This study focuses on the analysis of the sedimentary facies of the Middle–Late Permian, including the Qixia, Maokou, Wujiaoping/Longtan, and Changxing/Dalong Formations, in the Sichuan Basin, southwest China. Integrating drilling data and field outcrop data, various sedimentary facies indicators were employed to define eight sedimentary facies types in the Sichuan Basin during the Middle–Late Permian, namely, mixed tidal flat, tidal flat, restricted platform, open platform, platform margin, slope, basin, and volcanic facies. Detailed facies analysis was conducted on selected well logs, and sedimentary facies distribution maps were compiled for different time intervals, establishing depositional models. During the Qixia to Maokou stages, an extensive open platform was developed in the Sichuan Basin, accompanied by shallow intra-platform shoals. Towards the west along the Dayi–Ya’an line, platform margins were developed, followed by slope facies and basin facies in a northwest direction. During the Changxing stage, the Kaijiang–Liangping fault block subsided, forming the “Kaijiang-Liangping” paleochannel, which controls reef–shoal deposition in the region. This study provides comprehensive insights into the sedimentary facies characteristics and depositional environments of the Middle–Late Permian in the Sichuan Basin, contributing to the understanding of the regional sedimentary history and geological evolution.

Fractures are crucial as main natural gas transport channels in tight sandstone reservoirs. In order to reveal the correlation between the combination of fractures in Block Keshen 2 and sandstone, we have collected drilling core data, logging curve data, imaging logging data, and rock thin-section data from the Bashjiqike Formation in the Keshen 2 area, and by classifying and statistically analyzing the different influencing factors of fractures, we have established a correlation between the development of fractures and sandstone thickness, lithology, and sedimentary microfacies. The results reveal the following: (1) frequent vertical superposition and lateral migration occur in the sedimentary sand bodies of the Bashijiqike Formation. Three types of patterns of sand bodies have been identified according to the changes in microfacies. Type I refers to the patterns of sand bodies developed in main subaqueous distributary channels, type II refers to the patterns of sand bodies developed in secondary subaqueous distributary channels or mouth bars, and type III refers to the patterns of sand bodies developed in isolated subaqueous distributary channels; (2) three types of fracture patterns have been described in the various sand bodies of the Bashijiqike Formation in the Keshen area, including high–medium-angle branch-like fracture patterns, medium-angle reticular fracture patterns, and isolated fractures; (3) the coupling relationship among sedimentary microfacies, sand body patterns, and fracture patterns has been established. The high–medium-angle branch-like fracture patterns mainly develop in the main underwater distributary channel and the type I sand body patterns. The medium-angle reticular fracture patterns mainly develop in the secondary underwater distributary channel and mouth bars, as well as the type II sand body patterns. Isolated fractures can occur in all sedimentary microfacies but are sporadically distributed within the three types of sand body patterns. The research results present the regularity of fracture development in fractured reservoirs, which can be applied to oil and gas fields with the same background, providing certain geological evidence for exploration and development.

Taking the Zhongqiu 1 Gas Field in the Tarim Basin as an example, the heterogeneity of large-scale mono-block gas fields and their primary controlling factors have been analyzed. Based on drilling core data, well log data, scanning electron microscopy, thin-section analysis, and mercury injection experiments, combining sedimentological interpretation, research on the reservoir characteristics and variability was carried out. The results showed that: (1) The lithologic characteristics showed obvious variations among wells in the Zhongqiu 1 gas field. Specifically, the main lithology developed in the Zhongqiu 1 well is feldspar lithic sandstone, while the remaining wells predominantly consist of lithic feldspar sandstone. These differences in rock composition maturity reveal that a higher proportion of stable mineral components leads to poorer reservoir properties; (2) the main factors controlling oil and gas productivity include the variations in petrology, mineralogy, and diagenetic process characteristics. The high content of unstable mineral components and constructive diagenesis could increase reservoir porosity together. (3) Sedimentary facies of the Bashijiqike Formation in the Zhongqiu 1 Gas Field played a dominant role in the reservoir distribution. The division of sedimentary facies zones reflects variations in material composition and grain size, serving as the main material basis for reservoirs. Differences in mineral composition reflect the sedimentary environment of the reservoir. Additionally, mineral composition indicates the relationship between diagenetic processes and reservoir evolution. The high feldspar content in well ZQ1 corresponded to relatively favorable reservoir properties. The dominant feldspar type was plagioclase, suggesting that early-stage chemical weathering had undergone significant alteration. The above conclusions provided a microscopic perspective to explain the differences in oil and gas production capacity of large delta-front gas fields, serving as a geological basis for the exploration and exploitation of similar fields.

During the Early-Middle Ordovician, the Upper Yangtze Platform experienced extensive development of a distinctive set of mixed siliciclastic-carbonate deposits known as the Meitan Formation. To conduct a comprehensive study of the relationship between mixed sedimentation and sea-level changes, the Hailong section, situated at the southwest margin of the Upper Yangtze Platform in SW China, was selected as the study area due to its typical mixed sedimentary sequence. This section was effectively compared with sections in other regions. Clustering analysis of the point-count groups from the Honghuayuan and Meitan Formations revealed nine microfacies that developed during this period. Such a diverse range of microfacies provides the evidence of frequent sea-level changes in the Yangtze Platform throughout this period. Specifically, two sea-level rises were identified during the early TS.2b and early TS.3b, with the early TS.2b event occurring globally. Furthermore, four sea-level falls were observed in the late TS.2b, TS.2c, TS.3a, and late TS.3b periods. The late TS.2b sea-level fall was globally significant. From TS.2c onwards, distinct variations in sea-level changes among the Yangtze Platform, North China, Baltoscandia, Australia, and North America emerged due to alterations in the paleogeographic pattern. By comparing the sea-level curves in the Upper Yangtze Platform with the diversity curves of chitinozoans, acritarchs, and brachiopods, it became evident that environmental changes played a crucial role in the Great Ordovician Biodiversification Event (GOBE), especially during the Floian. The rising sea level and increased detrital materials fostered the development of diverse habitats, prompting organisms to adapt to varying environments. In general, rising sea levels favored increased brachiopod diversity, while falling sea levels favored enhanced planktonic diversity among chitinous and acritarch species. By shedding new light on the relationship between Ordovician sea-level changes and biodiversification in the Yangtze region, this study offers a fresh perspective on the subject from the microfacies analysis.