbidity currents. These system tracts SQ1-TST, SQ2-TST, and SQ2-EHST are the key layers of organic matter enrichment, and SQ3-TST is the secondary organic matter enrichment stratum.
2019, 37(2): 345-355.
doi: 10.14027/j.issn.1000-0550.2018.128
Abstract:
Correlation theory and seismic sedimentology and sequence stratigraphy methods, together with comprehensive utilization of drilling log data, seismic reflection configuration, root mean square amplitude attributes and shoreline migration trajectory recognition characteristics were used to investigate the evolution model and hydrocarbon significance based on a falling stage systems tract (FSST) in the northern Baiyun depression, Pearl River Mouth Basin, at about 21 Ma. It was concluded that the seismic reflection characteristics of the FSST indicates high-angle oblique progradation parallel to the source direction; the front near the basin center tended to develop a basin floor fan with a domed seismic reflection configuration; the shoreline migration trajectory shows a descending trend towards the basin. The result shows that incised U-type valleys are often observed along the vertical source direction, with an internal filling structure parallel to the seismic reflection configuration. The core log curve of the FSST is a combination of funnel-shaped and box-type curves, which indicates multiple parasequence sets controlled by the fourth-order relative eustatic cycle. Each parasequence set shows the characteristics of upward shallowing succession, with its top suddenly changing to a deep water sequence. The FSST in the study area is bounded at the base by prodelta shelf mudstones of the underlying highstand systems tract sequence, and it is overlain by dark mudstones of transgressive and highstand systems tracts. The shelf break has caused strata pinching and a fault system communicates to the oil source, thus forming a favorable source-reservoir-caprock assemblage. Lithological hydrocarbon accumulations usually occur in the area.
Correlation theory and seismic sedimentology and sequence stratigraphy methods, together with comprehensive utilization of drilling log data, seismic reflection configuration, root mean square amplitude attributes and shoreline migration trajectory recognition characteristics were used to investigate the evolution model and hydrocarbon significance based on a falling stage systems tract (FSST) in the northern Baiyun depression, Pearl River Mouth Basin, at about 21 Ma. It was concluded that the seismic reflection characteristics of the FSST indicates high-angle oblique progradation parallel to the source direction; the front near the basin center tended to develop a basin floor fan with a domed seismic reflection configuration; the shoreline migration trajectory shows a descending trend towards the basin. The result shows that incised U-type valleys are often observed along the vertical source direction, with an internal filling structure parallel to the seismic reflection configuration. The core log curve of the FSST is a combination of funnel-shaped and box-type curves, which indicates multiple parasequence sets controlled by the fourth-order relative eustatic cycle. Each parasequence set shows the characteristics of upward shallowing succession, with its top suddenly changing to a deep water sequence. The FSST in the study area is bounded at the base by prodelta shelf mudstones of the underlying highstand systems tract sequence, and it is overlain by dark mudstones of transgressive and highstand systems tracts. The shelf break has caused strata pinching and a fault system communicates to the oil source, thus forming a favorable source-reservoir-caprock assemblage. Lithological hydrocarbon accumulations usually occur in the area.
2019, 37(2): 356-370.
doi: 10.14027/j.issn.1000-0550.2018.130
Abstract:
The Jurassic strata of southern Altyn tagh in the western Qaidam Basin have a similar sedimentary background as that in the northern Qaidam Basin, with well-developed shale beds and promising resource prospects. Based on the sedimentary characteristics of outcrop and borehole cores, sequence stratigraphic framework of the Lower Jurassic Xiaomeigou Formation of southern Altyn tagh was established, the lithofacies paleogeography of third-order sequence was reconstructed, and the sedimentary evolution characteristics were analyzed. The lithology of the Xiaomeigou Formation mainly consists of mudstone, shale, siltstone, sandstone, and conglomerate. Three depositional systems were classified, including braided fluvial, fan delta, and lake.The braided fluvial system is composed of river bed and floodplain facies; the fan delta system consists of fan deltaic plain and fan deltaic front facies; and the lacustrine system includes shore-shallow lacustrine, lake-bay, and semi-deep lake facies. The sequence boundaries, including the regional unconformities, fluvial incision surfaces, and abrupt change surfaces of both lithology and color were identified. According to these sequence boundaries, the Xiaomeigou Formation was subdivided into three third-order sequences. Based on the analysis of the sedimentary facies in both single and comparative profiles, the single factor analysis and multifactor comprehensive mapping method were used to reconstruct the lithofacies palaeogeography of each third-order sequence. The semi-deep lake and shore-shallow lacustrine facies mainly developed in the north, while the fan delta and the river developed in the south and northeast of the research area. From southeast to northwest, the terrain gradually decreases, and Altyn tagh had not yet risen in this period. The uplift of the Qaidam Basin in the south and the ancient Alabashitao mountain in the northeast are mainly provenance. The northeast region of Qingshuigou and Xiaoxigou is the depocenter in the prototype basin, which developed shale with large thicknesses, and is the favorable area for exploration of Jurassic shale gas.
