2018 Vol. 36, No. 1
Display Method:
2018, 36(1): 1-11.
doi: 10.3969/j.issn.1000-0550.2018.002
Abstract:
Based on the analysis of petrology of Changxing Formation-Feixianguan Formation in eastern Longgang Area, NE Sichuan Basin, combing with analytical method such as rare earth elements(REE), fluid-inclusions and laser Laman, it is illustrated that there exist mineral assemblages including saddle dolomite-pyrite, fluorite-quartz and corresponding homogenization temperatures is above normal formation temperature. All the rock samples from reservoirs of Changxing Fm-Feixianguan Fm shares the same positive Ce anomaly with marine sedimentary limestone and most of them are characterized by the similar REE patterns and significant positive Eu anomaly of saddle dolomite. There exist bitumen-bearing inclusions, which are products of oil-bearing inclusions trapped by the period of oil generation peak of Longtan Formation after high-temperature cracking in hydrothermal minerals of fluorite and quartz. The hydrothermal activity can be divided into 2 periods on the basis of relationship between mineral occupation and hydrocarbon charging timing:The first stage corresponding to the late Permian-early Triassic and the action mode of is to promote the formation process and late-reformation of dolomite reservoir; the second stage corresponding to Late Triassic and the action mode is filling of saddle dolomite, quartz and fluorite in reservoir spaces.
Based on the analysis of petrology of Changxing Formation-Feixianguan Formation in eastern Longgang Area, NE Sichuan Basin, combing with analytical method such as rare earth elements(REE), fluid-inclusions and laser Laman, it is illustrated that there exist mineral assemblages including saddle dolomite-pyrite, fluorite-quartz and corresponding homogenization temperatures is above normal formation temperature. All the rock samples from reservoirs of Changxing Fm-Feixianguan Fm shares the same positive Ce anomaly with marine sedimentary limestone and most of them are characterized by the similar REE patterns and significant positive Eu anomaly of saddle dolomite. There exist bitumen-bearing inclusions, which are products of oil-bearing inclusions trapped by the period of oil generation peak of Longtan Formation after high-temperature cracking in hydrothermal minerals of fluorite and quartz. The hydrothermal activity can be divided into 2 periods on the basis of relationship between mineral occupation and hydrocarbon charging timing:The first stage corresponding to the late Permian-early Triassic and the action mode of is to promote the formation process and late-reformation of dolomite reservoir; the second stage corresponding to Late Triassic and the action mode is filling of saddle dolomite, quartz and fluorite in reservoir spaces.
2018, 36(1): 12-19.
doi: 10.3969/j.issn.1000-0550.2018.004
Abstract:
Gravel orientation can be used to judge the environment of coarse grain deposits. On the basis of the analysis and measurement of the gravel image from the core image, using the parameters a and parameters σ to determine the grading orientation and quantitative characterization of gravel orientation in the Baokuquan Formation sandstone in the Mahu sag. The parameter a is the maximum value of the sum of the radii of the gravitational axis of any adjacent three small fans, parameter σ is the degree of deviation of the small fan radius. It is found that the larger the a and σ is, the better the orientation of the gravel is. The method is applied to the Mahu area, and the quantitative division scheme of different levels of gravel orientation has been established:clear orientation (a is greater than 35% and σ is greater than 4), a certain orientation (a is greater than 35% and σ is less than 4), a fuzzy orientation (a is less than 35% and σ is greater than 4), no orientation(a is less than 35% and σ is less than 4). And the directivity of typical seasonal braided channel and temporary braided channel in the study area were studied, the results show that the value of σ in the seasonal braided channel is 4.8~8.13, the value of a is 40%~62%, and the value of σ in the braided channel is less than 4, the parameter a is less than 35%. It can be seen that the method can effectively characterize the orientation of gravel and provide the auxiliary basis for the judgment of sedimentary environment.
Gravel orientation can be used to judge the environment of coarse grain deposits. On the basis of the analysis and measurement of the gravel image from the core image, using the parameters a and parameters σ to determine the grading orientation and quantitative characterization of gravel orientation in the Baokuquan Formation sandstone in the Mahu sag. The parameter a is the maximum value of the sum of the radii of the gravitational axis of any adjacent three small fans, parameter σ is the degree of deviation of the small fan radius. It is found that the larger the a and σ is, the better the orientation of the gravel is. The method is applied to the Mahu area, and the quantitative division scheme of different levels of gravel orientation has been established:clear orientation (a is greater than 35% and σ is greater than 4), a certain orientation (a is greater than 35% and σ is less than 4), a fuzzy orientation (a is less than 35% and σ is greater than 4), no orientation(a is less than 35% and σ is less than 4). And the directivity of typical seasonal braided channel and temporary braided channel in the study area were studied, the results show that the value of σ in the seasonal braided channel is 4.8~8.13, the value of a is 40%~62%, and the value of σ in the braided channel is less than 4, the parameter a is less than 35%. It can be seen that the method can effectively characterize the orientation of gravel and provide the auxiliary basis for the judgment of sedimentary environment.
2018, 36(1): 20-32.
doi: 10.3969/j.issn.1000-0550.2018.005
Abstract:
As one of the major coal and uranium bearing basins in Northern China, Kailu Basin, which locates in the southwest of Songliao Basin, has always been an emphasis area for uranium exploration. Based on a large number of gamma anomalies found in the coal exploration in Shaogen area of Kailu Basin, a uranium geological survey launched few years ago and some uranium mineralization points were discovered. In this case, researches such as detailed stratigraphic correlation, serious analysis of sedimentary environment and tectonic evolution, discussion of uranium mineralization characteristics have been carried out. In view of the above comprehensive analysis, we get four main conclusions:①Shaogen area developes Fuxin, Yaojia, Nenjiang, Sifangtai and Taikang Formation from the bottom up with absence of Quantou to Qingshankou Formation and Mingshui Formation. ②Fuxin stage is in the end of fault depression period developing lacustrine swamp environment with several layers of coal; whilst due to compression and uplifting after Fuxin period, there has been no sediments from Quantou to early Yaojia Period; then it switches into a slight extensional environment and deposits lacustrine silt in Nenjiang stage; accompany with the following structrral inversion, alluvial fan deposits in the Sifangtai Formation. ③Both Nenjiang and Sifangtai Formation are the uranium ore-bearing strata, while mudstone type uranium develops in Nenjiang Formation and sandstone type uranium in Sifangtai Formation. ④Mudstone type uranium orebody which locates in trasition zone of the yellow green and gray mud in the up of Nenjiang Formation presents a thin plate with a central downward concave shape, indicating a synsedimentary deposition; While sandstone type uranium orebody which locates in transition zone of reddish brown and gray green sandy conglomerate in the bottom of Sifangtai Formation presents a short plank shape and may illustrate a phreatic oxidation type mineralization. These research results have the extensive applicability and practical instruction significance in Uranium exploration of Shaogen area.
