The petroleum system concept and related theory are systematically reviewed in this work using published studies. In light of the recent success in exploiting unconventional petroleum resources, the classic petroleum system concept cannot be used to account for the vast unconventional oil and gas accumulations within the petroleum system. The whole petroleum system model is here adopted to investigate both the conventional and unconventional hydrocarbon resources in the Mahu sag, Junggar Basin, China. The whole petroleum system in the study area developed in Permian strata deposited within a large, alkaline lacustrine basin, comprising conventional and unconventional reservoirs that coexist orderly. The Permian Fengcheng Formation in the Junggar Basin is a unique alkaline lacustrine source rock that ranges from low maturity to high maturity, contains abundant organic matter and volcanic materials, and has a high oil-generating potential. Different types of hydrocarbon reservoirs are distributed from the margin to the center of the sag and vary from conventional fan-delta accumulations in fold-thrust belts (i.e., conventional conglomerate reservoirs) to unconventional tight and shale oil accumulations located within the source rock sequences. The distribution and coexistence of different types of hydrocarbon accumulations in the Mahu sag provide new opportunities for exploration and insights into the development of petroleum systems. This whole petroleum system model that developed in the Junggar Basin has implications for the exploration of both conventional and unconventional hydrocarbons in petroleum basins worldwide, especially in deep strata.
{"title":"The whole petroleum system with ordered coexistence of conventional and unconventional hydrocarbons: Case from the Junggar Basin, China","authors":"Yong Tang, Jian Cao, Wenjun He, Yin Liu, Zhijun Qin, Liliang Huang","doi":"10.1306/06192322086","DOIUrl":"https://doi.org/10.1306/06192322086","url":null,"abstract":"The petroleum system concept and related theory are systematically reviewed in this work using published studies. In light of the recent success in exploiting unconventional petroleum resources, the classic petroleum system concept cannot be used to account for the vast unconventional oil and gas accumulations within the petroleum system. The whole petroleum system model is here adopted to investigate both the conventional and unconventional hydrocarbon resources in the Mahu sag, Junggar Basin, China. The whole petroleum system in the study area developed in Permian strata deposited within a large, alkaline lacustrine basin, comprising conventional and unconventional reservoirs that coexist orderly. The Permian Fengcheng Formation in the Junggar Basin is a unique alkaline lacustrine source rock that ranges from low maturity to high maturity, contains abundant organic matter and volcanic materials, and has a high oil-generating potential. Different types of hydrocarbon reservoirs are distributed from the margin to the center of the sag and vary from conventional fan-delta accumulations in fold-thrust belts (i.e., conventional conglomerate reservoirs) to unconventional tight and shale oil accumulations located within the source rock sequences. The distribution and coexistence of different types of hydrocarbon accumulations in the Mahu sag provide new opportunities for exploration and insights into the development of petroleum systems. This whole petroleum system model that developed in the Junggar Basin has implications for the exploration of both conventional and unconventional hydrocarbons in petroleum basins worldwide, especially in deep strata.","PeriodicalId":7124,"journal":{"name":"AAPG Bulletin","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141508327","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Hongdan Deng, Ken McClay, Hanlin Chen, Emma Finch, Dariusz Jablonski, Sukonmeth Jitmahantakul
The origin of the Exmouth and Dampier Sub-basins in the inner rift system of the North West Shelf, Australia, remain poorly understood, despite intensive industrial exploration for more than 50 yr. By integrating deep two-dimensional and basinwide three-dimensional seismic reflection data, it is concluded that the Exmouth and Dampier Sub-basins are primarily controlled by crustal-scale faults that separate different crustal entities of the Pilbara craton/Capricorn orogen and the Exmouth Plateau. These faults were first formed during late Paleozoic rifting and were reactivated during Late Triassic to Late Jurassic rifting. The reactivation of these faults was accommodated by monocline deformation in the stratigraphic cover due to the presence of thick (∼7 km), mechanically weak layers of upper Paleozoic and Lower to Middle Triassic units. The monocline is connected by a ramp syncline that constitutes the main part of the depocenters of the Exmouth and Dampier Sub-basins. It was partially breached by the Rankin fault, a northeast-trending, right-stepping fault system, during Callovian–Oxfordian extension and controlled the development of crestal-collapse grabens in the hanging wall. This study reveals crustal-scale, extensional fault-related folds and their complexity in secondary structures in unprecedented detail. It provides a guideline for understanding extensional fault-related folding in three dimensions and deep petroleum system exploration in other extensional basins worldwide.
