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

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.

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

2014 ◽  
Vol 1014 ◽  
pp. 228-232 ◽  
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.

scholarly journals Coupling between Source Rock and Reservoir of Shale Gas in Wufeng-Longmaxi Formation in Sichuan Basin, South China

Energies ◽  
2021 ◽  
Vol 14 (9) ◽  
pp. 2679
Author(s):  
Yuying Zhang ◽  
Shu Jiang ◽  
Zhiliang He ◽  
Yuchao Li ◽  
Dianshi Xiao ◽  
...  
Keyword(s):  
Source Rock ◽  
Shale Gas ◽  
Sichuan Basin ◽  
Gas Content ◽  
Potential Zone ◽  
Hydrocarbon Generation ◽  
Gas Generation ◽  
Longmaxi Formation ◽  
Siliceous Shale ◽  
Organic Pores

In order to analyze the main factors controlling shale gas accumulation and to predict the potential zone for shale gas exploration, the heterogeneous characteristics of the source rock and reservoir of the Wufeng-Longmaxi Formation in Sichuan Basin were discussed in detail, based on the data of petrology, sedimentology, reservoir physical properties and gas content. On this basis, the effect of coupling between source rock and reservoir on shale gas generation and reservation has been analyzed. The Wufeng-Longmaxi Formation black shale in the Sichuan Basin has been divided into 5 types of lithofacies, i.e., carbonaceous siliceous shale, carbonaceous argillaceous shale, composite shale, silty shale, and argillaceous shale, and 4 types of sedimentary microfacies, i.e., carbonaceous siliceous deep shelf, carbonaceous argillaceous deep shelf, silty argillaceous shallow shelf, and argillaceous shallow shelf. The total organic carbon (TOC) content ranged from 0.5% to 6.0% (mean 2.54%), which gradually decreased vertically from the bottom to the top and was controlled by the oxygen content of the bottom water. Most of the organic matter was sapropel in a high-over thermal maturity. The shale reservoir of Wufeng-Longmaxi Formation was characterized by low porosity and low permeability. Pore types were mainly <10 nm organic pores, especially in the lower member of the Longmaxi Formation. The size of organic pores increased sharply in the upper member of the Longmaxi Formation. The volumes of methane adsorption were between 1.431 m3/t and 3.719 m3/t, and the total gas contents were between 0.44 m3/t and 5.19 m3/t, both of which gradually decreased from the bottom upwards. Shale with a high TOC content in the carbonaceous siliceous/argillaceous deep shelf is considered to have significant potential for hydrocarbon generation and storage capacity for gas preservation, providing favorable conditions of the source rock and reservoir for shale gas.

scholarly journals 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

Energies ◽  
2021 ◽  
Vol 14 (12) ◽  
pp. 3662
Author(s):  
Hongzhi Yang ◽  
Liangbiao Lin ◽  
Liqing Chen ◽  
Yu Yu ◽  
Du Li ◽  
...  
Keyword(s):  
Mineral Composition ◽  
Sichuan Basin ◽  
Sedimentary Environment ◽  
Organic Matter Content ◽  
Upper Permian ◽  
Carbonaceous Shale ◽  
Carbonate Minerals ◽  
Thin Sections ◽  
Terrestrial Input ◽  
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.

scholarly journals Micropore Structural Heterogeneity of Siliceous Shale Reservoir of the Longmaxi Formation in the Southern Sichuan Basin, China

Minerals ◽  
2019 ◽  
Vol 9 (9) ◽  
pp. 548 ◽  
Author(s):  
Li ◽  
Tang ◽  
Zheng
Keyword(s):  
High Pressure ◽  
Fractal Dimension ◽  
Low Temperature ◽  
Shale Gas ◽  
Sichuan Basin ◽  
Nitrogen Adsorption ◽  
Structural Heterogeneity ◽  
Longmaxi Formation ◽  
Shale Reservoir ◽  
Siliceous Shale

In recent years, the shale gas in the southern Sichuan Basin has achieved great commercial development, and the Silurian Longmaxi Formation is the main development stratum. In order to solve the problems of great difference production and inaccurate gas content of the Longmaxi Formation shale gas field in the southern Sichuan Basin, based on thin section identification, argon ion polishing-field emission scanning electron microscopy, high pressure mercury injection, low temperature nitrogen adsorption and the fractal method, the micropore structural heterogeneity of the siliceous shale reservoir of the Longmaxi Formation has been studied. The results show the following: The pores of siliceous shale are mainly intergranular pores and organic pores. Image analysis shows that there are obvious differences in size and distribution of shale pores among different types. The micropore structural heterogeneity is as follows: intragranular pore > intergranular pore > organic pore. In the paper, the combination of low temperature nitrogen adsorption method and high-pressure mercury injection method is proposed to characterize the micropore size distribution and fractal dimension, which ensures the credibility of pore heterogeneity. The shale pores are mainly composed of mesopores (2–20 nm), followed by macropores (100–300 nm). For different pore sizes, the fractal dimension from large to small is mesopore, micropore and macropore. Shale pore structure and fractal dimension are correlated with mineral composition and total organic carbon (TOC) content, but the correlation is significantly different in different areas, being mainly controlled by the sedimentary environment and diagenesis.

scholarly journals The Early Silurian Sedimentary Environment of Middle-Upper Yangtze: Lithological and Palaeontological Evidence and Impact on Shale Gas Reservoir