As one of the major coal and uranium bearing basins in Northern China, Kailu Basin, which locates in the southwest of Songliao Basin, has always been an emphasis area for uranium exploration. Based on a large number of gamma anomalies found in the coal exploration in Shaogen area of Kailu Basin, a uranium geological survey launched few years ago and some uranium mineralization points were discovered. In this case, researches such as detailed stratigraphic correlation, serious analysis of sedimentary environment and tectonic evolution, discussion of uranium mineralization characteristics have been carried out. In view of the above comprehensive analysis, we get four main conclusions:①Shaogen area developes Fuxin, Yaojia, Nenjiang, Sifangtai and Taikang Formation from the bottom up with absence of Quantou to Qingshankou Formation and Mingshui Formation. ②Fuxin stage is in the end of fault depression period developing lacustrine swamp environment with several layers of coal; whilst due to compression and uplifting after Fuxin period, there has been no sediments from Quantou to early Yaojia Period; then it switches into a slight extensional environment and deposits lacustrine silt in Nenjiang stage; accompany with the following structrral inversion, alluvial fan deposits in the Sifangtai Formation. ③Both Nenjiang and Sifangtai Formation are the uranium ore-bearing strata, while mudstone type uranium develops in Nenjiang Formation and sandstone type uranium in Sifangtai Formation. ④Mudstone type uranium orebody which locates in trasition zone of the yellow green and gray mud in the up of Nenjiang Formation presents a thin plate with a central downward concave shape, indicating a synsedimentary deposition; While sandstone type uranium orebody which locates in transition zone of reddish brown and gray green sandy conglomerate in the bottom of Sifangtai Formation presents a short plank shape and may illustrate a phreatic oxidation type mineralization. These research results have the extensive applicability and practical instruction significance in Uranium exploration of Shaogen area.
2018, 36(1): 33-41.
doi: 10.3969/j.issn.1000-0550.2018.006
Abstract:
The study of pyrites preserved in fossils can provide useful information on the process of organic fossilization and the depositional microcondition of these fossils. Using the light and scanning electron microscopes, we observed pyritization tissues preserved in plant fossils from the Ningming Formation, Guangxi. Pyrite textures are preserved in two forms, which are dissolved crystals and framboidal clusters. Most of crystals are of irregular to spherulitic shapes with pits on the surface and indistinct edge, whereas few are of octahedron shapes with smooth surface and distinct edge. The size of crystals ranges from 0.79-1.58 μm. Pyrite framboids are densely packed. They are spheroidal in shape and 7.23-14.95 μm in diameter. The individual crystal units of pyrite framboids have an S/Fe ratio of 0.16-2.06, with the mean value of 1.54. The ratio of S/Fe is less than the standard value 2 and thus shows a relative sulfur deficiency. The sizes of these pyrite framboids are small and vary within a narrow range. Their mean diameters fall generally within the dysoxic field. The size distribution and S/Fe ratio of pyrite framboids indicate that the intervals between the abaxial and adaxial cuticles of plant detritus had a dysoxic water microcondition during the formation of pyrites. And in this microcondition, framboids were formed rapidly in a very restrictive time span. Numerous pyrite crystals and framboids infilling the intervals between the cuticles of plant detritus also support the conclusion that the formation of pyrite framboids is in association with the decay of organic matter.
The study of pyrites preserved in fossils can provide useful information on the process of organic fossilization and the depositional microcondition of these fossils. Using the light and scanning electron microscopes, we observed pyritization tissues preserved in plant fossils from the Ningming Formation, Guangxi. Pyrite textures are preserved in two forms, which are dissolved crystals and framboidal clusters. Most of crystals are of irregular to spherulitic shapes with pits on the surface and indistinct edge, whereas few are of octahedron shapes with smooth surface and distinct edge. The size of crystals ranges from 0.79-1.58 μm. Pyrite framboids are densely packed. They are spheroidal in shape and 7.23-14.95 μm in diameter. The individual crystal units of pyrite framboids have an S/Fe ratio of 0.16-2.06, with the mean value of 1.54. The ratio of S/Fe is less than the standard value 2 and thus shows a relative sulfur deficiency. The sizes of these pyrite framboids are small and vary within a narrow range. Their mean diameters fall generally within the dysoxic field. The size distribution and S/Fe ratio of pyrite framboids indicate that the intervals between the abaxial and adaxial cuticles of plant detritus had a dysoxic water microcondition during the formation of pyrites. And in this microcondition, framboids were formed rapidly in a very restrictive time span. Numerous pyrite crystals and framboids infilling the intervals between the cuticles of plant detritus also support the conclusion that the formation of pyrite framboids is in association with the decay of organic matter.
2018, 36(1): 42-56.
doi: 10.3969/j.issn.1000-0550.2018.007
Abstract:
Provenance and sedimentary age are still debated about Tangjiawu Formation from the South Anhui.The study focused on the petrography, geochemical features and detrital zircon ages of the sandstones in the Tangjiawu Formation. The sandstones, which are highly rounded and sorted, are essentially composed of metamorphic detritus and quartz with wave extinction. They exhibited relatively high compositional maturity. Their provenances were dominated by felsic materials that had undergone intensive chemical weathering or sedimentary recycling. LA-ICP-MS zircon U-Pb dating yields a youngest age of 424 Ma, which represents the lower limit of deposition age. In addition to the zircon ages, the Tangjiawu Formation uncomfortably overlain by the Devonian Guanshan Formation, suggesting that it should be deposited in Late Silurian that approached to the termination timing of the early Palaeozoic orogenic event. Seventy-nine detrital zircons with discordance <10% display a broadly age spectrum of 2 912 Ma to 424 Ma. Most of the detrital zircons have U-Pb age grouped between 731 and 1 031 Ma, with two clusters peaking at 981 and 756 Ma. A few populations with peak ages of 2 476 Ma, 517 Ma and 453 Ma are present as well. This suggested that the provenances of the Tangjiawu Formation were mainly derived from the early-to middle-Neoproterozoic igneous rocks, Late Neoproterozoic rift sequence and Sinian to Ordovician sediments with subordinate synorogenic magmatic or sedimentary rocks. The early Palaeozoic intra-continental orogeny caused the uplifting of the sediments in the pre-middle-Ordovician basins, which mostly contributed to sources of the deposits in the intra-continental foreland basin. The deposition and evolution of the foreland basin in the South China were controlled by the early Palaeozoic orogeny, reflecting the coupled material recycling between the orogen and the foreland basin.
Provenance and sedimentary age are still debated about Tangjiawu Formation from the South Anhui.The study focused on the petrography, geochemical features and detrital zircon ages of the sandstones in the Tangjiawu Formation. The sandstones, which are highly rounded and sorted, are essentially composed of metamorphic detritus and quartz with wave extinction. They exhibited relatively high compositional maturity. Their provenances were dominated by felsic materials that had undergone intensive chemical weathering or sedimentary recycling. LA-ICP-MS zircon U-Pb dating yields a youngest age of 424 Ma, which represents the lower limit of deposition age. In addition to the zircon ages, the Tangjiawu Formation uncomfortably overlain by the Devonian Guanshan Formation, suggesting that it should be deposited in Late Silurian that approached to the termination timing of the early Palaeozoic orogenic event. Seventy-nine detrital zircons with discordance <10% display a broadly age spectrum of 2 912 Ma to 424 Ma. Most of the detrital zircons have U-Pb age grouped between 731 and 1 031 Ma, with two clusters peaking at 981 and 756 Ma. A few populations with peak ages of 2 476 Ma, 517 Ma and 453 Ma are present as well. This suggested that the provenances of the Tangjiawu Formation were mainly derived from the early-to middle-Neoproterozoic igneous rocks, Late Neoproterozoic rift sequence and Sinian to Ordovician sediments with subordinate synorogenic magmatic or sedimentary rocks. The early Palaeozoic intra-continental orogeny caused the uplifting of the sediments in the pre-middle-Ordovician basins, which mostly contributed to sources of the deposits in the intra-continental foreland basin. The deposition and evolution of the foreland basin in the South China were controlled by the early Palaeozoic orogeny, reflecting the coupled material recycling between the orogen and the foreland basin.
