94 results on '"lower silurian"'
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2. Microscopic pore and fracture evolution characteristics and influencing factors during imbibition process of shale reservoirs: a case study of the first section of the first member of Longmaxi Formation, western Chongqing area, Sichuan Basin
- Author
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Ji'an QIAN, Yuqiang JIANG, Tongtong LUO, Yixiao YANG, Yonghong FU, Weiming CHEN, Chaoya SUN, and Zhanlei WANG
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imbibition process ,pore and fracture evolution ,shale reservoir ,longmaxi formation ,lower silurian ,western chongqing area ,sichuan basin ,Geophysics. Cosmic physics ,QC801-809 ,Geology ,QE1-996.5 - Abstract
Hydraulic fracturing has become an important means for shale gas exploration. Understanding the evolution characteristics and influencing factors of pores and micro-fractures during the imbibition process in shale reservoirs is crucial for optimizing post-fracturing production enhancement measures. This study focuses on the black shale at the base of the first section of the first member of the Longmaxi Formation (Long 1-1 sub-member), the main production layer in the Dazu area, western Chongqing area of the Sichuan Basin. Argon ion polishing and field-emission scanning electron microscopy (FE-SEM) experiments were conducted at fixed sites to observe the evolution pattern of microscopic pores and fractures in shale reservoirs at various stages of water imbibition process. The findings revealed: (1) After water imbibition for 7 days, organic pores at the edges of organic matter exhibited varying degrees of reduction, while the internal pore shapes and sizes remained largely unchanged. (2) Intragranular dissolution pores and intergranular pores exhibited noticeable dissolution effects, resulting in mineral particle dissolution and detachment, which increased the leakage area for shale gas. (3) The water imbibition did not induce a significant amount of new micro-fractures. Instead, it extended existing micro-fractures, with the fracture width expanding by 5 to 10 times after imbibition for 14 days. (4) The surface porosity of the shale reservoir reached its peak value at day 7 of water imbibition. After 7 days, due to the continuous swelling of clay minerals, micro-fracture widths experienced varying degrees of reduction. (5) The intensity of pore and fracture expansion in shale reservoirs was primarily affected by mineral composition and pore permeability properties. Higher contents of unstable minerals and brittle minerals with larger particle sizes led to more pronounced pore expansion effects, which were conducive to post-fracturing shale gas seepage.
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- 2024
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3. Fracture features and fault influence on gas accumulation in the Longmaxi Formation in Changning block, southern Sichuan Basin
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Bo Li, Shengxian Zhao, Yongyang Liu, Xuefeng Yang, Yong Liu, Jian Zhang, Chenglin Zhang, Jiajun Li, Gaoxiang Wang, and Meixuan Yin
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Changning ,Lower silurian ,Longmaxi formation ,Shale gas ,Preservation conditions ,Gas industry ,TP751-762 - Abstract
The Lower Silurian Longmaxi Formation is a major horizon for shale gas development in the Changning block in Sichuan Basin. In this study, the fracture features in the Longmaxi Formation in the Changning block were investigated through outcrop observation, core description, inclusion testing, and Fullbore Formation MicroImage logging. The results showed that tectogenetic shear fractures dominated the Longmaxi Formation, with maximum principal stress in the SSW, NW, and NE directions. According to fracture features and stress analysis, three phases of faults were generated by tectonic movements after the buried depth reached a maximum in the study area: phase 1 nearly EW-trending faults formed in the middle-late Yanshanian, phase 2 NE-trending faults formed from the end of the Yanshanian to the early Himalayan, and phase 3 NW-trending faults formed from the middle Himalayan to the present. According to the regression analysis of the tested shale gas production and faults, the faults with a throw of > 200 m could have a great effect on gas production, and high-yield wells were generally located over 1 km away from faults. Based on the dissection of tectonic styles and typical wells drilled in the Changning block, three shale gas accumulation models were established: wide gentle syncline + internal smalxl fault, subdued anticline + large fault, and slope + internal fault. The study reveals the mechanism of fault influence on shale gas accumulation in the Longmaxi Formation in the Changning block and provides a reference for efficient shale gas production in the Sichuan Basin.
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- 2024
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4. Insights into the Co-Exploration Potential of Gas in the Shale and Tight Sandstone of the Lower Silurian Formation in the Gongtan Syncline Area in Southeastern Sichuan Basin, SW China.
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Wang, Shengxiu, Zhang, Ye, Wang, Wei, Yang, Yang, Wang, Qiaoli, Yu, Chuan, Zhao, Difei, Zeng, Chunlin, and Xu, Yao
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OIL shales , *GEOLOGICAL formations , *SANDSTONE , *PERMEABILITY , *SHALE - Abstract
This work aims to explore the Lower Silurian shale gas and tight sandstone gas accumulation conditions in the Gongtan Syncline, southeastern Sichuan Basin. The sedimentary environment, organic geochemical characteristics, reservoir characteristics, gas content, and preservation conditions of the reservoir were comprehensively analyzed. The results show that the Wufeng–Longmaxi Formation shale formed in a deep-water shelf characterized by a large thickness (50–70 m), appropriate total organic carbon content (0.5–5.47%), high maturity (2.38%), high brittle mineral content (67.10%), and large gas content (0.71–1.64 m3/t), and the formations show the good resource potential of the shale gas. The Xintan Formation formed in a lower shore phase, and the tight sandstone is locally developed with a small thickness. The Xiaoheba Formation formed in an upper-middle shore phase, and the tight sandstone is stably distributed with large thicknesses. The porosity and permeability of the two sets of sandstone are small and some natural fractures are developed in the sandstone, but the fracture filling degree is higher. The results of well logging show that there are abnormally high values of total hydrocarbon in both the Xintan Formation and Xiaoheba Formation; this indicates that tight sandstone gas is developed in the Lower Silurian strata. A comprehensive study indicates that the Lower Silurian of the Gongtan Syncline has the geological conditions for the formation of shale gas and tight sandstone gas, which are the "Two gases" with good co-exploration prospects. [ABSTRACT FROM AUTHOR]
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- 2024
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5. Characteristics and formation stages of natural fractures in Lower Silurian Longmaxi Formation in Tiangongtang area of Sichuan Basin
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Linhao LI, Cunhui FAN, Shengxian ZHAO, Shaojun LIU, Fei XU, Shan NIE, and Yawei YU
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shale fracture ,fracture characteristic ,tectonic stage ,longmaxi formation ,lower silurian ,sichuan basin ,Geophysics. Cosmic physics ,QC801-809 ,Geology ,QE1-996.5 - Abstract
The Lower Silurian Longmaxi Formation on the southwestern margin of the Sichuan Basin holds significant shale gas reserves. The characteristics and formation stages of fractures play a crucial role in shale gas accumulation and productivity. Focusing on the Longmaxi Formation in the Tiangongtang area, this study employed core analysis, FMI (Formation Micro-Imager) logging, rock acoustic emission experiments, carbon-oxygen isotope analysis of fracture fillings, fluid inclusion homogenization temperature testing, and burial-thermal evolution history analysis to investigate the development characteristics and formation periods of natural fractures in the shale. The results indicate that the natural fractures in the Longmaxi Formation in the study area are characterized by the coexistence of tectonic vertical and low-angle fractures. The core fractures exhibit high development density, short extension, and high filling degree. Comparison of imaging log fracture dip angles, core fracture cross-cutting relationships, fracture filling fluid inclusion tests, and rock acoustic emission experiments suggested that the fractures in the Longmaxi Formation in the Tiangongtang area were associated with three tectonic events. Combined with burial-thermal evolution history analysis, the formation periods were confirmed as follows: the first stage involved NW-oriented and NNE-oriented planar shear fractures, and NEE-oriented cross-sectional shear fractures formed during the mid-late Yanshanian period (130-62 Ma) with tectonic stress orientation near SN (345°±5°) and inclusion homogenization temperatures of 185-206 ℃; the second stage involved NE-oriented and NW-oriented planar shear fractures, and NNW-trending cross-sectional shear fractures formed during the late Yanshanian to mid-Himalayan period (62-34 Ma) with tectonic stress orientation near EW (80°±5°) and inclusion homogenization temperatures of 165-184 ℃; the third stage involved near SN-oriented and NEE-oriented planar shear fractures, and NE-oriented cross-sectional shear fractures formed from the mid-Himalayan period to present (34 Ma to present) with tectonic stress orientation near NW (315°±5°) and inclusion homogenization temperatures of 125-162 ℃. Based on the geomechanical background, a three-stage tectonic fracture evolution model for the Longmaxi Formation in the Tiangongtang area was established.
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- 2024
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6. 四川盆地天宫堂地区下志留统龙马溪组天然裂缝特征及形成期次.
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李林豪, 范存辉, 赵圣贤, 刘绍军, 徐飞, 聂珊, and 余亚伟
- Abstract
Copyright of Petroleum Geology & Experiment is the property of Petroleum Geology & Experiment Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
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- 2024
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7. A world-class source rock in southern China formed during the periods from Katian to Rhuddanian: Biostratigraphic distribution, depositional model and shale gas potential.