The Jurassic strata of southern Altyn tagh in the western Qaidam Basin have a similar sedimentary background as that in the northern Qaidam Basin, with well-developed shale beds and promising resource prospects. Based on the sedimentary characteristics of outcrop and borehole cores, sequence stratigraphic framework of the Lower Jurassic Xiaomeigou Formation of southern Altyn tagh was established, the lithofacies paleogeography of third-order sequence was reconstructed, and the sedimentary evolution characteristics were analyzed. The lithology of the Xiaomeigou Formation mainly consists of mudstone, shale, siltstone, sandstone, and conglomerate. Three depositional systems were classified, including braided fluvial, fan delta, and lake.The braided fluvial system is composed of river bed and floodplain facies; the fan delta system consists of fan deltaic plain and fan deltaic front facies; and the lacustrine system includes shore-shallow lacustrine, lake-bay, and semi-deep lake facies. The sequence boundaries, including the regional unconformities, fluvial incision surfaces, and abrupt change surfaces of both lithology and color were identified. According to these sequence boundaries, the Xiaomeigou Formation was subdivided into three third-order sequences. Based on the analysis of the sedimentary facies in both single and comparative profiles, the single factor analysis and multifactor comprehensive mapping method were used to reconstruct the lithofacies palaeogeography of each third-order sequence. The semi-deep lake and shore-shallow lacustrine facies mainly developed in the north, while the fan delta and the river developed in the south and northeast of the research area. From southeast to northwest, the terrain gradually decreases, and Altyn tagh had not yet risen in this period. The uplift of the Qaidam Basin in the south and the ancient Alabashitao mountain in the northeast are mainly provenance. The northeast region of Qingshuigou and Xiaoxigou is the depocenter in the prototype basin, which developed shale with large thicknesses, and is the favorable area for exploration of Jurassic shale gas.
2019, 37(2): 371-378.
doi: 10.14027/j.issn.1000-0550.2018.191
Abstract:
The limestone deposits of the Upper Cretaceous Hartha Formation in the Iraqi HF oilfield are found in a carbonate ramp environment. The reservoir characteristics and main controlling factors are still unclear. Through drilling, logging, core, and seismic data, combined with thin section observations and analysis, the petrological characteristics, reservoir space types, and physical properties of the Hartha Formation in this oilfield are studied, and the controlling factors for the sedimentary facies and diagenesis are analyzed. The results show that the reservoir rocks of the Hartha Formation, with a thickness of about 50 m, are mainly wackstone, packstone and grainstone, with a porosity range of 10%-22% and permeability of (0.1-0.5)×10-3 μm2 and (1-5)×10-3 μm2, and the physical properties of the matrix are good. The upper part of the Hartha Formation has relatively good reservoir performance, while the lower part of the Hartha Formation develops external gentle slope mortar with poor reservoir performance. Sedimentation plays a major role in controlling the physical properties of reservoirs, the physical properties of reservoir rocks in shoal facies are better than that in non-shoal facies. The limestone reservoir develops inter-granular pores, biological mould pores, intra fossil pores, dissolved pores and micro fractures. During the exposure period of the Late Cretaceous, the dissolved pores were partially filled by cements under the epi-diagenesis, and there were strong cementation zones locally.