2018, 36(1): 57-71.
doi: 10.3969/j.issn.1000-0550.2018.008
Abstract:
Based on the macroscopic characteristics of profile, petrology and original structures, the microscopic characteristics of morphology and original textures of dolomite and microbial fossils and the corresponding geochemical characteristics, this paper studied the characteristics and geneses of algal dolostone of the Upper Sinian Dengying Formation in the Hanyuan-Ebian Area of Sichuan Province, China. The results show that the algal dolostone is a set of microbialites or microbial carbonates association formed in the tidal flat and lagoon, in which the laminated, stromatolithic, botryoidal and uniform (algal) dolostones are dominate. There are mainly two different texture and genesis types of dolomites, primary cryptocrystalline microbial dolomite and secondary fibrous mimetic dolomite. The geneses of the two types of dolomites are closely related to microbial biomineralization of Cyanobacteria, sulphate-reducing bacteria (SRB), moderately halophilic aerobic bacteria and red algae. In the precipitation and syngenetic stages, a large amount of nanometre-sized (pene-) cubical granular and (sub-) micron-sized sheeted dolomites is formed by microbially induced mineralization; meanwhile, fibrous aragonite and high-Mg calcite are developed. In the syngenetic and penecontemporaneous stages, nanometre-sized (spherulitic) granular and micron-sized irregular, spherical and ovoidal dolomites are formed by microbially influenced mineralization, in the meantime the fibrous aragonite and high-Mg calcite transform into the fibrous mimetic dolomite through microbially catalysed mineralization and mimetic dolomization. Then the microbial and mimetic dolomite form laminated stromatolithic and uniform dolostone together. The research of characteristics and geneses of algal dolostones is useful to comprehend the complexity and diversity of mineral-microbe interaction and process in this paper, and provides a new example of the investigation of microbial biomineralization, microbial dolomite and mimetic dolomite in the Precambrian era.
Based on the macroscopic characteristics of profile, petrology and original structures, the microscopic characteristics of morphology and original textures of dolomite and microbial fossils and the corresponding geochemical characteristics, this paper studied the characteristics and geneses of algal dolostone of the Upper Sinian Dengying Formation in the Hanyuan-Ebian Area of Sichuan Province, China. The results show that the algal dolostone is a set of microbialites or microbial carbonates association formed in the tidal flat and lagoon, in which the laminated, stromatolithic, botryoidal and uniform (algal) dolostones are dominate. There are mainly two different texture and genesis types of dolomites, primary cryptocrystalline microbial dolomite and secondary fibrous mimetic dolomite. The geneses of the two types of dolomites are closely related to microbial biomineralization of Cyanobacteria, sulphate-reducing bacteria (SRB), moderately halophilic aerobic bacteria and red algae. In the precipitation and syngenetic stages, a large amount of nanometre-sized (pene-) cubical granular and (sub-) micron-sized sheeted dolomites is formed by microbially induced mineralization; meanwhile, fibrous aragonite and high-Mg calcite are developed. In the syngenetic and penecontemporaneous stages, nanometre-sized (spherulitic) granular and micron-sized irregular, spherical and ovoidal dolomites are formed by microbially influenced mineralization, in the meantime the fibrous aragonite and high-Mg calcite transform into the fibrous mimetic dolomite through microbially catalysed mineralization and mimetic dolomization. Then the microbial and mimetic dolomite form laminated stromatolithic and uniform dolostone together. The research of characteristics and geneses of algal dolostones is useful to comprehend the complexity and diversity of mineral-microbe interaction and process in this paper, and provides a new example of the investigation of microbial biomineralization, microbial dolomite and mimetic dolomite in the Precambrian era.
2018, 36(1): 72-80.
doi: 10.3969/j.issn.1000-0550.2018.009
Abstract:
With the fine and complicate target of geological study, the scale of the geological body characterization is smaller and more difficult. Reservoir distribution patterns and the existing prediction methods need to be improved. This paper reviews the traditional limitations of field geological investigation, and introduced technical features of unmanned aerial vehicle (UAV) and oblique photography, based on which it is proposed that the 3D digital outcrop characterization technique with UAV oblique photography. Subsequently, reservoir architecture patterns are analyzed by UAV collection model for instance. Research shows that seven aspects of the limitations of traditional geological investigation. However, UAV oblique photography has obvious technology advantages and innovative aspects. The collection and processing 3D digital model have anywhere location coordinate and image information, which fully meet the field outcrop architecture analysis. Example analysis found that collection and processing model architecture analysis of high resolution about 3~5 centimeter, architecture of sand body was researched more quantitatively and fine understanding. UAV oblique photography technology not only make digital outcrop to become a reality, but also to improve efficiency of geologists field outcrop investigation.
With the fine and complicate target of geological study, the scale of the geological body characterization is smaller and more difficult. Reservoir distribution patterns and the existing prediction methods need to be improved. This paper reviews the traditional limitations of field geological investigation, and introduced technical features of unmanned aerial vehicle (UAV) and oblique photography, based on which it is proposed that the 3D digital outcrop characterization technique with UAV oblique photography. Subsequently, reservoir architecture patterns are analyzed by UAV collection model for instance. Research shows that seven aspects of the limitations of traditional geological investigation. However, UAV oblique photography has obvious technology advantages and innovative aspects. The collection and processing 3D digital model have anywhere location coordinate and image information, which fully meet the field outcrop architecture analysis. Example analysis found that collection and processing model architecture analysis of high resolution about 3~5 centimeter, architecture of sand body was researched more quantitatively and fine understanding. UAV oblique photography technology not only make digital outcrop to become a reality, but also to improve efficiency of geologists field outcrop investigation.
2018, 36(1): 81-91.
doi: 10.3969/j.issn.1000-0550.2018.010
Abstract:
The sandy braided rivers are widely distributed in the continental facies basin and the bar is important as a sedimentary unit. Domestic and overseas scholars have done researches based on the reservoirs, outcrop and modern sediments. However, no pattern of bar evolution has been built and the influence of braided channel on bar has not been clarified. Therefore, the paper uses the sediment numerical simulation to reproduce the evolution of bar, and verify through modern sediments, and finally build the pattern of bar evolution. The research shows that, firstly, the bar evolution can be divided into three stage, including the formation, growth and migration of the bar, lateral migration of the bar and the formation bar tail which lead to compound bar. Secondly, the head of the bar is eroded by the braided channel, which leads bar migration to downstream. As evolution time goes on, migration rate reduces gradually, and then the bar stabilizes on the position. Thirdly, because of the asymmetry of braided channel, sediment deposits on one side and sediment erodes on another side of the bar. The bar migrates laterally. At last, the sediment deposits on the tail of the bar and the bar tail formed. The length of the bar tail reveals the discharge of channel. The larger the discharge of channel is, the longer bar tail is. The elongation of bar tail induces the closure the braided channel and forms compound bar.
The sandy braided rivers are widely distributed in the continental facies basin and the bar is important as a sedimentary unit. Domestic and overseas scholars have done researches based on the reservoirs, outcrop and modern sediments. However, no pattern of bar evolution has been built and the influence of braided channel on bar has not been clarified. Therefore, the paper uses the sediment numerical simulation to reproduce the evolution of bar, and verify through modern sediments, and finally build the pattern of bar evolution. The research shows that, firstly, the bar evolution can be divided into three stage, including the formation, growth and migration of the bar, lateral migration of the bar and the formation bar tail which lead to compound bar. Secondly, the head of the bar is eroded by the braided channel, which leads bar migration to downstream. As evolution time goes on, migration rate reduces gradually, and then the bar stabilizes on the position. Thirdly, because of the asymmetry of braided channel, sediment deposits on one side and sediment erodes on another side of the bar. The bar migrates laterally. At last, the sediment deposits on the tail of the bar and the bar tail formed. The length of the bar tail reveals the discharge of channel. The larger the discharge of channel is, the longer bar tail is. The elongation of bar tail induces the closure the braided channel and forms compound bar.
