Abstract:

The shale gas exploration of the Longmaxi formation in the Lower Silurian in the upper Yangtze region obtained great
breakthrough in recent years. More and more attention is focused on the shale gas resource potential and exploration prospect in the
lower Yangtze zone, which is in the same tectonic block with the upper Yangtze. The Gaojiabian formation in the lower Yangtze is the
equivalent layer of the Longmaxi formation in the upper Yangtze. Due to the strong erosion on the surface and the bad exposure, the
distribution and the thickness of the black shale rock are unclear, which restrict the evaluation and prospection of the shale gas
exploration potential. In this respect, this study performed the shallow well drilling project for the black shale in the Tangshan in
Nanjing and Lunshan in Jurong. On basis of the analysis of the cores from these 5 boreholes, this study revealed the characteristics of
the black shale, including the thickness, geochemical features, petrology, and biostratigraphy. The results suggest that the black shale
is well comparable with the Jiaoshiba in the upper Yangtze and that at least 4 graptolite fossil zones are consistent with each other. The
thickness of the Wufeng-Gaojiabian black graptolite shale is larger than 80.5 m in Tangshan zone, and larger than 39.5 m in Lunshan.

The organic abundance is relatively high. The TOC content is from 1.2% to 4%, which implies relative strong hydrocarbon generation
capacity. The Ro ranges from 1.5% to 2.6%, which indicates the thermal evolution degree is high-over mature. The hydrocarbon
entered the gas generation stage. The organic pattern of the black shale is mainly kerogen Ⅰ and Ⅱ1. Therefore, we considered the
lower Silurian shale has good shale gas resource potential in the lower Yangtze zone.

Key words: Lower Yangtze, shale gas, Lower Silurian black shale, shallow borehole drilling, potential