{"title":"Structural inheritance controls crustal-scale extensional fault-related folding in the Exmouth and Dampier Sub-basins, North West Shelf, Australia","authors":"Hongdan Deng, Ken McClay, Hanlin Chen, Emma Finch, Dariusz Jablonski, Sukonmeth Jitmahantakul","doi":"10.1306/01242423035","DOIUrl":"https://doi.org/10.1306/01242423035","url":null,"abstract":"The origin of the Exmouth and Dampier Sub-basins in the inner rift system of the North West Shelf, Australia, remain poorly understood, despite intensive industrial exploration for more than 50 yr. By integrating deep two-dimensional and basinwide three-dimensional seismic reflection data, it is concluded that the Exmouth and Dampier Sub-basins are primarily controlled by crustal-scale faults that separate different crustal entities of the Pilbara craton/Capricorn orogen and the Exmouth Plateau. These faults were first formed during late Paleozoic rifting and were reactivated during Late Triassic to Late Jurassic rifting. The reactivation of these faults was accommodated by monocline deformation in the stratigraphic cover due to the presence of thick (∼7 km), mechanically weak layers of upper Paleozoic and Lower to Middle Triassic units. The monocline is connected by a ramp syncline that constitutes the main part of the depocenters of the Exmouth and Dampier Sub-basins. It was partially breached by the Rankin fault, a northeast-trending, right-stepping fault system, during Callovian–Oxfordian extension and controlled the development of crestal-collapse grabens in the hanging wall. This study reveals crustal-scale, extensional fault-related folds and their complexity in secondary structures in unprecedented detail. It provides a guideline for understanding extensional fault-related folding in three dimensions and deep petroleum system exploration in other extensional basins worldwide.","PeriodicalId":7124,"journal":{"name":"AAPG Bulletin","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141508328","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In petroliferous basins, oil and gas accumulations buried at depths of 4500 to 6000 m (14,764 to 19,685 ft) are generally referred as deep reservoirs, while those greater than 6000 m (>19,685 ft) are referred to as ultradeep reservoirs (Dyman et al., 1996; Dutton and Loucks, 2010). The exploration and understanding of deep petroleum systems have been at the forefront of research and industry interest for many decades. The first reported deep petroleum discovery in the United States is located in the Carter-Knox oil field, Oklahoma, in the 1950s (Reedy and Becker, 1956), which was...
{"title":"Introduction for the special issue on deep petroleum systems","authors":"Fang Hao, Keyu Liu","doi":"10.1306/bltnintro042324","DOIUrl":"https://doi.org/10.1306/bltnintro042324","url":null,"abstract":"In petroliferous basins, oil and gas accumulations buried at depths of 4500 to 6000 m (14,764 to 19,685 ft) are generally referred as deep reservoirs, while those greater than 6000 m (>19,685 ft) are referred to as ultradeep reservoirs (Dyman et al., 1996; Dutton and Loucks, 2010). The exploration and understanding of deep petroleum systems have been at the forefront of research and industry interest for many decades. The first reported deep petroleum discovery in the United States is located in the Carter-Knox oil field, Oklahoma, in the 1950s (Reedy and Becker, 1956), which was...","PeriodicalId":7124,"journal":{"name":"AAPG Bulletin","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141508324","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Peng Yang, Keyu Liu, Noreen J. Evans, Shuichang Zhang, Zhen Li, Jin Su, Kai Rankenburg, Jianliang Liu, Brent I. A. McInnes
The Tabei uplift in the Tarim Basin is one of the deepest and most important petroleum-producing areas in China, with more than 3 billion t (21 billion bbl) of oil equivalent discovered in the Paleozoic carbonate reservoirs. Further petroleum exploration and development in the Tabei and neighboring areas will greatly benefit from an in-depth understanding of the hydrocarbon charge and accumulation history of these deeply buried carbonate reservoirs. The molecular correlation of reservoir oils indicates that oils from major accumulations in the area share similar geochemical characteristics and were presumably derived from the same source rocks deposited in a marine environment. The Shunbei reservoir oil has the highest thermal maturity, followed by the Yuecan reservoir oil, whereas the Tahe reservoir oil has the lowest thermal maturity. Six generations of calcite cementation spanning over 130 m.y. have been delineated in calcite veins, with U-Pb ages ranging from ca. 446 Ma to ca. 316 Ma. The second and fifth generations of calcite cementation were accompanied by oil charge events, as indicated by the occurrence of bitumen and primary oil inclusions. Fluid inclusion analysis coupled with basin modeling results reveal that the Tabei area experienced two major oil charges, with the first charge occurring during the late Caledonian Orogeny, at 426 to 415 Ma, and the second charge during the middle−late Hercynian Orogeny, at 339 to 278 Ma. The Shunbei and Yuecan reservoirs contain well-preserved oils accumulated during the two charge events, whereas the Tahe reservoir oil has been partially biodegraded.
