2019 Vol. 37, No. 6
Display Method:
2019, 37(6): 0-0.
Abstract:
目前鄂尔多斯盆地是我国沉积面积最大的能源盆地之一，油气资源丰富，油藏规模巨大。盆地内岩性、地层发育齐全，其中中生界延长组属于最重要的含油层系，位于陇东地区的低渗透及特低渗透砂岩最具有典型性，储层中不仅含有丰富的油气资源，而且油藏结构复杂、储层沉积层序特征齐全、发育规模、形态、孔喉类型结构、组合面貌以及均质性的发育特征均具有代表性，储层在演化历程中，成岩类型及对储层微观结构的改造也具有重要石油地质意义。长期以来，长庆油田、西安石油大学、西北大学、长安大学等相关单位的学者，通过长期对低渗透致密储层及页岩气方面科技攻关、专项及专题分析研究，取得了一系列成果并获得了系统性深入的认识，借此在沉积学报平台与大家分享、讨论、并互相学习。
“低渗透致密储层及页岩气研究”专栏针对性地组织了一批相关文章，旨在对这些成果进行总结，进一步完善我国低渗透致密储层的理论认识，推动我国油气勘探事业。专栏共收集论文5篇，主要内容如下：
曹江骏等在合水地区长6段识别出7种骨架单砂体组合类型，分别为砂质碎屑流连续叠加型、砂质碎屑流间隔叠加型、砂质碎屑流+浊流间隔叠加型、浊流+砂质碎屑流间隔叠加型、浊流侧向尖灭型、浊流砂泥互层型、滑塌侧向尖灭型。其中，连续叠加型与间隔叠加型砂体为合水地区长6段优势砂体。认为合水地区优势砂体主要在东北部发育，沿东北—西南向以片状、宽条带状展布。而在合水地区西南部则只有少量以朵体状、窄条带状零散分布。
宋世骏等对鄂尔多斯盆地三叠系延长组黑色岩系成因进行了探讨，认为研究区东南缘延长组长73黑色岩系的部分“黑色泥岩”和“粉—细砂岩”分别为尘凝灰岩和粉—细砂级凝灰岩，并在垂向上与湖相泥页岩间互发育。另外，不同岩性地层中均存在水铵长石+黄钾铁矾+黄铁矿、重晶石+非晶质SiO2、斜长石的钠长石化等热液矿物组合。该黑色岩系实际上是受陆源碎屑沉积、火山碎屑沉积以及热水沉积共同控制的产物。
刘福田等系统分析了苏里格西部气田致密砂岩气藏天然气地球化学特征，认为该区天然气运聚成藏受“源”控制，并具有从西南向东北、从西向东及自下而上的运移特征。结合对气水关系的研究，认为在“源控”作用下，苏里格西部气田天然气驱动地层水区域性向北、向上运移，使研究区具有“南气北水”和地层水“上多下少”的气水分布总格局。
张帮胜等的研究认为鄂尔多斯盆地中部上古生界山西组页岩具有黏土矿物含量高、脆性指数低和储层致密的特点。虽然山西组页岩具有较好的生烃条件、含气量和页岩气保存条件，但较差的储层地质条件可能制约页岩气的规模开发。储层裂缝分析结果表明山西组页岩中微裂缝的发育提高了页岩渗透率，有利于页岩气聚集成藏。应加强鄂尔多斯盆地山西组页岩储层非均质性研究，在微裂缝发育、物性较好的页岩层位和地区仍然具有较好页岩气勘探开发潜力。
刘广林等通过对鄂尔多斯盆地姬塬地区延长组长6油藏的成藏条件和充注模式的研究，认为研究区西部与东部在成藏条件和成藏机理的差异导致充注模式的不同，西部为饱和充注型，东部为欠饱和充注型，而中部为欠充注型。研究结果为姬塬地区长6油层石油勘探开发提供了指导依据。
谨以此专栏纪念西安石油大学杨友运教授。
2019, 37(6): 1105-1116.
doi: 10.14027/j.issn.1000-0550.2019.051
Abstract:
Deepwater gravity-flow thick sedimentary sand bodies in the Chang 6 oil-bearing formation are developed in Heshui area,but sand particles are relatively compact,and oil accumulates only in a certain areas with poor continuity. To predict the location of high-quality sand bodies,and considering their different genesis and spatial superposition,the skeleton sand bodies were divided into four types:continuous superposition type;interval superposition type;lateral thinning-out type;and sand/mud interbedded type. This was done based on information gained from field sections,log interpretations,casting thin sections,high-pressure mercury injection testing,physical properties and so on,and taking into account previous research results on lake basin evolution,provenance and other related issues. On this basis,structural characteristics of four compound sand bodies in the Chang 6 oil-bearing formation were quantitatively characterized. Combinations of high-quality sand body types were determined and their distribution is discussed. The results show the following. (1) A sand body of the continuous superposition type is mainly composed of sandy clastic flows of average thickness 8.20 m. Most sand bodies of this type developed in the inner fan of a sublacustrine fan. They have good connectivity and are mainly intercalated. A sand body of the interval superposition type is mainly composed of sandy clastic flows,followed by turbidity flow;the average thickness of single sand body is 4.10 m. Most sand bodies of this type developed in the inner and middle fan of sublacustrine fan. They have barriers and are intercalated;connectivity is determined by the thickness of barrier and intercalation. A sand body of the lateral thinning-out type is mainly composed of sandy turbidity flow,followed by slump rock,and the average thickness of single sand body is 1.10 m. Most sand bodies of this type developed in the middle and outer fan of sublacustrine fan. They are either disconnected(or connected but obstructed),and mainly develop barriers. A sand body of the interbedded sand and mud type is mainly composed of turbidity flow,and have an average thickness of 0.38 m. Most sand bodies of this type are developed in the outer fan of sublacustrine fan. They have no connectivity and mainly develop barriers. (2) From the continuous superposition type to sand/mud interbedded type,the sand bodies become smaller with increased heterogeneity,and their physical properties become poorer,and the oil content lessens. Finally,combination types of high-quality sand body are continuous superposition type and interval superposition type. Planar distribution of high-quality sand bodies occur in the NE of the study area in the NE-SW direction and in plan they flakeshaped or in strips. The SW of the study area is basically undeveloped.