The limestone deposits of the Upper Cretaceous Hartha Formation in the Iraqi HF oilfield are found in a carbonate ramp environment. The reservoir characteristics and main controlling factors are still unclear. Through drilling, logging, core, and seismic data, combined with thin section observations and analysis, the petrological characteristics, reservoir space types, and physical properties of the Hartha Formation in this oilfield are studied, and the controlling factors for the sedimentary facies and diagenesis are analyzed. The results show that the reservoir rocks of the Hartha Formation, with a thickness of about 50 m, are mainly wackstone, packstone and grainstone, with a porosity range of 10%-22% and permeability of (0.1-0.5)×10-3 μm2 and (1-5)×10-3 μm2, and the physical properties of the matrix are good. The upper part of the Hartha Formation has relatively good reservoir performance, while the lower part of the Hartha Formation develops external gentle slope mortar with poor reservoir performance. Sedimentation plays a major role in controlling the physical properties of reservoirs, the physical properties of reservoir rocks in shoal facies are better than that in non-shoal facies. The limestone reservoir develops inter-granular pores, biological mould pores, intra fossil pores, dissolved pores and micro fractures. During the exposure period of the Late Cretaceous, the dissolved pores were partially filled by cements under the epi-diagenesis, and there were strong cementation zones locally.
2019, 37(2): 379-389.
doi: 10.14027/j.issn.1000-0550.2018.127
Abstract:
The pore structure parameters of carbonate rocks is quantified by digital image analysis (DIA) to determine the characteristics of the pores in this complex structure and their influence on its physical properties. A model for predicting the physical properties of the carbonate reservoir is established after selecting appropriate parameters. The carbonate reservoir is a typical porous reservoir dominated by secondary pores. Application of pore-structure parameters in this way enables the various pore types in the carbonate reservoirs in the Nanpu area to be distinguished. Pore types included:moldic pores with low perimeter-over-area (PoA) and high aspect ratio; intergranular pores with low PoA and high equivalent diameter (the latter having a large standard deviation); and matrix pores, typically of high PoA and high average equivalent diameter. Of all the pore parameters, the equivalent diameter, form factor, roundness and compactness are found to have the greatest effect on porosity and permeability. Further, 28 parameters are optimized by means of correlation matrix. The best-fit relationship between pore structure parameters and porosity and permeability is established by multivariate linear regression, giving the very reasonable R2 values of 0.778 for porosity and 0.916 for permeability. These results provide an ideal reference for evaluating the properties of porous carbonate reservoirs in Nanpu and in other areas.
The pore structure parameters of carbonate rocks is quantified by digital image analysis (DIA) to determine the characteristics of the pores in this complex structure and their influence on its physical properties. A model for predicting the physical properties of the carbonate reservoir is established after selecting appropriate parameters. The carbonate reservoir is a typical porous reservoir dominated by secondary pores. Application of pore-structure parameters in this way enables the various pore types in the carbonate reservoirs in the Nanpu area to be distinguished. Pore types included:moldic pores with low perimeter-over-area (PoA) and high aspect ratio; intergranular pores with low PoA and high equivalent diameter (the latter having a large standard deviation); and matrix pores, typically of high PoA and high average equivalent diameter. Of all the pore parameters, the equivalent diameter, form factor, roundness and compactness are found to have the greatest effect on porosity and permeability. Further, 28 parameters are optimized by means of correlation matrix. The best-fit relationship between pore structure parameters and porosity and permeability is established by multivariate linear regression, giving the very reasonable R2 values of 0.778 for porosity and 0.916 for permeability. These results provide an ideal reference for evaluating the properties of porous carbonate reservoirs in Nanpu and in other areas.
