The southern margin of the Sichuan Basin is characterized by strong structural deformation, complex fault structure styles and scales, and multistaged geological evolution stages, which together have created various shale gas preservation conditions. Taking Jianwu (JW)–Luochang (LC)–Shuanglong (SL) synclines as an example, the fault development characteristics and structural styles of the Longmaxi Formation were studied based on fine seismic interpretation and microscopic tests (rock acoustic emission experiments and fracture-filling inclusion tests), and the effects of the fault stage, fault class and scale, and fracture development degree on shale gas preservation conditions were analysed. Basement-involved faults, detachment faults, and intraformational microfaults are mainly developed from southeast to northwest. These fault structural types have affected the JW Syncline in the southeastern part, where faults are developed from the bottom of the Cambrian to the Wufeng–Longmaxi Formation and from the Wufeng–Longmaxi Formation to the Permian (Triassic). The SL-LC region in the northwestern part is dominated by the faults from the Wufeng–Longmaxi Formation to the Permian (Triassic). This region is dominated by NE-trending main control faults, supplemented by NW-trending, approximately EW-trending, SN-trending, and other small-scale regulating faults. Fault development can be divided into three stages, corresponding to the early, middle, and late Himalayan tectonic movements. In the early stage, a few small-scale approximately EW-trending faults had little impact on shale gas preservation. In the intermediate stage, the large number of large-scale NE-trending main control faults significantly impacted shale gas preservation. The JW Syncline mainly developed three types of faults with a high-filling degree, weak upwards penetration, and small-scale relevant fractures, which together created favourable conditions for shale gas preservation. The western and northern parts are dominated by I and II faults with large structural deformation, a low-filling degree, a large-scale, and strong penetration of related fractures, which have created unfavourable conditions for shale gas preservation. During the late stage, approximately SN- and NW-trending strike-slip reverse faults developed, and strong shear and fracture zones formed near the faults, producing unfavourable conditions for shale gas preservation. This research has clarified the characterization method of fault characteristics and stages and has established the influence of complex faults on shale gas preservation, which has an important reference value for the exploration and evaluation of shale gas reserves in complex tectonic regions.

The Da’anzhai Member limestone in the central Sichuan Basin holds significant importance as a tight oil-producing formation. Despite its crucial role, the intricate patterns of hydrocarbon enrichment and the elusive geological factors dictating high-yield production have impeded tight oil exploration and development in the Sichuan Basin. This study delves into the geological characteristics of tight oil and identifies key factors influencing high-yield production, utilizing comprehensive data derived from cores, thin sections, well logging, seismic studies, and production tests of the Da’anzhai Member in the western Gongshanmiao within the central Sichuan Basin. Our findings reveal that the primary productive strata for tight oil are the Da 1 (1st Submember of the Da’anzhai Member) and Da 3 (3rd Submember of the Da’anzhai Member) Submembers, characterized by high-energy and low-energy shell beach microfacies. The kerogen type is sapropelic, ranging from mature to highly mature, positioning it as a moderately good hydrocarbon source rock. The predominant lithology of the reservoir consists of coquina and argillaceous coquina, with secondary dissolved pores, fractures, and nano-scale micropores serving as the predominant reservoir spaces. The overall lithology represents a dense limestone reservoir of the pore-fracture type, featuring low porosity and permeability. Critical controlling factors for achieving high-yield production of tight oil encompass lithological composition, fracture development, tectonic position, and source-reservoir configuration. Notably, substantial coquina thickness, fracture development, and the strategic relationship between the lower reservoir and upper source rocks contribute significantly to unlocking high tight oil yields. Additionally, thin-layer coquina emerges as a potential area for realizing increased oil and gas production capacity during later stages of development. This comprehensive analysis sheds light on the intricate dynamics governing tight oil production in the Da’anzhai Member, offering valuable insights for advancing exploration and development strategies in the Sichuan Basin.

The southern Sichuan Basin is rich in natural gas and is a key area for hydrocarbon exploration. Due to multi-phase tectonic movements, structural characteristics and preservation conditions are critical for gas accumulation. Focusing on the Middle Permian Maokou Formation in the LY area, this study analyzes the regional and local structural framework to assess structural features and their impact on preservation conditions. Using indicators such as deformation intensity, caprock properties, formation water chemistry, and pressure coefficients, an evaluation system is established to identify favorable exploration zones. Results show that the LY area lies in the southern Sichuan low-steep structural belt, dominated by NE- and NWW-trending systems. Structural styles include back-thrust combinations, fault-propagation folds, and pop-up structures. Back-thrust and pop-up structures severely compromise preservation, while fault-propagation folds with small blind faults favor accumulation. Favorable preservation areas are mainly in Ziliujing and Kongtan, characterized by stable geology, thick caprocks, and younger exposed strata, indicating good sealing. Overall, the Maokou Formation exhibits favorable hydrocarbon accumulation conditions.