塔里木盆地的塔北隆起带是中国最深、最重要的石油产区之一，在古生代碳酸盐岩储层中发现的石油当量超过 30 亿吨（210 亿桶）。深入了解这些深埋碳酸盐岩储层的油气充注和聚集历史，将大大有利于田北及邻近地区的进一步石油勘探和开发。储油层石油的分子相关性表明，该地区主要储油层的石油具有相似的地球化学特征，可能来自海洋环境中沉积的同一源岩。顺北储层油的热成熟度最高，月坎储层油次之，而塔河储层油的热成熟度最低。方解石矿脉中已划分出六代方解石胶结，时间跨度超过 130 m.y.，U-Pb 年龄介于约 446 Ma 到约 316 Ma 之间。第二代和第五代方解石胶结伴随着石油充注事件，沥青和原生石油包裹体的出现表明了这一点。流体包裹体分析和盆地建模结果表明，田北地区经历了两次主要的石油充注事件，第一次充注发生在加里东造山运动晚期（426-415Ma），第二次充注发生在海西造山运动中晚期（339-278Ma）。顺北油藏和月坎油藏在两次充油过程中积累的石油保存完好，而塔河油藏的石油则部分发生了生物降解。
{"title":"Petroleum accumulation history of deeply buried carbonate reservoirs in the northern Tarim Basin, northwestern China","authors":"Peng Yang, Keyu Liu, Noreen J. Evans, Shuichang Zhang, Zhen Li, Jin Su, Kai Rankenburg, Jianliang Liu, Brent I. A. McInnes","doi":"10.1306/06212321210","DOIUrl":"https://doi.org/10.1306/06212321210","url":null,"abstract":"The Tabei uplift in the Tarim Basin is one of the deepest and most important petroleum-producing areas in China, with more than 3 billion t (21 billion bbl) of oil equivalent discovered in the Paleozoic carbonate reservoirs. Further petroleum exploration and development in the Tabei and neighboring areas will greatly benefit from an in-depth understanding of the hydrocarbon charge and accumulation history of these deeply buried carbonate reservoirs. The molecular correlation of reservoir oils indicates that oils from major accumulations in the area share similar geochemical characteristics and were presumably derived from the same source rocks deposited in a marine environment. The Shunbei reservoir oil has the highest thermal maturity, followed by the Yuecan reservoir oil, whereas the Tahe reservoir oil has the lowest thermal maturity. Six generations of calcite cementation spanning over 130 m.y. have been delineated in calcite veins, with U-Pb ages ranging from ca. 446 Ma to ca. 316 Ma. The second and fifth generations of calcite cementation were accompanied by oil charge events, as indicated by the occurrence of bitumen and primary oil inclusions. Fluid inclusion analysis coupled with basin modeling results reveal that the Tabei area experienced two major oil charges, with the first charge occurring during the late Caledonian Orogeny, at 426 to 415 Ma, and the second charge during the middle−late Hercynian Orogeny, at 339 to 278 Ma. The Shunbei and Yuecan reservoirs contain well-preserved oils accumulated during the two charge events, whereas the Tahe reservoir oil has been partially biodegraded.","PeriodicalId":7124,"journal":{"name":"AAPG Bulletin","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141508325","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Deep rift basins are geological environments that can contain large resources of petroleum and can be particularly rich in unconventional oil and gas reserves. However, due to deep burial and complex geological conditions, the occurrences and distributions of hydrocarbon are not easily delineated, which seriously hampers the exploration process. Based on comprehensive analyses of the exploration process and hydrocarbon accumulation characteristics in the deep basin of the Jizhong and Huanghua depressions in Bohai Bay Basin, it was found that the hydrocarbon accumulations appear to be distributed in a concentric pattern. The interplay among tectonics, sedimentation, and hydrocarbon generation-migration in the deep basin determines the distribution of hydrocarbon accumulation. The inner tectonic zone formed by the deep trough area is mainly defined by the deposition of (semi) deep lacustrine mudstone, which forms retained shale reservoirs. In the outer tectonic zone, prodelta (fan) and (fan) delta front fine-grained strata deposited within the low-middle slope area and shallow lake and the subsequent deposition of (fan) delta plain sandstone bodies form intercepted stratigraphic and lithologic reservoirs. Conventional and unconventional reservoirs are distributed in a concentric order. The mechanisms and patterns of concentric hydrocarbon accumulation in deep basin settings can provide useful analogs for oil and gas exploration in deep basins with similar structures, particularly for unconventional oil and gas resources.