2019, 37(2): 390-402.
doi: 10.14027/j.issn.1000-0550.2018.121
Abstract:
The Carboniferous Benxi Formation is rich in barrier bar sandstone reservoirs, and is one of the main production layers for tight gas in the Yanchang exploration block, Ordos Basin. To understand the physical properties of the reservoirs and how the porosity evolved, detailed analyses were conducted using thin sections, SEM combined with energy dispersive spectroscopy (EDS), cathodoluminescence (CL) microscopy and other techniques. Also, an integrated approach using an empirical formula for initial sandstone porosity combined with quantitative calculation of porosity enabled porosity evolution modes to be established for the whole geodynamic history of these materials. The results indicate that the reservoir lithology consists predominantly of moderately-to well-sorted quartzarenite, sublitharenite and litharenite. The mean porosity is 4.72% and the permeability is 1.22×10-3 μm2. The reservoirs contain a variety of pore types, mainly dissolved enlarged pores, intraparticle pores and intercrystal pores. Quantitative evaluation of the increase/decrease of porosity caused by different diagenetic conditions reveals that the sandstone (initial average porosity 38.1%) typically underwent four porosity evolution stages:(1) marked porosity loss (-30.7%) in conditions of low geothermal gradient and rapid burial (P1-T2, 285-208 Ma); (2) a slight porosity increase due to dissolution (+3.9%) in conditions of high geothermal gradient and slow burial (T2-J3, 208-153 Ma); (3) a stereotyping stage of the tight sandstone reservoir (-6.6%) in conditions of continuously high geothermal gradient and slow burial (J3-K1, 153-96 Ma); and (4) a weak reworking of the tight sandstone reservoir in conditions of low geothermal gradient and overall uplift characterized by fractures, from the Lower Cretaceous to the present time (K1~, 96 Ma~).
The Carboniferous Benxi Formation is rich in barrier bar sandstone reservoirs, and is one of the main production layers for tight gas in the Yanchang exploration block, Ordos Basin. To understand the physical properties of the reservoirs and how the porosity evolved, detailed analyses were conducted using thin sections, SEM combined with energy dispersive spectroscopy (EDS), cathodoluminescence (CL) microscopy and other techniques. Also, an integrated approach using an empirical formula for initial sandstone porosity combined with quantitative calculation of porosity enabled porosity evolution modes to be established for the whole geodynamic history of these materials. The results indicate that the reservoir lithology consists predominantly of moderately-to well-sorted quartzarenite, sublitharenite and litharenite. The mean porosity is 4.72% and the permeability is 1.22×10-3 μm2. The reservoirs contain a variety of pore types, mainly dissolved enlarged pores, intraparticle pores and intercrystal pores. Quantitative evaluation of the increase/decrease of porosity caused by different diagenetic conditions reveals that the sandstone (initial average porosity 38.1%) typically underwent four porosity evolution stages:(1) marked porosity loss (-30.7%) in conditions of low geothermal gradient and rapid burial (P1-T2, 285-208 Ma); (2) a slight porosity increase due to dissolution (+3.9%) in conditions of high geothermal gradient and slow burial (T2-J3, 208-153 Ma); (3) a stereotyping stage of the tight sandstone reservoir (-6.6%) in conditions of continuously high geothermal gradient and slow burial (J3-K1, 153-96 Ma); and (4) a weak reworking of the tight sandstone reservoir in conditions of low geothermal gradient and overall uplift characterized by fractures, from the Lower Cretaceous to the present time (K1~, 96 Ma~).
2019, 37(2): 403-415.
doi: 10.14027/j.issn.1000-0550.2018.135
Abstract:
Identification of reservoir availability and quantitative assessment are some of the most critical issues in tight sand oil and gas exploration. Multiple analysis scales from the microscale, drill core to well logging have been conducted to examine the reservoir heterogeneity of the first member of the Upper Paleozoic Shanxi Formation in the southeastern Ordos Basin. Three sandstone petrofacies have been defined in the gas reservoirs. Ductile grain-lean sublitharenite forms reservoir rocks with good petrophysics and gas show. A model based on principal component analysis has been constructed to predict high-quality reservoir rocks and understand their spatial distribution patterns using well logs corrected from thin section and drill core data. The micro-scale description of the petrofaceis has been upscaled for field-scale characterization, and the availability of tight gas sandstone reservoir has been quantitatively assessed.