2018, 36(1): 92-100.
doi: 10.3969/j.issn.1000-0550.2018.011
Abstract:
In overseas selection stage, extremely low exploration degree and poor data of basin lead to work hard to carry out regular deepwater sedimentary analysis. Slope geometries and shelf-edge trajectories have abundant geological information. In this paper, on the basis of 2D seismic data, apply combination of slope geometries and shelf-edge trajectories to look for favorable distribution of large-scale, sand-rich deepwater fan. A basin develops three types of shelf-edge trajectories, including increasing shelf-edge trajectories, flat shelf-edge trajectories, decreasing shelf-edge trajectories. Progradational distance of linear-decreasing shelf-edge trajectories corresponding slope is longer, more beneficial to develop of large-scale deepwater fan deposits. At the same time, A basin develops four types of slope, including up convex slope, down concave slope, linear slope, and ramp-flat slope. Up convex slope and down concave slope have smaller slope angle and bigger slope width, more beneficial to sand mud differentiation and thus form deepwater fan deposits with better physical property of reservoir. Overlap favorable distribution of deepwater fan with large-scale and good physical property of reservoir during the same period. Overlapping area is the favorable distribution of large-scale, sand-rich deepwater fan, mainly located in the eastern corner and western area in the basin. Also, applying combination method of slope geometries and shelf-edge trajectories can establish sedimentary evolution model of basin during drifting period and analyze history of sedimentary evolution.
In overseas selection stage, extremely low exploration degree and poor data of basin lead to work hard to carry out regular deepwater sedimentary analysis. Slope geometries and shelf-edge trajectories have abundant geological information. In this paper, on the basis of 2D seismic data, apply combination of slope geometries and shelf-edge trajectories to look for favorable distribution of large-scale, sand-rich deepwater fan. A basin develops three types of shelf-edge trajectories, including increasing shelf-edge trajectories, flat shelf-edge trajectories, decreasing shelf-edge trajectories. Progradational distance of linear-decreasing shelf-edge trajectories corresponding slope is longer, more beneficial to develop of large-scale deepwater fan deposits. At the same time, A basin develops four types of slope, including up convex slope, down concave slope, linear slope, and ramp-flat slope. Up convex slope and down concave slope have smaller slope angle and bigger slope width, more beneficial to sand mud differentiation and thus form deepwater fan deposits with better physical property of reservoir. Overlap favorable distribution of deepwater fan with large-scale and good physical property of reservoir during the same period. Overlapping area is the favorable distribution of large-scale, sand-rich deepwater fan, mainly located in the eastern corner and western area in the basin. Also, applying combination method of slope geometries and shelf-edge trajectories can establish sedimentary evolution model of basin during drifting period and analyze history of sedimentary evolution.
2018, 36(1): 101-109.
doi: 10.3969/j.issn.1000-0550.2018.012
Abstract:
In order to reveal the deposition diversity between platform margin and platform interior on the Late Ordovician carbonate rimmed platform of Tazhong area, we made an integrated microfacies analysis from both qualitative and quantitative aspects by using core and thin section data of the Lianglitage Formation. The result show that nine types of microfacies (MF1~MF9) can be recognized, and each type of the grainstones which represents different type of carbonate sand shoals has distinct shape of grain-size accumulation curves. The platform margin is composed of several types of microfacies (MF1~MF4) indicating high-energy sand shoals that form reef-shoal complex together with platform margin reefs. The platform interior is composed of these types of microfacies (MF5~MF9) that representing medium-to low-energy lagoon and tidal flat deposits. Combining with the quantitative grain-size analysis results, these microfacies including bioclast intraclast grainstone (MF1), bioclast rudstone (MF2) and ooid grainstone (MF3) were deposited in foreshore environment, respectively indicating platform margin bioclast sand shoals, ooid sand shoals, and reef-front gravel shoals. The peloid grainstone (MF5) was deposited in the barrier platform interior that was dominated by moderate wave energy. The enchinoid packstone and floatstone (MF4) was deposited just at the back of platform reef forming bioclast sand shoal.
In order to reveal the deposition diversity between platform margin and platform interior on the Late Ordovician carbonate rimmed platform of Tazhong area, we made an integrated microfacies analysis from both qualitative and quantitative aspects by using core and thin section data of the Lianglitage Formation. The result show that nine types of microfacies (MF1~MF9) can be recognized, and each type of the grainstones which represents different type of carbonate sand shoals has distinct shape of grain-size accumulation curves. The platform margin is composed of several types of microfacies (MF1~MF4) indicating high-energy sand shoals that form reef-shoal complex together with platform margin reefs. The platform interior is composed of these types of microfacies (MF5~MF9) that representing medium-to low-energy lagoon and tidal flat deposits. Combining with the quantitative grain-size analysis results, these microfacies including bioclast intraclast grainstone (MF1), bioclast rudstone (MF2) and ooid grainstone (MF3) were deposited in foreshore environment, respectively indicating platform margin bioclast sand shoals, ooid sand shoals, and reef-front gravel shoals. The peloid grainstone (MF5) was deposited in the barrier platform interior that was dominated by moderate wave energy. The enchinoid packstone and floatstone (MF4) was deposited just at the back of platform reef forming bioclast sand shoal.
2018, 36(1): 110-119.
doi: 10.3969/j.issn.1000-0550.2018.013
Abstract:
Gaoyou Sag, located in the south of Subei Basin, is a faulted lacustrine basin developed during the end of Late Cretaceous and Huangjue area is in the southwest part of Gaoyou Sag. Paleogene strata consisted of Funing Formation, Dainan Formation, Sanduo Formation and Yanchen Formation is deposited from bottom to top successively in Gaoyou Sag. Sanduo Formation consists of Duo1 and Duo2 member from bottom to top and Duo1 member is target strata of this research. During the sedimentary period of Duo1 member, tectonic movement in Gaoyou Sag dropped off gradually and the altitude difference between boundary and sag nearly disappeared, which made contributions to the characteristics of paleotopography in Gaoyou Sag such as a smooth slope. Several lines evidence have supported the fact that Duo1 member mainly deposited in shallow-water deltas, such as the brown mudstone with plenty of bioturbation structure, sedimentary structures which show strong hydropower, bad preservation of mouth bar and a large number of distributary channels, grain-size collection and analysis also indicate the influence of tractive current. However the upper Duo1 member belongs to fluvial sedimentary system. The sand content of mudstone increases obviously in the upper Duo1 member, and warm holes almost disappear. In addition to this, seismic reflection configuration also developed from imbricated progradation reflection to sub-parallel seismic reflection, which could be treated as transformation from shallow-water deltas to river. Strong fluvial-dominated function in shallow-water deltas always results in frequent changes of sand bodies. Lithological reservoirs are likely to form in such sedimentary environment and accurate reservoir description should be the key to exploration and development of such oilfields. Distribution of subtle traps in shallow-water deltas and fluvial facies is controlled by base-level cycles, so isochronous stratigraphic frameworks are foundation of reservoir prediction. Based on sufficient analysis of core, well logging and seismic data, this research identified two kinds of allo-cycle, respectively, dominated by tectonic movement and climatic variation. Generally, changes of base-level cycle dominated by a certain size of tectonic movement could always be identifiable in well logging curve. Usually convert interface of long-term base level cycle or return point in resistivity curve could be treated as recognition marks. Besides that, research suggests that a certain amount of changes in lake level could be easy to bring about big changes in the scope of lake, which makes it possible to recognize the interface between underwater deposit and continental sediment. In research found there exist a return point in resistivity logging curve, and treat such point as the surface of two sub-members. Baseline of natural gamma-ray logging above the return point is relatively lower, and AC figures of strata above the point are also distinctly smaller than that of the strata below the point. Differences in GR as well as AC shows mudstone above the point has higher sand content, and that could just be the differences of mudstone deposited in shallow-water environment and fluvial environment. Surface related to the return point was suggested to be the isochronous surface controlled by climate. There also exists a strange phenomenon; a successive seismic event appears near the climate correlatively interface while there does not develop any stable sandstone-mudstone boundary. Research makes a conclusion that mudstone with disparate sand content has different density and velocity, which generates the contrast in wave impedance, and forms the successive seismic events around the position where resistivity log begin to return. Isochronous stratigraphic framework based on interfaces mentioned above has been established all over the study area, and such framework has been used in seismic sedimentology research. Amplitude slices of strata below the climate-correlatively surface show typical characteristics of shallow-water deltas, range of reservoirs expand or shrink under control of lake level. However, slices of strata above the surface could be considered as fluvial deposit result in channels migration frequently while the entire scope of sand bodies do not change obviously. Recognition of two isochronous surfaces, especially the one controlled by climatic, could effectively guide the progressive exploration in mature oilfield. The research results above could bring about new ideas to help discover oil and gas resources in shallow-water delta and river sedimentary system.