{"title":"Concentric hydrocarbon accumulations in deep rift basins: A case study of Jizhong and Huanghua depressions, Bohai Bay Basin, China","authors":"Xianzheng Zhao, Fengming Jin, Xiugang Pu, Qun Luo, Xiongying Dong, Wenzhong Han, Chunyuan Han, Wenya Jiang, Wei Zhang, Zhannan Shi, Delu Xie","doi":"10.1306/12052322018","DOIUrl":"https://doi.org/10.1306/12052322018","url":null,"abstract":"Deep rift basins are geological environments that can contain large resources of petroleum and can be particularly rich in unconventional oil and gas reserves. However, due to deep burial and complex geological conditions, the occurrences and distributions of hydrocarbon are not easily delineated, which seriously hampers the exploration process. Based on comprehensive analyses of the exploration process and hydrocarbon accumulation characteristics in the deep basin of the Jizhong and Huanghua depressions in Bohai Bay Basin, it was found that the hydrocarbon accumulations appear to be distributed in a concentric pattern. The interplay among tectonics, sedimentation, and hydrocarbon generation-migration in the deep basin determines the distribution of hydrocarbon accumulation. The inner tectonic zone formed by the deep trough area is mainly defined by the deposition of (semi) deep lacustrine mudstone, which forms retained shale reservoirs. In the outer tectonic zone, prodelta (fan) and (fan) delta front fine-grained strata deposited within the low-middle slope area and shallow lake and the subsequent deposition of (fan) delta plain sandstone bodies form intercepted stratigraphic and lithologic reservoirs. Conventional and unconventional reservoirs are distributed in a concentric order. The mechanisms and patterns of concentric hydrocarbon accumulation in deep basin settings can provide useful analogs for oil and gas exploration in deep basins with similar structures, particularly for unconventional oil and gas resources.","PeriodicalId":7124,"journal":{"name":"AAPG Bulletin","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141522791","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Fault-controlled reservoirs are critical hydrocarbon-bearing reservoirs in carbonate rocks. The ultradeep Ordovician fault-karst reservoirs in the Tarim Basin are representative carbonate reservoirs whose formation was controlled by tectonics. An integrated analysis of seismic, drilling, logging, and core data and the petrology and geochemistry of the area suggest that the strike-slip fault, lithology, and diagenetic fluids affected the size and formation of the fault-karst reservoirs. The meteoric water dissolution during episodes I–III in the middle Caledonian Orogeny was critical in the formation of the fault-karst reservoirs. In contrast, organic acid, magmatic-hydrothermal fluid, and Mg-rich high-salinity fluid had a negligible effect on the development of these reservoirs. The impact of meteoric water was likely limited in the strike-slip fault zone due to its short exposure time. The releasing bend, grainstone, and packstone were more conducive than the restraining bend, single fault, wackestone, and mudstone to the development of the fault core and fault damage zone in the strike-slip fault, resulting in meteoric water dissolution. The size of the fault-karst reservoir increased from south to north due to the onlap of Upper Ordovician strata in the north. The formation mechanism and development pattern of fault-karst reservoirs in the study area provide information for the analysis of carbonate reservoirs formed under similar conditions.