Identification of reservoir availability and quantitative assessment are some of the most critical issues in tight sand oil and gas exploration. Multiple analysis scales from the microscale, drill core to well logging have been conducted to examine the reservoir heterogeneity of the first member of the Upper Paleozoic Shanxi Formation in the southeastern Ordos Basin. Three sandstone petrofacies have been defined in the gas reservoirs. Ductile grain-lean sublitharenite forms reservoir rocks with good petrophysics and gas show. A model based on principal component analysis has been constructed to predict high-quality reservoir rocks and understand their spatial distribution patterns using well logs corrected from thin section and drill core data. The micro-scale description of the petrofaceis has been upscaled for field-scale characterization, and the availability of tight gas sandstone reservoir has been quantitatively assessed.
2019, 37(2): 416-423.
doi: 10.14027/j.issn.1000-0550.2018.137
Abstract:
Distribution and composition of organic carbon is the key to demonstrating the early diagenesis of organic carbon in the formation of oil and gas. Surface sediments were collected and analyzed to determine the content and form composition of lipid biomarkers in the estuary of the Pearl River Basin and adjacent areas in the South China Sea. The sources and occurrence of lipid compounds are also discussed. Results show that the organic carbon content range was 0.22%-0.66% in the sediment samples. The δ13C was -20.88‰ to -22.93‰, which implies a marine source of organic carbon. In total, 21 fatty acids, 6 fatty alcohols, 8 sterols and phytol were detected in the sediments. The content of total fatty acids, fatty alcohols, sterols and phytol ranged from 12.57 to 40.27 μg/g, 5.35-8.98 μg/g, 0.15-3.75 μg/g and 0.01-3.99 μg/g dry weight, respectively. The higher contents were located at the stations closest to the Pearl River estuary and Taiwan Strait. Lipid compounds mainly existed as free (FR) and base hydrolytic (BH) forms, with very little in acidic hydrolytic (AH) form. Phytol and sterols dominated BH components, but AH phytol was not detected. Lipid compounds primarily originate from marine microalgae and bacteria, with a small contribution from higher plants. The specific fatty acids produced by marine microalgae and bacteria contributed 21.18%-33.78% and 11.02%-15.64% to total fatty acids, respectively. The content of branched chain fatty acids (possibly derived from sulfate-reducing bacteria) was higher, at 1.79-2.62 μg/g dry weight, and accounted for 5.14%-6.50% of total fatty acids in sediments closest to the Pearl River estuary. These consisted of archaea microbes, implying sulfate reduction.
Distribution and composition of organic carbon is the key to demonstrating the early diagenesis of organic carbon in the formation of oil and gas. Surface sediments were collected and analyzed to determine the content and form composition of lipid biomarkers in the estuary of the Pearl River Basin and adjacent areas in the South China Sea. The sources and occurrence of lipid compounds are also discussed. Results show that the organic carbon content range was 0.22%-0.66% in the sediment samples. The δ13C was -20.88‰ to -22.93‰, which implies a marine source of organic carbon. In total, 21 fatty acids, 6 fatty alcohols, 8 sterols and phytol were detected in the sediments. The content of total fatty acids, fatty alcohols, sterols and phytol ranged from 12.57 to 40.27 μg/g, 5.35-8.98 μg/g, 0.15-3.75 μg/g and 0.01-3.99 μg/g dry weight, respectively. The higher contents were located at the stations closest to the Pearl River estuary and Taiwan Strait. Lipid compounds mainly existed as free (FR) and base hydrolytic (BH) forms, with very little in acidic hydrolytic (AH) form. Phytol and sterols dominated BH components, but AH phytol was not detected. Lipid compounds primarily originate from marine microalgae and bacteria, with a small contribution from higher plants. The specific fatty acids produced by marine microalgae and bacteria contributed 21.18%-33.78% and 11.02%-15.64% to total fatty acids, respectively. The content of branched chain fatty acids (possibly derived from sulfate-reducing bacteria) was higher, at 1.79-2.62 μg/g dry weight, and accounted for 5.14%-6.50% of total fatty acids in sediments closest to the Pearl River estuary. These consisted of archaea microbes, implying sulfate reduction.
