Journal of Natural Gas Geoscience最新文献

{"title":"Erratum to “Generation and resource potential of abiogenic alkane gas under organic–inorganic interactions in petroliferous basins” [J. Nat. Gas Geosci 6(2) (December 2021) 79–87]","authors":"Quanyou Liu , Xiaoqi Wu , Dongya Zhu , Qingqiang Meng , Huiyuan Xu , Weilong Peng , Xiaowei Huang , Jiayi Liu","doi":"10.1016/j.jnggs.2022.02.001","DOIUrl":"https://doi.org/10.1016/j.jnggs.2022.02.001","url":null,"abstract":"","PeriodicalId":100808,"journal":{"name":"Journal of Natural Gas Geoscience","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2022-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S2468256X22000013/pdfft?md5=24182be8293bd867d634dccd1e73b3ea&pid=1-s2.0-S2468256X22000013-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91696772","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The occurrence of tight oil in the Chang 8 lacustrine sandstone of the Huaqing area, Ordos Basin, China: Insights into the content of adsorbed oil and its controlling factors","authors":"Chao Li ,&nbsp;Guojun Chen ,&nbsp;Xiaotian Li ,&nbsp;Qianshan Zhou ,&nbsp;Zhaotong Sun","doi":"10.1016/j.jnggs.2021.11.001","DOIUrl":"https://doi.org/10.1016/j.jnggs.2021.11.001","url":null,"abstract":"<div><p>Tight oil is a great potential resource for unconventional oil exploration and development. Determining the content of adsorbed tight oil in sandstone reservoirs and the factors controlling its content is crucial for the evaluation and development of tight oil resources. Using fluorescence petrography, environmental scanning electron microscopy, porosity as well as permeability analyses, high-pressure mercury intrusion, and nuclear magnetic resonance imaging, the present study analyzed the occurrence form, location, and relative content of free and adsorbed tight oils and effect of controlling factors on the content of adsorbed tight oil in sandstone reservoirs of the Chang 8 member in the Huaqing area of the Ordos Basin. The free tight oil mainly exists in residual intergranular, intergranular dissolved, intragranular dissolved, and dissolution-enlarged pores as well as some throats in the form of flakes with various areas and slender strips. The adsorbed tight oil mainly occurs on the surfaces of the mineral particles and mica fragments as well as in fractures, some throats or the intragranular as well as intergranular dissolved pores in the form of films with variable thicknesses and long strips. The lower limit of the pore radius at which free tight oil occurs in sandstone is approximately 0.1 μm and the adsorbed tight oil occurs on the surface of mineral particles and in spaces with pore radii of 0.02–0.3 μm. The contribution of free tight oil to total tight oil in the present study has highest and lowest content of 60.95% and 32.48%, respectively, with an average content of 50.14%. The contribution of adsorbed tight oil to total tight oil has highest and lowest content of 67.52% and 39.05%, respectively, with an average content of 49.86%. The content of adsorbed tight oil is generally proportional to the median pressure and inversely proportional to the porosity as well as permeability of the reservoir; particularly, porosity is relevant. The content of adsorbed tight oil is inversely proportional to the quartz content and directly proportional to the feldspar, carbonate cement, and clay mineral content of the sandstone.</p></div>","PeriodicalId":100808,"journal":{"name":"Journal of Natural Gas Geoscience","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2022-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S2468256X2100078X/pdfft?md5=cb76d67b31ba9c83e9aa8c29c578b7a0&pid=1-s2.0-S2468256X2100078X-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91696778","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Microfracture development at Ziliujing lacustrine shale reservoir and its significance for shale-gas enrichment at Fuling in eastern Sichuan Basin, China","authors":"Pengwei Wang ,&nbsp;Zhongbao Liu ,&nbsp;Dongjun Feng ,&nbsp;Xiao Chen ,&nbsp;Fei Li ,&nbsp;Jingyu Hao ,&nbsp;Ruyue Wang","doi":"10.1016/j.jnggs.2022.03.002","DOIUrl":"https://doi.org/10.1016/j.jnggs.2022.03.002","url":null,"abstract":"<div><p>Microfractures at the Ziliujing lacustrine shale at Fuling in eastern Sichuan Basin were investigated through core observation, SEM image observation and high-pressure mercury injection. and quantifies the impact of micro fracture development to reservoir capacity, leads to the following understanding: (1) fracture types in lacustrine shale reservoir are defined; (2) the contribution of fractures to lacustrine shale reservoir is determined. Results show that the microfractures in the Lower Jurassic Ziliujing lacustrine shale reservoirs in eastern Sichuan Basin can be divided into three types, each with four groups: micro fractures related to sedimentation (bedding fractures), microfractures related to diagenesis (clay–mineral shrinkage fractures), and micro fractures related to hydrocarbon generation (organic-matter shrinkage fractures and organic-matter-cracking fractures). High-pressure mercury injection and plane porosity determination confirm that microfractures in lacustrine shale reservoirs exhibit good reservoir performance, whose contribution to shale reservoir capacity is about 25%.