{"title":"Characteristics and origin of the ultradeep Ordovician fault-karst reservoirs: An example from the Shunbei-Yuejin area, Tarim Basin","authors":"Jian Wang, Xintong Wang, Yingchang Cao, Fang Hao, Yuhan Pang, Lu Yun, Haijun Yang, Mingfeng Xie","doi":"10.1306/10052321152","DOIUrl":"https://doi.org/10.1306/10052321152","url":null,"abstract":"Fault-controlled reservoirs are critical hydrocarbon-bearing reservoirs in carbonate rocks. The ultradeep Ordovician fault-karst reservoirs in the Tarim Basin are representative carbonate reservoirs whose formation was controlled by tectonics. An integrated analysis of seismic, drilling, logging, and core data and the petrology and geochemistry of the area suggest that the strike-slip fault, lithology, and diagenetic fluids affected the size and formation of the fault-karst reservoirs. The meteoric water dissolution during episodes I–III in the middle Caledonian Orogeny was critical in the formation of the fault-karst reservoirs. In contrast, organic acid, magmatic-hydrothermal fluid, and Mg-rich high-salinity fluid had a negligible effect on the development of these reservoirs. The impact of meteoric water was likely limited in the strike-slip fault zone due to its short exposure time. The releasing bend, grainstone, and packstone were more conducive than the restraining bend, single fault, wackestone, and mudstone to the development of the fault core and fault damage zone in the strike-slip fault, resulting in meteoric water dissolution. The size of the fault-karst reservoir increased from south to north due to the onlap of Upper Ordovician strata in the north. The formation mechanism and development pattern of fault-karst reservoirs in the study area provide information for the analysis of carbonate reservoirs formed under similar conditions.","PeriodicalId":7124,"journal":{"name":"AAPG Bulletin","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141508326","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Lacustrine organic-rich shales have recently become important petroleum exploration targets. Adequate reservoir characterization is vital for determining the potential for shale oil exploration and development. Fluid–rock interaction and diagenetic mass transfer in organic-rich shales are essential processes during shale oil reservoir formation. Based on detailed petrographic investigation, in situ element and isotope measurement, and organic geochemistry analysis, diagenetic mass transfers and related organic–inorganic interactions were investigated using a suite of organic-rich shales from the Triassic Yanchang Formation of the Ordos Basin. Organic-rich shales consist of silt-sized felsic laminae and organic-rich laminae. Silt-sized felsic laminae are dominated mainly by K-feldspar, whereas illite is the most abundant mineral in organic-rich laminae. Authigenic quartz and euhedral pyrite are the major diagenetic minerals in organic-rich laminae, whereas K-feldspar dissolution occurs extensively in silt-sized felsic laminae. Smectite-to-illite conversion has played a significant role in the diagenetic alteration of organic-rich shales. This reaction not only induced overpressure to generate microfractures for authigenic quartz growth but it also provided the required silica source for authigenic quartz precipitation. Petrographic and geochemical evidence indicates that organic acids generated in organic-rich laminae have migrated to silt-sized felsic laminae, and K+ and aqueous SiO2 yielded from K-feldspar dissolution in silt-sized felsic laminae have been transported to organic-rich laminae. Based on organic–inorganic interactions related to authigenic quartz formation, we conclude that the lamina-scale open diagenetic system allows mass transfer to occur at the microscale within shales. The lamina-scale diagenetic mass transfer and material redistribution may contribute significantly to effective pore space formation in shales.
