In recent years, extensive low-resistivity shale reservoirs have been discovered in the Sichuan Basin, especially in the Lower Cambrian Qzs Fm (Qiongzhusi Formation). However, significant variations in gas production from these low-resistivity reservoirs across different regions have posed challenges in selecting and predicting sweet spots for the exploration and development of shale gas. Therefore, the shale samples were subjected to the analysis of a series of experiments, including core resistivity measurements, thermal simulations, and Raman spectroscopy, in order to explore the genesis mechanisms behind low-resistivity shale reservoirs and analyze their response characteristics to pore structure. The results show that HMG-OM (highly mature graphitized organic matter) and formation water stored in pores and fractures provide more conductive pathways, which are the primary mechanisms driving the low-resistivity characteristics of shale within the study area. As graphitization increases, shale resistivity significantly decreases, while maturity increases. Additionally, there are notable changes in the shale mineral composition and pore structure, including quartz breakage, clay minerals transforming into quartz, feldspar, and other minerals, and the dissolution of calcite and pyrite, which leads to a significant increase in inorganic pores. Meanwhile, the graphitization of OM causes the continuous deformation, shrinkage, and collapse of OM pores, resulting in poor development of OM pores. In this study, we integrate theoretical analysis and the experimental results and identify the Weiyuan-Ziyang area in southwestern Sichuan as a key area for future shale development in the Qzs Fm, with the aim of providing theoretical guidance for the exploration and development of shale gas in the Sichuan Basin.

The dynamic changes in shale pore structure due to tectonic uplift are crucial for understanding the processes of shale gas enrichment and accumulation, particularly in complex tectonic regions. To explore the heterogeneous changes in pore structure and their influencing factors during the last tectonic uplift of Longmaxi shale, triaxial creep experiments were performed under varying confining pressure conditions. In addition, FE-SEM, MIP, LN2GA, and LCO2GA experiments were employed to both qualitatively and quantitatively characterize the pore structure of three distinct groups of Longmaxi shale samples. To further investigate pore heterogeneity, the multifractal dimension was applied to examine the evolution of the shale pore structure under the influence of the last tectonic uplift. The results revealed that the primary pore types in Longmaxi shale include organic matter pores, microfractures, intergranular pores, and intragranular pores. The shale’s mechanical properties and mineral content have a significant impact on the heterogeneity of these pores. Notably, the shale pores exhibit distinct multifractal characteristics, highlighting the complex nature of pore heterogeneity. The singular index (α₀) and ten other multifractal dimension parameters provide valuable insights into the heterogeneity characteristics of shale pores from various perspectives. Additionally, dynamic changes in pore heterogeneity are primarily controlled by the mineral composition. Under identical creep pressure variation conditions, significant differences are observed in the pore rebound behavior of Longmaxi shale with different mineral compositions. Under high-pressure conditions, the content of TOC and quartz plays a dominant role in controlling pore heterogeneity, with their influence initially decreasing and then increasing as pressure decreases. The reduction in creep pressure emphasizes the controlling effect of TOC, quartz, and feldspar content on pore connectivity. This study introduces high-pressure triaxial creep experiments to simulate the stress response behavior of pore structures during tectonic uplift, offering a more comprehensive reflection of pore evolution in organic-rich shale under realistic geological conditions.

Coalbed methane (CBM) is an important unconventional natural gas resource, and coal seam gas content is a key parameter for CBM resource evaluation and favorable-zone prediction. Taking the Jiulongchuan exploration area in Gansu Province as the study area, this study integrated drilling, well-logging, and measured gas content data to establish a multivariate regression model for coal seam gas content prediction. On this basis, three-dimensional geological modeling and variogram analysis were applied to characterize the spatial distribution of gas content in the main mineable coal seams (Nos. 5, 6, and 8). The results indicate that the regression model constructed using acoustic transit time, natural gamma-ray values, density logging parameters, and burial depth shows generally reasonable predictive capability for coal seam gas content. Cross-validation results suggest that the predicted gas contents are generally consistent with measured values. Spatial modeling results show that gas content in Seam No. 8 is generally higher than that in Seams No. 5 and No. 6, and gas content tends to increase with burial depth and coal seam thickness. In addition, relatively high gas contents are commonly observed along synclinal zones, whereas lower values occur near anticlinal areas. The integrated application of well-log interpretation and three-dimensional geological modeling provides a reasonable characterization of the spatial variation in coal seam gas content in the study area. The results may provide useful references for CBM resource evaluation and favorable-zone prediction in the Jiulongchuan exploration area.

The pore structure of shale defines the space available for gas generation and storage, with the evolution of these pores being closely linked to shale gas accumulation and migration. Investigating the evolution of shale pores under basin-orogenic tectonic settings is crucial for under-standing the variations in resource potential across different blocks of the Anchang Syncline. This study focuses on the Longmaxi Formation shale within the Anchang Syncline, systematically examining the differences in the lateral pore structure evolution across three distinct blocks during basin-mountain tectonic development. By integrating reservoir property characterization with burial-hydrocarbon generation modeling, and employing experimental techniques including X-ray diffraction (XRD), low-pressure nitrogen adsorption (LN₂GA), and low-pressure carbon dioxide adsorption (CO₂GA), this research reveals the pore evolution mechanisms in contemporaneous shale strata during tectonic uplift from the perspectives of multifractal theory and controlling factor correlation analysis. The results indicate that (1) Pore characteristics differ significantly among the three blocks. Samples from block A (e.g., MAY2) are predominantly microporous, while samples from block C (e.g., MAD4) exhibit a higher proportion of mesopores (2–50 nm). Samples from block B (e.g., MAD3) show an intermediate pore structure. (2) Despite similar thermal maturity evolution levels and TOC contents across the blocks, as well as comparable burial and hydrocarbon generation histories, the primary factors controlling the pore differences are the magnitude of latestage tectonic uplift, the duration of thermal maturity evolution, and preservation conditions. (3) Analysis of fractal dimensions suggests that mineral composition promotes the complexity of microporous structures while inhibiting the complexity of mesoporous structures. (4) Based on the interblock variations, two distinct evolutionary models are established: model 1 (“rapid evolutionsustained overpressureweak uplift modification”) features a shorter maturity evolution duration, longer overpressure preservation, and minor late-stage uplift; model 2 (“slow evolutiontransient overpressurestrong uplift modification”) is characterized by a longer maturity evolution duration, shorter overpressure preservation, and significant latestage uplift.