Characteristics of Mineralogy, Lithofacies of Fine-Grained Sediments and Their Relationship with Sedimentary Environment: Example from the Upper Permian Longtan Formation in the Sichuan Basin

The Longtan Formation of the Upper Permian in the Sichuan Basin has become a significant target for shale gas exploration in recent years. Multiple methods, including outcrop observations, thin sections, total organic matter content, X-ray diffraction and scanning electron microscopy were used to investigate the mineralogy, shale lithofacies assemblages and their relationships with the deposition environment. The mineral composition of the Longtan Formation has strong mineral heterogeneity. The TOC values of the Longtan Formation have a wide distribution range from 0.07% to 74.67% with an average value of 5.73%. Four types of shale lithofacies assemblages of the Longtan Formation could be distinguished, as clayey mudstone (CLS), carbonaceous shale (CAS), siliceous shale (SS) and mixed shale (MS) on the basis of mineral compositions. The TOC values of various types of shale lithofacies assemblages in the Longtan Formation varied widely. The shore swamp of the Longtan Formation is most influenced by the terrestrial input and mainly develops CLS and MS. The tidal flat is influenced by the terrestrial input and can also deposit carbonate minerals, developing CLS, CAS and MS. The shallow water melanged accumulation shelf develops CAS and MS, dominated by clay and carbonate minerals. The deep water miscible shelf develops CLS and SS, whose mineral composition is similar to that of the shore swamp, but the quartz minerals are mainly formed by chemical and biological reactions, which are related to the Permian global chert event. The depositional environment of the Longtan Formation controls the shale mineral assemblage of the Longtan Formation and also influences the TOC content.

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Lithology and sedimentary heterogeneity of the Longmaxi Shale in the southern Sichuan Basin, China

Interpretation ◽

10.1190/int-2020-0198.1 ◽

2021 ◽

pp. 1-49

Author(s):

Boling Pu ◽

Dazhong Dong ◽

Ning Xin-jun ◽

Shufang Wang ◽

Yuman Wang ◽

...

Keyword(s):

Continental Shelf ◽

Deep Water ◽

Shale Gas ◽

Sichuan Basin ◽

Sedimentary Environment ◽

Gas Production ◽

Carbonaceous Shale ◽

Gas Wells ◽

Longmaxi Shale ◽

Siliceous Shale

Producers have always been eager to know the reasons for the difference in the production of different shale gas wells. The Southern Sichuan Basin in China is one of the main production zones of Longmaxi shale gas, while the shale gas production is quite different in different shale gas wells. The Longmaxi formation was deposited in a deep water shelf that had poor circulation with the open ocean, and is composed of a variety of facies that are dominated by fine-grained (clay- to silt-size) particles with a varied organic matter distribution, causing heterogeneity of the shale gas concentration. According to the different mother debris and sedimentary environment, we recognized three general sedimentary subfacies and seven lithofacies on the basis of mineralogy, sedimentary texture and structures, biota and the logging response: (1) there are graptolite-rich shale facies, siliceous shale facies, calcareous shale facies, and a small amount of argillaceous limestone facies in the deep - water shelf in the Weiyuan area and graptolite-rich shale facies and carbonaceous shale facies in the Changning area; (2) there are argillaceous shale facies and argillaceous limestone facies in the semi - deep - water continental shelf of the Weiyuan area and silty shale facies in the Changning area; (3) argillaceous shale facies are mainly developed in the shallow muddy continental shelf in the Weiyuan area, while silty shale facies mainly developed in the shallow shelf in the Changning area. Judging from the biostratigraphy of graptolite, the sedimentary environment was different in different stages.

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Mineral Composition and Its Control on Nanopores of Marine-Continental Transitional Shale from the Ningwu Basin, North China

Journal of Nanoscience and Nanotechnology ◽

10.1166/jnn.2021.18750 ◽

2021 ◽

Vol 21 (1) ◽

pp. 168-180

Author(s):

Bao-Xin Zhang ◽

Xue-Hai Fu ◽

Yu-Lin Shen ◽

Qing-Hui Zhang ◽

Ze Deng

Keyword(s):