Deepwater gravity-flow thick sedimentary sand bodies in the Chang 6 oil-bearing formation are developed in Heshui area,but sand particles are relatively compact,and oil accumulates only in a certain areas with poor continuity. To predict the location of high-quality sand bodies,and considering their different genesis and spatial superposition,the skeleton sand bodies were divided into four types:continuous superposition type;interval superposition type;lateral thinning-out type;and sand/mud interbedded type. This was done based on information gained from field sections,log interpretations,casting thin sections,high-pressure mercury injection testing,physical properties and so on,and taking into account previous research results on lake basin evolution,provenance and other related issues. On this basis,structural characteristics of four compound sand bodies in the Chang 6 oil-bearing formation were quantitatively characterized. Combinations of high-quality sand body types were determined and their distribution is discussed. The results show the following. (1) A sand body of the continuous superposition type is mainly composed of sandy clastic flows of average thickness 8.20 m. Most sand bodies of this type developed in the inner fan of a sublacustrine fan. They have good connectivity and are mainly intercalated. A sand body of the interval superposition type is mainly composed of sandy clastic flows,followed by turbidity flow;the average thickness of single sand body is 4.10 m. Most sand bodies of this type developed in the inner and middle fan of sublacustrine fan. They have barriers and are intercalated;connectivity is determined by the thickness of barrier and intercalation. A sand body of the lateral thinning-out type is mainly composed of sandy turbidity flow,followed by slump rock,and the average thickness of single sand body is 1.10 m. Most sand bodies of this type developed in the middle and outer fan of sublacustrine fan. They are either disconnected(or connected but obstructed),and mainly develop barriers. A sand body of the interbedded sand and mud type is mainly composed of turbidity flow,and have an average thickness of 0.38 m. Most sand bodies of this type are developed in the outer fan of sublacustrine fan. They have no connectivity and mainly develop barriers. (2) From the continuous superposition type to sand/mud interbedded type,the sand bodies become smaller with increased heterogeneity,and their physical properties become poorer,and the oil content lessens. Finally,combination types of high-quality sand body are continuous superposition type and interval superposition type. Planar distribution of high-quality sand bodies occur in the NE of the study area in the NE-SW direction and in plan they flakeshaped or in strips. The SW of the study area is basically undeveloped.
2019, 37(6): 1117-1128.
doi: 10.14027/j.issn.1000-0550.2019.053
Abstract:
The genesis of the black rock series of the Triassic Chang 73 member has been controversial. It is gradually gaining acceptance that pyroclastic deposition and hydrothermal deposition are the genesis,along with normal terrigenous sedimentation. In this study,of the Chang 73 member was sampled from top to bottom,and the samples were analyzed by SEM, XRD and optical microscopy to determine the sedimentary properties of the Yaoqu-Yishi village section in Tongchuan. It was found that(1) so-called "black mudstone" is dust tuff and "silt-fine sandstone" is silt to fine-sand tuff,and(2) hydrothermal deposition is abundant in the section,with typical hydrothermal mineral assemblages such as buddingtonite + jarosite + pyrite,amorphous SiO2 + barite,and albitized plagioclase. Pyroclastic deposits and hydrothermal deposits are interbedded with normal terrigenous sediments from deposited semi-deep and shallow lake facies,gravity flow deposits,and massive pyroclastic deposits far from the eruption source,with modified hydrothermal fluid. This particular genesis and sedimentary setting makes the black rock series a potentially highquality hydrocarbon source rock and reservoir favoring significant hydrocarbon accumulation.
The genesis of the black rock series of the Triassic Chang 73 member has been controversial. It is gradually gaining acceptance that pyroclastic deposition and hydrothermal deposition are the genesis,along with normal terrigenous sedimentation. In this study,of the Chang 73 member was sampled from top to bottom,and the samples were analyzed by SEM, XRD and optical microscopy to determine the sedimentary properties of the Yaoqu-Yishi village section in Tongchuan. It was found that(1) so-called "black mudstone" is dust tuff and "silt-fine sandstone" is silt to fine-sand tuff,and(2) hydrothermal deposition is abundant in the section,with typical hydrothermal mineral assemblages such as buddingtonite + jarosite + pyrite,amorphous SiO2 + barite,and albitized plagioclase. Pyroclastic deposits and hydrothermal deposits are interbedded with normal terrigenous sediments from deposited semi-deep and shallow lake facies,gravity flow deposits,and massive pyroclastic deposits far from the eruption source,with modified hydrothermal fluid. This particular genesis and sedimentary setting makes the black rock series a potentially highquality hydrocarbon source rock and reservoir favoring significant hydrocarbon accumulation.
2019, 37(6): 1129-1139.
doi: 10.14027/j.issn.1000-0550.2019.052
Abstract:
Tight sandstone gas reservoirs are distributed over a wide area in the western Sulige gas field,with interconnected and superposed gas-bearing sands. The main gas-bearing sands occur in the eighth member of the Shihezi Formation and the first member of the Shanxi Formation. These are sand bodies of a river delta sedimentary system. In this study,the geochemical characteristics of the gas from the study area were analyzed together with the characteristics of the source rocks and hydrocarbon generation in the basin to determine the gas accumulation characteristics and the extent to which the gas-water relationship is controlled by the source rocks. It is shown that the gas in the study area mainly migrated from SW to NE,from west to east,and from bottom to top. It was found that the study area,which is located within the triangular zone of three high-intensity hydrocarbon generation centers,produces abundant gas, not only from the three hydrocarbon generation areas but also in the study area itself,which is continually producing gas to this day. The effect of the source rocks is that,as the gas migrates and accumulates,it drives formation water northward and upward regionally. The general pattern in the study area is summed up as "southern gas and northern water, more water above and less below".
Tight sandstone gas reservoirs are distributed over a wide area in the western Sulige gas field,with interconnected and superposed gas-bearing sands. The main gas-bearing sands occur in the eighth member of the Shihezi Formation and the first member of the Shanxi Formation. These are sand bodies of a river delta sedimentary system. In this study,the geochemical characteristics of the gas from the study area were analyzed together with the characteristics of the source rocks and hydrocarbon generation in the basin to determine the gas accumulation characteristics and the extent to which the gas-water relationship is controlled by the source rocks. It is shown that the gas in the study area mainly migrated from SW to NE,from west to east,and from bottom to top. It was found that the study area,which is located within the triangular zone of three high-intensity hydrocarbon generation centers,produces abundant gas, not only from the three hydrocarbon generation areas but also in the study area itself,which is continually producing gas to this day. The effect of the source rocks is that,as the gas migrates and accumulates,it drives formation water northward and upward regionally. The general pattern in the study area is summed up as "southern gas and northern water, more water above and less below".
2019, 37(6): 1140-1151.
doi: 10.14027/j.issn.1000-0550.2019.054
Abstract:
Shanxi Formation shale is a stratum of marine-continental transitional facies with potential for shale gas exploration in the Ordos Basin. The petrology, mineralogy,reservoir space,pore structure and reservoir quality of the shale show that Shanxi Formation shale comprises black mud shale,grey-black mudstone and dark grey silty mudstone. It mainly consists of 59.6% clay minerals and 36.9% quartz,on average. Fractures are classified into macroand microfractures;the latter mainly occur in the shale and organic macerals, with an average surface density of 116.6/m. In addition to mineral and diagenetic pores,organic pores occur in organic macerals,formed by hydrocarbon generation as a result of the high degree of thermal evolution. Shanxi Formation mud shale has an average porosity of 0.77% and an average permeability of 0.06×10-3 μm2.A positive correlation was found between total organic carbon (TOC), vitrinite reflectance(Ro) and clay mineral content;quartz content and shale porosity are negatively correlated. The general development of fractures increases the permeability of shale,favorable to the accumulation of shale gas. Comprehensive analysis shows that the geological conditions of the shale gas reservoir in the Shanxi Formation are general and difficult to develop. However,there are good prospects for shale gas in the layers and regions with fractures and associated properties.