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Nie, Haikuan, Li, Pei, Chen, Qing, Jin, Zhijun, Liu, Quanyou, Dang, Wei, Chen, Qian, Ding, Jianghui, and Zhai, Changbo
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[Display omitted] • Organic-rich shales mainly formed from late Katian to early-middle Rhuddanian. • Occurrence pattern of organic-rich shales within graptolite biozones was delineated. • Graptolite biozones are crucial in evaluating gas-enriched, productive intervals. Typical outcrops and shale gas wells from the upper Ordovician (Katian and Hirnantian) Wufeng Formation to the lower Silurian (Rhuddanian) Longmaxi Formation in the Sichuan Basin of southern China were selected to investigate the shale quality and shale gas potential. The chronostratigraphy was studied based on the graptolite biozones and well logging. The sedimentary environment, depositional facies, biostratigraphic distribution, depositional model and lithological characteristics were characterized. Organic-rich shale primarily developed in the late Katian to the early–middle Rhuddanian. Two organic-rich shale depocentres were identified in the southern and eastern-north-eastern Sichuan Basin. The spatial distribution of organic-rich shale of different graptolite biozones was determined and showed gradual migration northwest. The depocentre of the Dicellograptus complexus Biozone to the Cystograptus vesiculosus Biozone was controlled by paleo-uplift and a submarine high. The black shale typically lacks some graptolite biozones, and even if it is fully developed, the thickness of organic-rich shale is thin and has a poor shale gas source potential. The control effect of the graptolite biozone on shale-gas-enrichment helps to evaluate the shale-gas-enriched and productive intervals accurately. This study characterises the organic-rich shale distribution in the Sichuan Basin and helps in assessing organic-rich shale and identifying sweet spots of shale gas potential. [ABSTRACT FROM AUTHOR]
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- 2024
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8. Characteristics of the deep and ultra-deep shale reservoirs of the Wufeng-Longmaxi formations in the southeastern Sichuan Basin and the significance of shale gas exploration
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Fubin WEI, Zhujiang LIU, Feiran CHEN, Tao YUAN, and Fei LI
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shale reservoir ,deep and ultra-deep shale gas ,wufeng-longmaxi formations ,upper ordovician ,lower silurian ,southeastern sichuan basin ,Geophysics. Cosmic physics ,QC801-809 ,Geology ,QE1-996.5 - Abstract
Fruitful achievements have been made in shale gas exploration in the middle and deep areas from the Upper Ordovician Wufeng Formation to the Lower Silurian Longmaxi Formation in the southeastern Sichuan Basin, and in the research on shale reservoir characteristics and main controlling factors. As the key direction of current shale exploration, the deep and ultra-deep areas are limited by drilling and other factors, and the research on reservoir development characteristics and differences with the middle and deep shale reservoirs is insufficient. In order to clarify the characteristics of the deep and ultra-deep shale reservoirs of the Wufeng-Longmaxi formatiosns, four typical shale gas wells at the depth of 2 000-6 000 m in the southeastern Sichuan exploration area were selected to systematically carry out a comparative study of deep and ultra-deep shale reservoir development characteristics and differences, and the causes of pore development were discussed. The results show that: (1) With a burial depth of less than 6 000 m, the shale reservoirs of the Wufeng-Longmaxi formations are effective reservoirs with high porosity, and the porosity has no obvious change with the change of burial depth. However, there are certain differences in the morphology, structure and connectivity of organic matter pores, that is, with the increase of burial depth, the size of organic matter pores relatively decreases, and the pore connectivity deteriorates; (2) It has been clarified that biogenic silica is the foundation of pore development, and fluid overpressure is the key to maintaining reservoir pores. Under the combined action of biogenic silica and biogenic silica, the deep and ultra-deep shale reservoirs with high porosity and high quality can be developed and maintained; (3) Based on the research of reservoir development, shale gas exploration will be extended to 6 000 m, which provides a clear direction for shale gas exploration in the next step. It is preliminarily assessed that the deep and ultra-deep shale gas (buried depth of 4 000-5 000 m) resources in the Wufeng-Longmaxi formations in the Sichuan Basin and its surrounding areas exceed 2×1012 m3.
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- 2023
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9. Insights into the Co-Exploration Potential of Gas in the Shale and Tight Sandstone of the Lower Silurian Formation in the Gongtan Syncline Area in Southeastern Sichuan Basin, SW China
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Shengxiu Wang, Ye Zhang, Wei Wang, Yang Yang, Qiaoli Wang, Chuan Yu, Difei Zhao, Chunlin Zeng, and Yao Xu
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Gongtan Syncline ,Lower Silurian ,shale gas ,tight sandstone gas ,gas co-exploration ,Technology - Abstract
This work aims to explore the Lower Silurian shale gas and tight sandstone gas accumulation conditions in the Gongtan Syncline, southeastern Sichuan Basin. The sedimentary environment, organic geochemical characteristics, reservoir characteristics, gas content, and preservation conditions of the reservoir were comprehensively analyzed. The results show that the Wufeng–Longmaxi Formation shale formed in a deep-water shelf characterized by a large thickness (50–70 m), appropriate total organic carbon content (0.5–5.47%), high maturity (2.38%), high brittle mineral content (67.10%), and large gas content (0.71–1.64 m3/t), and the formations show the good resource potential of the shale gas. The Xintan Formation formed in a lower shore phase, and the tight sandstone is locally developed with a small thickness. The Xiaoheba Formation formed in an upper-middle shore phase, and the tight sandstone is stably distributed with large thicknesses. The porosity and permeability of the two sets of sandstone are small and some natural fractures are developed in the sandstone, but the fracture filling degree is higher. The results of well logging show that there are abnormally high values of total hydrocarbon in both the Xintan Formation and Xiaoheba Formation; this indicates that tight sandstone gas is developed in the Lower Silurian strata. A comprehensive study indicates that the Lower Silurian of the Gongtan Syncline has the geological conditions for the formation of shale gas and tight sandstone gas, which are the “Two gases” with good co-exploration prospects.
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- 2024
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10. Analysis on distribution and main controlling factors of OM carbonization in marine shale in the Sichuan Basin of China and its periphery
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Yuman Wang, Guoqi Wei, Junjun Shen, Zhen Qiu, Xinjing Li, Qin Zhang, Leifu Zhang, Canhui Wang, and Wen Liu
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Sichuan Basin ,Lower Cambrian ,Lower Silurian ,Thermal maturity ,Carbonification of organic matters ,Low resistance response ,Gas industry ,TP751-762 - Abstract
The distribution and main controlling factors of the organic matter carbonization points/zones of over-mature marine shale are important issues for shale gas exploration. This paper focuses on the Lower Cambrian and Lower Silurian shales in the Sichuan Basin and its periphery. Based on the detailed anatomy of key carbonization zones, predictions of shale organic matter carbonization zones and regional mapping of thermal maturity are carried out to explore and reveal the distribution and main controlling factors of the carbonization zones of organic matter in the two sets of shales. Four preliminary conclusions were obtained: (1) There are four organic matter carbonization zones in the Lower Silurian shale distribution area, namely eastern Sichuan-western Hubei, northwestern Hubei, west of southern Sichuan, and Renhuai-southwestern Chongqing, covering an area of nearly 40 × 103 km2. The main part of the western carbonization zone in the southern Sichuan is located in the Emei basalt distribution area. (2) The organic matter carbonization zone accounts for more than 80% of the Lower Cambrian shale distribution area, The non-carbonization zone is only distributed in Weiyuan-Ziyang, Moxi-Gaoshiti, Changyang, and Weng'an-Zhenyuan with an area of about 62.6 × 103 km2. (3) The Lower Silurian and Lower Cambrian shales in the west of southern Sichuan experienced an increase in thermal maturity RO values of 0.2%–0.4% and 0.2%–1.0%, respectively, as a result of the Emei large igneous province, an extreme heat event in the Late Permian. The Lower Cambrian and Lower Silurian shales have the highest degree of carbonization of organic matter in Mabian-Ebian, which is also in the high-value area of the Emei basalt thickness. (4) The main controlling factors of organic matter carbonization of the Lower Cambrian and Lower Silurian shales have similarities and differences. The main controlling factor of the former is the long-term deep burial background, and the extreme thermal event in the Late Permian only exacerbated the degree of carbonization in some areas more seriously. The latter's main controlling factors are relatively complex and are controlled by deep burial background in the three regions of Renhuai-southwestern Chongqing, eastern Sichuan-western Hubei, and northwestern Hubei. It was governed by a deep burial background and a high geotemperature in the Late Permian.
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- 2022
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11. Pore types and microstructure of the black shale in the Lower Silurian, Southeast of Chongqing, China
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Juan Li, Yukun Tian, Shan Chen, Hui Zhou, Huanpeng Chi, Yanyan Ma, and Liyun Kong
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black shale ,pore type ,microfractures ,Lower Silurian ,Southeast of Chongqing ,Science - Abstract
The Lower Silurian black shale in the Southeast of Chongqing is of great potential in the accumulation of shale gas in South China. In order to understand the pore system of these black shales, mercury porosimetry, surface area study, mineralogy and image analyses by scanning electronic microscopy were performed. Four major pore types (interparticle pores, intraparticle pores, organic-matter pores and microfractures) were classified under the observation of the samples. Interparticle pores, which associate with mineral particles and mostly in micro-scale, can be subdivided into pores among rigid particles, ductile particles, and rigid-ductile particles. Intraparticle pores, which can be subdivided into cleavage-plane pores within clay minerals, intercrystalline pores within pyrite framboids and pores formed by partial or complete dissolution, are in nanometer scale and more common exist in unweathered rocks. Organic-matter pores are one type of intraparticle pores which are found within organic matter and appear to be prone to form effective networks and main permeable pathway. The rocks are abundant with microfractures where absorbed gas can be transformed to free gas. Microfractures which are partly cemented by residual organic residue are of great importance. Comparing the two sets of samples from Lujiao section and Well Yuye-1, we note that the outcrop samples from Lujiao section have much more interparticle pores than core samples, while the latter own more intraparticle pores. The results of quantitative and visual qualitative analyses about the gas shale reservoir pore system are similar. With the increasing of quartz, the number of interparticle pores and macropores increase. And intraparticle pores and micro-mesopores increase with clay minerals.
