Influence of Low-Temperature Hydrothermal Events and Basement Fault System on Low-Resistivity Shale Reservoirs: A Case Study from the Upper Ordovician to Lower Silurian in the Sichuan Basin, SW China

High graphitization is responsible for low-resistivity shale development with poor reservoir quality. This paper provides an explanation of organic matter and determines the impact high graphite content on quality at Wufeng-Longmaxi Formation in Southern Sichuan Basin. Fine veins are frequently developed samples Ro > 3.5%, graphitized 25%, resistivity < 5 Ω•m, which dominated by three mineral assemblages: brunsvigite, barite-hyalophane-barium feldspar-potassium feldspar-anhydrite, calcite-ankerite. These filling minerals characterized Eu positive anomaly Ba, Fe, Mn contents, suggesting that was modified magmatic-related low-temperature hydrothermal fluid. Temperature measurements brine inclusions a semi-empirical geothermometer chlorite show fluid experienced stage (150–180 °C), low-sulfidation (120–150 calcitization stage. Paleozoic fault systems late Permian activities associated Emeishan mantle plume control shale. The water formation seawater infiltrated into deep crust along basement faults under gravity, developing alkaline hot through heating then causing water-rock reaction rocks. They migrated upward large convective thermal circulation Tiangongtang area, Shuanglong-Luochang Xuyong area. Cation exchange redox reactions occurred during interaction between high-temperature cool wall migration via introduced subsequent reaction, resulting assemblages intricately filled fractures. It increased temperature enhanced maturity shale, wide distribution Changning Block.