{"title":"Lamina-scale diagenetic mass transfer in lacustrine organic-rich shales and impacts on shale oil reservoir formation","authors":"Yingchang Cao, Kelai Xi, Xiaobing Niu, Miruo Lin, Weijiao Ma, Zehan Zhang, Helge Hellevang","doi":"10.1306/12212323018","DOIUrl":"https://doi.org/10.1306/12212323018","url":null,"abstract":"Lacustrine organic-rich shales have recently become important petroleum exploration targets. Adequate reservoir characterization is vital for determining the potential for shale oil exploration and development. Fluid–rock interaction and diagenetic mass transfer in organic-rich shales are essential processes during shale oil reservoir formation. Based on detailed petrographic investigation, in situ element and isotope measurement, and organic geochemistry analysis, diagenetic mass transfers and related organic–inorganic interactions were investigated using a suite of organic-rich shales from the Triassic Yanchang Formation of the Ordos Basin. Organic-rich shales consist of silt-sized felsic laminae and organic-rich laminae. Silt-sized felsic laminae are dominated mainly by K-feldspar, whereas illite is the most abundant mineral in organic-rich laminae. Authigenic quartz and euhedral pyrite are the major diagenetic minerals in organic-rich laminae, whereas K-feldspar dissolution occurs extensively in silt-sized felsic laminae. Smectite-to-illite conversion has played a significant role in the diagenetic alteration of organic-rich shales. This reaction not only induced overpressure to generate microfractures for authigenic quartz growth but it also provided the required silica source for authigenic quartz precipitation. Petrographic and geochemical evidence indicates that organic acids generated in organic-rich laminae have migrated to silt-sized felsic laminae, and K+ and aqueous SiO2 yielded from K-feldspar dissolution in silt-sized felsic laminae have been transported to organic-rich laminae. Based on organic–inorganic interactions related to authigenic quartz formation, we conclude that the lamina-scale open diagenetic system allows mass transfer to occur at the microscale within shales. The lamina-scale diagenetic mass transfer and material redistribution may contribute significantly to effective pore space formation in shales.","PeriodicalId":7124,"journal":{"name":"AAPG Bulletin","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141522789","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ping Gao, Xianming Xiao, Dongfeng Hu, Gary G. Lash, Ruobing Liu, Baoyue Zhang, Yanming Zhao
The lower Cambrian and lower Silurian shale reservoirs of southern China display significant differences in pore characteristics that may reflect the varying effects of silica diagenesis. The lower Cambrian and lower Silurian mudstone samples from the middle–upper Yangtze platform were analyzed to elucidate silica diagenetic modifications, including their influences on pore evolution. Quartz of the studied mudstone samples includes detrital quartz, overgrowths, siliceous skeletal fragments, microquartz aggregates, silica nanospheres, and matrix-dispersed microquartz. Much of the authigenic silica precipitated in association with diagenetic alteration of the studied deposits appears to have been derived from dissolution of siliceous skeletal fragments and the smectite–illite reaction. A paucity of siliceous organisms populating the early Cambrian ocean gave rise to more complicated silica diagenetic pathways during alteration. Silica precipitation from silica-rich seawater/pore water and silica replacement by carbonate/carbonate-fluorapatite may have supplemented diagenetic modification of lower Cambrian mudstone. The species types of organisms that contributed skeletal grains to the sediments and the amount of precipitated authigenic quartz appear to have impacted organic pore evolution. The abundance of early Cambrian benthic siliceous sponge spicules appears to have muted formation of rigid microquartz aggregates and silica nanospheres that would have shielded organic pores. In contrast, the early Silurian bloom of planktonic radiolarians was associated with accumulation of organic-rich siliceous mudstone and the formation of abundant microquartz aggregates and silica nanospheres that shielded organic pores during burial. In summary, the amount and type of diagenetic quartz influenced pore characteristics of lower Cambrian and lower Silurian shale reservoir rocks of southern China.