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- 2023
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12. Basic characteristics of key interfaces in Upper Ordovician Wufeng Formation – Lower Silurian Longmaxi Formation in Sichuan Basin and its periphery, SW China
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Yuman WANG, Hongyan WANG, Zhen QIU, Junjun SHEN, Qin ZHANG, Leifu ZHANG, Canhui WANG, and Xinjing LI
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Sichuan Basin ,Upper Ordovician ,Wufeng Formation ,Lower Silurian ,Longmaxi Formation ,Guanyinqiao Member ,Petroleum refining. Petroleum products ,TP690-692.5 - Abstract
Based on anatomy of key areas and data points and analysis of typical features of shell layer in Guanyinqiao Member, basic characteristics of key interfaces, mainly bentonite layers, in the Upper Ordovician Wufeng Formation—Lower Silurian Longmaxi Formation in the Sichuan Basin and its surrounding areas and the relationship between these key interfaces with the deposition of organic-rich shale have been examined systematically. The Wufeng Formation—Longmaxi Formation has four types of marker beds with interface attributes, namely, the characteristic graptolite belt, Guanyinqiao Member shell layer, section with dense bentonite layers, and concretion section, which can be taken as key interfaces for stratigraphic division and correlation of the graptolite shale. The shell layer in Guanyinqiao Member is the most standard key interface in Wufeng Formation—Longmaxi Formation, and can also be regarded as an important indicator for judging the depositional scale of organic-rich shale in key areas. There are 8 dense bentonite sections of two types mainly occurring in 7 graptolite belts in these formations. They have similar interface characteristics with the shell layer in Guanyinqiao Member in thickness and natural gamma response, and belong to tectonic interfaces (i.e., event deposits). They have three kinds of distribution scales: whole region, large part of the region, and local part, and can be the third, fourth and fifth order sequence interfaces, and have a differential control effect on organic-rich shale deposits. The horizon the characteristic graptolite belt occurs first is the isochronous interface, which is not directly related to the deposition of organic-rich shale. Concretions only appear in local areas, and show poor stability in vertical and horizontal directions, and have no obvious relationship with the deposition of the organic-rich shale.
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- 2022
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13. Characteristics of methane isothermal adsorption of deep shale from Lower Silurian Longmaxi Formation in southeastern Sichuan Basin and its geological significance
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Qiang WANG, Yapeng MU, Xian CHEN, Zhenxiang SONG, Zhongliang MA, and Qi QIU
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isothermal adsorption ,absolute adsorption capacity ,deep shale gas ,longmaxi formation ,lower silurian ,southeast sichuan basin ,Geophysics. Cosmic physics ,QC801-809 ,Geology ,QE1-996.5 - Abstract
Breakthrough of the exploration of deep shale gas in the Sichuan Basin, Southwest China, has been achieved for decades, there are still some controversies about the adsorption performance and occurrence state of shale gas in deep strata. Isothermal adsorption experiments were carried out under high temperature and high pressure with typical shale samples from deep stratum of the Lower Silurian Longmaxi Formation in Fuling and Dingshan areas in the southeastern Sichuan Basin. Results show that there is a big difference between absolute adsorption and excess adsorption, thus, it is proposed that the excess adsorption capacity should be corrected to the absolute adsorption capacity when evaluating the adsorption performance of deep shale gas. After correction, the variation of absolute shale adsorption with pressure appeared to have three stages including "rapid rise", "slow rise" and "steady rise". The absolute adsorption capacity of deep shale samples from Fuling and Dingshan areas is higher than 2.0 m3/t at 110℃ and 70 MPa, and combined with the adsorption and free gas ratios of deep shale, the total gas content is more than 4.0 m3/t, indicating that deep shale may still have good adsorption performance under high temperature and high pressure. The evaluation of deep shale adsorption capacity can provide reliable parameters for the study of shale gas content and the evaluation of resource potential and reserve for shale gas. Considering the difference of ratio of free gas to adsorbed gas between deep shale and shallow-medium shale, different exploration and production methods can be adopted to effectively improve the production capacity and production cycle of shale gas.
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- 2022
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14. Co-occurring characteristics of pore gas and water in shales: a case study of the Lower Silurian Longmaxi Formation in the southeastern Sichuan Basin
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Lingjie YU, Keyu LIU, Ming FAN, and Youxiang LIU
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bounding water ,water vapor adsorption ,monolayer adsorption ,occurrence characteristics ,shale ,longmaxi formation ,lower silurian ,southeastern sichuan basin ,Geophysics. Cosmic physics ,QC801-809 ,Geology ,QE1-996.5 - Abstract
In this paper, the co-occurring characteristics of pore gas and water in the Longmaxi Formation shales in the Sichuan Basin, South China were investigated. Water vapor and methane adsorption by the means of gravimetric methods were carried out to quantitatively determine the behavior of gas and bounding water in micro-nano pores. The impact of the shale compositions and pore structures on the occurring characteristics were discussed. Results showed that the storage capacity of bound water in different types of shales varied dramatically, and the characteristics of bound water could be described by the water vapor adsorption curve and the GAB model. There is an apaprent positive correlation between the maximum monolayer water molecule adsorption capacity and the clay mineral content in shales, indicating that clay minerals provide the main active adsorption sites for water molecules. The adsorption capacity of shale to water molecule is higher than that of methane molecule overall, and methane molecule mainly exist in pores with the form of monolayer adsorption. Bound water, adsorbed gas and free gas could be stored in different pore ranges of different shales. Pores with diameters lower than 2 nm are occupied by bounding water and adsorbed gas. For shales with TOC < 2.5%, free gas would be stored in pores with diameters larger than 5 nm approximately, while for the shales with TOC>2.5%, free gas would be stored in pores with diameters larger than 3 nm approximately. The higher the TOC content, the higher the proportion of the free-gas storage space.
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- 2021
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15. Diagenetic evolution of key minerals and its controls on reservoir quality of Upper Ordovician Wufeng-Lower Silurian Longmaxi shale of Sichuan Basin
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Ruyue WANG, Zongquan HU, Hanyong BAO, Jing WU, Wei DU, Pengwei WANG, Zeyang PENG, and Ting LU
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mineral type ,diagenetic evolution sequence ,shale gas ,wufeng formation ,longmaxi formation ,upper ordovician ,lower silurian ,sichuan basin ,Geophysics. Cosmic physics ,QC801-809 ,Geology ,QE1-996.5 - Abstract
Based on core, thin section, scanning electron microscopy observations, X-ray diffraction analysis, as well as carbon and oxygen isotopes and energy spectrum analysis of carbonate rocks, the quartz, feldspar, pyrite, carbonate and clay minerals in shale of the Upper Ordovician Wufeng-Lower Silurian Longmaxi formations of Sichuan Basin were effectively characterised and classified, and the influences of their diagenetic evolution sequence on the development of shale reservoir were discussed. The results showed that good material basis and unique diagenetic sequence were the key factors for the formation of high-quality shale reservoirs. (1) Framboidal/euhedral pyrite, bio-quartz and microbial dolomite were mainly formed from the syngenetic stage to the A-substage of early diagenetic stage. They were both destructive and constructive for maintaining the original pores in shale, and the constructive supporting framework of which was critical for the formation of high-quality shale reservoir. The rigid framework formed by these early-formed minerals and terrigenous debris facilitated the maintenance of original pores and the reservoir stimulation of shale gas exploitation. (2) The co-evolution of hydrocarbon generation and diagenesis promoted the development of reservoir spaces. In the A-substage of middle diagenetic stage, the production and consumption of organic acids, the dissolution/alteration of unstable minerals (feldspar and carbonate minerals), clay mineral conversion and oil generation from kerogen were synchronic, which provided favorable space for the charging and retention of liquid hydrocarbons during the oil generation period. From the B-substage of middle diagenetic stage to the late diagenetic stage, the shale gas/organic pore generation and pressure increase of kerogen and retained hydrocarbon cracking promoted the development of organic pores and micro-fractures, which was conducive to the enrichment and high production of shale gas.
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- 2021
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16. 云南保山地区下仁和桥组页岩特征、有机质 富集因素及富集模型.
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王瑶琳, 徐胜林, 侯明才, 陈安清, 石坻石, 张 聪, and 覃英伦
- Abstract
Copyright of Petroleum Geology & Oilfield Development in Daqing is the property of Editorial Department of Petroleum Geology & Oilfield Development in Daqing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
- Published
- 2022
- Full Text
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17. 水岩作用对页岩岩石物理性质的影响 ——以四川盆地下志留统龙马溪组页岩为例.