The Longmen–Wushankan area, a newly emerging region in the Sichuan Basin, has seen significant exploration activities across the Permian marine shale gas following a breakthrough in the Hongxing area. Recently, well DY1H achieved a high test output from the Wujiaping Formation, highlighting the promising exploration potential for shale gas. To better understand the lithofacies types and their sedimentological significance in the Wujiaping Formation shale of the Longmen-Wushankan area, an integrated approach of conodont analysis, total organic carbon (TOC), X-ray diffraction, argon ion polishing scanning electron microscopy, and major and trace element data is implemented. This study defines the stratigraphy of the Wujiaping Formation, clarifying its top–bottom boundaries and the boundaries between its three members. The lithofacies are classified, and the sedimentary paleoenvironment is analyzed to explore the relationship between lithofacies, environment, and organic matter enrichment, thereby establishing a sedimentary model. Two conodonts identified in the upper part of the section correspond to the conodont belt at the base of the Permian Dalong Formation, dated to approximately 253–254 Ma. The lower boundary is marked by an unconformity, indicated by the appearance of Wangpo Shale. Four lithofacies types are identified in the study area, which are further categorized into 36 lithofacies types based on TOC content, including high-carbon, medium-carbon, low-carbon, and ultra-low-carbon, with high-carbon siliceous shale being the most favorable. The First and Second members of the Wujiaping Formation were deposited during a phase of sea-level transgression with significant terrigenous input compared to the Third Member that was deposited during a sea-level regression. Enrichment factor values of redox-sensitive elements indicated a change from oxic to anoxic water column settings, which were predominated during deposition of the studied succession. This was consistent with a change from shallow to deep sea-level, with siliceous material primarily derived from terrigenous to biogenic sources. The deposition of the Third Member was controlled by the Kaijiang-Liangping Trough, resulting in a deep-water shelf with anoxic conditions and enhanced productivity of labile organic matter. This indicates predominant organic matter production and preservation conditions at this time compared to decomposition and dilution of organic matter during deposition of the First and Second members. As high-quality lithofacies in the study area, environmental conditions significantly influenced the deposition of high-carbon siliceous shale, positioning siliceous shale as a key target for future exploration.

The Longmaxi Formation in the southern Sichuan Basin is an important target for shale gas exploration and development. The characteristics and stages of structural development significantly impact shale gas preservation and enrichment. Taking the Longmaxi Formation in the Yanjin–Junlian area of the southern Sichuan Basin as an example and based on the results of surface and underground structural analysis, fluid inclusion tests, apatite fission track experiments, and burial-thermal evolution history analysis, a comprehensive study of the development characteristics and structural stages of the Longmaxi Formation was carried out, and an evolution model was developed. (1) The Longmaxi Formation of the Yanjin–Junlian area has been affected by multistage structural movements and exhibits structural compounding and superposition corresponding to different stages. The formation of surface tracks of the folds and faults has been affected by multidirectional extrusion stresses of the near SN, NE, and near EW. There are three stages of underground faults in the Longmaxi Formation, and the strikes are nearly EW, NE, and nearly SN. (2) Three distribution intervals for the homogenization temperature ranges of fracture fillings are 161–195°C, 121–143°C, and 74–105°C. The apatite thermal history simulation reveals that the Longmaxi Formation experienced three stages of tectonic movement after its formation. (3) There were clearly three stages in the structural development of the Longmaxi Formation in this area: the late Jurassic–Palaeocene (55 ± 5–38 ± 2 Ma), Eocene–early Miocene (38 ± 2–15.5 ± 3.5 Ma), and late Miocene-present (15.5 ± 3.5 Ma–present). Thus, a compound fracture system with superimposed structural deformations in different directions and at different stages formed in the study area. (4) A model for the stages and development of structural tracks in the Longmaxi Formation was established in conjunction with structural analysis and geomechanical theory. The results have guiding significance for the evaluation of shale gas preservation conditions and accumulation in the study area.