Shale characteristics and shale gas potentials in the Lower Devonian Tangding Formation in Tian'e area of the Nanpanjiang Basin, SW China

Shale gas, a clean energy source with large reserves and wide distribution, is gaining global attention. The Nanpanjiang Basin, in the southern part of Yangtze Block, is a strategic area for marine shale gas exploration, with the Tian'e region as a key target. Field investigations and previous studies have confirmed the distribution of Lower Devonian Tangding shale in the Nanpanjiang Basin. This study, using organic geochemistry, X-ray diffraction, and scanning electron microscopy (SEM), analyzed the geochemical characteristics of source rocks, shale reservoir properties, gas content, and preservation conditions. The Tangding shale is primarily 100-250 m thick, with burial depths of 2100-4200 m. Total Organic Carbon (TOC) values of the shales exceed 2.0 wt.%, with kerogen types mainly Type II 1 -II 2 and high- to over-mature organic matter, indicating excellent source rock potential. The shales contain a high percentage of brittle minerals, with well-developed pore spaces and adsorption capacities, suggesting a well shale gas reservoir. Relatively high clay mineral content, along with strong compaction and cementation, enhances the shale's self-sealing capacity, ensuring good preservation conditions for shale gas. The gas content is relatively high, indicating significant shale gas accumulation. Multi-episode tectonic movements have significantly influenced shale gas preservation. Compared to typical shale gas accumulation conditions in other basins, the Tangding shales in the Tian'e Area offer favorable conditions for shale gas accumulation, making the northwestern part of the Tian'e Area a target zone for shale gas exploration in the Nanpanjiang Basin.