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熊 健, 李羽康, 刘向君, 梁利喜, 丁 乙, and 侯连浪
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SHALE gas ,OIL shales ,SPEED of sound ,WATER-rock interaction ,POROSITY ,WATER immersion - Abstract
Copyright of Natural Gas Industry is the property of Natural Gas Industry Journal Agency and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
- Published
- 2022
- Full Text
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18. 四川盆地及其周缘海相页岩有机质炭化区分布规律与主控因素浅析.
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王玉满, 魏国齐, 沈均均, 邱振, 李新景, 张琴, 张磊夫, 王灿辉, and 刘雯
- Subjects
HEAT waves (Meteorology) ,SHALE gas ,IGNEOUS rocks ,OIL shales ,EARTH temperature ,CARBONIZATION - Abstract
Copyright of Natural Gas Geoscience is the property of Natural Gas Geoscience and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
- Published
- 2022
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- View/download PDF
19. Basic characteristics of key interfaces in Upper Ordovician Wufeng Formation – Lower Silurian Longmaxi Formation in Sichuan Basin and its periphery, SW China.
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WANG, Yuman, WANG, Hongyan, QIU, Zhen, SHEN, Junjun, ZHANG, Qin, ZHANG, Leifu, WANG, Canhui, and LI, Xinjing
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- 2022
- Full Text
- View/download PDF
20. Reservoir characteristics and genetic mechanisms of gas-bearing shales with different laminae and laminae combinations: A case study of Member 1 of the Lower Silurian Longmaxi shale in Sichuan Basin, SW China
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Zhensheng SHI, Dazhong DONG, Hongyan WANG, Shasha SUN, and Jin WU
- Subjects
gas-bearing shale ,lamina ,reservoir characteristics ,genetic mechanism ,Lower Silurian ,Longmaxi Formation ,Petroleum refining. Petroleum products ,TP690-692.5 - Abstract
Based on thin-section, argon-ion polished large-area imaging and nano-CT scanning data, the reservoir characteristics and genetic mechanisms of the Lower Silurian Longmaxi shale layers with different laminae and laminae combinations in the Sichuan Basin were examined. It is found that the shale has two kinds of laminae, clayey lamina and silty lamina, which are different in single lamina thickness, composition, pore type and structure, plane porosity and pore size distribution. The clayey laminae are about 100 μm thick each, over 15% in organic matter content, over 70% in quartz content, and higher in organic pore ratio and plane porosity. They have abundant bedding fractures and organic matter and organic pores connecting with each other to form a network. In contrast, the silty laminae are about 50 μm thick each, 5% to 15% in organic matter content, over 50% in carbonate content, higher in inorganic pore ratio, undeveloped in bedding fracture, and have organic matter and organic pores disconnected from each other. The formation of mud lamina and silt lamina may be related to the flourish of silicon-rich organisms. The mud lamina is formed during the intermittent period, and silt lamina is formed during the bloom period of silicon-rich organisms. The mud laminae and silt laminae can combine into three types of assemblages: strip-shaped silt, gradating sand-mud and sand-mud thin interlayers. The strip-shaped silt assemblage has the highest porosity and horizontal/vertical permeability ratio, followed by the gradating sand-mud assemblage and sand-mud thin interlayer assemblage. The difference in the content ratio of the mud laminae to silt laminae results in the difference in the horizontal/vertical permeability ratio.
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- 2020
- Full Text
- View/download PDF
21. Characteristics of organic matter-hosted pores in Lower Silurian Longmaxi shale with different maturities, Sichuan Basin
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Yunfeng YANG, Fang BAO, Tenger BORJIGIN, Anyang Pan, and Baojian SHEN
- Subjects
organic matter-hosted pore ,thermal maturity ,maceral ,solid bitumen ,shale ,longmaxi formation ,lower silurian ,sichuan basin ,Geophysics. Cosmic physics ,QC801-809 ,Geology ,QE1-996.5 - Abstract
Organic matter-hosted pores provide reservoir space and migration pathways for shale gas. The evolution of organic matter-hosted pores (OM pores) of different macerals from Longmaxi shale with a wide variety of thermal maturities has been investigated using field emission scanning electron microscopy (FE-SEM). The Longmaxi shale contains rare graptolites which are the main component of structured organic matter. No OM pores occur in graptolite fragments, irrespective of thermal maturity. OM pores locally developed in graptolite fragments are formed from hydrocarbon generation of organic matter which was replaced by macromolecular material from surrounding sediment or in situ polymerized by lipids from the organism itself. Solid bitumen is not only the major organic component in the Longmaxi shale, but also the main host of OM pore development. The diagenesis of fine-grained sediments and thermal evolution of organic matter have been combined with the morphology of solid bitumen to distinguish pre-oil solid bitumen and post-oil solid bitumen. The post-oil solid bitumen is dominant. The evolution of OM pores within solid bitumen is closely related to thermal maturity. Generally, OM pores within solid bitumen become greater as thermal maturity increases. During the mature to early postmature (GRo < 2.3%) stages, OM pores within solid bitumen are not well developed probably due to the masking by oil and bitumen generated from organic matter. OM pores within solid bitumen are well developed during the late postmature to early overmature (2.3% < GRo < 4.5%) stages, with two main types being spongy and bubble-shaped. For organic-rich Longmaxi shale, the contribution of OM porosity to total porosity is more than 50%. During the late overmature (GRo>4.5%) stage, organic matter carbonization will cause intense damage to shale pores so that the exploration risk of shale gas increases.
- Published
- 2020
- Full Text
- View/download PDF
22. 水化作用下页岩微观孔隙结构的动态表征 —— 以四川盆地长宁地区龙马溪组页岩为例.
- Author
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曾凡辉, 张 蔷, 陈斯瑜, 郭建春, 范 宇, 任文希, and 王星皓
- Subjects
SHALE gas reservoirs ,CLAY minerals ,WATER temperature ,FRACTURING fluids ,SCANNING electron microscopy ,SHALE gas ,MERCURY - Abstract
Copyright of Natural Gas Industry is the property of Natural Gas Industry Journal Agency and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
- Published
- 2020
- Full Text
- View/download PDF
23. A Lithological and Geochemical Description of Lower Silurian Graptolite Shales (Yangtze Platform, People's Republic of China).
- Author
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Hao Yuexiang, Shardanova, T. A., and Chongxing, Huang
- Abstract
The major lithological rock types that compose the highest-carbon part of the lower Silurian Longmaxi Formation section in the Sichuan province of the People's Republic of China have been identified and characterized. The analyzed distribution of rare and trace elements in graptolite shales has made it possible to propose the redox conditions for high-carbon sedimentation. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
24. 中上扬子地区下志留统龙马溪组有机质碳化区预测.
- Author
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王玉满, 李新景, 王皓, 吴伟, 蒋珊, 陈波, 沈均均, and 周国晓
- Subjects
SHALE gas ,CONTINUOUS distributions ,ORGANIC compounds ,CARBONIZATION ,NATURAL gas prospecting ,IDENTIFICATION ,FUSION reactor blankets - Abstract
Copyright of Natural Gas Geoscience is the property of Natural Gas Geoscience and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
- Published
- 2020
- Full Text
- View/download PDF
25. Differences of Pore Features in Marine Shales between Lower Cambrian and Lower Silurian Formations of Upper Yangtze Area, South China
- Author
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Minghui Li, Mingliang Li, Haiping Huang, Lei Gong, and Debao Zheng
- Subjects
marine shale ,lower Cambrian ,lower Silurian ,pore types ,pore properties ,porosity development mechanism ,Technology - Abstract
Lower Cambrian shale and lower Silurian shale are both typical of oil-prone kerogen and siliceous composition, but different in thermal maturities. Porosity differences were determined in marine shales between the two shales. Measurements were utilized including organic geochemistry, XRD, scanning electron microscopy (SEM) and N2 gas adsorption. Pore volume (PV) of lower Silurian shale was approximately 1.5 times higher than that of lower Cambrian shale, and pore surface area (PSA) of lower Silurian shale was almost 2.5 times higher than that of lower Cambrian shale. Lower Cambrian shale and lower Silurian shale possess similar materials, but distinctive thermal degrees. Evolution mechanisms of different types of pores, especially organic matter (OM)-hosted pores, may trigger this different pore features. Pores of rigid framework are the residue of primary interparticle pores during the burial history. Pores associated with clay flakes can be preserved well adjacent to rigid grains or secondary minerals acting as rigid frameworks or grain supporters. Dissolved pores in both lower Cambrian shale and lower Silurian shale barely contribute to the total porosity and mean little to the permeability. Both excessive OM content and over thermal maturity are detrimental to development of OM-hosted pores. Rigid particles, clay flakes, and OM commonly co-exist within shale matrix. Rigid grains act as supporters, clay flakes confine ample space, and OM first migrates into and provides secondary OM-hosted pores. In this condition, pores can be preserved owing to associating matrix with good mechanic and chemical stability. The significant differences of structural settings result into various hydrocarbon explosion efficiency and different pressure circumstance, which consequently leads to the different pore features between the two shales. For lower Cambrian shale, overpressure circumstance diminish if hydrocarbon expels outside of the shale system, and OM-hosted pores destroy through compaction. Sustaining overpressure and abundant residue hydrocarbon (migrated OM) make positive contributions to the pore properties, in terms of numbers, diameters and connectivity of the lower Silurian shale samples.