{"title":"Comparison of silica diagenesis between the lower Cambrian and lower Silurian shale reservoirs in the middle–upper Yangtze platform (southern China)","authors":"Ping Gao, Xianming Xiao, Dongfeng Hu, Gary G. Lash, Ruobing Liu, Baoyue Zhang, Yanming Zhao","doi":"10.1306/01242422096","DOIUrl":"https://doi.org/10.1306/01242422096","url":null,"abstract":"The lower Cambrian and lower Silurian shale reservoirs of southern China display significant differences in pore characteristics that may reflect the varying effects of silica diagenesis. The lower Cambrian and lower Silurian mudstone samples from the middle–upper Yangtze platform were analyzed to elucidate silica diagenetic modifications, including their influences on pore evolution. Quartz of the studied mudstone samples includes detrital quartz, overgrowths, siliceous skeletal fragments, microquartz aggregates, silica nanospheres, and matrix-dispersed microquartz. Much of the authigenic silica precipitated in association with diagenetic alteration of the studied deposits appears to have been derived from dissolution of siliceous skeletal fragments and the smectite–illite reaction. A paucity of siliceous organisms populating the early Cambrian ocean gave rise to more complicated silica diagenetic pathways during alteration. Silica precipitation from silica-rich seawater/pore water and silica replacement by carbonate/carbonate-fluorapatite may have supplemented diagenetic modification of lower Cambrian mudstone. The species types of organisms that contributed skeletal grains to the sediments and the amount of precipitated authigenic quartz appear to have impacted organic pore evolution. The abundance of early Cambrian benthic siliceous sponge spicules appears to have muted formation of rigid microquartz aggregates and silica nanospheres that would have shielded organic pores. In contrast, the early Silurian bloom of planktonic radiolarians was associated with accumulation of organic-rich siliceous mudstone and the formation of abundant microquartz aggregates and silica nanospheres that shielded organic pores during burial. In summary, the amount and type of diagenetic quartz influenced pore characteristics of lower Cambrian and lower Silurian shale reservoir rocks of southern China.","PeriodicalId":7124,"journal":{"name":"AAPG Bulletin","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141170783","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Trace element paleoenvironmental proxies were used to constrain depositional environments for several black shales of the midcontinent United States to better understand the formation of metalliferous shales. These shales range in age from Cambrian to Pennsylvanian. The proxies evaluated were for paleoredox (U/Th, U-[Th/3], Ni/Co, V/Cr, V/[V+Ni], Mo concentration, Mo/total organic carbon), basin restriction (Cd/Mo, Co × Mn) and paleosalinity (Sr/Ba). The results of the paleoredox proxies indicate a range of depositional conditions from oxic to dysoxic to anoxic. The findings suggest that the Cambrian Mt. Simon, Eau Claire, and Tunnel City samples in the northern part of the study area were deposited under oxic marine conditions influenced by upwelling. The Ordovician black shales from the Ouachita Mountains and the Pennsylvanian shales from the Cherokee and Forest City Basins were likely formed under anoxic, open marine conditions. The basin restriction and paleoredox proxies suggest decreasing oxygen levels during the deposition of the Ordovician shales, whereas the paleosalinity proxy, the Sr/Ba ratios, during this time suggests decreasing salinity. The Devonian Chattanooga Shale from the Ozark Dome and the New Albany Shale from the Illinois Basin were likely deposited under similar anoxic to dysoxic conditions. Paleoredox proxies suggest that the Mississippian Fayetteville Shale in the Ozark Dome formed under a range of oxic to anoxic conditions. Similarly, the Pennsylvanian Atoka and Jackfork Formations in the Ouachitas were deposited under oxic marine conditions. The results of this study also highlight the importance of using multiple proxies to interpret paleoenvironments.
{"title":"Paleoenvironmental constraints on Paleozoic shale deposition in the midcontinent United States","authors":"Noah Morris, Adriana Potra, John R. Samuelsen","doi":"10.1306/03212422156","DOIUrl":"https://doi.org/10.1306/03212422156","url":null,"abstract":"Trace element paleoenvironmental proxies were used to constrain depositional environments for several black shales of the midcontinent United States to better understand the formation of metalliferous shales. These shales range in age from Cambrian to Pennsylvanian. The proxies evaluated were for paleoredox (U/Th, U-[Th/3], Ni/Co, V/Cr, V/[V+Ni], Mo concentration, Mo/total organic carbon), basin restriction (Cd/Mo, Co × Mn) and paleosalinity (Sr/Ba). The results of the paleoredox proxies indicate a range of depositional conditions from oxic to dysoxic to anoxic. The findings suggest that the Cambrian Mt. Simon, Eau Claire, and