Shanxi Formation shale is a stratum of marine-continental transitional facies with potential for shale gas exploration in the Ordos Basin. The petrology, mineralogy,reservoir space,pore structure and reservoir quality of the shale show that Shanxi Formation shale comprises black mud shale,grey-black mudstone and dark grey silty mudstone. It mainly consists of 59.6% clay minerals and 36.9% quartz,on average. Fractures are classified into macroand microfractures;the latter mainly occur in the shale and organic macerals, with an average surface density of 116.6/m. In addition to mineral and diagenetic pores,organic pores occur in organic macerals,formed by hydrocarbon generation as a result of the high degree of thermal evolution. Shanxi Formation mud shale has an average porosity of 0.77% and an average permeability of 0.06×10-3 μm2.A positive correlation was found between total organic carbon (TOC), vitrinite reflectance(Ro) and clay mineral content;quartz content and shale porosity are negatively correlated. The general development of fractures increases the permeability of shale,favorable to the accumulation of shale gas. Comprehensive analysis shows that the geological conditions of the shale gas reservoir in the Shanxi Formation are general and difficult to develop. However,there are good prospects for shale gas in the layers and regions with fractures and associated properties.
2019, 37(6): 1152-1161.
doi: 10.14027/j.issn.1000-0550.2019.087
Abstract:
Chang 6 reservoirs of different regions in the Jiyuan area have large differences in oil-bearing characteristics. Large lithologic reservoirs are developed in the west and east,but there are many wells producing water in the middle region. By studying source rocks,reservoir characteristics,transmission systems,shielding conditions,reservoir forming dynamics,accumulation period,and filling degree of the three regions,the differences between reservoir forming conditions and accumulation mechanisms are clarified. In the western region,the reservoir forming conditions,characterized by high hydrocarbon generation intensity,developed fracture networks,high excess pressure, and high filling degree,are the best. In the east,the reservoir forming conditions,characterized by thin hydrocarbon source rocks,but well-developed fractures,good reservoir properties,large pressure difference between source and reservoir,lateral migration of oil,and high degree of filling,are better. In the central region,the reservoir forming conditions,characterized by thin source rocks,undeveloped fractures,poor shielding conditions,low excess pressure,and low filling degree,are poor. The differences in reservoir forming conditions and accumulation mechanism lead to different types of filling. The western region belongs to the saturated filling type,the eastern part belongs to the under saturated filling type,and the central region belongs to the under-filled type. The research results provide guidance for petroleum exploration and development for Chang 6 reservoirs in Jiyuan.
Chang 6 reservoirs of different regions in the Jiyuan area have large differences in oil-bearing characteristics. Large lithologic reservoirs are developed in the west and east,but there are many wells producing water in the middle region. By studying source rocks,reservoir characteristics,transmission systems,shielding conditions,reservoir forming dynamics,accumulation period,and filling degree of the three regions,the differences between reservoir forming conditions and accumulation mechanisms are clarified. In the western region,the reservoir forming conditions,characterized by high hydrocarbon generation intensity,developed fracture networks,high excess pressure, and high filling degree,are the best. In the east,the reservoir forming conditions,characterized by thin hydrocarbon source rocks,but well-developed fractures,good reservoir properties,large pressure difference between source and reservoir,lateral migration of oil,and high degree of filling,are better. In the central region,the reservoir forming conditions,characterized by thin source rocks,undeveloped fractures,poor shielding conditions,low excess pressure,and low filling degree,are poor. The differences in reservoir forming conditions and accumulation mechanism lead to different types of filling. The western region belongs to the saturated filling type,the eastern part belongs to the under saturated filling type,and the central region belongs to the under-filled type. The research results provide guidance for petroleum exploration and development for Chang 6 reservoirs in Jiyuan.
2019, 37(6): 1162-1180.
doi: 10.14027/j.issn.1000-0550.2019.066
Abstract:
A thermal spring travertine is a form of terrestrial carbonate rock/deposit formed in Ca2+ and HCO3- enriched hot springs(generally T ≥ 30℃). Its unique depositional environment,petrological and mineralogical characteristics, geochemical features,and fluid characteristics are of great significance to studies of paleoenvironment,paleoclimate,origin of early life,neotectonic evolution,terrestrial hydrothermal sedimentology,geothermal resources,etc. Although geologists have carried out many studies related to thermal spring travertines,their spatial and temporal distribution,sedimentary characteristics,mineral composition,geochemical characteristics,microbial processes,fluid origins,diagenesis,and paleoclimate significance are still unclear because of the complex depositional and diagenetic conditions of thermal spring travertines,and further studies are needed. Based on a detailed literature review and our previous studies, this study:1) reviewed the current research progress of thermal spring travertines, 2) summarized the significance of thermal spring travertine research,and 3) proposed the current problems and next directions in thermal spring travertine research. Combining this information,this study can help us better understand the geological features of thermal spring travertines and their significance and provide new insights into further research.
A thermal spring travertine is a form of terrestrial carbonate rock/deposit formed in Ca2+ and HCO3- enriched hot springs(generally T ≥ 30℃). Its unique depositional environment,petrological and mineralogical characteristics, geochemical features,and fluid characteristics are of great significance to studies of paleoenvironment,paleoclimate,origin of early life,neotectonic evolution,terrestrial hydrothermal sedimentology,geothermal resources,etc. Although geologists have carried out many studies related to thermal spring travertines,their spatial and temporal distribution,sedimentary characteristics,mineral composition,geochemical characteristics,microbial processes,fluid origins,diagenesis,and paleoclimate significance are still unclear because of the complex depositional and diagenetic conditions of thermal spring travertines,and further studies are needed. Based on a detailed literature review and our previous studies, this study:1) reviewed the current research progress of thermal spring travertines, 2) summarized the significance of thermal spring travertine research,and 3) proposed the current problems and next directions in thermal spring travertine research. Combining this information,this study can help us better understand the geological features of thermal spring travertines and their significance and provide new insights into further research.