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- 2022
- Full Text
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26. LIETUVOS APATINIO SILŪRO DUJŲ SKALŪNŲ PERSPEKTYVOS - GEOLOGINIS VERTINIMAS.
- Author
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Lozovskis, Saulius, Šliaupa, Saulius, Lazauskienė, Jurga, and Šliaupienė, Rasa
- Subjects
GEOPHYSICAL well logging ,DATA logging ,SHALE ,ORGANIC compounds ,SHALE gas reservoirs ,NATURAL gas - Abstract
Copyright of Geologijos Akiračiai is the property of Geologijos Akiraciai and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
- Published
- 2020
27. 笔石与页岩有机质的富集关系及其贡献率 --以四川盆地南缘YS118 井为例.
- Author
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李季林, 张廷山, 林 丹, 张万里, 刘 君, 李 虹, and 李延钧
- Subjects
BLACK shales ,SHALE ,ORGANIC compounds ,ROCKS ,HYDROCARBONS ,CARBON nanofibers - Abstract
Copyright of Natural Gas Industry is the property of Natural Gas Industry Journal Agency and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
- Published
- 2019
- Full Text
- View/download PDF
28. 川南地区龙马溪组页岩高压甲烷等温吸附特征.
- Author
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王曦蒙, 刘洛夫, 汪 洋, and 盛 悦
- Subjects
SHALE gas reservoirs ,SURFACE area ,SHALE gas ,MICROPORES ,ADSORPTION (Chemistry) ,METHANE ,ADSORPTION capacity ,PORE size distribution - Abstract
Copyright of Natural Gas Industry is the property of Natural Gas Industry Journal Agency and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
- Published
- 2019
- Full Text
- View/download PDF
29. Features of the Structure of Carbon-Rich Rocks (Based on the Example of the Lower Silurian Sediments of the Sichuan Depression of the Yangtze Platform).
- Author
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Hao Yuexiang, Shardanova, T. A., and Chongxing, Huang
- Abstract
The petrophysical, geochemical, and lithological features of the structure of graptolite shales from the lower part of the Longmaxi Formation of the Lower Silurian age of the Sichuan Province of the People's Republic of China are considered. The basic patterns of the formation of carbon-rich sediments in the intrashelf depressions are revealed. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
30. Developmental characteristics and geological significance of the bentonite in the Upper Ordovician Wufeng – Lower Silurian Longmaxi Formation in eastern Sichuan Basin, SW China.
- Author
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WANG, Yuman, LI, Xinjing, WANG, Hao, JIANG, Shan, CHEN, Bo, MA, Jie, and DAI, Bing
- Abstract
Based on the Qiliao section of the Upper Ordovician Wufeng Formation – Lower Silurian Longmaxi Formation in Shizhu, Chongqing city, the development characteristics of bentonite in eastern Sichuan Basin was examined systematically, and its geological significance and scientific value were analyzed. The main understandings are as follows: (1) Six bentonite dense layers were found in the Qiliao section, mainly occurring in 6 graptolitic belts of the Katian, Rhuddanian and Aeronian. Most of the bentonite dense layers showed obvious increase in clay, peak response of GR curve, and indistinct relationship between volcanic ash and total organic carbon (TOC). (2) The bentonite dense layers of Longmaxi Formation were widely distributed in eastern Sichuan Basin and its periphery, and generally showed GR peak, which can be an important reference interface for dividing the bottom boundary of the Coronograptus cyphus belt and the top boundary of the Rhuddanian in eastern Sichuan Basin and western Hubei province. (3) Taking the bentonite dense layers as the stratification basis of the Rhuddanian and Aeronian, it was determined that the sediment thickness of the Rhuddanian in the eastern Sichuan depression was generally 10–40 m, but only the upper part of the Coronograptus cyphus belt was deposited in the hinderland of Yichang Uplift, and the sedimentary thickness was only 3–7 m. (4) In the hinderland of the Yichang Uplift, at least five and a half graptolitic belts were missing in Wufeng Formation – Rhuddanian, and the deposition time of Rhuddanian was less than 0.4 Ma. (5) The bentonite dense layers were important sedimentary responses to the strong deflection of the Yangtze basin at the turn of the Ordovician–Silurian, which suggested that four tectonic activity periods existed in the eastern Sichuan depression, including the early stage of the depression, the middle-late stage of the depression, the early stage of the foreland flexure and the development stage of the foreland flexure. The high-quality shale was mainly developed from the early stage to the middle-late stage in the depression. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
31. Sedimentary characteristics, formation mechanisms and geological significance of the Shiniulan Formation reefs (lower Silurian) in the Upper Yangtze Platform.
- Author
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Wang, P., Tan, X. F., Chen, H., Wang, J., Luo, L., Kuang, H., Ran, T., Liang, M., and Jiang, W
- Subjects
- *
GEOLOGICAL formations , *REEFS , *OCEAN temperature , *FACTOR analysis , *SEA level ,TROPICAL climate - Abstract
The lower Silurian Shiniulan Formation of the Upper Yangtze Platform contains small-scale coral–stromatoporoid reefs, generally from less than 10 km long and from 10 to 30 m in thickness, especially in the middle–upper parts. The reef-building organisms were dominantly tabulate and rugose corals, with fewer stromatoporoids. Reef-inserted organisms include bryozoans, brachiopods, cephalopods, algae, crinoids and bivalves. The Shiniulan Formation is characterised by biohermal limestone, bioclastic limestone, sandstone and mudstone, and is divided into four members according to lithological characteristics. The reefs generally occur in the middle–upper layer, which corresponds to four growth stages: stabilisation, colonisation, diversification and domination. In the reefs, the argillaceous and sandy contents decrease, and the carbonates increase from the base to the top. The growth characteristics, evolution, scale and size of the reefs in the Shiniulan Formation were influenced by three factors: agitation of terrigenous debris, fluctuation of sea level and seawater temperature. The Upper Yangtze region was mainly a shallow marine environment with a warm or torrid tropical and subtropical climate and high salinity in the late Aeronian. However, the Shiniulan Formation has significant differences in growth, evolution and extension scale compared with corresponding reefs in Laurentia and the Siberia and Kazakhstan blocks. Analysis of the geological factors of the Shiniulan Formation and the Menier Formation of Anticosti Island, which has revealed that the two sections have similar reef types, lithology and biology, aims to explain the under-development of large-scale reefs in the Upper Yangtze Platform during the middle–upper Silurian. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
32. Stratigraphic sequence and sedimentary characteristics of Lower Silurian Longmaxi Formation in Sichuan Basin and its peripheral areas
- Author
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Yuman Wang, Dazhong Dong, Xinjing Li, Jinliang Huang, Shufang Wang, and Wei Wu
- Subjects
Sichuan Basin ,Peripheral areas ,Lower Silurian ,Demirastrites ,Spirograptus ,Stratigraphic sequence ,Sedimentary microfacies ,Black shale ,Shale gas ,Exploration potential ,Gas industry ,TP751-762 - Abstract
A high-precision sedimentary environment study of the Lower Silurian Longmaxi Formation is an important subject for shale gas exploration and development in Sichuan Basin and its surrounding areas. On the basis of outcrops and drilling data, its isochronous stratigraphic framework was built according to a particular graptolite zone and an important marker bed, and lithofacies, paleontology, calcareous content, well logging, geochemistry and other geologic information were combined to describe the sedimentary microfacies of Longmaxi Formation and its stratigraphic sequence, sedimentary evolution process and high quality shale distribution features as follows: ① with regional diachronism of the top and the bottom, the Longmaxi Formation is divided into two third-order sequences (SQ1 and SQ2), of which SQ1 is mainly an abyssal sedimentary assemblage deposited in the marine transgression period, and SQ2 is a bathyal to shallow sea sedimentary assemblage deposited in the marine regression period; ② there are eight microfacies such as deep calcareous shelf and deep argillaceous shelf in this formation and the organic-rich shale was mainly deposited in the deep water area of SQ1; and ③ from SQ1 to SQ2, the depocenter moved from the depression area in southern-eastern to northern Sichuan Basin, but the central Sichuan uplift remained an underwater one. It is concluded from this study that: ① shale gas production layers were mainly deposited in SQ1, the southern-eastern depression area was the depocenter in SQ1 and a shale gas enrichment area; and ② black shale in northern Sichuan was deposited in late SQ2, with limited distribution and relatively insufficient exploration potential, but the potential of shale gas exploration in western Hubei area is between southern-eastern and northern Sichuan Basin.
- Published
- 2015
- Full Text
- View/download PDF
33. Analysis of influence factors of methane adsorption capacity of the Lower Silurian shale.
- Author
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Sun, Yaxiong, Ding, Wenlong, Lu, Lin, Li, Mingzhu, Chen, Peng, and Ji, Xiang
- Subjects
- *
METHANE analysis , *ADSORPTION capacity , *SHALE gas industry , *MINERALOGICAL research , *CLAY mineral absorption & adsorption - Abstract
The Lower Silurian marine shale gas in South China has great potential. In order to study the influence factors of methane adsorption capacity of the marine shale in Sangzhi block, six samples from the Lower Silurian were investigated by a series of experiments. The total organic carbon (TOC) content ranges from 1.97 to 3.49% and organic matter are in the state of over-maturity. The dominant mineralogical compositions are quartz and clay minerals. The methane adsorption capacity of the studied shale ranges from 1.5627 to 2.2033 cm3/g, and is mainly influenced by the TOC content. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
34. 四川盆地南部深层海相页岩气勘探开发前景.