Clay Minerals ◽

Mineral Composition ◽

Shale Gas ◽

Gas Adsorption ◽

Sedimentary Environment ◽

Nitrogen Adsorption ◽

Shanxi Province ◽

Parallel Plates ◽

Carbonate Minerals ◽

Quartz Content

There is a large difference between the sedimentary environment and maturity of organic matter between marine shale and marine-continental transitional shale. It is of great significance to discuss the effect of inorganicminerals on the pores for marine-continental transitional shale gas exploration. In this study, scanning electron microscopy (SEM), low temperature liquid nitrogen adsorption and Xray diffraction (XRD) were conducted on eight marine-continental transitional shale samples from the Ningwu Basin, Shanxi Province, China. The pore structure differences in the different minerals were discussed, and the relationship between the mineral content and pore parameters was analysed. The results show that the mineral composition of shale is dominated by clay minerals, quartz, carbonate minerals and a small amount of pyrite. The clay minerals content is between 39.5% and 77.0%, with an average of 59.9%. The quartz content ranges from 21.8% to 47.8%, with an average of 31.9%. The carbonate minerals content in shale is between 0.6% and 23.9%, and the average is 6.3%. The clay minerals are composed of mixed illite-montmorillonite layer, kaolinite and chlorite. The content of mixed illite-montmorillonite layer is between 13.8% and 27.4%, with an average of 20.4%. The kaolinite content ranges from 57.0% to 86.2%, with an average of 76.0%. The content of chlorite is between 0 and 15.6%, with an average of 5.7%. The types of pores are mainly intergranular pores and interlaminar pores, which are mostly presented as slit and parallel plates. The mixed illite-montmorillonite layer contributes more to the specific surface area, which is favourable for shale gas adsorption. The pores in kaolinite are more developed than those of the mixed illite-montmorillonite layer, but the pore diameter is relatively large. The quartz granule has a complete crystal type, and intergranular pores with a large pore size are often developed at the mineral contacts. Compared with clay minerals and quartz, the pore development in the carbonate minerals is relatively poor and develops more micro-fractures. The pyrite contributes a certain number of intergranular pores and mold pores.

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Prospect Analysis of Shale Gas Resource Exploration in the Lower Silurian Longmaxi Formation, Southeastern Margin of the Sichuan Basin, China

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.1014.228 ◽

2014 ◽

Vol 1014 ◽

pp. 228-232 ◽

Cited By ~ 1

Author(s):

Chen Lin Hu ◽

Yuan Fu Zhang ◽

Zhi Feng Wang ◽

Hai Bo Zhang

Keyword(s):

Shale Gas ◽

Sedimentary Environment ◽

Source Rocks ◽

Guizhou Province ◽

Mature Stage ◽

Carbonaceous Shale ◽

Thin Sections ◽

Longmaxi Formation ◽

Lower Silurian ◽

Longmaxi Shale

In order to understand the sedimentary characteristics of shale and prospects of shale gas exploration in the lower Silurian Longmaxi Formation northern of Guizhou Province, outcrop and core observations, thin sections, X-ray diffraction analysis and other means are used. Studies show that the thickness of Longmaxi formation shale is generally large, range from 20m to 200m, mainly develop in the water shelf. The mineral mainly compose of detrital quartz and clay minerals, and five lithofacies can be identified: black shale, silty shale, carbonaceous shale, calcareous shale and argillaceous siltstone. Longmaxi shale kerogen type is mainlyIand II, and Ro value is average of 1.87%, mainly in the mature - over mature stage. In addition, the TOC content and gas content of Longmaxi shale is high, what’s more, these two parameters have good positive correlation. Compared with the Barnett shale, both of them have some similarities in the development environment shale, shale thickness and type of organic matter and TOC content, while, Longmaxi shale is deeply buried and post-destruction more intense. Longmaxi shale sedimentary environment is stable, high shale thickness and stable distribution, good quality source rocks and high brittle mineral content, which has meet the basic parameters of shale gas exploration and development, and has a large shale gas exploration potential in study area.

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Evolution and migration of shale facies and their control on shale gas: A case study from the Wufeng-Longmaxi Formations in the Sichuan Basin and its surroundings

Interpretation ◽

10.1190/int-2018-0015.1 ◽

2018 ◽

Vol 6 (4) ◽

pp. SN57-SN70 ◽

Cited By ~ 1

Author(s):

Zongquan Hu ◽

Wei Du ◽

Chuanxiang Sun ◽

Jing Wu ◽

Tong Zhu ◽

...

Keyword(s):

Shale Gas ◽

Sichuan Basin ◽

Early Stage ◽

Carbonate Content ◽

Thin Sections ◽

Longmaxi Formation ◽

Material Basis ◽

The Sichuan Basin ◽

Siliceous Shale ◽

Sweet Spots

The Fuling gas field, the largest commercial discovery of shale gas in China, has been producing from the organic-rich shale in the Upper Ordovician Wufeng Formation and Lower Silurian Longmaxi Formation in the Sichuan Basin, China. A refined shale gas E&P and sweet spots identification require studies to be carried out not only at the sedimentary facies scale but also at the petrographic scale. This paper focuses on the characteristics of organic-rich shales. Based on data from outcrops, drilling cores, X-ray diffraction, thin sections, and scanning electric microscope, a systematic analysis of wells and well-correlation sections indicates that shales in the study area underwent two progressive and regressive cycles. In addition, differences in lithofacies and their organic or inorganic components are significant either in the vertical or in the horizontal direction, which generally controls the material basis of shale gas. The early-stage siliceous shale distributes in the east, whereas the late-stage carbonate-bearing shale extends to the west. In the southeastern Sichuan Basin, the siliceous composition decreases, whereas the clay minerals increase upward. In the central Sichuan uplift, there is a higher carbonate content. And with our new lithofacies maps, distribution of the sweet spots was identified. The northeastern Sichuan Basin has the siliceous shale in the Wufeng Formation and the silicon-bearing shale in the Longmaxi Formation, making it a play area with the greatest gas potential. The southern Sichuan Basin occurs as a favorable lithofacies area with the stacked siliceous shale in the Wufeng Formation and the calcareous shale in the Longmaxi Formation. The relatively favorable lithofacies area covers the regions extending from the periphery of southern Sichuan Basin toward the central Sichuan uplift and the northern Guizhou uplift, featuring stacked carbonate-bearing shale and clay mineral-bearing shale in the Longmaxi Formation. The shallow-marine areas close to the uplifts are dominated by mudstone and silty mudstone, thereby possessing poor material basis.