2019, 37(6): 1181-1192.
doi: 10.14027/j.issn.1000-0550.2019.092
Abstract:
In the Middle and Neoproterozoic in Jixian county,Tianjin in the north-central part of the North China Plate,a set of breccia was developed above the Jingeryu Formation of the QingBaikou system and the Fujunshan Formation of the Early Cambrian. There is no definitive evidence of whether it belongs to the Late Proterozoic or Early Cambrian. The author speculates that it is the Late Proterozoic and named the formation the "Xijingyu Formation." The sedimentary characteristics of the breccia in the Xijingyu Formation are described in detail through field measurements and thin slice observation,and its genesis and provenance were analyzed. The results show that the Xijingyu Formation is 155 m thick and can be divided into 9 sections according to the change of breccia composition and size. The composition of the breccia is mainly dolomite,with a small amount of chert and limestone; the formation is blockshaped,without bedding or layering;the breccia content is 80%-90%,disorderly arranged,and mixed in size,The sorting and roundness are poor,and it is generally angular and sub-angular. The interstitial is mainly dolomite mud and silt,and the structural maturity is extremely low. The parent rock of the breccia is mainly the Wumishan Formation from the Middle Proterozoic,and a small amount is from the Tieling Formation. This breccia is glacial in nature and is a typical tillite. The discovery of the tillite is of great significance for restoring the characteristics of the Late Proterozoic Earth's climate, and its emergence may be related to the "Snowball Earth".
In the Middle and Neoproterozoic in Jixian county,Tianjin in the north-central part of the North China Plate,a set of breccia was developed above the Jingeryu Formation of the QingBaikou system and the Fujunshan Formation of the Early Cambrian. There is no definitive evidence of whether it belongs to the Late Proterozoic or Early Cambrian. The author speculates that it is the Late Proterozoic and named the formation the "Xijingyu Formation." The sedimentary characteristics of the breccia in the Xijingyu Formation are described in detail through field measurements and thin slice observation,and its genesis and provenance were analyzed. The results show that the Xijingyu Formation is 155 m thick and can be divided into 9 sections according to the change of breccia composition and size. The composition of the breccia is mainly dolomite,with a small amount of chert and limestone; the formation is blockshaped,without bedding or layering;the breccia content is 80%-90%,disorderly arranged,and mixed in size,The sorting and roundness are poor,and it is generally angular and sub-angular. The interstitial is mainly dolomite mud and silt,and the structural maturity is extremely low. The parent rock of the breccia is mainly the Wumishan Formation from the Middle Proterozoic,and a small amount is from the Tieling Formation. This breccia is glacial in nature and is a typical tillite. The discovery of the tillite is of great significance for restoring the characteristics of the Late Proterozoic Earth's climate, and its emergence may be related to the "Snowball Earth".
2019, 37(6): 1193-1209.
doi: 10.14027/j.issn.1000-0550.2019.018
Abstract:
The North China Platform began to accept deposition following the late Cambrian Series 2,overlapping the ‘Great Unconformity’ between the Precambrian and Cambrian as a complete second-order cycle of transgression and regression. The depositional sequence of thick epeiric siliceous clastic-carbonate mixtures involves a variety of microbialites(reefs) formed against this background. The Miaolingian in the study area is well represented by outcrops of the Maozhuang Formation,Xuzhuang Formation,Zhangxia Formation and Gushan Formation,constitutes four third order sequences:SQ1 to SQ4. Particular biostromes,simple biomounds and biomound complexes composed of microbialites developed in the HST and FRST of SQ2,and in the HST of SQ3. Type I maceriate microbialites formed in the low-energy environment of the subtidal zone below the normal wave base;Types II and III formed in the upper subtidal to intertidal zone. Leiolites formed in shallow water above the storm wave base. Short-columnar stromatolites formed in the intertidal zone;stromatolites with gentle wavy and blurred laminae formed in the supratidal zone;and small stromatolitic mounds formed in high-energy oolitic banks. It is generdy believed that the microbialitic reefs of the Cambrian Miaolingian are characterized by thrombolites and dendrites. The discovery of maceriate microbialites in the Miaolingian enriches our understanding of the diversity and complexity of Cambrian microbialites. Fossils or fossil assemblages of calcified cyanobacteria Girvanella,Epiphyton and Hedstroemia were found in mazelike carbonates,leiolites and stromatolites,suggesting that these microbial rocks are the products of calcified microbial mats dominated by cyanobacteria,while a large number of dispersed pyrite crystals or particles indicate that nonphotosynthetic and heterotrophic bacteria such as sulfate-reducing bacteria may play important roles in facilitating carbonate precipitation.
The North China Platform began to accept deposition following the late Cambrian Series 2,overlapping the ‘Great Unconformity’ between the Precambrian and Cambrian as a complete second-order cycle of transgression and regression. The depositional sequence of thick epeiric siliceous clastic-carbonate mixtures involves a variety of microbialites(reefs) formed against this background. The Miaolingian in the study area is well represented by outcrops of the Maozhuang Formation,Xuzhuang Formation,Zhangxia Formation and Gushan Formation,constitutes four third order sequences:SQ1 to SQ4. Particular biostromes,simple biomounds and biomound complexes composed of microbialites developed in the HST and FRST of SQ2,and in the HST of SQ3. Type I maceriate microbialites formed in the low-energy environment of the subtidal zone below the normal wave base;Types II and III formed in the upper subtidal to intertidal zone. Leiolites formed in shallow water above the storm wave base. Short-columnar stromatolites formed in the intertidal zone;stromatolites with gentle wavy and blurred laminae formed in the supratidal zone;and small stromatolitic mounds formed in high-energy oolitic banks. It is generdy believed that the microbialitic reefs of the Cambrian Miaolingian are characterized by thrombolites and dendrites. The discovery of maceriate microbialites in the Miaolingian enriches our understanding of the diversity and complexity of Cambrian microbialites. Fossils or fossil assemblages of calcified cyanobacteria Girvanella,Epiphyton and Hedstroemia were found in mazelike carbonates,leiolites and stromatolites,suggesting that these microbial rocks are the products of calcified microbial mats dominated by cyanobacteria,while a large number of dispersed pyrite crystals or particles indicate that nonphotosynthetic and heterotrophic bacteria such as sulfate-reducing bacteria may play important roles in facilitating carbonate precipitation.