- Author
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龙胜祥, 冯动军, 李凤霞, and 杜 伟
- Abstract
Copyright of Natural Gas Geoscience is the property of Natural Gas Geoscience and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
- Published
- 2018
- Full Text
- View/download PDF
35. Trace fossils from Furnas formation (Paraná Basin) reveal a marine depositional environment.
- Author
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Richter, Kevin William, Bosetti, Elvio Pinto, Tavares, Isabelle de Siqueira, and Sedorko, Daniel
- Subjects
- *
TRACE fossils , *DATA analysis , *FACIES - Abstract
Trace fossils are important biogenic signatures in sedimentary environments because they indicate the paleoecologic controls during deposition. In some cases, trace fossils are the unique preserved biologic evidence, allowing to infer paleoenvironments in controversial stratigraphic units. This is the case of Furnas Formation from Paraná Basin, Brazil. This unit was widely interpreted as fluvial-generated up to 1990's, but facies association analysis and the ichnologic data have been used as tools to suggest a marine origin for the unit. However, some recent studies have been ignored that information and continuous to interpret Furnas Formation as a fluvial-generated unit. In this study we analyzed some outcrops at northeast of the Ponta Grossa Arch aiming to infer depositional processes and paleoenvironments for basal and intermediated units of Furnas Formation (Lower Silurian). Nine ichnotaxa (Cruziana, Didymaulichnus lyelli, Didymauliponomos rowei, Heimdallia chatwini, Palaeophycus tubularis, Rusophycus, Skolithos, Taenidium dieslingi, and Thalassinoides) expressing proximal and depauperate Cruziana ichnofacies were reported for the studied outcrops, corroborating the shallow marine paleoenvironment inferred for the unit. • The Furnas Formation presents Cruziana ichnofacies. • Lower and middle units of Furnas Formation were deposited in Lower Silurian. • Trace fossils from Furnas Formation indicate a shallow marine depositional setting. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
36. Structural analysis of the Baolun gold deposit, Hainan Island, South China: Implications for metallogeny.
- Author
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Cai, Jianxin, Wu, Chuanjun, Xu, Deru, Hou, Maozhou, Shan, Qiang, Zhu, Yuhua, and Lin, Di
- Subjects
- *
GOLD mining , *METALLOGENY , *FAULT zones , *SILICICLASTIC rocks , *SHEAR strength , *MINERALIZATION - Abstract
The Baolun gold deposit is a mesothermal orogenic gold deposit located in the southwestern part of Hainan Island, South China. The deposit comprises a series of NNW-trending quartz-sulfide lodes situated within a parallel array of fault zones traversing a sequence of variably foliated flysch siliciclastic rocks of the Lower Silurian. Detailed field mapping documented at least five phases of deformation in the deposit including NNW-trending folding of the Lower Silurian rocks (D1), development of NNW-trending, steeply dipping ductile shear zones with an oblique dextral sense corresponding to NNE-SSW shortening (D2), WNW-ESE shortening and extension associated with an early oblique sinistral ductile shearing along the NNW-trending fault zones (D3), ENE-WSW shortening (D4), and near N-S extension (D5). The gold-bearing quartz lodes cut the strata folded in the D1, show some laminar layering related to ductile shear in the D2 and are overprinted by brittle structures formed in the D3 to D5. 40 Ar– 39 Ar dating on muscovite from an auriferous quartz lode yielded an age of 242 ± 2.5 Ma, which, together with the age of 232 ± 2.5 Ma for an aplite vein in the deposit, suggests that the mineralization may be related to a tectono-thermal event in the Triassic. In the context of the southern South China plate tectonics, the formation of the Baolun gold deposit is interpreted to be related to the oblique dextral ductile shearing (D2) along the NNW-trending fault zones during the Indosinian orogeny, in relation to the convergence between the Indochina and South China plates. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
37. Lower Silurian stromatolites in shallow-marine environments of the South China Block (Guizhou Province, China) and their palaeoenvironmental significance.
- Author
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Li, Yue, Wang, Guan, Kershaw, Stephen, Yu, Shenyang, and Ni, Chao
- Subjects
- *
STROMATOLITES , *SILURIAN Period , *WATER depth , *MARINE resources , *CYANOBACTERIA - Abstract
In northern Guizhou Province (Upper Yangtze Platform, South China Block) two types of reef communities developed in the Lower Silurian (upper Aeronian, Llandovery) Shihniulan Formation; they are calcimicrobial- and metazoan-dominated structures, and existed because of northward deepening of the shallow-marine ramp setting in which they grew. Stromatolitic communities are the focus of the present study and dominated the shallowest reef structures, while metazoan-dominated reefs, previously described in other papers, grew in the outer shelf portion of the ramp. Stromatolitic reefs occur in several sections (Daijiagou, Baishanxi, Jianba and Lianghekou), palaeogeographically close to Qianzhong Land. Within the stromatolite units, laminar sheets of microbial mats and columns are pronounced, with individual stromatolite thicknesses generally less than 1 m. Some very small stromatolites are only centimeters in diameter and thickness. Stromatolitic units are cyanobacterial bindstones mostly associated with shales, siltstones and thin-bedded bioclastic limestones. Their growth was frequently punctuated by siliciclastic sediments, and their shallow-water nature is demonstrated by association with birds-eye structures, cross-stratified sediments, and Lingulella -bearing silts in intertidal or/and lagoonal environments. The stromatolites formed during a regression and erosion surfaces are common at the top of the Shihniulan Formation. The Tongzi Uplift, a short-duration expansion of Qianzhong Land, ended the deposition of the late Aeronian limestones. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
38. Shale gas reservoir characteristics of Ordovician-Silurian formations in the central Yangtze area, China.
- Author
-
Shan, Chang'an, Zhang, Tingshan, Wei, Yong, and Zhang, Zhao
- Abstract
The characteristics of a shale gas reservoir and the potential of a shale gas resource of Ordovician-Silurian age in the north of the central Yangtze area were determined. Core samples from three wells in the study area were subjected to thin-section examination, scanning electron microscopy, nuclear magnetic resonance testing, X-ray diffraction mineral analysis, total organic carbon (TOC) testing, maturity testing, gas-bearing analysis, and gas component and isothermal adsorption experiments. A favorable segment of the gas shale reservoir was found in both the Wufeng Formation and the lower part of the Longmaxi Formation; these formations were formed from the late Katian to early Rhuddanian. The high-quality shale layers in wells J1, J2, and J3 featured thicknesses of 54.88 m, 48.49 m, and 52.00 m, respectively, and mainly comprised carbonaceous and siliceous shales. Clay and brittle minerals showed average contents of 37.5% and 62.5% (48.9% quartz), respectively. The shale exhibited type II kerogens with a vitrinite reflectance ranging from 1.94% to 3.51%. TOC contents of 0.22%-6.05% (average, 2.39%) were also observed. The reservoir spaces mainly included micropores and microfractures and were characterized by low porosity and permeability. Well J3 showed generally high gas contents, i.e., 1.12-3.16 m/t (average 2.15 m/t), and its gas was primarily methane. The relatively thick black shale reservoir featured high TOC content, high organic material maturity, high brittle mineral content, high gas content, low porosity, and low permeability. Shale gas adsorption was positively correlated with TOC content and organic maturity, weakly positive correlated with quartz content, and weakly negatively correlated with clay content. Therefore, the Wufeng and Longmaxi formations in the north of the central Yangtze area have a good potential for shale gas exploration. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
39. Reservoir characteristics and genetic mechanisms of gas-bearing shales with different laminae and laminae combinations: A case study of Member 1 of the Lower Silurian Longmaxi shale in Sichuan Basin, SW China
- Author
-
Jin Wu, Zhensheng Shi, Hongyan Wang, Dazhong Dong, and Shasha Sun
- Subjects
Lamina ,Bedding ,0211 other engineering and technologies ,Energy Engineering and Power Technology ,Mineralogy ,02 engineering and technology ,Silt ,010502 geochemistry & geophysics ,01 natural sciences ,reservoir characteristics ,chemistry.chemical_compound ,Geochemistry and Petrology ,genetic mechanism ,parasitic diseases ,Organic matter ,021108 energy ,Porosity ,Quartz ,lcsh:Petroleum refining. Petroleum products ,0105 earth and related environmental sciences ,gas-bearing shale ,chemistry.chemical_classification ,Lower Silurian ,lamina ,Geology ,Geotechnical Engineering and Engineering Geology ,chemistry ,Longmaxi Formation ,lcsh:TP690-692.5 ,Carbonate ,Economic Geology ,Oil shale - Abstract
Based on thin-section, argon-ion polished large-area imaging and nano-CT scanning data, the reservoir characteristics and genetic mechanisms of the Lower Silurian Longmaxi shale layers with different laminae and laminae combinations in the Sichuan Basin were examined. It is found that the shale has two kinds of laminae, clayey lamina and silty lamina, which are different in single lamina thickness, composition, pore type and structure, plane porosity and pore size distribution. The clayey laminae are about 100 μm thick each, over 15% in organic matter content, over 70% in quartz content, and higher in organic pore ratio and plane porosity. They have abundant bedding fractures and organic matter and organic pores connecting with each other to form a network. In contrast, the silty laminae are about 50 μm thick each, 5% to 15% in organic matter content, over 50% in carbonate content, higher in inorganic pore ratio, undeveloped in bedding fracture, and have organic matter and organic pores disconnected from each other. The formation of mud lamina and silt lamina may be related to the flourish of silicon-rich organisms. The mud lamina is formed during the intermittent period, and silt lamina is formed during the bloom period of silicon-rich organisms. The mud laminae and silt laminae can combine into three types of assemblages: strip-shaped silt, gradating sand-mud and sand-mud thin interlayers. The strip-shaped silt assemblage has the highest porosity and horizontal/vertical permeability ratio, followed by the gradating sand-mud assemblage and sand-mud thin interlayer assemblage. The difference in the content ratio of the mud laminae to silt laminae results in the difference in the horizontal/vertical permeability ratio.