</p></div>","PeriodicalId":100808,"journal":{"name":"Journal of Natural Gas Geoscience","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2022-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S2468256X22000037/pdfft?md5=6491901b2b9ab66fd2211fb3b87ee6b5&pid=1-s2.0-S2468256X22000037-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91696779","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Isotopic geochemical characteristics and identification indexes of shale gas hydraulic fracturing flowback/produced water","authors":"Yunyan Ni ,&nbsp;Limiao Yao ,&nbsp;Jianli Sui ,&nbsp;Jianping Chen","doi":"10.1016/j.jnggs.2022.03.001","DOIUrl":"10.1016/j.jnggs.2022.03.001","url":null,"abstract":"<div><p>China is rich in shale gas resources, which are mainly distributed in densely populated southern marine carbonate areas. The geological and surface conditions are complex, the ecological environment is fragile, and water resources are scarce or unevenly distributed. Therefore, large-scale fracturing mining has high pressure of water resources utilization and serious risk of water environment pollution. In this paper, the geochemical characteristics of traditional and non-traditional stable isotopes such as hydrogen, oxygen, boron, lithium, strontium in shale gas hydraulic fracturing flowback/produced water (FP water) were comprehensively analyzed. The results show that, the hydrogen and oxygen isotopic composition of the FP water in Sichuan Basin, China has similar evolution trend with the produced water of conventional wells from Cambrian, Permian and Triassic Xujiahe, Jialingjiang and Leikoupo formations, but different from that of the Sinian conventional produced water. It indicates that the FP water in Sichuan Basin is a mixture of fracturing injected fluid and formation brine retained in Silurian shale. The saline end member is close to the formation water of Cambrian, but with higher δ¹¹B values. The FP water in Sichuan Basin has δ¹¹B values close to that of the Marcellus FP water, and both are derived from the evaporated seawater. The δ¹¹B values of FP water in Sichuan Basin have overlap with that of the conventional produced water from different strata, so it can not be precisely distinguished. However, the δ¹¹B and B/Cl values of the FP water in Sichuan Basin can be clearly distinguished from the river and the FP water from non-marine facies shale in Qaidam Basin. The FP water in Sichuan Basin has slightly higher δ⁷Li values than that of the Marcellus FP water, but has overlap with that of the Yangtze River. The average value of ⁸⁷Sr/⁸⁶Sr of FP water is 0.7197 in Weiyuan and 0.7193 in Changning, which is much higher than that of the produced water from conventional wells in different formations. This is because the Silurian shale is affected by terrestrial siliceous sediments and the underlying Sr-rich fluids. As a result, ⁸⁷Sr/⁸⁶Sr values measured in the Silurian strata in southern Sichuan Basin are high, which makes ⁸⁷Sr/⁸⁶Sr values become an effective index to distinguish shale gas fracturing FP water from conventional gas well produced water and shallow groundwater in Sichuan Basin.</p></div>","PeriodicalId":100808,"journal":{"name":"Journal of Natural Gas Geoscience","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2022-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S2468256X22000025/pdfft?md5=660a31fa487fa9b21885df6c3fcc7686&pid=1-s2.0-S2468256X22000025-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89938495","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Study on temperature distribution prediction of horizontal wells during fracturing treatment","authors":"Haitao Li ,&nbsp;Yuxing Xiang ,&nbsp;Hongwen Luo ,&nbsp;Hao Yu ,&nbsp;Qin Zhang ,&nbsp;Ying Li ,&nbsp;Beibei Jiang ,&nbsp;Naiyan Zhang","doi":"10.1016/j.jnggs.2022.03.004","DOIUrl":"https://doi.org/10.1016/j.jnggs.2022.03.004","url":null,"abstract":"<div><p>In recent years, fiber-optic distributed temperature sensors (DTS) have been widely used for the dynamic monitoring of horizontal well during fracturing treatments. It is proposed to address the frequent issues of unknown artificial fracture initiation location, unclear crack extension pattern, unknown fracturing fluid injection success, and difficult fracturing effect evaluation in the hydraulic fracturing of horizontal wells. The temperature prediction model is the basis for fracturing diagnosis based on DTS monitoring, however, the quantitative prediction of temperature