Minerals ◽  
2019 ◽  
Vol 9 (8) ◽  
pp. 494 ◽  
Author(s):  
Qu ◽  
Zhu ◽  
Wang ◽  
Shang
Keyword(s):  
Shallow Water ◽  
Deep Water ◽  
Tidal Flat ◽  
Sedimentary Environment ◽  
Gas Diffusion ◽  
Organic Carbon Content ◽  
High Porosity ◽  
Gas Reservoir ◽  
Longmaxi Shale ◽  
Tight Gas Reservoir

The organic-enriched thick shale at the bottom of Longmaxi Formation is laterally continuous distributed and has been proven to be of good production capability in Fuling of Upper Yangtze. Uplifts that developed during the sedimentation influenced the reservoir characteristics by taking control of the sedimentary environment and provenance. The sedimentary environments are mainly deep-water shelf, shallow-water shelf, and tidal flat. By analyzing reservoir characteristic of these three environments, the deep-water shelf, which dominated the early stage of sedimentation, formed a high-quality reservoir with high TOC (Total Organic Carbon) content, porosity, and brittleness, while the environment was maintained around the basin centre until the Early Silurian. The shales deposited under the shallow-water environment were of low porosity because of the increasing calcareous and argillaceous contents. Sediments which formed on the tidal flat were arenaceous and of the lowest TOC content as the organic preservation conditions deteriorated. The good correlation of graptolite abundance and TOC content, and high porosity within graptolite fossils emphasize the importance of palaeontological development. The argillaceous cap over the Longmaxi shale is of good sealing capability, and the continuous sedimentation zone along southern Sichuan–eastern Chongqing is the best optimized hydrocarbon-bearing system. However, a weak interface on the discontinuity is the potential lateral pathway for gas diffusion at Northern Guizhou and Western Hunan, but on the southeast margin where the dark shale and the tidal sandstone contact, it promises to form a tight gas reservoir.

scholarly journals Depositional environment and pore structure of mixed lithofacies shale of the Longmaxi Formation in the DM Block, the Southern Sichuan Basin, China

2019 ◽  
Vol 38 (3) ◽  
pp. 629-653 ◽  
Author(s):  
Jijun Tian ◽  
Chuanzheng Xu ◽  
Xin Li ◽  
Wenfeng Wang ◽  
Wen Lin
Keyword(s):  
Organic Carbon ◽  
Total Organic Carbon ◽  
Sichuan Basin ◽  
Depositional Environment ◽  
Sedimentary Environment ◽  
Nitrogen Adsorption ◽  
X Ray Diffraction ◽  
Low Field ◽  
Water Wetting ◽  
Longmaxi Shale

Distinguishing the differences of pore characters between different mixed lithofacies shales is helpful for improving shale gas development efficiencies. In this study, the targeted Longmaxi shale ( L1) of the Southern Sichuan Basin was selected as the research object. Two kinds of mixed lithofacies shale were identified by analyzing total organic carbon and X-ray diffraction results. The forming depositional environment of mixed lithofacies shale was researched by elements analyses. Pores in different mixed lithofacies shale were observed using field emission scanning electronic microscope. Low-field nuclear magnetic resonance and low-temperature nitrogen adsorption were conducted to analyze pore characters of different mixed lithofacies shale. The results showed that L1 were mainly composed of organic rich clay–siliceous mixed shales (OR-M-1) and organic extreme rich calcareous–siliceous mixed shales (OER-M-3). OR-M-1 and OER-M-3 were formed in high paleo-producing dysoxic–oxic seawater and anoxic waterbody, respectively. Micro-pore and meso-pore volumes of OER-M-3 were greater than those of OR-M-1 while macro-pore volume of OER-M-3 was lower than that of OR-M-1. Meso-pore surficial and structural complexities of OER-M-3 were greater than those of OR-M-1. OER-M-3 were greater in oil-wetting micro-pore structural complexities while lower in water-wetting micro-pore structural complexities, compared with OR-M-1. The inherent relationships between lithofacies type and sedimentary environment, total organic carbon, as well as pore characters, respectively, were quite close.

Analysis of Fractured Sections in Shale Gas Wells Based on PCA - Logistic Regression Model

2020 ◽  
Vol 980 ◽  
pp. 483-492
Author(s):  
Lei Ji ◽  
Ju Hua Li ◽  
Guan Qun Li ◽  
Jia Lin Xiao ◽  
Sean Unrau
Keyword(s):  
Logistic Regression ◽  
Shale Gas ◽  
Logistic Regression Model ◽  
Gas Production ◽  
Gas Wells ◽  
Gas Reservoirs ◽  
Discriminant Model ◽  
Economic Exploitation ◽  
High Production ◽  
Pca Algorithm

In order to optimize the layout and economic exploitation of horizontal fracturing wells and completion in shale gas reservoirs, we propose a model for evaluating shale gas fractured sections based on an improved principle component analysis (PCA) algorithm with logistic regression. The 229 gas production sections in 22 fractured shale gas wells in the main block of the Fuling Shale Development Demonstration Zone were selected, and PCA is used for dimensionalite reduction. According to the PCA results, 6 key parameters are chosen to determine the productivity of fractured wells. Taking the probability distribution of high production after fracturing as the research objective, a logistic regression discriminant model was constructed using the dichotomy method. The prediction results show that the model has 82.1% accuracy and is reliable. The model can be used to classify and gas wells to be fractured, and it provides guiding significance for reasonable optimization of well sections in the area selected for fracturing.

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