2019, 37(6): 1210-1223.
doi: 10.14027/j.issn.1000-0550.2019.031
Abstract:
The Xikang Group is the main body of Songpan-Ganzi flysch sedimentary basin. It has a single lithology and is widely distributed. The original stratigraphic sequence and sedimentary structure was destroyed by tectonic deformation and widespread folding. Few sedimentological studies have been done on the outcrop,and sedimentation models do not give a reasonable explanation for the huge amount of flysch observed. In this study,the sedimentary structure,sand plate ratio,paleocurrent direction,sandstone grain size and mineral composition of typical sections in the Maerkang-Jinchuan area in western Sichuan Province were researched in detail,and the sedimentary environment and sedimentary model of the Xikang Group is discussed. It is inferred that the flysch sedimentary environment was a middle-to terminal submarine fan,with sand debris flow and deep flow action and transportation. Two submarine fans were formed triggered by falling sea levels,causing progradation of the delta to the edge of the shelf. As the alluvial plain and delta complex were gradually consumed,the sediment supply and the scale and extent of the submarine fan gradually decreased until finally the second submarine fan was formed by deposition of shore retrogradational material. The flysch formation in the Songpan-Ganzi Basin probably originated as a submarine fan deposit dominated by fine-grained turbidite with multi-period superposition and multi-or single provenance. Coarse sediments were further broken down after the coastal alluvial plain and delta complex depositions were moved for the second time, and finally the main fan was deposited, consisting of middle-to fine-grained sandstone and mudstone.
The Xikang Group is the main body of Songpan-Ganzi flysch sedimentary basin. It has a single lithology and is widely distributed. The original stratigraphic sequence and sedimentary structure was destroyed by tectonic deformation and widespread folding. Few sedimentological studies have been done on the outcrop,and sedimentation models do not give a reasonable explanation for the huge amount of flysch observed. In this study,the sedimentary structure,sand plate ratio,paleocurrent direction,sandstone grain size and mineral composition of typical sections in the Maerkang-Jinchuan area in western Sichuan Province were researched in detail,and the sedimentary environment and sedimentary model of the Xikang Group is discussed. It is inferred that the flysch sedimentary environment was a middle-to terminal submarine fan,with sand debris flow and deep flow action and transportation. Two submarine fans were formed triggered by falling sea levels,causing progradation of the delta to the edge of the shelf. As the alluvial plain and delta complex were gradually consumed,the sediment supply and the scale and extent of the submarine fan gradually decreased until finally the second submarine fan was formed by deposition of shore retrogradational material. The flysch formation in the Songpan-Ganzi Basin probably originated as a submarine fan deposit dominated by fine-grained turbidite with multi-period superposition and multi-or single provenance. Coarse sediments were further broken down after the coastal alluvial plain and delta complex depositions were moved for the second time, and finally the main fan was deposited, consisting of middle-to fine-grained sandstone and mudstone.
2019, 37(6): 1224-1233.
doi: 10.14027/j.issn.1000-0550.2019.009
Abstract:
The Adams formula and Couch formula are commonly used for quantitative estimation of the paleosalinity of sedimentary water by measuring the concentration of boron in the sediment. However, the paleosalinity values are open to doubt due to the great difference between the values calculated by the two methods. To test the reliability of the two formulas, samples were collected from surface sediments and underlying water in different sedimentary environments in the Buha River estuary of Qinghai Lake. The concentration of boron, total organic carbon (TOC) and mineral composition of the deposits were derived, and the salinity and boron concentration of the water body were measured. The results for the lake water showed an excellent linear positive correlation between the concentration of boron and salinity, but no direct correlation between the concentration of boron in sediments and in sedimentary water. Based on the concentration of boron in sediments and the content and composition of clay minerals, the water salinity was calculated by both the Adams formula and the Couch formula. The calculated water salinity was higher than the measured salinity; although the value calculated by the Adams formula differed most from the measured values, it was positively correlated with the boron content in the sediments.The boron in the sediments mainly comprises boron inherited from the mother rock, boron adsorbed by clay minerals and boron-enriched organic matter. Of these, only the adsorbed boron reflects the salinity of water. The sediments in the Buha River estuary of Qinghai Lake are rich in organic matter. The strong enrichment effect of organic matter on boron content is an important reason for the failure of the salinity estimation by both formulas. Differences in the boron adsorption capacity of different types of clay minerals also significantly influence the results:the immersion tests of clay minerals in salt water showed that montmorillonite has the strongest affinity for boron adsorption, followed by illite and kaolinite. This contradicts Couch's understanding that illite has the strongest boron adsorptive capacity. Neither the original Adams formula nor the Couch formula consider the effect of organic matter on the boron content, and the misunderstanding of the adsorptive capacity of different types of clay minerals renders both formulas unsuitable for estimating paleosalinity in terrestrial sediments. Nevertheless, the concentration of adsorbed boron in clay minerals in the sediment remains a reliable index of the salinity of sedimentary water.The recovery of paleosalinity must first eliminate the influence of organic matter on the boron content, then determine the boron adsorption coefficient of the different clay minerals by carrying out a series of immersion tests and establishing a new formula.
The Adams formula and Couch formula are commonly used for quantitative estimation of the paleosalinity of sedimentary water by measuring the concentration of boron in the sediment. However, the paleosalinity values are open to doubt due to the great difference between the values calculated by the two methods. To test the reliability of the two formulas, samples were collected from surface sediments and underlying water in different sedimentary environments in the Buha River estuary of Qinghai Lake. The concentration of boron, total organic carbon (TOC) and mineral composition of the deposits were derived, and the salinity and boron concentration of the water body were measured. The results for the lake water showed an excellent linear positive correlation between the concentration of boron and salinity, but no direct correlation between the concentration of boron in sediments and in sedimentary water. Based on the concentration of boron in sediments and the content and composition of clay minerals, the water salinity was calculated by both the Adams formula and the Couch formula. The calculated water salinity was higher than the measured salinity; although the value calculated by the Adams formula differed most from the measured values, it was positively correlated with the boron content in the sediments.The boron in the sediments mainly comprises boron inherited from the mother rock, boron adsorbed by clay minerals and boron-enriched organic matter. Of these, only the adsorbed boron reflects the salinity of water. The sediments in the Buha River estuary of Qinghai Lake are rich in organic matter. The strong enrichment effect of organic matter on boron content is an important reason for the failure of the salinity estimation by both formulas. Differences in the boron adsorption capacity of different types of clay minerals also significantly influence the results:the immersion tests of clay minerals in salt water showed that montmorillonite has the strongest affinity for boron adsorption, followed by illite and kaolinite. This contradicts Couch's understanding that illite has the strongest boron adsorptive capacity. Neither the original Adams formula nor the Couch formula consider the effect of organic matter on the boron content, and the misunderstanding of the adsorptive capacity of different types of clay minerals renders both formulas unsuitable for estimating paleosalinity in terrestrial sediments. Nevertheless, the concentration of adsorbed boron in clay minerals in the sediment remains a reliable index of the salinity of sedimentary water.The recovery of paleosalinity must first eliminate the influence of organic matter on the boron content, then determine the boron adsorption coefficient of the different clay minerals by carrying out a series of immersion tests and establishing a new formula.