distribution throughout the horizontal well fracturing process remains a challenge. In this paper, a set of temperature-distribution prediction model for multi-stage fracturing in horizontal wells is established, with various micro-heat effects taken into account, and the models are solved through coupling. The temperature distribution during multi-cluster fracturing, and the temperature distribution characteristics during staged fracturing of horizontal wells have been analyzed. Moreover, the influence of fracturing fluid displacement, formation filtration coefficient, fracture width, and height on temperature distribution has also been clarified. The findings of this study provide theoretical support for fracturing performance diagnosis, fracture initiation identification, and analysis of the whereabouts of fracturing fluids using DTS monitoring. It has a great significance on fracturing effect evaluation and fracturing design optimization for horizontal wells.</p></div>","PeriodicalId":100808,"journal":{"name":"Journal of Natural Gas Geoscience","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2022-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S2468256X22000050/pdfft?md5=f21d509bb9f83acc87c5eaf8a139063c&pid=1-s2.0-S2468256X22000050-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90019924","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The occurrence of tight oil in the Chang 8 lacustrine sandstone of the Huaqing area, Ordos Basin: Insights into the content of adsorbed oil and its controlling factors","authors":"Chaowen Li, Guojun Chen, Xiaotian Li, Qianshan Zhou, Zhaotong Sun","doi":"10.1016/j.jnggs.2021.11.001","DOIUrl":"https://doi.org/10.1016/j.jnggs.2021.11.001","url":null,"abstract":"","PeriodicalId":100808,"journal":{"name":"Journal of Natural Gas Geoscience","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74436977","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Seismic prediction of oolitic beach thin-bed reservoir based on favorable facies belt constraints: Taking the second member of Feixianguan Formation in Jiulongshan area, Northwest Sichuan, China","authors":"Lu Zhou ,&nbsp;Yujie Qian ,&nbsp;Lianjin Zhang ,&nbsp;Xuemei Lan ,&nbsp;Yong Wu ,&nbsp;Qi Wang ,&nbsp;Gao Zhong","doi":"10.1016/j.jnggs.2021.12.002","DOIUrl":"10.1016/j.jnggs.2021.12.002","url":null,"abstract":"<div><p>The second member of Triassic Feixianguan Formation in Jiulongshan area of northwestern Sichuan Basin has made breakthroughs in natural gas exploration and has great exploration potential. Drilling data show that the second section of Feixianguan Formation has developed multiple sets of reservoirs, which are mainly concentrated in the upper sub-member of the second member of Feixianguan Formation. The overall heterogeneity is strong, the lithology and physical properties are complex and changeable, the reservoir thickness is thin, and drilling is less, so it is difficult to determine the spatial distribution characteristics of oolitic beach reservoir, which restricts the natural gas exploration process in this area. For the oolitic beach reservoir in the upper sub-member of the second member of Feixianguan Formation of Jiulongshan area, using downhole reservoir characteristics and 3D seismic data, the reflection characteristics of oolitic beach reservoir are analyzed, and then the seismic response model of oolitic beach reservoir is established by forward modeling. It is clear that the seismic response characteristics of the reservoir in this area are weak amplitude-continuous reflection; through the use of layer flattening impression method to restore the ancient landscape of the second section of Feixianguan Formation, combined with seismic facies analysis and seismic amplitude attribute characteristics, The distribution characteristics of favorable facies belt for oolitic beach development are determined. Based on the distribution of favorable facies belt, this paper uses the relative impedance-based tuning amplitude inversion and waveform difference inversion method to make a fine prediction of the spatial distribution of the reservoir, defines the spatial distribution characteristics of the reservoir, and predicts the thickness and fracture development of oolitic beach reservoir. The prediction results of the reservoir thickness are in good agreement with the actual drilling results, which confirms the application of this prediction method in this area. According to the fracture development, wave impedance value less than 1.6×10⁶ g/(cm²·s), reservoir thickness, and other indicators, the favorable development area of oolitic beach reservoir is further delineated, which provides a favorable basis for the next exploration and development.