- Published
- 2020
40. MINERALOGY AND SHALE GAS POTENTIAL OF LOWER SILURIAN ORGANIC-RICH SHALE AT THE SOUTHEASTERN MARGIN OF SICHUAN BASIN, SOUTH CHINA.
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LING GUO, ZAIXING JIANG, and CHAO LIANG
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MINERALOGY ,SHALE gas ,SILURIAN Period ,NATURAL gas prospecting ,BLACK shales ,CLAY minerals ,QUARTZ - Abstract
Exploration for unconventional gas resources from Paleozoic formations in the Sichuan Basin in South China is just getting started. Large, potential gas reservoirs are presumed to exist in the southern and southeastern Sichuan Basin where Silurian marine organic-rich shale occurs. This paper provides geochemical and mineralogical data and other relevant information on potentially economic black shale formations of the Lower Silurian. The results show that in the shale, mineral components are dominated by clay minerals and quartz with minor amounts of plagioclase, potash feldspar, calcite and pyrite. The brittle mineral content ranges from 38 to 73% by weight (average content 56.2 wt%). In general, the Lower Silurian organic-rich shale of the Longmaxi Formation in the Sichuan Basin is highly mature, with the vitrinite reflectance between 1.6 and 3%. The shale has a high content of organic carbon, with an average of 1.8%, is tens of meters thick and of large areal extent. It can be regarded as a potential gas shale target. [ABSTRACT FROM AUTHOR]
- Published
- 2016
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41. 川东地区下志留统龙马溪组热演化.
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曹环宇, 朱传庆, and 邱楠生
- Abstract
Thermal evolution of shale, which is the maturity stage in different geological times, has great importance in hydrocarbon exploration and development as well as hydrocarbon resource assessment. Thermal evolution of shale is mostly controlled by time and temperature, and especially by temperature. The thermal history in the eastern Sichuan Basin was reconstructed by geothermometer data of equivalent vitrinite reflectance and apatite fission track; the thermal evolution history of Lower Silurian Longmaxi Formation in the eastern Sichuan Basin was analyzed; the relationship between thermal evolution of shale and shale gas accumulation was discussed. The results show that the thermal state is stable from Late Proterozoic to Late Paleozoic in the eastern Sichuan Basin, and the heat flow is low (45-50 mW·m-2); the heat flow begins to increase during Hercynian, and reaches the peak (60-80 mW·m-2) in Late Permian (about 250 Ma), and then persistently decreases to the present value (45-65 mW·m-2); the maturity evolution and hydrocarbon generation process of Longmaxi Formation have two rapid maturation stages, including the crust extension of Dongwu movement in Hercynian and rapid bury of stratum since Late Triassic; the thermal evolution of Longmaxi Formation reaches the peak in Late Cretaceous (about 80 Ma), and the following intensive uplift and cooling lead to the termination of hydrocarbon generation; the thermal evolution has close relationship with shale gas accumulation, which can be divided into biogenic gas stage (250-430 Ma), pyrolysis gas stage (80-250 Ma) and uplifting and reforming stage (0-80 Ma) in Longmaxi Formation; rapid maturation and hydrocarbon generation provide the abundance of gas, and accelerate the formation of reservoir space, and the following rapid uplift and cooling improve the reservoir property of shale, and are advantageous for the preservation of shale gas. [ABSTRACT FROM AUTHOR]
- Published
- 2015
42. Lower Silurian stratigraphy and brachiopods of the Chingiz range, eastern Kazakhstan.
- Author
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Nikitina, O., Nikitin, I., Olenicheva, M., and Palets, L.
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- *
BRACHIOPODA , *BIOSTRATIGRAPHY , *SILURIAN paleontology , *ORDOVICIAN paleontology - Abstract
New data on the stratigraphy and faunal assemblages of the Lower Silurian of the Chingiz region are presented. Owing to the discovery of Ruddanian brachiopods in the basal Alpeis Formation, the position of the Ordovician-Silurian boundary has been revised. The stratigraphic range of the Alpeis Formation has been revised to correspond to the range of the Alpeis Horizon in the stratotype and is limited to the beds with the brachiopod Eospirifer cinghizicus and the beds with the graptolites of the Coronograptus gregarius Zone. Beds with Pentamerus longiseptatus of the Donenzhal Horizon are assigned to the Zhumak Formation. A new Ruddanian brachiopod assemblage (ten species) is recognized in the lower part of the beds with E. cinghizicus. [ABSTRACT FROM AUTHOR]
- Published
- 2015
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43. Mineralogy and fracture development characteristics of marine shale-gas reservoirs: A case study of Lower Silurian strata in southeastern margin of Sichuan Basin, China.
- Author
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Guo, Ling, Jiang, Zai-xing, and Guo, Feng
- Abstract
Mineral contents and fractures of shale from well Yuye-1 and outcrops were examined mainly based on systematic description of the cores and outcrops, and data from experimental analyses. The data enabled us to thoroughly explore the mineralogy and developmental features of shale of the Lower Silurian Longmaxi Formation in the study area. The results show that, the Lower Silurian Longmaxi Shale (SLS) in the southeastern margin of Sichuan Basin, China, is primarily characterized by a high content of brittle minerals and a relatively low content of clay minerals. The total content of brittle minerals is approximately 57%, including 27% quartz, 12.2% feldspar, 11.2% carbonate and 2.4% pyrite. The total content of clay minerals reaches 41.6%, composed of illite (23.8%), mixed-layer of illite and smectite (I/S) (10.8%) and chlorite (7.0%). The SLS accommodates the widespread development of various types of fractures, including tectonic fractures, diagenetic fractures, inter-layer fractures and slip fractures. The developmental level of the fracture in the SLS is mainly influenced by faults, lithology, mineral contents and total organic carbon content (TOC) in study area. [ABSTRACT FROM AUTHOR]
- Published
- 2015
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44. Bryozoans from the lower Silurian (Wenlock) Steinsfjorden Formation of Ringerike, southern Norway.
- Author
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ERNST, ANDREJ and NAKREM, HANS ARNE
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- *
BRYOZOA , *INVERTEBRATES , *GEOLOGICAL formations , *CYSTOPORATA , *TREPOSTOMATA , *CRYPTOSTOMATA - Abstract
A stenolaemate bryozoan fauna from the lower Silurian (Wenlock) Steinsfjorden Formation of the Ringerike district, southern Norway contains 10 species (2 cystoporates, 6 trepostomes, and 2 cryptostomes). Six species are new: Heterotrypa ringerikensis sp. nov., Trematopora maculata sp. nov., Amplexopora cras sip arietum sp. nov., A. evae sp. nov., Orthopora worsleyi sp. nov., and Mediaporina kiaeri sp. nov. One species is described in open nomenclature: Eridotrypella sp. Trepostome bryozoans dominate this assemblage, both by diversity and abundance. The bryozoans occur in carbonates associated with evaporite minerals and sedimentary structures indicating very shallow depositional settings. [ABSTRACT FROM AUTHOR]
- Published
- 2015
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45. Vitrinite equivalent reflectance of Silurian black shales from the Holy Cross Mountains, Poland.
- Author
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Smolarek, Justyna, Marynowski, Leszek, Spunda, Karol, and Trela, Wiesław
- Subjects
- *
VITRINITE , *HYDROCARBONS , *ORGANIC compounds , *PYROLYSIS , *REFLECTANCE - Abstract
A number of independent methods have been used to measure the thermal maturity of Silurian rocks from the Holy Cross Mountains in Poland. Black shales are characterized by diverse TOC values varying from 0.24-7.85%. Having calculated vitrinite equivalent reflectance using three different formulas, we propose that the most applicable values for the Silurian rocks are those based on Schmidt et al. (2015) equation. Based on this formula, the values range from % 0.71 VReqvVLR (the vitrinite equivalent reflectance of the vitrinite-like macerals) to % 1.96 VReqvVLR. Alternative, complementary methods including Rock Eval pyrolysis and parameters based on organic compounds (CPI, Pr/ n-C17, Ph/ n-C18, MPI1, and MDR) from extracts did not prove adequate as universal thermal maturity indicators. We have confirmed previous suggestions that Llandovery shales are the most likely Silurian source rocks for the generation of hydrocarbons in the HCM. [ABSTRACT FROM AUTHOR]
- Published
- 2014
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46. A Lower Silurian (Aeronian) radiolarian assemblage from black cherts of the Armorican Massif (France).