2019, 37(2): 424-431.
doi: 10.14027/j.issn.1000-0550.2018.103
Abstract:
Petroleum is produced through biogeological action. Oil generation follows regularity in the deposition of marine or terrestrial facies. The composition and structure of the organic matter exert an influence on the formation of petroleum and natural gas in sediments. For example, materials that easily dissolve in water and have low molecular weight, join with simple compounds in the petroleum formation first. Source materials of lower-maturation oils mainly include algae, low aquatic organisms, low plants, and twigs, leaves, fruits, etc. from terrestrial plants. Their compositions mainly consist of carbohydrates, starch, hemicelluloses, chlorophyll, etc., as well as the short chain and easily dissolved fatty acids and proteins. Microbia mainly include amylolytic bacteria, carbohydrate-splitting bacteria hydrogen-producing bacteria, and others.
The organic matter of mature oils mainly originates from the lopoid and protein in organisms and algae, or from the carbohydrates in terrestrial organic matter, in which fat-decomposing bacteria, protelytic bacteria, H2-producing bacteria, etc. grow. In the early stages, fatty acids cannot be dissolved in water. Only when no other superior carbon materials existed in the environment could the microbia grow by using and decomposing lipoids. Fatty acid takes the linear bonding of carbon and hydrogen as the dominant structure within the carboxyl group. Oxygen-containing groups are eliminated, and petroleum can be generated in great quantity. Amino acids are also mainly straight chain structures, and eliminated end carboxyl groups might form hydrocarbons. Fatty acids and protein are transformed to petroleum at the same time, and therefore, the high peak of the generated oil is formed. Source rocks containing abundant organisms are excellent hydrocarbon-generating materials.
Thermophile and superthermophilic methanogens subsist at high evolutional stages with great quantity. Their methane-generating model is H2+CO2. Cellulose, xylem, high polymers, and others from terrestrial plants were degraded at the mature stage with difficulty, and yet they might be decomposed and provide carbon for forming CO2 at a high evolutional stage.
Microbia degrade organic matter to form petroleum and natural gas. Not only is there a successively settled basin, but also abundant organic matter from source rocks, and oil-generation might take place, which will require the degradation of original materials, elimination of oxygen-containing group, H2-producing bacteria to generate hydrogen H2-expending bacteria to use hydrogen, and other processes, which is more complicated than natural gas formation. Natural gas might be formed at a depth of 10 m in Quaternary reserves, but oil reserves need to be buried below 1 000 m depth within Tertiary strata for formation to occur.
Petroleum is produced through biogeological action. Oil generation follows regularity in the deposition of marine or terrestrial facies. The composition and structure of the organic matter exert an influence on the formation of petroleum and natural gas in sediments. For example, materials that easily dissolve in water and have low molecular weight, join with simple compounds in the petroleum formation first. Source materials of lower-maturation oils mainly include algae, low aquatic organisms, low plants, and twigs, leaves, fruits, etc. from terrestrial plants. Their compositions mainly consist of carbohydrates, starch, hemicelluloses, chlorophyll, etc., as well as the short chain and easily dissolved fatty acids and proteins. Microbia mainly include amylolytic bacteria, carbohydrate-splitting bacteria hydrogen-producing bacteria, and others.
The organic matter of mature oils mainly originates from the lopoid and protein in organisms and algae, or from the carbohydrates in terrestrial organic matter, in which fat-decomposing bacteria, protelytic bacteria, H2-producing bacteria, etc. grow. In the early stages, fatty acids cannot be dissolved in water. Only when no other superior carbon materials existed in the environment could the microbia grow by using and decomposing lipoids. Fatty acid takes the linear bonding of carbon and hydrogen as the dominant structure within the carboxyl group. Oxygen-containing groups are eliminated, and petroleum can be generated in great quantity. Amino acids are also mainly straight chain structures, and eliminated end carboxyl groups might form hydrocarbons. Fatty acids and protein are transformed to petroleum at the same time, and therefore, the high peak of the generated oil is formed. Source rocks containing abundant organisms are excellent hydrocarbon-generating materials.