Tunnel City samples in the northern part of the study area were deposited under oxic marine conditions influenced by upwelling. The Ordovician black shales from the Ouachita Mountains and the Pennsylvanian shales from the Cherokee and Forest City Basins were likely formed under anoxic, open marine conditions. The basin restriction and paleoredox proxies suggest decreasing oxygen levels during the deposition of the Ordovician shales, whereas the paleosalinity proxy, the Sr/Ba ratios, during this time suggests decreasing salinity. The Devonian Chattanooga Shale from the Ozark Dome and the New Albany Shale from the Illinois Basin were likely deposited under similar anoxic to dysoxic conditions. Paleoredox proxies suggest that the Mississippian Fayetteville Shale in the Ozark Dome formed under a range of oxic to anoxic conditions. Similarly, the Pennsylvanian Atoka and Jackfork Formations in the Ouachitas were deposited under oxic marine conditions. The results of this study also highlight the importance of using multiple proxies to interpret paleoenvironments.","PeriodicalId":7124,"journal":{"name":"AAPG Bulletin","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141170782","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The CO2-gas reservoirs have been recorded in many petroliferous basins worldwide. However, the impact of deep inorganic CO2 influx on reservoir quality has received little attention. Here, a new set of mineralogical and geochemical data collected from the Lower Cretaceous Quantou Formation sandstones in the southern Songliao Basin are presented to address this issue. The sandstones were broadly subdivided into two zones based on their mineralogical compositions: (1) a normal zone with higher porosity (average 13.7%) and permeability (average 3.27 md) that is located >10 km from the Gudian fault (composed of ferrocalcite, ankerite, quartz, mixed-layer illite/smectite (I/S), kaolinite, illite, and chlorite); and (2) a dawsonite-bearing zone with relatively poor reservoir quality (average 10.1% and 0.4 md) adjacent to the Gudian fault (consisting of dawsonite, ankerite, quartz, I/S, and illite). The carbon sources for dawsonite and ankerite in the dawsonite-bearing zone (δ13C = −5.7‰ to −0.8‰ and δ18O = −20.6‰ to −17.1‰, and Sr = 0.710216–0.712472) are mostly a mix of mantle magmatic CO2 and crustal CO2, with a small amount of organic CO2, which is the opposite of that for the ferrocalcite and ankerite in the normal zone (δ13C = −10.5‰ to −2.3‰, δ18O = −19.3‰ to −14.9‰, and Sr = 0.712060–0.714030). Observations of the dawsonite-bearing zone demonstrate higher contents of carbonate and quartz cements, specific clay mineral types (mixed-layer I/S with Reichweite order of R = 3 and illite), and poor reservoir quality and oil productivity due to the influx of deep inorganic CO2 dating to circa 65–44 Ma.
{"title":"Impact of CO2 influx on sandstone reservoir quality: A case study of the Quantou Formation, southern Songliao Basin, China","authors":"Zheng Cao, Chengyan Lin, Chunmei Dong, Lihua Ren, Keyu Liu, Karem Azmy, Hairuo Qing, Jason Cosford","doi":"10.1306/03052418150","DOIUrl":"https://doi.org/10.1306/03052418150","url":null,"abstract":"The CO2-gas reservoirs have been recorded in many petroliferous basins worldwide. However, the impact of deep inorganic CO2 influx on reservoir quality has received little attention. Here, a new set of mineralogical and geochemical data collected from the Lower Cretaceous Quantou Formation sandstones in the southern Songliao Basin are presented to address this issue. The sandstones were broadly subdivided into two zones based on their mineralogical compositions: (1) a normal zone with higher porosity (average 13.7%) and permeability (average 3.27 md) that is located >10 km from the Gudian fault (composed of ferrocalcite, ankerite, quartz, mixed-layer illite/smectite (I/S), kaolinite, illite, and chlorite); and (2) a dawsonite-bearing zone with relatively poor reservoir quality (average 10.1% and 0.4 md) adjacent to the Gudian fault (consisting of dawsonite, ankerite, quartz, I/S, and illite). The carbon sources for dawsonite and ankerite in the dawsonite-bearing zone (δ13C = −5.7‰ to −0.8‰ and δ18O = −20.6‰ to −17.1‰, and Sr = 0.710216–0.712472) are mostly a mix of mantle magmatic CO2 and crustal CO2, with a small amount of organic CO2, which is the opposite of that for the ferrocalcite and ankerite in the normal zone (δ13C = −10.5‰ to −2.3‰, δ18O = −19.3‰ to −14.9‰, and Sr = 0.712060–0.714030). Observations of the dawsonite-bearing zone demonstrate higher contents of carbonate and quartz cements, specific clay mineral types (mixed-layer I/S with Reichweite order of R = 3 and illite), and poor reservoir quality and oil productivity due to the influx of deep inorganic CO2 dating to circa 65–44 Ma.","PeriodicalId":7124,"journal":{"name":"AAPG Bulletin","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141193396","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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