Gaoyou Sag, located in the south of Subei Basin, is a faulted lacustrine basin developed during the end of Late Cretaceous and Huangjue area is in the southwest part of Gaoyou Sag. Paleogene strata consisted of Funing Formation, Dainan Formation, Sanduo Formation and Yanchen Formation is deposited from bottom to top successively in Gaoyou Sag. Sanduo Formation consists of Duo1 and Duo2 member from bottom to top and Duo1 member is target strata of this research. During the sedimentary period of Duo1 member, tectonic movement in Gaoyou Sag dropped off gradually and the altitude difference between boundary and sag nearly disappeared, which made contributions to the characteristics of paleotopography in Gaoyou Sag such as a smooth slope. Several lines evidence have supported the fact that Duo1 member mainly deposited in shallow-water deltas, such as the brown mudstone with plenty of bioturbation structure, sedimentary structures which show strong hydropower, bad preservation of mouth bar and a large number of distributary channels, grain-size collection and analysis also indicate the influence of tractive current. However the upper Duo1 member belongs to fluvial sedimentary system. The sand content of mudstone increases obviously in the upper Duo1 member, and warm holes almost disappear. In addition to this, seismic reflection configuration also developed from imbricated progradation reflection to sub-parallel seismic reflection, which could be treated as transformation from shallow-water deltas to river. Strong fluvial-dominated function in shallow-water deltas always results in frequent changes of sand bodies. Lithological reservoirs are likely to form in such sedimentary environment and accurate reservoir description should be the key to exploration and development of such oilfields. Distribution of subtle traps in shallow-water deltas and fluvial facies is controlled by base-level cycles, so isochronous stratigraphic frameworks are foundation of reservoir prediction. Based on sufficient analysis of core, well logging and seismic data, this research identified two kinds of allo-cycle, respectively, dominated by tectonic movement and climatic variation. Generally, changes of base-level cycle dominated by a certain size of tectonic movement could always be identifiable in well logging curve. Usually convert interface of long-term base level cycle or return point in resistivity curve could be treated as recognition marks. Besides that, research suggests that a certain amount of changes in lake level could be easy to bring about big changes in the scope of lake, which makes it possible to recognize the interface between underwater deposit and continental sediment. In research found there exist a return point in resistivity logging curve, and treat such point as the surface of two sub-members. Baseline of natural gamma-ray logging above the return point is relatively lower, and AC figures of strata above the point are also distinctly smaller than that of the strata below the point. Differences in GR as well as AC shows mudstone above the point has higher sand content, and that could just be the differences of mudstone deposited in shallow-water environment and fluvial environment. Surface related to the return point was suggested to be the isochronous surface controlled by climate. There also exists a strange phenomenon; a successive seismic event appears near the climate correlatively interface while there does not develop any stable sandstone-mudstone boundary. Research makes a conclusion that mudstone with disparate sand content has different density and velocity, which generates the contrast in wave impedance, and forms the successive seismic events around the position where resistivity log begin to return. Isochronous stratigraphic framework based on interfaces mentioned above has been established all over the study area, and such framework has been used in seismic sedimentology research. Amplitude slices of strata below the climate-correlatively surface show typical characteristics of shallow-water deltas, range of reservoirs expand or shrink under control of lake level. However, slices of strata above the surface could be considered as fluvial deposit result in channels migration frequently while the entire scope of sand bodies do not change obviously. Recognition of two isochronous surfaces, especially the one controlled by climatic, could effectively guide the progressive exploration in mature oilfield. The research results above could bring about new ideas to help discover oil and gas resources in shallow-water delta and river sedimentary system.
2018, 36(1): 120-131.
doi: 10.3969/j.issn.1000-0550.2018.014
Abstract:
The continent slope of the South Dongsha Uplift of the Pearl River Mouth Basin (water depth is between 900 m~2 600 m) with series of contourite developed exist prominent water exchange between South China Sea and Western North Pacific, but the researches on depositional characteristics and formation mechanisms of contourite are still lack of sufficient evidences. Based on the analysis of regional seismic data and drilling data from ODP1144 site, 5 types of bottom current deposition can be established:plastered drift、elongated-mounded drift、separated drift、sediment wave and sheeted drift. Through the characteristics and distribution of contour current, the contourite developed successively from continent slope to abyssal, and sediment wave mainly developed in continent slope. The development and evolution of contourite in South Dongsha Uplift during the Quaternary controlled by various factors, the main factors including:the "two-layers" circulation pattern of intermediate and deep-water masses between South China Sea and Western North Pacific、Coriolis effect、the interaction between bottom current and gravity current which induced by eustacy during glaciation and interglacial periods and the topography of seafloor which was modified by neotectonic movement.
The continent slope of the South Dongsha Uplift of the Pearl River Mouth Basin (water depth is between 900 m~2 600 m) with series of contourite developed exist prominent water exchange between South China Sea and Western North Pacific, but the researches on depositional characteristics and formation mechanisms of contourite are still lack of sufficient evidences. Based on the analysis of regional seismic data and drilling data from ODP1144 site, 5 types of bottom current deposition can be established:plastered drift、elongated-mounded drift、separated drift、sediment wave and sheeted drift. Through the characteristics and distribution of contour current, the contourite developed successively from continent slope to abyssal, and sediment wave mainly developed in continent slope. The development and evolution of contourite in South Dongsha Uplift during the Quaternary controlled by various factors, the main factors including:the "two-layers" circulation pattern of intermediate and deep-water masses between South China Sea and Western North Pacific、Coriolis effect、the interaction between bottom current and gravity current which induced by eustacy during glaciation and interglacial periods and the topography of seafloor which was modified by neotectonic movement.
2018, 36(1): 132-141.
doi: 10.3969/j.issn.1000-0550.2018.015
Abstract:
East China Sea basin is located in the eastern edge of the Eurasian plate, which is the margin rift basin by the strike-slip pulling of residual Diaoyu Island arc. Xihu Sag is the largest of all the tectonic units in the study area. Yuquan movement of late Eocene corresponded to Eocene-Oligocene Oi-1 quench event that caused about 70 m dropping of sea level, and Huagang movement of late Oligocene corresponds to the Paleogene-Neogene global Mi-1 cooling event that caused about 50 m dropping of sea level. All of these have a significant impact for tectonic-sedimentary evolution of Pinghu-Huagang Formation. Cenozoic the seven global sea level significant drops because of global climate changes corresponding to seven "tectonics" in East China Sea basin. Therefore, seven second sequences can be recognized. Pinghu-Huagang Formations can be divided into two second sequences (SSQ3-SSQ4) and six third sequences (SQ1-SQ6) in Xihu sag. LST that is located in the slope zone of the east Xihu secondary sag is composed of sublacustrine fan, slope fan and lowstand wedge. In the western gentle slope zone TST is composed of predelta-shelf (or deep lake) mud that sourced from Haijiao-Yushan uplift, and in the eastern steep slope zone TST is composed of fan delta or nearshore subaqueous fan delta gravel-shelf (or deep lake) mud that sourced from Diaoyu uplift. In the western gentle slope zone HST is composed of delta plain gravel-delta front sand-prodelta and shelf (or lake) mud that sourced from Haijiao-Yushan uplift, and in eastern steep slope zone HST is composed of fan delta or nearshore subaqueous fan delta sand and gravel-shelf (or deep lake) mud that sourced from Diaoyu uplift zone. Tectonics, paleoclimate, sea-level and source are the main controlling factors for the third sequence and system tracts.
