Citation: | GAO Tian,LIU Rui,XU Lu,et al. Genetic mechanism of low resistance in shale analyzed via triaxial compression tests[J]. Bulletin of Geological Science and Technology,2025,44(2):1-14 doi: 10.19509/j.cnki.dzkq.tb20230533 |
The gas-rich Wufeng-Longmaxi shale of the southern Sichuan Basin exhibits low-resistance anomalies in multiple areas. Statistical analysis reveals that the low-resistivity zone (<10 Ω·m) in the Wufeng-Longmaxi shale is spatially associated with tectonic faults. This study aims to reveal the coupling mechanism between shale resistivity and tectonic faults.
This study determines the petrological and geochemical characteristics of outcrop samples obtained from the Wufeng-Longmaxi shale in the southern Sichuan Basin through thin-section identification, X-ray diffraction, laser Raman spectroscopy, whole-rock asphalt reflectance, and conventional physical property analyses. The characteristics of resistivity change in the shale during deformation were analyzed through triaxial compression tests. The impacts of fracture system generation and conductive fluid intrusion on low-resistivity shale were also clarified.
The results show that the resistivity of shale samples, which have similar characteristics of clay minerals, pyrite, organic matter content, and thermal maturity level, significantly decreased after saturation with brines of various salinities. A positive correlation was observed between the resistivity reduction (95.07%-98.70%) and brine salinity. After reaching the compressive strength, the resistivity reduction of the brine-saturated samples varies from 5.7 Ω·m to 25.7 Ω·m (average: 13.3 Ω·m). This reduction shows a linearly positive correlation with the resistivity observed post cracking. The intrusion of conductive fluid and the generation of the fracture system in shale are the primary controlling factors for resistivity reduction. The resistivity after cracking is influenced by both the intruded saltwater salinity and fracture density.
This research elucidates the influence mechanism of tectonic fault zones on shale resistivity and enhances the theoretical framework for understanding the genesis of low-resistivity shale, with significant implications for the exploration and development of low-resistivity shale formations.
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