2019, 37(6): 1234-1243.
doi: 10.14027/j.issn.1000-0550.2019.004
Abstract:
Sediment grain size parameters provide important information about depositional processes and environments because the size range,mixing and sorting of sediment populations vary systematically in response to the sedimentation processes,dynamics and provenance. Thus the analysis of textural parameters is the basis for determining the process/response behavior of individual sedimentary units and their environment. Grain size distribution distinguishes the surface sedimentary environment in the Houtao plain,and was therefore adopted in this sedimentary facies interpretation of two drill cores from the Houtao plain reach of the Yellow River. The results show that the sedimentary environment underwent many transformations,dominated by fluvial channel facies(68% in Core DKZ04, and 57% in Core HDZ04). This indicates that the channel of the Yellow River has experienced extensive migration in this region. In addition,since aeolian sand appears only at the top of Core DKZ04,we speculate that the present desert landform of the northern Ulan Buh Desert started to form only 2 000 years ago,probably triggered by river migration and large-scale human activity.
Sediment grain size parameters provide important information about depositional processes and environments because the size range,mixing and sorting of sediment populations vary systematically in response to the sedimentation processes,dynamics and provenance. Thus the analysis of textural parameters is the basis for determining the process/response behavior of individual sedimentary units and their environment. Grain size distribution distinguishes the surface sedimentary environment in the Houtao plain,and was therefore adopted in this sedimentary facies interpretation of two drill cores from the Houtao plain reach of the Yellow River. The results show that the sedimentary environment underwent many transformations,dominated by fluvial channel facies(68% in Core DKZ04, and 57% in Core HDZ04). This indicates that the channel of the Yellow River has experienced extensive migration in this region. In addition,since aeolian sand appears only at the top of Core DKZ04,we speculate that the present desert landform of the northern Ulan Buh Desert started to form only 2 000 years ago,probably triggered by river migration and large-scale human activity.
2019, 37(6): 1244-1257.
doi: 10.14027/j.issn.1000-0550.2019.013
Abstract:
Ichnology in sediments is the result of interaction of organisms and environment,and it is a good indicator of both sedimentary and ecological environment. In this study,the results of fieldwork and experimental methods (box corer,grain analysis,X-ray computed tomography,three-dimensional reconstruction) revealed the composition and distribution of biogenic sedimentary structures in the tidal flat of the Yellow River delta. The two main results were:(1) The distribution of biogenic sedimentary structures varies at the micro-environment scale of the tidal flat. The biogenic sedimentary structures are mainly distributed in the intertidal flat. The abundance declines from mudflat to mixed-flat to sandflat. Specifically,there are feeding trails on the surface and Y-shaped and U-shaped burrows produced by Macrophthalmus japonicus in the supratidal zone. There are a number of feeding trail on the surface and Yshaped,U-shaped burrows produced by Macrophthalmus japonicus,crawling trails produced by Periophthalmus cantonensis,trails produced by Bullacta exarata on the surface,grazing trails produced by Nassarius succinctus,and a small number of crawling trails,grazing trails and vertical Y-shaped burrows in the mudflat. A large number of these occur in the sediment:grazing trails produced by Umbonium thomasi,vertical burrow produced by Mactra veneriformis Reeve,Bullacta exarata trails on the surface,and a small number of feeding trails and Yand U-shaped burrows in the sediment,grazing trails on the surface and Y-shaped burrow produced by Philyra pisum de Haan in the mixed flat,and vertical feeding and dwelling burrows of Solen gouldi,grazing trails of Turritella bacillum Kiener,and grazing trail produced by Nassaurius festiva.(2) We reconstructed the burrows of Macrophthalmus japonicus,Perinereis aibuhitensis and Mactra veneriformis Reeve to obtain three-dimensional images,providing an image basis for reconstructing the nature of burrows.
Ichnology in sediments is the result of interaction of organisms and environment,and it is a good indicator of both sedimentary and ecological environment. In this study,the results of fieldwork and experimental methods (box corer,grain analysis,X-ray computed tomography,three-dimensional reconstruction) revealed the composition and distribution of biogenic sedimentary structures in the tidal flat of the Yellow River delta. The two main results were:(1) The distribution of biogenic sedimentary structures varies at the micro-environment scale of the tidal flat. The biogenic sedimentary structures are mainly distributed in the intertidal flat. The abundance declines from mudflat to mixed-flat to sandflat. Specifically,there are feeding trails on the surface and Y-shaped and U-shaped burrows produced by Macrophthalmus japonicus in the supratidal zone. There are a number of feeding trail on the surface and Yshaped,U-shaped burrows produced by Macrophthalmus japonicus,crawling trails produced by Periophthalmus cantonensis,trails produced by Bullacta exarata on the surface,grazing trails produced by Nassarius succinctus,and a small number of crawling trails,grazing trails and vertical Y-shaped burrows in the mudflat. A large number of these occur in the sediment:grazing trails produced by Umbonium thomasi,vertical burrow produced by Mactra veneriformis Reeve,Bullacta exarata trails on the surface,and a small number of feeding trails and Yand U-shaped burrows in the sediment,grazing trails on the surface and Y-shaped burrow produced by Philyra pisum de Haan in the mixed flat,and vertical feeding and dwelling burrows of Solen gouldi,grazing trails of Turritella bacillum Kiener,and grazing trail produced by Nassaurius festiva.(2) We reconstructed the burrows of Macrophthalmus japonicus,Perinereis aibuhitensis and Mactra veneriformis Reeve to obtain three-dimensional images,providing an image basis for reconstructing the nature of burrows.
2019, 37(6): 1258-1268.
doi: 10.14027/j.issn.1000-0550.2019.008
Abstract:
Detailed analysis of the petrologic characteristics,carbonate cements and clay minerals of the reservoir rocks of the Paleogene Lulehe Formation in the central Pingtai region at the northern margin of the Qaidam Basin showed that the reservoir rocks in the platform area are mainly lithic sandstone and feldspar lithic sandstone,commonly with point contact and/or line contact between the clastic particles. As a result there are few primary interstices,only individual intragranular secondary pores. The clay mineral content is relatively high,up to 21.92% on average,mainly in mixed layers of illite/montmorillonite and illite. Montmorillonite and chlorite are predominant,and show obvious montmorillonite transformation into illite-montmorillonite. The pore fluid is alkaline water,which promotes the decarboxylation of organic matter and reflects hydrocarbon generation during compaction. The average paleotemperature at the time of carbonate cement formation was 75.20℃,mainly at the early diagenetic stage B. Elemental geochemical analyses showed carbon isotope values(δ13C) from -8.77‰ to -3.91‰(average -5.66‰);the carbon source was mainly decarboxylated organic carbon and inorganic carbon in carbonate rocks. Leaching also reduced the amount of the δ13C isotope in cements. The oxygen isotope(δ18O) ranged from -12.97‰ to -8.75‰(average 10.68‰). The paleosalinity(Z) was in the range 103.79 to 114.27(average 110.38). The carbonate precipitation temperature ranged from 62.89℃ to 90.53℃(average 75.20℃). Trace element determination gave average values for Sr,Cu,Th,U,Ba,Ni,Co,V and Cr of 195.25 μg/g,19.48 μg/g,7.32 μg/g,21.8 μg/g,735.52 μg/g,22.41 μg/g,9.40 μg/g,59.11 μg/g and 85.55 μg/g,in that order. The average values of the U/Th,V/Cr,Ni/Co and Cu/Zn ratios were 0.25,0.72,2.26 and 0.42,indicating that the Lulehe Formation(E1+2) is currently in a sedimentary oxidizing environment with high redox potential. Since the combined Sr/Ba and U averages 0.30 and 0.85 are both less than 1,together with the C and O isotope content in the carbonate cement,the ancient salinity was estimated to be 110.38 wt%; this indicates a freshwater sedimentation paleoenvironment with a brackish water phase.