East China Sea basin is located in the eastern edge of the Eurasian plate, which is the margin rift basin by the strike-slip pulling of residual Diaoyu Island arc. Xihu Sag is the largest of all the tectonic units in the study area. Yuquan movement of late Eocene corresponded to Eocene-Oligocene Oi-1 quench event that caused about 70 m dropping of sea level, and Huagang movement of late Oligocene corresponds to the Paleogene-Neogene global Mi-1 cooling event that caused about 50 m dropping of sea level. All of these have a significant impact for tectonic-sedimentary evolution of Pinghu-Huagang Formation. Cenozoic the seven global sea level significant drops because of global climate changes corresponding to seven "tectonics" in East China Sea basin. Therefore, seven second sequences can be recognized. Pinghu-Huagang Formations can be divided into two second sequences (SSQ3-SSQ4) and six third sequences (SQ1-SQ6) in Xihu sag. LST that is located in the slope zone of the east Xihu secondary sag is composed of sublacustrine fan, slope fan and lowstand wedge. In the western gentle slope zone TST is composed of predelta-shelf (or deep lake) mud that sourced from Haijiao-Yushan uplift, and in the eastern steep slope zone TST is composed of fan delta or nearshore subaqueous fan delta gravel-shelf (or deep lake) mud that sourced from Diaoyu uplift. In the western gentle slope zone HST is composed of delta plain gravel-delta front sand-prodelta and shelf (or lake) mud that sourced from Haijiao-Yushan uplift, and in eastern steep slope zone HST is composed of fan delta or nearshore subaqueous fan delta sand and gravel-shelf (or deep lake) mud that sourced from Diaoyu uplift zone. Tectonics, paleoclimate, sea-level and source are the main controlling factors for the third sequence and system tracts.
2018, 36(1): 142-153.
doi: 10.3969/j.issn.1000-0550.2018.016
Abstract:
Since there are little provenance documents about Permian of southwest Ordos Basin, this paper focuses on the provenance analysis of Permain Shan 1 and He 8 Formation in Permian to figure out provenance of the two formations and whether there are differences between these two contiguous formation. Based on provenance analysis methods, the characteristics of paleocurrent, heavy mineral, feldspar, fragments, and REE have been analyzed. The result will benefit for the prediction of favorable reservoir. The character of paleocurrent shows that the provenance of Permian in the southwest Ordos Basin is multiplied, and we can divide He 8 formation into four parts based on the combination of heavy mineral:the north, southwest, southeast and the middle part of the study area. Besides the north study area can be divided into two parts based on the content of zircon and leucosphenite, the provenance of this two parts are the northwest and the northeast of Yin mountain divided by Ural mountains; The character of fragments and REE reflect that the north of study area have the character of distant deposition and the south of study area are close deposition. The provenance characters of Shan 1 and He 8 Formation are very similar. The information above draw the conclusion that in the study area the deposition in the north part of Shan1 Formation came from the Yin Mountains in the north of the basin, the southwest part from the middle north of Qilian Mountains and west Qinling Mountains and southeast part from the north Qinling Mountains in the south of the basin. And the sediment came across around Huanxian and Huachi. The provenance of He 8 Formation is similar to Shan1 Formation, the sediments in north part of the study area is from Yin Mountains in the north of Ordos basin;The middle east of Qilian Mountain and west Qinling Mountain provide sediments for southwest of study area,the provenance of southeast part of the study area is north Qinling Mountain in the south of the basin and the catchment area is also around Huanxian and Huachi. Results show that the provenance of the two formations did not change so much and the two formations have the character of succession. Besides The characters of REE shows that there are two locations in the study area have a lower altitude which shows a reducing environment.
Since there are little provenance documents about Permian of southwest Ordos Basin, this paper focuses on the provenance analysis of Permain Shan 1 and He 8 Formation in Permian to figure out provenance of the two formations and whether there are differences between these two contiguous formation. Based on provenance analysis methods, the characteristics of paleocurrent, heavy mineral, feldspar, fragments, and REE have been analyzed. The result will benefit for the prediction of favorable reservoir. The character of paleocurrent shows that the provenance of Permian in the southwest Ordos Basin is multiplied, and we can divide He 8 formation into four parts based on the combination of heavy mineral:the north, southwest, southeast and the middle part of the study area. Besides the north study area can be divided into two parts based on the content of zircon and leucosphenite, the provenance of this two parts are the northwest and the northeast of Yin mountain divided by Ural mountains; The character of fragments and REE reflect that the north of study area have the character of distant deposition and the south of study area are close deposition. The provenance characters of Shan 1 and He 8 Formation are very similar. The information above draw the conclusion that in the study area the deposition in the north part of Shan1 Formation came from the Yin Mountains in the north of the basin, the southwest part from the middle north of Qilian Mountains and west Qinling Mountains and southeast part from the north Qinling Mountains in the south of the basin. And the sediment came across around Huanxian and Huachi. The provenance of He 8 Formation is similar to Shan1 Formation, the sediments in north part of the study area is from Yin Mountains in the north of Ordos basin;The middle east of Qilian Mountain and west Qinling Mountain provide sediments for southwest of study area,the provenance of southeast part of the study area is north Qinling Mountain in the south of the basin and the catchment area is also around Huanxian and Huachi. Results show that the provenance of the two formations did not change so much and the two formations have the character of succession. Besides The characters of REE shows that there are two locations in the study area have a lower altitude which shows a reducing environment.
2018, 36(1): 154-165.
doi: 10.3969/j.issn.1000-0550.2018.017
Abstract:
Comprehensive analysis of drilling, palaeontology, seismic, sections and other data, the large reservoirs development conditions, types, characteristics and the favorable exploration directions of the southern steep slope zone in Wushi depression was analyze. It proposed that the lake level, provenance, fracture and paleogeomorphology coupling controlled the development of large reservoirs in the steep slope of fault-depressed lacustrine basin. Among them, the strong lake retreat was the basic condition of the Palaeo-lake evolution for developing large reservoirs, the enough supply of provenance was the material guarantee for forming large reservoirs, the significant fracture accumulated sand effect and suitable topography were the important catchment mechanism for constructing large reservoirs.The main types of large reservoirs were fan delta and braided river delta.The fan delta was mainly controlled by the fracture surface gentle slope zone and valley topography, the lithology was relatively coarse, the sedimentary microfacies were mainly underwater distributary channel and subaqueous inter-distributary bay.The braided river delta was mainly controlled by transition fault zone, broom fault zone as well as relatively wide and gentle topography, the lithology was relative fine, the sedimentary microfacies were mainly distributary mouth bar and distal bar, besides underwater distributary channel and subaqueous inter-distributary bay.On this basis and combined with the characteristics of large reservoirs, it suggested that the favorable exploration layer for the eastern part of the southern steep slope zone was the highstand system tracts of lower sequence and for the western part of the southern steep slope zone was the lowstand and transgression systems tracts of upper sequence in the second member of Liushagang, Wushi depression.Due to the front of the large reservoirs lithologic traps, lithological-structural traps and structural traps were developed, and were shallow buried, closed to the hydrocarbon supply center, at the same time located in the dominant direction of oil and gas accumulation, therefore, was the favorable exploration area.
