Different Formation Mechanisms of the Wufeng and Longmaxi Shale Reservoirs in Xianfeng Area, Western Hubei, China

Shale reservoir heterogeneity, characterized by significant spatial and temporal variations, critically influences shale gas exploration and production. This study investigated the Upper Ordovician Wufeng Formation and Lower Silurian Longmaxi Formation in the Xianfeng area─a pivotal region for shale gas exploration in western Hubei─through integrated analyses of core samples, drilling data, and advanced experimental techniques. Systematic comparisons of lithological, geochemical, mineralogical, and petrophysical properties reveal that the Wufeng Formation exhibits superior reservoir quality, including higher total organic carbon content (TOC content: 1.72%–4.52%, avg. 3.34%), elevated brittle mineral content (quartz: 30.9%–80%, avg. 61.19%), greater porosity (avg. 3.20%), wider pore throats, and enhanced gas storage capacity (1.40–2.42 m 3 /t, avg. 1.67 m 3 /t) compared to the Longmaxi Formation (TOC content: 0.56%–4.60%, avg. 1.53%; quartz: 22.6%–48%, avg. 34.31%; porosity: avg. 1.25%; gas content: 0.26–2.36 m 3 /t, avg. 1.02 m 3 /t). Sedimentary environment is the primary factor controlling reservoir heterogeneity. The rapid uplift of the Hunan-Hubei Submarine High led to increased terrigenous clastic input, which diluted organic matter accumulation and reduced pore formation efficiency, degrading reservoir quality. Diagenesis and tectonic modification further modified pore networks but played secondary roles. These results suggest that the Wufeng Formation should be the primary exploration target in structurally complex areas of Xianfeng area, western Hubei, South China.