Detailed analysis of the petrologic characteristics,carbonate cements and clay minerals of the reservoir rocks of the Paleogene Lulehe Formation in the central Pingtai region at the northern margin of the Qaidam Basin showed that the reservoir rocks in the platform area are mainly lithic sandstone and feldspar lithic sandstone,commonly with point contact and/or line contact between the clastic particles. As a result there are few primary interstices,only individual intragranular secondary pores. The clay mineral content is relatively high,up to 21.92% on average,mainly in mixed layers of illite/montmorillonite and illite. Montmorillonite and chlorite are predominant,and show obvious montmorillonite transformation into illite-montmorillonite. The pore fluid is alkaline water,which promotes the decarboxylation of organic matter and reflects hydrocarbon generation during compaction. The average paleotemperature at the time of carbonate cement formation was 75.20℃,mainly at the early diagenetic stage B. Elemental geochemical analyses showed carbon isotope values(δ13C) from -8.77‰ to -3.91‰(average -5.66‰);the carbon source was mainly decarboxylated organic carbon and inorganic carbon in carbonate rocks. Leaching also reduced the amount of the δ13C isotope in cements. The oxygen isotope(δ18O) ranged from -12.97‰ to -8.75‰(average 10.68‰). The paleosalinity(Z) was in the range 103.79 to 114.27(average 110.38). The carbonate precipitation temperature ranged from 62.89℃ to 90.53℃(average 75.20℃). Trace element determination gave average values for Sr,Cu,Th,U,Ba,Ni,Co,V and Cr of 195.25 μg/g,19.48 μg/g,7.32 μg/g,21.8 μg/g,735.52 μg/g,22.41 μg/g,9.40 μg/g,59.11 μg/g and 85.55 μg/g,in that order. The average values of the U/Th,V/Cr,Ni/Co and Cu/Zn ratios were 0.25,0.72,2.26 and 0.42,indicating that the Lulehe Formation(E1+2) is currently in a sedimentary oxidizing environment with high redox potential. Since the combined Sr/Ba and U averages 0.30 and 0.85 are both less than 1,together with the C and O isotope content in the carbonate cement,the ancient salinity was estimated to be 110.38 wt%; this indicates a freshwater sedimentation paleoenvironment with a brackish water phase.
2019, 37(6): 1269-1279.
doi: 10.14027/j.issn.1000-0550.2019.010
Abstract:
As a positive sub-tectonic unit in the Junggar Basin,the accumulation background of the Zhongguai Uplift is very favorable for gas exploration. The physical properties and main controlling factors of the Sangonghe Formation sandstone reservoir were studied by observing the petrographic characteristics of rock cores and thin sections in selected main wells,and by X-ray diffraction(XRD) analyses,well logging,scanning electron microscopy(SEM) and mercury injection,revealing that the sandstone reservoir consists mainly of feldspathic litharenite and lithic sandstone. Particles in phase 2 of the Sangonghe Formation are larger than those in phase 1 and were mainly of average size,with medium structure maturation and low composition maturation. The porosity and permeability of the reservoir was low in places,but it was mainly of medium porosity and permeability. Sedimentary microfacies at the foreedge of underwater distributary channels in braided river deltas accounted for pore and sand particle development in the reservoir. Analyses of the evolution over this period indicated that reservoir compactness was mainly influenced by compaction and cementation;following the latter,dissolution may have increased the porosity of the reservoir to some extent and offered favorable pathways for gas accumulation.
As a positive sub-tectonic unit in the Junggar Basin,the accumulation background of the Zhongguai Uplift is very favorable for gas exploration. The physical properties and main controlling factors of the Sangonghe Formation sandstone reservoir were studied by observing the petrographic characteristics of rock cores and thin sections in selected main wells,and by X-ray diffraction(XRD) analyses,well logging,scanning electron microscopy(SEM) and mercury injection,revealing that the sandstone reservoir consists mainly of feldspathic litharenite and lithic sandstone. Particles in phase 2 of the Sangonghe Formation are larger than those in phase 1 and were mainly of average size,with medium structure maturation and low composition maturation. The porosity and permeability of the reservoir was low in places,but it was mainly of medium porosity and permeability. Sedimentary microfacies at the foreedge of underwater distributary channels in braided river deltas accounted for pore and sand particle development in the reservoir. Analyses of the evolution over this period indicated that reservoir compactness was mainly influenced by compaction and cementation;following the latter,dissolution may have increased the porosity of the reservoir to some extent and offered favorable pathways for gas accumulation.
2019, 37(6): 1280-1295.
doi: 10.14027/j.issn.1000-0550.2019.007
Abstract:
Fourteen sublacustrine fans are located in the northern sub-sag of the Liaozhong Sag in the lower Ed2 Formation. A systematic study of their sedimentary characteristics,genesis and space time evolution,combined with gravity flow sedimentation theory and the degree of development of water channels and the characteristics of the gravity flow fluid indicated three types of sedimentation:non-channelized sandy-debris flow(SDF) sublacustrine fans, non-channelized turbidite-current(TC) sublacustrine fans,and channelized fans. The SDF and TC fans have no evident channel;the SDF is rich in sand,and the TC fan is rich in mud. The sand in the channelized fan is mainly confined to the channel,and the mud is outside the channel. The main factors that determined the formation of the different fan types depends on(a) whether the source is rich in sand,and(b) the scale of the slope break belt. The nonchannelized fans were formed when the sand content exceeded 30% of the sand content of the channelized fans. Both SDF and TC fans were found when the scale of the slope break was relatively large and the transport distance was greatest. Only SDF fans were formed when the slope break was small. Sand-rich source material(non-viscous and easily mixed with water in slump tests) did not readily form channels. Mud-rich source material(viscous and not readily mixed with water in slump tests) formed obvious channels.