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Upwelling-induced organic matter enrichment of the Upper Permian Dalong Formation in the Sichuan Basin, SW China and its paleoenvironmental implications

Palaeogeography Palaeoclimatology Palaeoecology ◽

10.1016/j.palaeo.2021.110510 ◽

2021 ◽

pp. 110510

Author(s):

Yamin Yu ◽

Pingping Li ◽

Ruixin Guo ◽

Yizhen Zhao ◽

Shan Li ◽

...

Keyword(s):

Organic Matter ◽

Sichuan Basin ◽

Upper Permian ◽

Sw China ◽

Dalong Formation ◽

The Sichuan Basin

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Geochemical features of the Middle–Upper Permian cherts and implications for origin, depositional environment in the Sichuan Basin, SW China

Geological Journal ◽

10.1002/gj.3511 ◽

2019 ◽

Vol 55 (2) ◽

pp. 1493-1506

Author(s):

Yu Yu ◽

Liangbiao Lin ◽

Xiaoliang Deng ◽

Yanan Wang ◽

Yehan Li ◽

...

Keyword(s):

Sichuan Basin ◽

Depositional Environment ◽

Upper Permian ◽

Sw China ◽

The Sichuan Basin

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Geochemical characteristics and geological significance of the bedded chert during the Ordovician and Silurian transition in the Shizhu area, Chongqing, South China

Canadian Journal of Earth Sciences ◽

10.1139/cjes-2018-0160 ◽

2019 ◽

Vol 56 (4) ◽

pp. 419-430 ◽

Cited By ~ 4

Author(s):

Bin Lu ◽

Zhen Qiu ◽

Baohua Zhang ◽

Jian Li

Keyword(s):

Rare Earth ◽

Continental Margin ◽

South China ◽

Sichuan Basin ◽

Hydrothermal Fluid ◽

Sedimentary Environment ◽

Major Elements ◽

Key Factor ◽

Bedded Chert ◽

The Sichuan Basin

A large amount of bedded chert widely deposited during the Ordovician and Silurian transition in South China. In this study, analyses of the petrographic characteristics, the major elements and rare earth elements (REEs), were conducted on 31 bedded chert samples obtained from the Wufeng and Longmaxi Formations at the Qiliao section in the Shizhu area of the Sichuan Basin to determine the sedimentary environment and the origin of the bedded chert during the Ordovician and Silurian transition. The following conclusions were obtained: (i) the bedded chert in the Wufeng and Longmaxi Formations at the Qiliao Section originated mainly from terrigenous input and siliceous organisms and was slightly influenced by hydrothermal fluid, (ii) siliceous organisms were a key factor controlling the differences in the SiO2 content of the bedded chert in the Wufeng and Longmaxi Formations at the Qiliao Section, and (iii) the bedded chert in the Wufeng and Longmaxi Formations deposited in a continental margin environment during the Ordovician and Silurian transition.

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Mineral Composition of Prospective Section of Wufeng-Longmaxi Shale in Luzhou Shale Play, Sichuan Basin

Minerals ◽

10.3390/min12010020 ◽

2021 ◽

Vol 12 (1) ◽

pp. 20

Author(s):

Hongzhi Yang ◽

Xuewen Shi ◽

Chao Luo ◽

Wei Wu ◽

Yi Li ◽

...

Keyword(s):

Mineral Composition ◽

Shale Gas ◽

Sichuan Basin ◽

Focal Point ◽

Quartz Content ◽

Biological Origin ◽

Longmaxi Formation ◽

Longmaxi Shale ◽

The Sichuan Basin ◽

Identification And Characterization

Currently, Luzhou in the Sichuan Basin is a focal point for shale-gas exploration and development in China. However, a lack of detailed research on the mineral composition of the Wufeng Formation-Longmaxi Formation (WF-LF) shale is hindering the extraction of deep-buried shale gas in the Luzhou shale play. Herein, a field emission scanning electron microscope (FESEM) equipped with the Advanced Mineral Identification and Characterization System (AMICS) software was employed to analyze the mineral composition of the WF-LF shale from six wells in Luzhou. Quartz was the dominant mineral type, (16.9–87.21%, average 51.33%), followed by illite, calcite, dolomite, and pyrite. Our study revealed that (1) quartz content showed a moderate positive correlation with the total organic carbon (TOC) content, indicating that the quartz found in the shale is mostly of biological origin; and (2) the sum content of siliceous minerals and carbonaceous minerals was moderately positively correlated with the brittleness index (BRIT) in well SS1H2-7 and in the well group of RS8 and RS5, indicating that the siliceous minerals and carbonaceous minerals had an active effect on reservoir compressibility. Finally, according to the mineralogical features of each sublayer, we identified four types of reservoirs to determine their scope for exploration.

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