- Author
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Tetard, Martin, Danelian, Taniel, Ghienne, Jean-François, and Dabard, Marie-Pierre
- Subjects
- *
OUTCROPS (Geology) , *LLANDOVERY series , *GLACIATION , *RADIOLARIA , *GRAPTOLITES , *HYDROFLUORIC acid - Abstract
The Chalonnes-sur-Loire outcrop is the most complete Llandovery section in the Ligerian domain (Armorican Massif, NW France); it displays a ca. 10 m-thick sequence of organic-rich black bedded cherts alternating with black graptolitic shales, which were deposited above glaciomarine diamictites of the Hirnantian glaciation. It is likely the black cherts accumulated under eutrophic waters, on the outer shelf part (distal offshore) of a Gondwanan margin, situated at intermediate to high latitudes of the Southern hemisphere. Hydrofluoric acid processing allowed the extraction of radiolarians; seven species are identified in the best preserved sample discovered so far. All seven are common species in tropical assemblages known from Alaska and Nevada, which are characteristic of the Orbiculopylorum assemblage, of Aeronian to early Telychian age. This age is in good agreement with independent age control from graptolites in the Chalonnes section, suggestive of an Aeronian age for the radiolarian-yielding level. [ABSTRACT FROM AUTHOR]
- Published
- 2014
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47. Ascocerid cephalopods from the Hirnantian?–Llandovery stages of the southern Paraná Basin (Paraguay, South America): first record from high paleolatitudes
- Author
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Norberto Javier Uriz, Marta Alfaro, Marcela Cichowolski, and J.C. Galeano Inchausti
- Subjects
Juvenile ,Structural basin ,Conch ,SW GONDWANA ,Demersal zone ,purl.org/becyt/ford/1 [https] ,purl.org/becyt/ford/1.5 [https] ,Paleontology ,PALEOGEOGRAPHY ,Stage (stratigraphy) ,Geología ,Nekton ,Gondwana ,Marine transgression ,PALEOECOLOGY ,Geology ,ASCOCERIDA ,LOWER SILURIAN - Abstract
Ascocerid cephalopods are described for the first time from high paleolatitudes of Gondwana. Studied material was collected from the Hirnantian?-Llandovery strata of the Eusebio Ayala and Vargas Pena formations, Parana Basin, southeastern Paraguay. The specimens are poorly preserved and were questionably assigned to the subfamily Probillingsitinae Flower, 1941, being undetermined at genus and species rank because diagnostic characters are not visible. A particular feature seen in our material is the presence of both parts of the ascocerid conch (the juvenile or cyrtocone and the mature or brevicone) joined together, which is a very rare condition in the known paleontological record. The specimens are interpreted as at a subadult stage of development because fully grown ascocerids would have lost the juvenile shell. A planktonic vertical migrant mode of life with a subvertical attitude is proposed for the juvenile, and a horizontal demersal nektonic mode for the adult form, as has been previously suggested. A subvertical orientation near the bottom is proposed for the subadult stage. We suggest that the immigration of ascocerids to southwestern Gondwana was possible through ocean currents that would carry the planktonic juveniles from low to high latitudes during the end-Ordovician postglacial transgression that flooded the intracratonic basins of the region., Facultad de Ciencias Naturales y Museo
- Published
- 2018
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48. Lower Silurian
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Herrmann, Helmut and Bucksch, Herbert
- Published
- 2014
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49. Late Ordovician ice-marginal processes and sea-level change from the north Gondwana platform: Evidence from the Valongo Anticline (northern Portugal).
- Author
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Couto, Helena, Knight, Jasper, and Lourenço, Alexandre
- Subjects
- *
ORDOVICIAN Period , *ABSOLUTE sea level change , *GLACIAL landforms , *GLACIATION , *PALEOGEOGRAPHY , *QUARTZITE ,GONDWANA (Continent) - Abstract
Abstract: In the Valongo Anticline, northern Portugal, the Upper Ordovician-age Sobrido Formation records glacioeustatic sea-level changes and glacially-influenced depositional environments on the north Gondwana platform associated with the Hirnantian glaciation. New stratigraphic data from the Sobrido Formation, taking into account lateral facies variations not exposed in the type section, allow for a better understanding of Hirnantian glacial sedimentary processes, sea-level changes and palaeogeography. The lower member of the Sobrido Formation is composed of quartzites alternating with siltstones and mudstones. The transition to the upper member is most commonly an erosional contact marked by a ferruginous horizon. The lowermost part of the upper member contains a thinly laminated and rhythmically-bedded mudstone that is capped by a thin (mm-scale) shelly bed and overlain by massive diamictites. Laterally, conglomerate beds that have erosion bases are rhythmically interbedded with slates and diamictites that sometimes contain outsized mudstone clasts. The uppermost part of the upper member is very variable in thickness laterally and contains massive to laminated diamictite beds intercalated with quartzites, conglomerates and slates. Massive diamictites commonly exhibit thin horizons with Fe-oxides and occasionally manganese, phosphate and oolitic chamosite. The lower member of the Sobrido Formation is interpreted as ice-proximal outwash that is transitional laterally to subaqueous ice-contact fans formed by debris and mass flows. Erosion followed by chemical weathering of the lower member and variably within the lowermost part of the upper member is interpreted as a response to sea-level fluctuations and development of spatially-variable anoxic conditions and groundwater migration within isolated marine basins. Facies within the upper member of the Sobrido Formation are interpreted as ice-distal (laminated diamictites) and ice-proximal deposits (massive diamictites, quartzites and conglomerates). Groove casts and hummocky cross-stratification within quartzite beds suggest deposition in a shallow shelf setting. The Upper Ordovician–Lower Silurian transition is locally marked by a ferruginous horizon. Black basal quartzites are interpreted to record development of an erosional unconformity during Silurian sea-level rise. In other areas a chloritoid layer indicates proximity to dry land. These palaeoenvironmental interpretations suggest dynamic changes in sedimentary and geochemical processes in response to sea level and related palaeogeographic changes during the Upper Ordovician and transitional to the Lower Silurian on the north Gondwana platform. [Copyright &y& Elsevier]
- Published
- 2013
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- View/download PDF
50. Characteristics of the Shale Gas Reservoir Rocks in the Lower Silurian Longmaxi Formation, East Sichuan Basin, China.
- Author
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Liu, Shugen, Ma, Wenxin, Jansa, Lubomir, Huang, Wenming, Zeng, Xiangliang, and Zhang, Changjun
- Abstract
The Sichuan basin is an oil-bearing and gas-rich basin with extensive development of the Lower Silurian Longmaxi Formation shale in southwestern China. The gas shows in the shale were identified in exploration wells mainly located between southeastern Sichuan basin and Western Hubei-Eastern Chongqing. The thickness of the Lower Silurian Longmaxi Formation shale ranges from 65 to 516 m. The base of the Longmaxi Formation shale is graptolite-rich transgressive black shale. Its thickness increases eastward in the study area, similarly as the sand content in the formation, with the latter also increasing stratigraphically upward. The Longmaxi Formation is comprised by eight lithofacies, including laminated and nonlaminated mudstone/shale, dolomitic siltstone, laminated lime mudstone/shale, argillaceous siltstone, laminated and nonlaminated silty mudstone/shale, fine grained silty sandstone, calcareous concretions and nonlaminated shale enriched organic matter. The biota in the formation is dominated by graptolites, ostracods, echinoderms, brachiopods, trilobites and radiolarian. Longmaxi Formation contains 0.2% to 6.7% of organic carbon (TOC). The organic matter is overmature, with Ro 2.4%−3.6% and dominated by Type II-kerogen. Quartz silt, which is the second important component of the shale gas reservoir quality, occurs as laminae and/or disseminated and varies from 2% – 93% in the shale. The size of quartz silt ranges from 0.03 to 0.05mm, with terrigenous origin. Porosity measured on the core samples of the shale from the Longmaxi Formation in exploratory wells ranges from 0.58% to 0.67%. The microporosity observed in the thin sections of the shale is about 2%, and dominated by the intercrystal and intragranular pores, with the pore size ranging from 100nm to 50μm. The other pore types are related to fractures, with the width of ranging from 2 to 5μm. The formation mechanism of the shale reservoir rocks includes favorable mineral composition, diagenesis and thermal cracking of organic component. There are some differences between Longmaxi Formation shale and Barnett shale in USA. The former is buried deeper, higher degree of thermal evolution, lower gas content, denser, more quartz of terrigenous origin. The prevailing low content of organic matter and highly variable quartz content in the Longmaxi Formation shale suggests there are only marginal conditions for exploration of shale gas resource. However, the high variability in both the content of TOC and quartz in the shale indicates that locally, particularly in the southeastern part of the basin, favorable conditions for shale gas may have developed. More detailed paleogeographic, burial history, gas content and quartz origin studies are needed to better access shale-gas potential of the Lower Silurian Longmaxi Formation shale. [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
- View/download PDF
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