Comprehensive analysis of drilling, palaeontology, seismic, sections and other data, the large reservoirs development conditions, types, characteristics and the favorable exploration directions of the southern steep slope zone in Wushi depression was analyze. It proposed that the lake level, provenance, fracture and paleogeomorphology coupling controlled the development of large reservoirs in the steep slope of fault-depressed lacustrine basin. Among them, the strong lake retreat was the basic condition of the Palaeo-lake evolution for developing large reservoirs, the enough supply of provenance was the material guarantee for forming large reservoirs, the significant fracture accumulated sand effect and suitable topography were the important catchment mechanism for constructing large reservoirs.The main types of large reservoirs were fan delta and braided river delta.The fan delta was mainly controlled by the fracture surface gentle slope zone and valley topography, the lithology was relatively coarse, the sedimentary microfacies were mainly underwater distributary channel and subaqueous inter-distributary bay.The braided river delta was mainly controlled by transition fault zone, broom fault zone as well as relatively wide and gentle topography, the lithology was relative fine, the sedimentary microfacies were mainly distributary mouth bar and distal bar, besides underwater distributary channel and subaqueous inter-distributary bay.On this basis and combined with the characteristics of large reservoirs, it suggested that the favorable exploration layer for the eastern part of the southern steep slope zone was the highstand system tracts of lower sequence and for the western part of the southern steep slope zone was the lowstand and transgression systems tracts of upper sequence in the second member of Liushagang, Wushi depression.Due to the front of the large reservoirs lithologic traps, lithological-structural traps and structural traps were developed, and were shallow buried, closed to the hydrocarbon supply center, at the same time located in the dominant direction of oil and gas accumulation, therefore, was the favorable exploration area.
2018, 36(1): 166-175.
doi: 10.3969/j.issn.1000-0550.2018.018
Abstract:
Using the data of drilling cores, thin sections and well loggings, focused on the reservoir characteristics and pore evolution, this paper gives a comparative analysis about the diversity of the Triassic Chang 81 low permeability reservoirs in Jiyuan and Xifeng area. On the one hand, the commonalities of Chang 81 reservoirs in both areas are:1) Reservoir sand bodies are underwater distributary channel sands of shallow water delta front, which are thick sand bodies of multiphase superposition with great continuity on the space. 2) The sandstones are lithic arkose and feldspathic litharenite and belong to fine sandstones and very fine sandstones with good sorting in both areas. 3) Reservoir porosity is mainly composed of primary pores and dissolution pores. The original porosity is around 38% in the study area. The loss of primary pores accounts for about 35% because of compaction and cementation. The final reservoir porosity is 7%. On the other hand, the differences of Chang 81 reservoirs in both areas are:1) The underwater distributary channel sands of Chang 81 in Jiyuan area hold the unobvious superposition and belong to "continuous retrogradation" depositional model. In contrast, the sands in Xifeng area have the obvious vertical accretion and belong to "see-saw" depositional model. 2) The intergranular pores, lithic dissolved pores and intracrystalline pores in Jiyuan area are inferior to Xifeng area. However, the dissolved pores in Jiyuan area are superior to Xifeng area. 3) In the late diagenetic evolution stages of reservoirs, the average cementation porosity loss ratio of Chang 81 sands accounts for about 13.87% and 11.99% in Jiyuan and Xifeng area, respectively. The degree of cementation pores loss in Jiyuan area is higher than Xifeng area. In addition, the dissolution pores increase ratio accounts for about 3.71% and 2.79% in Jiyuan and Xifeng area, respectively. The Jiyuan area is superior to Xifeng area.
Using the data of drilling cores, thin sections and well loggings, focused on the reservoir characteristics and pore evolution, this paper gives a comparative analysis about the diversity of the Triassic Chang 81 low permeability reservoirs in Jiyuan and Xifeng area. On the one hand, the commonalities of Chang 81 reservoirs in both areas are:1) Reservoir sand bodies are underwater distributary channel sands of shallow water delta front, which are thick sand bodies of multiphase superposition with great continuity on the space. 2) The sandstones are lithic arkose and feldspathic litharenite and belong to fine sandstones and very fine sandstones with good sorting in both areas. 3) Reservoir porosity is mainly composed of primary pores and dissolution pores. The original porosity is around 38% in the study area. The loss of primary pores accounts for about 35% because of compaction and cementation. The final reservoir porosity is 7%. On the other hand, the differences of Chang 81 reservoirs in both areas are:1) The underwater distributary channel sands of Chang 81 in Jiyuan area hold the unobvious superposition and belong to "continuous retrogradation" depositional model. In contrast, the sands in Xifeng area have the obvious vertical accretion and belong to "see-saw" depositional model. 2) The intergranular pores, lithic dissolved pores and intracrystalline pores in Jiyuan area are inferior to Xifeng area. However, the dissolved pores in Jiyuan area are superior to Xifeng area. 3) In the late diagenetic evolution stages of reservoirs, the average cementation porosity loss ratio of Chang 81 sands accounts for about 13.87% and 11.99% in Jiyuan and Xifeng area, respectively. The degree of cementation pores loss in Jiyuan area is higher than Xifeng area. In addition, the dissolution pores increase ratio accounts for about 3.71% and 2.79% in Jiyuan and Xifeng area, respectively. The Jiyuan area is superior to Xifeng area.
2018, 36(1): 176-187.
doi: 10.3969/j.issn.1000-0550.2018.019
Abstract:
Early shallow burial for a long time, the late quickly buried deep and lateral extrusion in western foreland basin are common geological evolution process in China. Affected by such geological evolution process, a high-quality reservoir can be formed in deep horizon. Clearing this kind of reservoir parameters such as porosity, pore diameter and throat diameter of evolution characteristics and quantitative evaluation, it has great significance for oil and gas exploration. Based on analysis of diagenetic physical modeling experiment, combined with the actual geological research, the evolution of deep-reservoir porosity in a foreland basin can be divided into four stages:1) long-term, shallow burial; 2) a transition from shallow burial to rapid, deep burial; 3) early, rapid, deep burial; and 4) late, rapid, deep burial. Of these, the third stage is crucial to the improvement of deep-reservoir porosity and permeability, and thus to the formation of favorable reservoirs. The two kinds of transformation mechanism are tectonic lateral extrusion and particles broken crack. Deep reservoir porosity prediction model has been established. Reservoir pores and pore throats show a significant increase at a burial depth of 7 000-8 000 m.
Early shallow burial for a long time, the late quickly buried deep and lateral extrusion in western foreland basin are common geological evolution process in China. Affected by such geological evolution process, a high-quality reservoir can be formed in deep horizon. Clearing this kind of reservoir parameters such as porosity, pore diameter and throat diameter of evolution characteristics and quantitative evaluation, it has great significance for oil and gas exploration. Based on analysis of diagenetic physical modeling experiment, combined with the actual geological research, the evolution of deep-reservoir porosity in a foreland basin can be divided into four stages:1) long-term, shallow burial; 2) a transition from shallow burial to rapid, deep burial; 3) early, rapid, deep burial; and 4) late, rapid, deep burial. Of these, the third stage is crucial to the improvement of deep-reservoir porosity and permeability, and thus to the formation of favorable reservoirs. The two kinds of transformation mechanism are tectonic lateral extrusion and particles broken crack. Deep reservoir porosity prediction model has been established. Reservoir pores and pore throats show a significant increase at a burial depth of 7 000-8 000 m.