</p></div>","PeriodicalId":100808,"journal":{"name":"Journal of Natural Gas Geoscience","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S2468256X21000754/pdfft?md5=165b211cb0614b64d19d154dd212c369&pid=1-s2.0-S2468256X21000754-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73288979","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Characteristics of rock types and exploration significance of the shale strata in the Chang 73 sub-member of Yanchang Formation, Ordos Basin, China","authors":"Xianyang Liu ,&nbsp;Shixiang Li ,&nbsp;Qiheng Guo ,&nbsp;Xinping Zhou ,&nbsp;Jiangyan Liu","doi":"10.1016/j.jnggs.2021.12.003","DOIUrl":"10.1016/j.jnggs.2021.12.003","url":null,"abstract":"<div><p>For a long time, the Chang 7₃ sub-member of the Ordos Basin was mostly investigated as a single source rock, with hardly any investigation into the characteristics of various rock types or the integration of source and reservoir. Based on correlation analysis of lithology and physical properties combined with a fine interpretation of logging, the characteristics of the Chang 7₃ sub-member are discussed in detail, and the reservoir characteristics and exploration significance of different types of rocks are analyzed. The results show that: (1) There are five types of lithology in the Chang 7₃ sub-member: black shale, dark mudstone, fine sandstone, siltstone, and tuff. (2)The storage space of sandy rocks is primarily made up of feldspar dissolution pores and residual intergranular pores, which are held together by rigid grains. The sandstone with high feldspar and quartz mineral content, low carbonate cementation, low clay mineral content, and a large accumulated thickness is the optimal shale oil reservoirs of Chang 7₃ sub-member. (3) The Chang 7₃ sub-member has the most organic-rich shale deposits. Clay mineral intercrystalline pores, pyrite intercrystalline pores, and clastic grain intergranular pores make up the majority of the reservoir space. Although organic matter pores are largely undeveloped, organic matter contraction fractures are prevalent. Despite the porosity and pore size of shale in the Chang 7₃ sub-member being microscopic, it possesses specific reservoir performance and hydrocarbon fluid mobility. It is estimated that the total amount of retained hydrocarbon resources in Chang 7 Member shale is about 15 × 10⁹ t, with movable hydrocarbon resources of about 6 × 10⁹ t; (4)The oil saturation of Chang 7₃ sub-member is generally higher than that in Chang 7₁ and Chang 7₂ sub-members. Several factors play a key role in rapidly increasing shale oil production, including further optimizing the vertical and plane distribution characteristics of sand bodies, improving the drilling encounter rate of sandstone in horizontal wells, strengthening the research of pilot production scheme, and ensuring sufficient oil-water infiltration and replacement. (5) Optimizing black shale with high brittleness index and oil content, developing high-efficiency permeability improvers, adopting pressure drive production integrated design, increasing fracture width and height, and improving the conductivity of artificial fractures are all important technical means to realize shale oil production.</p></div>","PeriodicalId":100808,"journal":{"name":"Journal of Natural Gas Geoscience","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S2468256X21000766/pdfft?md5=2c52a78e963926cd631e377c5a31ea0a&pid=1-s2.0-S2468256X21000766-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89711872","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Hydrocarbon generation and expulsion quantification and contribution of multiple source rocks to hydrocarbon accumulation in Yanchang Formation, Ordos Basin, China","authors":"Jingwei Cui ,&nbsp;Zhongyi Zhang ,&nbsp;Jianliang Liu ,&nbsp;Guanglin Liu ,&nbsp;Xiu Huang ,&nbsp;Yalin Qi ,&nbsp;Zhiguo Mao ,&nbsp;Yang Li","doi":"10.1016/j.jnggs.2021.12.001","DOIUrl":"10.1016/j.jnggs.2021.12.001","url":null,"abstract":"<div><p>There are several sets of source rocks in the Yanchang Formation of Mesozoic in the Ordos Basin. At present, Chang 7 source rock is considered to be the main source rock of the Yanchang Formation, although there are no evaluation methods for hydrocarbon generation and expulsion of other source rocks, as well as the hydrocarbon accumulation contribution of source rocks. Utilizing basin simulation and based on a large number of basic geological data and exploration results, the geological body model and thermal history model are established to carry out simulation research on hydrocarbon generation, expulsion, and accumulation of multi-source layers in the Yanchang Formation under geological constraints. The results show that the conversion rate of hydrocarbon generation of each source rock in the Yanchang Formation is mainly distributed in the range of 45%–75%, indicating that the formation still has significant hydrocarbon generation potential and has the geological conditions for in-situ exploitation of shale oil. At present, accumulative hydrocarbon generation is 123.3 × 10⁹ t while hydrocarbon