Fourteen sublacustrine fans are located in the northern sub-sag of the Liaozhong Sag in the lower Ed2 Formation. A systematic study of their sedimentary characteristics,genesis and space time evolution,combined with gravity flow sedimentation theory and the degree of development of water channels and the characteristics of the gravity flow fluid indicated three types of sedimentation:non-channelized sandy-debris flow(SDF) sublacustrine fans, non-channelized turbidite-current(TC) sublacustrine fans,and channelized fans. The SDF and TC fans have no evident channel;the SDF is rich in sand,and the TC fan is rich in mud. The sand in the channelized fan is mainly confined to the channel,and the mud is outside the channel. The main factors that determined the formation of the different fan types depends on(a) whether the source is rich in sand,and(b) the scale of the slope break belt. The nonchannelized fans were formed when the sand content exceeded 30% of the sand content of the channelized fans. Both SDF and TC fans were found when the scale of the slope break was relatively large and the transport distance was greatest. Only SDF fans were formed when the slope break was small. Sand-rich source material(non-viscous and easily mixed with water in slump tests) did not readily form channels. Mud-rich source material(viscous and not readily mixed with water in slump tests) formed obvious channels.
2019, 37(6): 1296-1308.
doi: 10.14027/j.issn.1000-0550.2019.088
Abstract:
Previous studies have shown that the deposition of volcanic ash from modern volcanic activity into seawater can improve marine surface productivity,promote the flourishing of plankton,and facilitate the formation and enrichment of organic matter. However,there are few studies on the relationship between volcanic ash deposition and organic matter enrichment in geological history,which has always been controversial. A large number of volcanic ash layers developed in the gas shales of the Wufeng-Longmaxi Formation during the Ordovician-Silurian transition in South China,providing a typical strata system for this research. Total organic carbon(TOC) content,paleo-productivity, and redox conditions of the shale horizons, including volcanic ash layers and no volcanic ash layers, were comparatively analyzed. The results show that the volcanic ash deposition during the Ordovician-Silurian transition had a relatively weak effect on marine productivity and did not significantly promote the accumulation of organic matter. The redox condition has a close relationship with TOC content,suggesting it could be the main controlling factor. The influence of volcanic activity on the sedimentary environment is a very complicated process. Therefore,in the future, comprehensive studies with higher resolution(such as centimeter-scale and millimeter-scale) should be carried out by using geological,geochemical,and other testing methods to finely analyze the impact of volcanic activity on the formation and enrichment of organic matter. Sediments related to volcanic activity are one of the research targets of unconventional petroleum sedimentology,and the determination of the relationship between them and organic enrichment in shale would have an important role in the exploration and development of unconventional petroleum,such as shale oil and gas.
Previous studies have shown that the deposition of volcanic ash from modern volcanic activity into seawater can improve marine surface productivity,promote the flourishing of plankton,and facilitate the formation and enrichment of organic matter. However,there are few studies on the relationship between volcanic ash deposition and organic matter enrichment in geological history,which has always been controversial. A large number of volcanic ash layers developed in the gas shales of the Wufeng-Longmaxi Formation during the Ordovician-Silurian transition in South China,providing a typical strata system for this research. Total organic carbon(TOC) content,paleo-productivity, and redox conditions of the shale horizons, including volcanic ash layers and no volcanic ash layers, were comparatively analyzed. The results show that the volcanic ash deposition during the Ordovician-Silurian transition had a relatively weak effect on marine productivity and did not significantly promote the accumulation of organic matter. The redox condition has a close relationship with TOC content,suggesting it could be the main controlling factor. The influence of volcanic activity on the sedimentary environment is a very complicated process. Therefore,in the future, comprehensive studies with higher resolution(such as centimeter-scale and millimeter-scale) should be carried out by using geological,geochemical,and other testing methods to finely analyze the impact of volcanic activity on the formation and enrichment of organic matter. Sediments related to volcanic activity are one of the research targets of unconventional petroleum sedimentology,and the determination of the relationship between them and organic enrichment in shale would have an important role in the exploration and development of unconventional petroleum,such as shale oil and gas.
2019, 37(6): 1309-1324.
doi: 10.14027/j.issn.1000-0550.2019.030
Abstract:
A full understanding of the properties of the pore structure in organic-rich shales is beneficial for determining the shale oil and gas accumulation mechanism,and thus is significant in guiding exploration and exploitation. Methods of characterizing the pore structure of organic-rich shales embody quantitative analysis and qualitative description,both of which should be combined during investigations. Factors such as total organic carbon(TOC),thermal maturity,origin of organic matter,mineral constituents and tectonism have considerable impacts on the nature of the pore structure in organic-rich shales. Of these,the origin of organic matter determines the potential for organic pores formation;TOC and mineralogy control the types of nanopores;and thermal maturity influences nanopore evolution. Tectonism has a secondary effect,in that it may modify the nanopore structure. Pyrolysis experiments play a crucial role in investigating the evolution of pore structure in shales,since the factors are controlled artificially;however,experimental conditions should match the actual geological conditions. At present,pore structure evolution in shales is still inconclusive and controversial. Due to the diverse origins of organic matter,the evolution of the pore structure in organic-rich shales may differ from one sedimentary environment to another,and thus require further separate study. Dilemmas such as the impacts of TOC on the characteristics of pores in shales,the mature stage of the development of secondary organic pores and the evolutionary scenarios and mechanisms of pores at the envolution stage (Ro>3%) need to be further explored. In addition,the methods identifying the microscopic compositions of organic matter using scanning electron microscopy need to be established,and the usage of some terminologies should be standardized to reduce the confusion that is currently caused by researchers who engage in different fields.
A full understanding of the properties of the pore structure in organic-rich shales is beneficial for determining the shale oil and gas accumulation mechanism,and thus is significant in guiding exploration and exploitation. Methods of characterizing the pore structure of organic-rich shales embody quantitative analysis and qualitative description,both of which should be combined during investigations. Factors such as total organic carbon(TOC),thermal maturity,origin of organic matter,mineral constituents and tectonism have considerable impacts on the nature of the pore structure in organic-rich shales. Of these,the origin of organic matter determines the potential for organic pores formation;TOC and mineralogy control the types of nanopores;and thermal maturity influences nanopore evolution. Tectonism has a secondary effect,in that it may modify the nanopore structure. Pyrolysis experiments play a crucial role in investigating the evolution of pore structure in shales,since the factors are controlled artificially;however,experimental conditions should match the actual geological conditions. At present,pore structure evolution in shales is still inconclusive and controversial. Due to the diverse origins of organic matter,the evolution of the pore structure in organic-rich shales may differ from one sedimentary environment to another,and thus require further separate study. Dilemmas such as the impacts of TOC on the characteristics of pores in shales,the mature stage of the development of secondary organic pores and the evolutionary scenarios and mechanisms of pores at the envolution stage (Ro>3%) need to be further explored. In addition,the methods identifying the microscopic compositions of organic matter using scanning electron microscopy need to be established,and the usage of some terminologies should be standardized to reduce the confusion that is currently caused by researchers who engage in different fields.