2018, 36(1): 188-197.
doi: 10.3969/j.issn.1000-0550.2018.020
Abstract:
Xihu sag has the characteristics of deep burial depth, low porosity and permeability, Reservoir cannot be produced at economic flow rates without assistance from reservoir reconstruction, and the prediction of "sweet spot" reservoir distribution is the important process of reservoir reconstruction. The elastic parameter which is sensitive to "sweet spot" can be found by petro-physics analysis, and its threshold value can also be set. The characteristic of seismic reflection for "sweet spot" is analyzed by seismic forward modeling, and the feasibility of porosity and gas bearing prediction can also be analyzed. The accurate parameter is predicted by pre-stack synchronous inversion with the constraint of AVO parameter, and then it describes the distribution characteristic of sand thickness, strata slices, porosity, gas bearing and brittleness index. According to the lower limit of "sweet spot" in the study area, the favorable area of each attribute is delineated, and the favorable zone of "sweet spot" reservoir in study area is obtained, which gives a base for the well location design of horizontal multi-stage fracturing. The prediction result is verified by drilling, furthermore, it has achieved "double hundred" rate of sand and gas drilling encountered in target layer.
Xihu sag has the characteristics of deep burial depth, low porosity and permeability, Reservoir cannot be produced at economic flow rates without assistance from reservoir reconstruction, and the prediction of "sweet spot" reservoir distribution is the important process of reservoir reconstruction. The elastic parameter which is sensitive to "sweet spot" can be found by petro-physics analysis, and its threshold value can also be set. The characteristic of seismic reflection for "sweet spot" is analyzed by seismic forward modeling, and the feasibility of porosity and gas bearing prediction can also be analyzed. The accurate parameter is predicted by pre-stack synchronous inversion with the constraint of AVO parameter, and then it describes the distribution characteristic of sand thickness, strata slices, porosity, gas bearing and brittleness index. According to the lower limit of "sweet spot" in the study area, the favorable area of each attribute is delineated, and the favorable zone of "sweet spot" reservoir in study area is obtained, which gives a base for the well location design of horizontal multi-stage fracturing. The prediction result is verified by drilling, furthermore, it has achieved "double hundred" rate of sand and gas drilling encountered in target layer.
2018, 36(1): 198-205.
doi: 10.3969/j.issn.1000-0550.2018.021
Abstract:
The igneous rock of shallow layer developed in NanPu Depression has many types and strong heterogeneity laterally and vertically present, which are difficult to describe the spatial distribution of igneous rocks and sandstone reservoirs. As the identification of the igneous rock distribution is very critical for the confirmation of sandstone gas/oil reservoir development feature, so, multiple technologies integration is urgent need instead of only by single geology and geophysical technology. The prediction of sandstone reservoirs restricts the exploration and development of sandstone reservoirs in shallow layers. In this study, based on the rock physical property analysis, combined P-wave impedance, Gamma, Poisson ratio and Sweet seismic attributes which are sensitive to various lithology and PCA dimension reduction technology, four lithologies which are basalt, altered volcanic rock, sandstone and mudstone have been effectively distinguished. And lithology cube is built by using innovative technology of well constrained interpretation, so that, the identification of sandstone reservoir with high accuracy can be achieved. From the comparison, the final seismic prediction result is consistent with the regional geology distribution feature, and with coefficient of 87.1% matching with well data. The distribution of igneous rocks and sandstones are matched with regional geology.
The igneous rock of shallow layer developed in NanPu Depression has many types and strong heterogeneity laterally and vertically present, which are difficult to describe the spatial distribution of igneous rocks and sandstone reservoirs. As the identification of the igneous rock distribution is very critical for the confirmation of sandstone gas/oil reservoir development feature, so, multiple technologies integration is urgent need instead of only by single geology and geophysical technology. The prediction of sandstone reservoirs restricts the exploration and development of sandstone reservoirs in shallow layers. In this study, based on the rock physical property analysis, combined P-wave impedance, Gamma, Poisson ratio and Sweet seismic attributes which are sensitive to various lithology and PCA dimension reduction technology, four lithologies which are basalt, altered volcanic rock, sandstone and mudstone have been effectively distinguished. And lithology cube is built by using innovative technology of well constrained interpretation, so that, the identification of sandstone reservoir with high accuracy can be achieved. From the comparison, the final seismic prediction result is consistent with the regional geology distribution feature, and with coefficient of 87.1% matching with well data. The distribution of igneous rocks and sandstones are matched with regional geology.
2018, 36(1): 206-214.
doi: 10.3969/j.issn.1000-0550.2018.022
Abstract:
Based on the GC and GC-MS analysis, modification of saturate fractions in waterflooded oils from Qu9 reservoir was dynamically investigated. The results indicate that with the advance of waterflooding, saturates characterize obvious alterations during 9-months dynamic surveillance. Saturate concentration, C15-RD/C15-D, C158β(H)-D/C168β(H)-HD, TTs/17α-H and RS/17α-H ratios, are progressively increasing in values. Aromatic concentration∑nC21-/∑nC22+ and ∑nC14-/∑nC15+reduce continually. Isoalkane related ratios of Pr/Ph, iC18/Pr, iC18/Ph, terpane related ratios of C21/C22TT, C24/C23TT, ∑C19-26/∑C28-29TTs, C30*/C29Ts, C35R/C34R, Ol/C30H, G/C31R, C3122S/(22S+22R), C30M/C30H, Ts/(Ts+Tm) and C29Ts/(C29Ts+C29H), and sterane related ratios of C27-DS/C27-RS, C2920S/(20S+20R), C29ββ/(ββ+αα) and C27-rearranged sterane 20S/(20S+20R), keep relatively unchanged. However, irregular variation of Pr/nC17 and Ph/nC18 shows an initial increase and subsequent decrease, or the opposite. Water washing leads to the decrease of aromatics and light/heavy alkane values, while the biodegradation results in the concentration of tricyclic terpanes and regular sterane compared to the hopanes. Although they have minor effect on the ratios respectively composed of two isoalkanes, terpanes and steranes with similar carbon numbers, they cause the increase of drimane parameters in combination. Mixed with the geo-chromatography and wettability transformation in water flooding, saturates compositions were further altered.
Based on the GC and GC-MS analysis, modification of saturate fractions in waterflooded oils from Qu9 reservoir was dynamically investigated. The results indicate that with the advance of waterflooding, saturates characterize obvious alterations during 9-months dynamic surveillance. Saturate concentration, C15-RD/C15-D, C158β(H)-D/C168β(H)-HD, TTs/17α-H and RS/17α-H ratios, are progressively increasing in values. Aromatic concentration∑nC21-/∑nC22+ and ∑nC14-/∑nC15+reduce continually. Isoalkane related ratios of Pr/Ph, iC18/Pr, iC18/Ph, terpane related ratios of C21/C22TT, C24/C23TT, ∑C19-26/∑C28-29TTs, C30*/C29Ts, C35R/C34R, Ol/C30H, G/C31R, C3122S/(22S+22R), C30M/C30H, Ts/(Ts+Tm) and C29Ts/(C29Ts+C29H), and sterane related ratios of C27-DS/C27-RS, C2920S/(20S+20R), C29ββ/(ββ+αα) and C27-rearranged sterane 20S/(20S+20R), keep relatively unchanged. However, irregular variation of Pr/nC17 and Ph/nC18 shows an initial increase and subsequent decrease, or the opposite. Water washing leads to the decrease of aromatics and light/heavy alkane values, while the biodegradation results in the concentration of tricyclic terpanes and regular sterane compared to the hopanes. Although they have minor effect on the ratios respectively composed of two isoalkanes, terpanes and steranes with similar carbon numbers, they cause the increase of drimane parameters in combination. Mixed with the geo-chromatography and wettability transformation in water flooding, saturates compositions were further altered.