expulsion is 90 × 10⁹ t, with heavy hydrocarbons of C₁₄₊ dominating. The Early Cretaceous had the highest concentration of hydrocarbon generation and expulsion, accounting for 68%–82% of total hydrocarbon generation and expulsion. The simulation of hydrocarbon accumulation revealed that before the deposition of the Cretaceous, only a limited amount of hydrocarbon charging occurred in each layer of the Yanchang Formation, with the early Cretaceous being the key period of hydrocarbon charging and accumulation. The “near-source accumulation” characterizes the upper and lower hydrocarbon source layers, and the basin simulation results are in good agreement with proven oil reservoirs and predicted oil reservoir distribution ranges. The study proposed for the first time that the “Chang 7 source rock make major contribution to multi-layer reservoir” mode could be modified to “proximal hydrocarbon accumulation from diverse source rock” mode to stimulate shale oil production and potential layer exploration in the Yanchang Formation of Mesozoic in the Ordos Basin.</p></div>","PeriodicalId":100808,"journal":{"name":"Journal of Natural Gas Geoscience","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S2468256X21000742/pdfft?md5=3a5074183110fe6ee51a8af65b389a81&pid=1-s2.0-S2468256X21000742-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83004817","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Characteristics and environmental significance of concretions in the Lower Cambrian Qiongzhusi Formation in the Middle–Upper Yangtze region, China","authors":"Yuman Wang ,&nbsp;Junjun Shen ,&nbsp;Zhen Qiu ,&nbsp;Xinjing Li ,&nbsp;Leifu Zhang ,&nbsp;Qin Zhang ,&nbsp;Canhui Wang","doi":"10.1016/j.jnggs.2021.12.004","DOIUrl":"10.1016/j.jnggs.2021.12.004","url":null,"abstract":"<div><p>Based on the outcrop and drilling data of the Sichuan Basin and its periphery, this paper reveals the concretion development characteristics of the Lower Cambrian Qiongzhusi Formation and its significance to the environment. Three preliminary conclusions are drawn as follows. (1) The exposure layers and lithofacies characteristics of the concretions in the Qiongzhusi Formation are very different from area to area. In the eastern Sichuan-western Hubei-Hunan &amp; Guizhou and southern Sichuan depression areas, the concretionsare developed in the section of SQ1, and are mainly composed of calcareous siliceous mixed shale facies, siliceous shale facies, dolomitic shale facies and dolomite facies. The clay content is generally less than 25% and is significantly less than the surrounding rocks, and the <em>TOC</em> is generally higher in the lower concretion layers and less in the upper concretion layers. In the central Sichuan and northern Sichuan depression areas, the concretions appear in the sections of SQ1 and SQ2, and are dominated by calcareous shale facies and marl facies. The calcic content is obviously higher than that of surrounding rocks, and the clay content is less than that of surrounding rocks, and the <em>TOC</em> is less than 1.50%. Because mineral composition difference is high, most of the GR curves of the concretions show trough response characteristics, reflecting the central region enriched with calcium or siliceous, and the edge enriched with clay and organic matter. (2) The concretion layers generally occur in carbonaceous shale, silty shale and siliceous shale with a <em>TOC</em> over 0.7%, and are especially developed in carbonaceous shale and siliceous shale of SQ1, and occasionally appear in grey silty shale with a <em>TOC</em> over 0.2%, showing that the concretion layers are basically symbiotic with grey shale (especially with high-quality shale). (3) The concretions are a kind of important sedimentary response of rifting activities in Yangtze marine basin. According to the distribution characteristics of concretions and black shale in the Qiongzhusi Formation, the rifting activities of Yangtze marine basin can be divided into three periods including development period (SQ1), adjustment period (SQ2) and abortion period (SQ3). In the period of SQ1, controlled by massive rifting and upwelling ocean currents in Yangtze marine basin, the concretions and organic-rich shale were widely developed in the Lower Qiongzhusi Formation. In the periods of SQ2 and SQ3, while rifting activity of Yangtze marine basin decreased and aborted, and while sea level fell and upwelling ocean currents receded to the southeast, the concretions and organic-rich shale just appeared in the local depression areas in small scale.</p></div>","PeriodicalId":100808,"journal":{"name":"Journal of Natural Gas Geoscience","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S2468256X21000778/pdfft?md5=3ddc07283f650ce0fde60ef91eba6a4b&pid=1-s2.0-S2468256X21000778-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81812711","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}