Thermophile and superthermophilic methanogens subsist at high evolutional stages with great quantity. Their methane-generating model is H2+CO2. Cellulose, xylem, high polymers, and others from terrestrial plants were degraded at the mature stage with difficulty, and yet they might be decomposed and provide carbon for forming CO2 at a high evolutional stage.
Microbia degrade organic matter to form petroleum and natural gas. Not only is there a successively settled basin, but also abundant organic matter from source rocks, and oil-generation might take place, which will require the degradation of original materials, elimination of oxygen-containing group, H2-producing bacteria to generate hydrogen H2-expending bacteria to use hydrogen, and other processes, which is more complicated than natural gas formation. Natural gas might be formed at a depth of 10 m in Quaternary reserves, but oil reserves need to be buried below 1 000 m depth within Tertiary strata for formation to occur.
2019, 37(2): 432-442.
doi: 10.14027/j.issn.1000-0550.2018.131
Abstract:
The Huoshiling Formation is a favorable exploration layer for deep natural gas in the Dehui fault depression. Based on the analysis of the tectonic evolution in the study area, typical gas reservoirs in the Huoshiling Formation are dissected in detail. Combined with the basic seismic, well logging, and drilling data, integrated analyses of light hydrocarbon, source rock, and fluid inclusion data were used to study the gas accumulation mechanism of the deep Huoshiling Formation in the Dehui fault depression. The results show that the average total organic carbon (TOC) of the source rocks in the Huoshiling Formation is more than 1.0%, and the average value of S1+S2 is 0.5-2.0 mg/g. The types of the source rock are mainly Type Ⅱ1-Ⅱ2, and Type Ⅲ is supplemented. The organic matter has reached maturity, The Ro mean value is 1.5%, and source rocks have greater potential for hydrocarbon generation. The natural gas in the lower part of the Huoshiling Formation comes from the source rock of the Huoshiling Formation, and the natural gas in the upper part of the Huoshiling Formation is mainly derived from the source rocks of the Huoshiling Formation but is influenced by the source of the overlying Shahezi Formation. The migration of natural gas is dominated by vertical fault propagation, and the lateral transport of sand bodies in the reservoir is supplemented. Based on the analyses of fluid inclusions, gas-source correlation, and hydrocarbon generation and the expulsion of source rocks, three episodes of hydrocarbon migration can be identified, namely 130 Ma, corresponding to the deposition of the Yingcheng Formation, 115-105 Ma, corresponding to the Quantou Formation, and 95-75 Ma, corresponding to the deposition of the Qingshankou Formation-Nenjiang Formation.
The Huoshiling Formation is a favorable exploration layer for deep natural gas in the Dehui fault depression. Based on the analysis of the tectonic evolution in the study area, typical gas reservoirs in the Huoshiling Formation are dissected in detail. Combined with the basic seismic, well logging, and drilling data, integrated analyses of light hydrocarbon, source rock, and fluid inclusion data were used to study the gas accumulation mechanism of the deep Huoshiling Formation in the Dehui fault depression. The results show that the average total organic carbon (TOC) of the source rocks in the Huoshiling Formation is more than 1.0%, and the average value of S1+S2 is 0.5-2.0 mg/g. The types of the source rock are mainly Type Ⅱ1-Ⅱ2, and Type Ⅲ is supplemented. The organic matter has reached maturity, The Ro mean value is 1.5%, and source rocks have greater potential for hydrocarbon generation. The natural gas in the lower part of the Huoshiling Formation comes from the source rock of the Huoshiling Formation, and the natural gas in the upper part of the Huoshiling Formation is mainly derived from the source rocks of the Huoshiling Formation but is influenced by the source of the overlying Shahezi Formation. The migration of natural gas is dominated by vertical fault propagation, and the lateral transport of sand bodies in the reservoir is supplemented. Based on the analyses of fluid inclusions, gas-source correlation, and hydrocarbon generation and the expulsion of source rocks, three episodes of hydrocarbon migration can be identified, namely 130 Ma, corresponding to the deposition of the Yingcheng Formation, 115-105 Ma, corresponding to the Quantou Formation, and 95-75 Ma, corresponding to the deposition of the Qingshankou Formation-Nenjiang Formation.
